GROUNDWATER PROCESSES AND ENVIRONMENTAL … · USE OF HYDROCHEMISTRY AND STABLE ISOTOPES, FRASER...

DETERMINATION OF COASTAL GROUND AND

SURFACE WATER PROCESSES AND CHARACTER BY

USE OF HYDROCHEMISTRY AND STABLE

ISOTOPES, FRASER COAST, QUEENSLAND

by

Genevieve R Larsen

Bachelor of Science (Applied Physics) (University of Technology, Sydney) - 1999

Master of Applied Science (Queensland University of Technology) - 2007

Thesis submitted in accordance with the regulations for

the Degree of Doctor of Philosophy

School of Earth, Environmental and Biological Sciences

Science and Engineering Faculty

Queensland University of Technology

February 2012

i

Keywords

Hydrochemical characterisation, coastal aquifers, marine and fresh water interaction,

stable water isotopes, hierarchical cluster analysis, surface water/groundwater

interaction, hydrochemical processes, major ion chemistry, subtropical coastal

catchment, microbial activity, dissolved iron transport, redox conditions, Fe(III)

organic complexation, iron reduction, iron oxidation, sulphate reduction, dissolved

organic carbon, 13

CDIC, 34

SSO4, 15

NDIN, nutrients, iron curtain

iii

Abstract

Increasing population density is a growing concern in southeast Queensland,

particularly in the Brisbane area, but also along other coastal zones. This population

growth will result in substantial changes in landuse and impacts to a wide range of

natural systems. Land modifications in coastal zones can impact on the quality of

both surface and groundwaters. In many cases, levels of nutrients and/or metals may

be elevated and result in degradation of estuarine waters and the transport of solutes

to marine ecosystems. Of particular concern in southeast Queensland are solutes such

as Fe, N and C which are known to contribute to the growth of the toxic

cyanobacterium Lyngbya majuscula as well as impact on the general health of

benthic flora and fauna.

These coastal settings are often complex hydrologically and chemically, factors

which are assessed in this thesis. The main aim of this study is to determine sources

and transport mechanisms for various solutes. The overall approach is to (a)

determine where potential pathways for solute transport between water bodies exist

on a catchment scale, and (b) identify processes occurring within these water bodies

that affect the mobilisation of nutrients, in particular Fe. An additional goal is to

establish the hydrochemical settings within this region of limited modification as an

indication of baseline values prior to further development. No previous detailed

investigation of water chemistry and hydrochemical processes has been carried out in

this study area and so this thesis is an important first step in evaluating current water

quality within the various ground and surface water bodies in this region.

Information relating to mechanisms that influence the chemistry of waters within

these catchments and the adjacent marine waters at both micro- and macro- scales is

essential to future management of this hydrologically complex coastal region.

This investigation is structured around three linked papers. Paper 1 describes

dynamic settings with complex hydrological systems at various scales and with

multiple processes operating; further it defines the types of ground and surface

waters that exist, their host materials and their potential hydrological connectivity.

Although there is a large range in the concentrations of major ions within waters (EC

= 80 to 73,000 µScm-1

), limited proportional major ionic variability among the

iv Abstract

samples made the assignment of some waters to hydrochemical facies difficult using

only the graphical methods. Consequently, in Paper 2, hierarchical cluster analysis

(HCA) is used to support and expand on the results from Paper 1 in order to clarify

aquifer types and connection, and define hydrochemical character on a catchment

scale. The HCA of temporal data is also used to further support interpretation. In the

third paper several different types of data are used to characterise waters and identify

sources and processes contributing to concentrations, form and potential transport of

dissolved Fe, C, S and N on a local scale.

Assessment of this coastal region and its catchments identified three regimes of fresh

groundwater, (a) zones within weathered bedrock, (b) Tertiary alluvial paleovalley in

the north, and (c) Quaternary unconsolidated materials of the tidal coastal strip. All

waters in the study area are dominated by Na cations and Cl anions, fall on a

common dilution line, and overall have very limited proportional major ionic

variability due to the location, lithology and limited water-rock interaction occurring

within the study area. Findings relating to transport of solutes within these

catchments include: (a) groundwater contribution to surface waters in elevated

catchment areas is limited and the primary mechanism for solute transport would be

overland flow and runoff to the drainage system, (b) there is potential for solute

transport from forestry areas to marine and fresh surface waters through small

alluvial aquifers adjacent to the drainage system in the coastal plain, and (c) small

aquifers in the villages along the coastal strip are saline-intruded, possibly due to

overuse, and are a potential pathway for contaminants to the Great Sandy Strait

during times of high rainfall. The close grouping of stable water isotopes (δ18

O = -

4.45 to -3.6‰, δ2H = -21.8 to -15.7‰) on the local meteoric water line (LMWL) and

an overall trend of depletion with distance inland indicates local recharge to nearly

all groundwaters. In addition, isotope ratios indicate significant evaporation of fresh

surface waters and enrichment of 2H and

18O at a surface water site in the coastal

plain suggests groundwater contribution.

HCA results overall partitioned samples to the same hydrochemical groups defined

by the graphical methods. However, these results also indicated: (a) ground/surface

water interaction and unsaturated zone/semi-confined groundwater interaction not

indicated by the graphical methods, and (b) unconfined or semi-confined conditions

at four sites that were thought to be confined. HCA results using temporal data (a)

Abstract v

defined sites of aquifer confinement and groundwater baseflow and (b) showed

minimal seasonal variation in proportions of ions occurs for most waters except

under seasonal extremes. The use of HCA was beneficial to the study by clarifying

aquifer types in relation to confinement and hydrological links, characteristics that

influence transport of solutes.

Environmental aspects were considered in Paper 3, which combines hydrochemical,

isotopic and microbial data to provide information in relation to the mobilisation and

transport of Fe that can be utilised in many catchments Australia-wide. Organic

(DOC), physicochemical parameters (Eh, pH and DO), ionic forms of iron (Fe(II),

Fe(III), environmental isotopes (δ15

N, δ34

SSO4 and δ13

CDIC) and cultivable bacterial

numbers (CBNs) are incorporated in order to further characterise waters. Three sites

that have high Fe concentrations are used to illustrate micro-scale processes that

affect the mobility and transport of Fe in different hydromorphological settings.

These processes include microbial activity, organic complexation, cyclic oxidising

and reducing conditions, and ―iron curtain‖ effects occurring at the saline/fresh water

interface. This component of the study provides a better understanding of the

controls on the distribution, concentration and speciation of Fe in ground and surface

waters of southeast Queensland.

The use of stable environmental isotopes to determine sources of solutes and

processes had mixed success. Values of δ34

SSO4 indicated sulphate sourced from

rainfall/seaspray and/or soils/sediments for most samples and fresh/seawater mixing

at most sites subject to tidal influence. Sulphate reduction was indicated at one

surface water site (δ34

SSO4=32.6‰ VCDT) and sulphur oxidation at a residential

groundwater site (δ34

SSO4=-1.1‰ VCDT). However, sulphate reduction indicated by

Fe, DOC and CBN data, was not reflected in the δ34

SSO4 ratios at other sites most

likely due to the dominance of rainfall/seaspray input of sulphate sourced from

marine waters. The δ15

NDIN data were found to be less useful due to the absence of

anthropogenic N input and the nutrient-poor nature of the study area, although one

incidence of septic effluent-sourced N (δ15

NDIN=22.4‰ AIR) was indicated.

However, the use of δ13

CDIC isotopic data was quite successful in determining

sources of carbon and supporting micro-processes occurring within the micro-

environments discussed.

vi Abstract

The findings from this paper emphasise the need to analyse for Fe(II) and Fe(III)

species when investigating solute transport. Surprisingly high levels of ‗dissolved‘

Fe(III) were found in ground and surface waters which is assumed to be in

organically complexed form. The form of Fe in waters has major implications for

transport through aquifers and drainage systems.

The study has been of value in identifying individual components of the total

spatially and temporally complex hydrological system within these coastal

catchments and adjacent coastal plain. It provides a valuable insight into the many

processing occurring in these settings and their relationships which will support

future management of these environments. The findings of the study are also

applicable to many areas along the coast of southeast Queensland and other parts of

Australia that have similar geomorphological features and landuse.

vii

TABLE OF CONTENTS

KEYWORDS ..................................................................................................................... I

ABSTRACT .................................................................................................................... III

LIST OF FIGURES .......................................................................................................... XI

LIST OF TABLES ........................................................................................................... XII

ABBREVIATIONS ......................................................................................................... XIII

THESIS PUBLICATIONS ................................................................................................. XV

CONFERENCE SUBMISSIONS ......................................................................................... XV

ACKNOWLEDGEMENTS ............................................................................................... XVI

1. INTRODUCTION .......................................................................... 1

Solute transport................................................................................................................... 1

Significance of Fe ............................................................................................................... 2

Landuse .............................................................................................................................. 4

1.1 AIMS AND APPROACH ............................................................................................ 6

1.2 RELATIONSHIP TO OTHER RESEARCH ....................................................................... 8

1.2.1 Previous research ......................................................................................... 8

1.2.2 Concurrent research ................................................................................... 10

1.3 STRUCTURE OF THESIS ......................................................................................... 11

2. BACKGROUND ........................................................................... 13

2.1 REGIONAL SETTING.............................................................................................. 13

2.1.1 Landuse ..................................................................................................... 13

2.1.2 Climate ...................................................................................................... 16

2.1.3 Geomorphology .......................................................................................... 16

2.1.4 Geology ..................................................................................................... 19

2.1.5 Soils ........................................................................................................... 20

2.1.6 Surface water ............................................................................................. 22

2.1.7 Groundwater .............................................................................................. 22

2.2 COASTAL HYDROCHEMISTRY ............................................................................... 23

2.2.1 Water quality constituents........................................................................... 23

2.2.2 Iron ............................................................................................................ 26

2.2.3 Macronutrients ........................................................................................... 33

2.2.4 Organic matter ........................................................................................... 36

2.2.5 The role of microbes ................................................................................... 37

2.2.6 Physicochemical parameters ...................................................................... 39

2.3 ENVIRONMENTAL ISOTOPES ................................................................................. 43

2.3.1 Oxygen and hydrogen isotopes, δ18O and δ2H ............................................. 43

2.3.2 Stable isotopes of dissolved inorganic carbon, δ13CDIC ................................ 46

viii

2.3.3 Stable isotopes of dissolved organic nitrogen, δ15NDIN ................................. 48

2.3.4 Stable isotopes of sulphate sulphur, δ34SSO4 ................................................. 49

3. METHODS AND APPROACHES ...............................................53

3.1 DATA COLLECTION .............................................................................................. 53

3.1.1 Data Collection Sites .................................................................................. 53

Location ........................................................................................................................... 53

Surficial geology and geomorphology ............................................................................... 60

3.1.2 Sampling programme ................................................................................. 61

3.2 LABORATORY METHODS ...................................................................................... 63

3.2.1 Ferrozine method for determination of ferrous iron ..................................... 64

3.2.2 Methylene blue method for determination of sulphide .................................. 64

3.2.3 AQ2 methods .............................................................................................. 65

3.2.4 Charge balance errors ................................................................................ 65

3.2.5 Isotope analysis .......................................................................................... 66

3.3 DATA ANALYSIS .................................................................................................. 67

3.3.1 Graphical methods ..................................................................................... 68

3.3.2 Hierarchical cluster analysis (HCA) ........................................................... 69

4. PAPER 1: Hydrochemical and isotopic characterisation of

groundwaters to define aquifer type and connectivity in a subtropical

coastal setting, Fraser Coast, Queensland ........................................75

5. PAPER 2: Cluster analysis to support graphical methods in the

characterisation of ground and surface waters in a subtropical coastal

zone, Fraser Coast, Queensland ..................................................... 113

6. PAPER 3: Sources, distribution and transport of iron and nutrients

within the groundwaters and surface waters of a subtropical coastal

setting, Fraser Coast, Queensland, using hydrochemical and isotopic

data ............................................................................................... 147

7. DISCUSSION .............................................................................. 221

7.1 IMPLICATIONS FOR FURTHER LANDUSE DEVELOPMENT......................................... 225

7.2 IMPLICATIONS FOR PLANTATION FORESTRY ......................................................... 226

7.3 RECOMMENDATIONS FOR FURTHER SAMPLING AND ANALYSIS .............................. 226

7.3.1 Surface waters .......................................................................................... 226

7.3.2 Groundwaters .......................................................................................... 227

7.3.3 Effects of forestry practices ....................................................................... 227

8. CONCLUSIONS ......................................................................... 229

8.1.1 Groundwater occurrence .......................................................................... 229

ix

8.1.2 Sources of solutes in ground and surface waters ....................................... 230

8.1.3 Processes/characteristics affecting hydrochemical composition ................ 231

8.1.4 Solute transport ........................................................................................ 232

9. REFERENCES 235

APPENDIX A Conference abstracts.................................................251

APPENDIX B Monitoring well graphic borelogs............................257

APPENDIX C Data collection site photos........................................265

APPENDIX D Transect Conceptual Cross-section...........................273

APPENDIX E Map of data collection sites and topography............275

xi

List of Figures

Figure 1 Map of Australia and a section of the southeast coast of Queensland. 14

Figure 2 Extent of the area of the study showing drainage systems, landuse,

coastal villages and catchments. Pine plantations are the dominant land-

use in this coastal region. Boonooroo, Little Tuan and Poona are all small

coastal villages. Tuan Forestry Office supplied some of the rainfall data

used to describe climate conditions during data collection time periods.

15

Figure 3 Daily rainfall for Tuan Forestry Office (blue), Maryborough (green) and

Rainbow Beach (red) from 01/08/2007 to 31/07/2008. FT1 – FT4 are

sample collection field trips and are shown as black dots to indicate

conditions at the time of sample collection. Note that Rainbow Beach is

plotted on the secondary axis. 17 Figure 4 View from the top of Poona Creek catchment eastward across the coastal

plain to the Great Sandy Strait and Fraser Island 18 Figure 5 Topography gradients and drainage system in the study area. Note the

flatter gradients in the northern areas of the Tuan catchment. 18 Figure 6 Geology of the study area showing the location of data collection sites

and the boundaries of the Tertiary alluvium aquifer described in Laycock

(1969). Most of the area is covered by a deep weathering profile

overlying sandstone bedrock. See Figure 12 for a closer view of the sites

in the rectangle in the eastern central region of the figure. 21

Figure 7 Model for C and electron flow in groundwater with major potential

terminal-electron accepting processes (modified from Falkowski et al.

(2008) and Lin (2011)) 38 Figure 8 Eh-pH diagram for the system Fe-O2-CO2-H2O at 25ºC ignoring ferrosic

hydroxide [Fe3(OH)8] and assuming pKsp=37.1 for amorphous Fe(OH)3.

Bicarbonate is fixed at 10-2.7

mol/kg. Aqueous/solid boundaries are drawn

for total dissolved iron concentrations of 10-5

mol/kg (solid line). 41 Figure 9 Eh-pH diagram for thermodynamically stable substances in the system S-

O2-H2O at 25ºC, showing the fields of predominance of the aqueous

species and of elemental sulphur for ΣS(aq) = 10-3

mol/kg. 42

Figure 10 Location of data collection sites and topography. The dashed rectangle

shows the location of Figure 12. Please note map available in Appendix

D. 56 Figure 11 Cross-section of Poona Creek catchment going from southwest to

northeast indicating the hydromorphological settings of monitoring wells

and surface water data collection sites. 57

Figure 12 Poona Creek estuary and nearby monitoring wells. 58 Figure 13 Conceptual model of geology, hydromorphology and location of

monitoring wells at the transect adjacent to Poona Creek estuary. 59 Figure 14 Cumulative rainfall data for four sites (going from southwest to northeast

– Rainbow Beach, Toolara, Tuan Forestry Office, Maryborough), within

a 40 km radius of the study area during the data collection period. 63

xii

List of Tables

Table 1 Typical EC and TDI ranges for waters of variable salinities 26 Table 2 Typical DOC ranges for different water types 37

Table 3 Isotope ranges for different sources and processes from the literature

44

Table 4 Site names, sample type, site description and borehole depth or screening

interval 55

Table 5 Sampling runs, climatic conditions, sites and analytes 62

xiii

Abbreviations

AHD ……………. Australian Height Datum AMTD ……………. Adopted Middle Thread Distance

ASL ……………. Above Sea Level

ASS ……………. Acid Sulphate Soils bgs ……………. Below ground surface

BMWL ……………. Brisbane Meteoric Water Line (used as LMWL in this study)

BoM ……………. Bureau of Meteorology

CBE ……………. Charge Balance Error CBN ……………. Cultivable Bacteria Number

DIC ……………. Dissolved Inorganic Carbon

DIN ……………. Dissolved Inorganic Nitrogen DO ……………. Dissolved Oxygen

DOC ……………. Dissolved Organic Carbon

DOM ……………. Dissolved Organic Matter

EC ……………. Electrical Conductivity FeOB ……………. Iron Oxidising Bacteria

FeRB ……………. Iron Reducing Bacteria

FPQ ……………. Forestry Plantations Queensland HCA ……………. Hierarchical Cluster Analysis

GNS ……………. Institute of Geological and Nuclear Sciences, New Zealand

GSS ……………. Great Sandy Strait GW ……………. Groundwater

Khyd ……………. Hydraulic Conductivity

LMWL ……………. Local Meteoric Water Line

SOB ……………. Sulphur Oxidising Bacteria SRB ……………. Sulphate Reducing Bacteria

SW ……………. Surface water

T ……………. Temperature TDI ……………. Total Dissolved Ions

TFO ……………. Tuan Forestry Office (rain gauging station)

VCDT ……………. Vienna Canyon Diablo Troilite (standard for 34

SSO4 isotopes) VPDB ……………. Vienna Pee Dee Belemnitella americana (standard for

13CDIC

isotopes from the Cretaceous Pee Dee Formation in South Carolina)

VSMOW ……………. Vienna Standard Mean Ocean Water (standard for 18

O and 2H

isotopes)

xiv

STATEMENT OF ORIGINAL AUTHORSHIP

“The work contained in this thesis has not been previously submitted to meet

requirements for an award at this or any other higher education institution. To the

best of my knowledge and belief, the thesis contains no material previously published

or written by another person except where due reference is made.”

Signature ________________________________________

Date ________________________________________

xv

Thesis Publications

PAPER 1: Larsen, G. and Cox, M.E. (2011) Hydrochemistry and isotopic

character of groundwater types and connectivity in a subtropical coastal

setting, Fraser Coast, Queensland. Environmental Earth Sciences 64(7):

1885-1909.

Manuscripts for submission

PAPER 2: Larsen, G. and Cox, M.E. (2011) Cluster analysis to support graphical

methods in the characterisation of ground and surface waters in a

subtropical coastal zone, Fraser Coast, Queensland (for submission to

Hydrogeology Journal)

PAPER 3: Larsen, G., Cox, M.E. and Smith, J.J. (2011) Sources, distribution

and transport of iron and nutrients within the groundwaters and surface

waters of a subtropical coastal setting, Fraser coast, Queensland, using

hydrochemical and isotopic data (for submission to Biogeochemistry)

Conference Submissions

2010 Larsen, G. and Cox, M.E. Hydrochemical characterisation of groundwaters and

surface waters within a subtropical coastal catchment, Fraser Coast,

Queensland. Australia Earth Sciences Convention Conference, Canberra,

Australia, July 2010 (abstract and powerpoint presentation on CD ROM).

2010 Larsen, G. and Cox, M.E. Cluster analysis to support graphical methods in the

characterisation of chemically similar ground and surface waters in coastal

catchment, subtropical Fraser Coast, Queensland. Groundwater 2010

Conference, Canberra, Australia, November 2010 (abstract and oral

presentation).

2011 Larsen, G., Cox, M.E. and Smith, J.J. Controls over dissolved Fe within

groundwater and surface water micro-environments in a subtropical coastal

setting, Fraser Coast, Queensland. HydroEco Conference, Vienna, Austria,

May 2011 (poster presentation).

xvi

Acknowledgements

Thank you to my supervisors Associate Professor Malcolm Cox and Dr Jim Smith

for their encouragement, guidance and assistance for the term of this research

project. I would also like to thank Dr Scott Bryan, Dr Ian Williamson, Dr David

Rowling and, of course, the two examiners of this thesis for their excellent

suggestions for the improvement of the presentation and interpretation in earlier

drafts.

I am also grateful to Lin Chaofeng, Pavel Dvoracek, Eloise Larsen, Stefan Löhr,

Shona Smith and Rachel Smith who all assisted me with sample collection and field

measurements.

I also thank the Australian Research Council and Forestry Plantations Queensland

(FPQ) for funding and also for LiDAR data supplied by FPQ for mapping and

interpretation. Many thanks also to Biogeosciences at QUT for extra funds in relation

to equipment and field trips.

I would also like to thank Shane Russell and Bill Kwiecien for assistance with

laboratory work and particularly Martin Labadz for help in the lab and also with

many other queries along the way. Tanya Scharaschkin, Melody Fabillo and Peraj

Karbaschi were also very helpful in assisting me with plant photosynthetic cycles

research.

And finally I am most grateful to my Mum and Dad. They have been hugely

supportive of me throughout my studies and are, I am sure, thrilled to see the end in

sight!

1

1. INTRODUCTION

Coastal zones globally are commonly areas of high population density and/or

intensive landuse and as such are vulnerable to a wide range of water quality issues.

The quality of ground and surface waters is important as often they are not only a

source of water supply for residential and agricultural use but because they also

support a range of ecosystems. In southeast Queensland, many catchments discharge

to environmentally sensitive marine habitats such as Pumicestone Passage (a

Ramsar-listed wetlands) in northern Moreton Bay, and the Great Sandy Strait (also

Ramsar-listed) between the mainland and the UNESCO-listed Fraser Island World

Heritage Area. Numerous other such areas occur around the Australian coastline, and

consequently, these settings are of high environmental, economic, social and cultural

importance.

This study is part of an integrated project funded by an ARC Linkage grant, with

Forest Plantations Queensland (FPQ) as industry partner. The project is entitled

Hydrological Controls over Distribution of Fe within a Forested Coastal Catchment

and was developed in response to concerns regarding current and future land

practices. This project focuses on coastal catchments on the Fraser Coast, a region of

relatively low-level modification where landuse is predominantly for Pinus

plantations. The main focus of this study is to confirm the hydrological settings and

determine the primary processes for solute transport within these catchments and to

the marine environment, with emphasis on processes affecting the mobilisation of Fe.

The following sections discuss fundamental aspects of solute transport, significance

of Fe, and landuse in relation to potential negative environmental impacts on ground

and surface water systems that commonly occur in such settings.

Solute transport

Urbanisation, agriculture and other anthropogenic activities can negatively impact on

the water quality of both surface and groundwater bodies. For example, nutrients

such as nitrogen and phosphorus can infiltrate aquifers as a result of agricultural

practices and can discharge to coastal waters (Zekster et al. 1983; Cable et al. 1997;

Ensign and Mallin 2001; Howarth et al. 2002; Trojan et al. 2003; Church 2006;

Nakano et al. 2007). These nutrients can also enter surface waters via direct runoff

(Crossland et al. 1997; Dyer 1997; Soicher and Peterson 1997; Iversen et al. 1998;

2 Chapter 1 Introduction

Pointon et al. 2003; Withers and Sharpley 2008). Reduced rainfall, increased

vegetation and over-pumping for irrigation or residential use can lead to reduced

recharge to aquifers and surface drainage systems. In some coastal zones this can

result in landward movement of the seawater/freshwater interface in both ground and

surface water bodies (Mulligan et al. 2007; Werner 2009). This type of modification

can limit freshwater supply to users and also impact on the natural environment.

Conversely, significant rainfall events often increase discharge and runoff of

dissolved and suspended nutrients and metals from anthropogenic and natural

sources to adjacent lakes, rivers and estuaries (Shaffelke et al. 2002; Campbell and

McKenzie 2004; BMRG 2005). The result can be the general degradation of water

quality within catchments and nearby estuarine/marine waters eventually resulting in

eutrophication and damage to benthic and terrestrial ecosystems.

The pathways solutes take to reach the marine environment are often indirect and

involve interaction between the drainage system, unconfined, semi-confined and

confined aquifers and the ocean. The links between these different water bodies are

often not well understood. We need to identify these transport pathways in order to

determine solute sources and to enable the future management and prevention of

negative landuse impacts.

Significance of Fe

Iron (Fe) is an important biological and geochemical trace element in terrestrial and

marine aquatic ecosystem processes (Martin and Fitzwater 1988; Martin et al. 1990;

Croot and Hunter 2000). However, excess iron is of environmental concern and may

pose ecological risks due to its common involvement in certain biological and abiotic

processes (Liaghati et al. 2005). Despite being a prominent element, the surface and

near-surface distribution, reaction kinetics and chemical speciation of iron are not

fully understood (Kuma et al. 1998; Rose 2003; Rose and Waite 2003). This lack of

knowledge is particularly the case with respect to catchment-based biogeochemical

and environmental processes which sequester or mobilise Fe pools.

The growth of Lyngbya majuscula, and algae generally, is promoted by high levels of

nutrients and iron and the presence of humic substances from land runoff that make

the iron bioavailable (Pointon et al. 2003). Lyngbya majuscula is a toxic blue-green

algae (cyanobacterium) that may kill seagrass and deplete fish and coral populations.

Chapter 1 Introduction 3

It also emits a foul odour and has caused irritation and injury to fisherman and

bathers (Moreton Bay Catchment Water Quality Management Strategy Team 1998).

Lyngbya is a current environmental issue in many parts of the world (Lin and Hung

2004; Titlyanov and Titlyanova 2008; Keeley 2009; Paerl and Huisman 2009; Joyner

et al. 2010) as well as along the coast of Queensland; and it has been proposed that

anthropogenic activities such as forestry and urbanisation may promote these algal

blooms (Abal and Watkinson 2000; Ahern et al. 2006a; Al-Shehri and Mohamed

2007; Bell and Elmetri 2007). According to the Burnett Mary Regional Group

(BMRG 2005), the area stretching from Double Island Point north through to Wide

Bay, adjacent to Poona Creek catchment, has suffered from occasional Lyngbya algal

blooms in summer. Seasonal blooms of Lyngbya have also been reported in the

Deception Bay/Pumicestone Passage region (approximately 150 km south of Poona

village) for the last decade (Dennison and Abal 1999) and closer to the study area at

Noosa Main Beach, where Lyngbya blooms are becoming increasingly prevalent

(BMRG 2005). It is the overall aim of this study to provide information that can

assist in the management of these types of landscapes to avoid degradation of water

quality and the growth of algal blooms.

Various international studies have investigated different aspects, such as: the

hydrochemistry of Fe in rivers and streams (Crerar et al. 1981; Allard et al. 2004;

Björkvald et al. 2008; Lofts et al. 2008; Fritsch et al. 2009); behaviour of Fe in

subterranean estuaries (Charette and Sholkovitz 2002; Testa et al. 2002; Spiteri et al.

2006); submarine groundwater discharge of Fe (Windom et al. 2006; Roy et al.

2010); and factors influencing the dissolved iron concentrations in estuaries and

seawater (Eckert and Sholkovitz 1976; Boyle et al. 1977; Sholkovitz 1978; Crerar et

al. 1981; Krachler et al. 2005; Laglera and van den Berg 2009). There are also

numerous Australian studies focusing on: the behaviour of Fe and DOC in catchment

and coastal waters (Naidu et al. 1993; Rose 2003; Rose and Waite 2003) and its

effects on the growth of Lyngbya majuscula (Watkinson et al. 2005; Isaacson et al.

2009); abundance, form and processes involving Fe in tidally inundated former acid

sulphate soils (ASS) (Johnston et al. 2010; Johnston et al. 2010; Keene et al. 2010;

Johnston et al. 2011); behaviour and form of Fe in coastal sediments (Cox and Preda

2005; Liaghati et al. 2005; Burton et al. 2008; Löhr et al. 2010) and in salinised


waterways (Isaacson et al. 2009), and the dynamics of Fe in lake water (Zaw and

Chiswell 1999).

A different approach is taken in this study which considers factors affecting the

transport of Fe. The distribution of Fe is determined and in three cases where high

levels occur, a suite of data including Fe(II), Fe(III), DOC, δ13

CDIC, δ34

SSO4, δ15

N is

used to explain and support processes that result in these high concentrations. This

study addresses the different processes that affect the mobilisation and transport of

Fe occurring in different hydromorphological settings throughout this coastal region;

settings and processes that are typical of much of coastal Queensland.

Landuse

Vegetation plays a key role in the interactions between groundwater and surface

water systems, because of its direct and indirect influence on recharge and the

dependence of vegetation communities on groundwater. Changes in vegetation cover

and structure, particularly from low vegetation such as grassland to tall vegetation

such as a forest can have a significant impact on groundwater recharge by altering

components of the hydrological cycle such as interception and transpiration (Le

Maitre et al. 1999). Watercourses from the extensive areas of exotic pine plantations

within the study area drain into the Great Sandy Strait (Figure 2). Riparian zones

exist throughout the plantation, with the width of the zone often relating to stream

order. There has been continued debate regarding the role of plantation forestry on

release of reduced, soluble iron (Fe(II)) species from soils during planting and

harvesting stages, and transport into waterways, and ultimately into the marine

environment (Pointon et al. 2003; Albert et al. 2005; Ahern et al. 2006a; Löhr 2010).

In association with N, P and organic C, this excess iron has been shown to stimulate

blooms of a toxic cyanobacterium Lyngbya majuscula (Albert et al. 2005; Watkinson

et al. 2005; Roelfsema et al. 2006; Ahern et al. 2006b).

The region of southeast Queensland is the fastest growing urban area in Australia,

and from 2006 to 2031 its population is expected to grow from 2.8 million to 4.4

million people. The region covers 22,890 km2, and stretches 240 km from the

Queensland-New South Wales border in the south to Noosa in the north (Department

of Infrastructure and Planning 2010). This population growth will result in

substantial changes in landuse and impacts to a wide range of natural systems, of


note the hydrological and hydrochemical processes which support a variety of

ecosystems. In addition to this, there is the real potential of sea level rise which in

low-lying settings with tidal systems can be substantially impacted by storm surges.

Although more sparsely populated than the Brisbane area to the south, the Fraser

Coast has many similar geomorphological features and is also under pressure from

urbanisation with around 1500 new dwellings and a population growth of 3 to 4%

each year (Department of Infrastructure and Planning 2008).

Elevated nutrients and metals in surface and groundwater can be due to both natural

and anthropogenic influences. Studies in the region have shown that although urban

and industrialised landuse has a strong influence over metal release, natural

processes exert the dominant influence (Eyre and McConchie 1993; Kawaguchi et al.

1997; Preda and Cox 2002). Within Australia, numerous baseline metal studies have

been undertaken within estuaries, bays and floodplains adjacent to major population

centres which are related to either natural or anthropogenic events (see review in Cox

and Preda, 2005). A common finding is the association between elevated metals and

industrial activities locally, but also the importance of natural processes on a broader

scale. To date, no whole-of-catchment study has been reported in Australia to trace

Fe fluxes from source to estuarine or shallow marine sinks. In particular,

determination of the relative contributions of biotic (biogeochemical) and abiotic

(geochemical) processes to Fe mobilisation/sequestration and transport are poorly

understood.

Due to the timing and location of data collection, the effects of forestry practices

have not been assessed in this study. As no phosphate fertilisation treatments were

carried out and no harvesting took place close the sampling points during the data

collection period in the study area, results appear to reflect background values. A

goal here is to provide baseline values for future monitoring and management. In any

environmental assessment, it is important to establish the role of natural processes in

the mobilisation of solutes so that these can be monitored and accounted for in future

studies. To obtain some understanding of these processes in such settings with

comparatively low-level modification prior to urban development, we have chosen

this area on the Fraser Coast in the southeast Queensland region to conduct an

integrated investigation of hydrological systems.


1.1 Aims and Approach

This coastal zone of the Fraser Coast of Queensland and the adjacent Great Sandy

Strait are important areas, both environmentally and economically. Although there

has been continuous water quality monitoring of other areas within the Great Sandy

Strait, there has been no continuous water quality monitoring (estuarine or

freshwater) prior to this study in this project area (BMRG 2005). For such an

ecologically sensitive area, the collection, analysis and interpretation of

hydrochemical data are invaluable to future assessments and monitoring. In order to

preserve and improve the economic and environmental value of this region, it is

essential to obtain a sound understanding of processes that can potentially contribute

to the degradation of ground and surface waters within these catchments and the

marine environment, the overall aim of this study. In broad terms, the two main aims

of this thesis are:

1) Determine how solutes are transported within the catchment and to the marine

environment

2) Identify and describe processes within these ground and surface waters that

affect the mobilisation of Fe

In order to achieve these aims the following information is required.

The distribution of the relevant solutes within the study area

The sources of these solutes

Processes affecting solute concentrations and/or mobilisation of solutes

This study is a thesis by publication, and is based on three linked papers which are

described below. Papers 1 and 2 primarily address the first aim.

PAPER 1 Hydrochemistry and isotopic character of groundwater types and

connectivity in a subtropical coastal setting, Fraser Coast, Queensland. The focus of

this paper is to characterise the aquifers and determine connectivity and catchment-

ocean linkages within this plantation. Hydrochemical, physicochemical, isotopic,

geological and lithological information are integrated in order to (a) characterise

ground and surface waters within the study area, (b) establish where hydrological

links exist between surface and subsurface water bodies, and (c) determine how


solutes can be transported from these freshwater coastal catchments to the adjacent

marine environment via subsurface and surface processes. This study also provides a

discussion of the sedimentology, geological character and groundwater occurrence in

this region. Stable isotopes in water (δ18

O, δ2H) are used to investigate surface water

and groundwater recharge sources. This paper encompasses a number of catchments

and identifies potential mechanisms for the transport of solutes.

PAPER 2 Cluster analysis to support graphical methods in the characterisation of

ground and surface waters in a subtropical coastal zone, Fraser Coast, Queensland.

Due to the uncertain nature of some of the conclusions made in Paper 1, a result of

the limitations of the graphical methods used, more objective statistical methods are

applied to support, augment and/or reject the earlier interpretation. This paper further

develops and clarifies conclusions and ideas from Paper 1 using hierarchical cluster

analysis (HCA).

Paper 3 primarily addresses the second aim.

PAPER 3 Iron and nutrient sources, distribution and transport within the

groundwaters and surface waters of a subtropical coastal setting, Fraser Coast,

Queensland, using hydrochemical and isotopic data. A dataset including δ13

CDIC,

δ34

SSO4, δ15

N, Fe(II), Fe(III), DOC and H2S concentrations is used to characterise

waters in the study in relation to potential Fe mobilisation and transport as well as

forms and sources of nutrients, S, C and N. This paper further develops the

characterisation of waters begun in Paper 1. Here, waters are characterised in relation

to Eh, pH, Fe, dissolved organic carbon (DOC), DIC (dissolved inorganic carbon), N

and S. In addition, smaller-scale processes relating to the mobilisation and transport

of Fe are described using three different hydromorphological environments (one

surface and two groundwater sites) to illustrate relevant processes. In this way

smaller scale processes that affect the transport of Fe are identified in addition to

larger-scale mechanisms such as ground-surface water interaction. These are

subsystems within the overall coastal zone system where different scale processes

can affect transport.

The results and findings from these three papers provide:

An initial assessment of water chemistry in an area where no previous work

has been carried out and identification of solute sources


Information relating to nutrient and Fe transport and distribution that can

assist in the management of these types of landscapes to avoid degradation of

water quality and the growth of algal blooms. In relation to Lyngbya

majuscula, the first and second papers in this thesis establish the distribution

of nutrients of concern (nitrate and phosphate) and potential transport

pathways for these nutrients in the study area. The third paper looks in detail

at processes contributing to the form and transport of Fe and C. This

information is highly relevant to the consideration of nutrient input and

processes that may contribute to algal blooms.

As well as determining where anthropogenic activities are already influencing

water quality in this region, an aim of this thesis is to provide an initial

assessment of water chemistry in this relatively low-level modification area

prior to further modification, i.e. further urban development or forestry

activities such as harvesting or fertilization.

Valuable insight into natural processes affecting the concentrations and

mobilisation of Fe within both ground and surface waters in these types of

settings at both a micro- and macro- scale.

These findings will be applicable to many other areas along the southeast

Queensland with similar morphological and landuse characteristics, many of which

are subject to increasing pressure from urbanisation.

Additional aims are related to methodology. In Paper 2 the use of hierarchical cluster

analysis to assign sites to hydrochemical groups and identify areas of interaction is

assessed. In Paper 3, the efficacy of using different environmental isotopes for these

processes in this type of terrain is discussed.

1.2 Relationship to other research

1.2.1 Previous research

Bubb and Croton (2002) carried out a study in two catchments on the Fraser Coast in

southeast Queensland. The chosen catchments are similar in geomorphology and are

in close proximity to this project‘s study area. The catchments studied had ephemeral

creeks and perched watertables above a semi-confining layer and plantations were

regularly affected by extended periods of waterlogging. Little change was observed


in waterlogging characteristics following harvesting whereas stream flow increased

for 3 years with evidence of a decline after 5 years and the annual average increase in

stream flow was 28 mm following 90% clearing, considerably lower than the general

trends reported in the literature. Water level data indicated that lateral drainage from

the perched-watertable differed from that of surface flows. The perched watertable

drainage fluxes from the study catchments seemed minor and off-site movement of

solutes would therefore be limited.

Widespread waterlogging occurs in this region and has been of some concern to

plantation management, notably the effects on catchment water balance as discussed

in Bubb and Croton (2002). These authors concluded that surface topography is not a

fully reliable tool for predicting the location of waterlogging in their study area

(located in Toolara State Forest to the south of the Poona catchment) and that

knowledge of the topography of clay aquitards occurring in the catchment would be

more useful for this purpose. They also stress the need for a better understanding of

the interaction between the perched watertable, the clay aquitard and the lower semi-

confined aquifer. The piezometric head in a deeper aquifer in this forestry area

showed a relatively quick response to rainfall events even though the hydraulic

conductivity of the aquitard was low. In addition, a number of bores showed little

evidence of vertical water movement at lower depths, suggesting that there are

localised recharge areas within these forestry compartments, where the aquitards may

be discontinuous or have a considerably higher hydraulic conductivity (Bubb and

Croton 2002). These characteristics complicate the investigation of harvesting effects

on unconfined aquifers in the region. This type of waterlogging is also evident in the

Poona coastal zone, the main study area for this project.

Wang (2008) further investigated waterlogging in this region in her PhD thesis,

Impacts of climate, topography, and weathering profile on vadose zone hydrology

and coastal pine plantations management - a multi-scale investigation, southeast

Queensland, Australia. Wang concluded that low forest productivity to the north of

the Poona catchment was due to waterlogging and soil salinisation. She found that

the waterlogging was due to perched groundwater on top of aquitard layers of

ferricrete and mottled saprolite while the soil salinisation was due to the discharge of

brackish groundwater occurring within the mottled saprolite. Four sites from this

study are included among the data collection sites for this project.


The extensive waterlogging throughout these catchments can have a significant

impact on Fe transport. This is discussed in Löhr, et al. (2010) and also in Paper 3 of

this thesis.

1.2.2 Concurrent research

There were two other PhD studies concurrent with this one as part of the integrated

project Hydrological Controls over Distribution of Fe within a Forested Coastal

Catchment. These two studies focussed on the Poona catchment.

Lin (2011) investigated microbial activity in this study area in her thesis, Iron

biogeochemistry and associated greenhouse gas evolution in a forested subtropical

Australian coastal catchment: Poona Creek, Southeast Queensland, within a number

of ground and surface water sites in the Poona catchment. In Paper 4 of her thesis,

‗Bacterially-mediated iron cycling in subtropical shallow coastal groundwater‘, Lin

(2011) noted that, where Fe levels were abundant, they were often associated with

high carbon levels and Fe and S reducing and oxidising bacteria. Lin‘s study focused

on a number of monitoring wells drilled specifically for this project, two of which are

used to illustrate processes affecting the transport of Fe in Paper 3 of this thesis;

monitoring well P5 at the boundary of the supratidal flats adjacent to Poona Creek

estuary (Figure 10, Figure 12) and monitoring well P6, a fresh surface water ca.

120m inland from P5. Lin (2011) concludes that bacterially-mediated Fe redox

reactions and aerobic, heterotrophic respiration were integral to groundwater Fe-C

cycling in this aquifer and that these processes have implications for mineral

dissolution, Fe mobilisation and water quality in similar settings.

Löhr et al. (2010) identified processes controlling the distribution and phases of Fe in

soils and sediments in this study area in the paper ‗Iron occurrence in soils and

sediments of a coastal catchment. A multivariate approach using self organising

maps‘. The findings from this study are also referred to in Paper 3 in relation to Fe

sources and the reduction and organic complexation of Fe in waterlogged areas and

stream sediments that enables the mobilisation of Fe in the Poona catchment. The

results from this study showed no difference between the effect of pine plantation

and native vegetation organic materials on the complexation of Fe (and consequently

enhancing the solubility of Fe in soils) even though organic ligands from Pinus


species are thought to have stronger iron complexation properties (Rose and Waite

2003) than Australian native vegetation.

In the paper ‗The effect of Pinus vegetation and soil type on the speciation of iron in

soil solution‘ in Löhr‘s thesis (Löhr 2010), however, modelling results showed that

Pinus DOM can significantly increase the amount of dissolved ferric iron remaining

in solution in oxidising conditions. Consequently, inputs of ferrous iron together with

Pinus DOM to surface waters may reduce precipitation of hydrous ferric oxides and

increase the flux of dissolved iron out of the catchment.

1.3 Structure of Thesis

Chapter 2 comprises the background material for this study. The setting for this study

is described in relation to location, climate, landuse, geomorphology, geology, soils

and the occurrence of ground and surface waters. A more detailed description of

these aspects of the study area can be found in Paper 1. The literature review section

of this thesis is also included in this chapter which discusses hydrochemistry in the

coastal environment in relation to major ions, Fe and other nutrients. The forms and

occurrence of iron in ground and surface waters and processes effecting Fe mobility

and transport are described. Organic matter, microbial activity, pH and redox are also

discussed in relation to relevant processes. The theory and interpretation of stable

environmental isotopes δ2H, δ

18O, δ

13CDIC, δ

15N and δ

34SSO4 are then described in

Section 2.3. The information in this chapter is primarily literature review material

relating to Paper 3.

In Chapter 3, the project design is described in relation to data collection site

selection, geomorphological, geological and landuse characteristics of data collection

sites, the sampling programme, and field, laboratory and analysis methods used to

obtain and interpret data.

As this is a ‗Thesis by Publication‘, three stand-alone but related papers, as described

above, constitute the main body of the thesis. Chapters 4, 5 and 6 contain Papers 1, 2

and 3, respectively.

In the discussion chapter, Chapter 7, the main findings from the study are discussed

in relation to the aims of this thesis, as are potential implications for further

development and plantation forestry. Finally, the conclusions from the three papers


are stated in relation to the objectives of the thesis; groundwater occurrence, sources

of solutes in ground and surface water, processes/characteristics affecting

hydrochemical composition and solute transport.

13

2. BACKGROUND

This chapter gives a brief overview of the study area and places the work presented

in the papers included in this thesis in the context of previous work. The study area is

described briefly in the following section in relation to location, climate, landuse,

geomorphology, geology and ground and surface water occurrence. For a more in-

depth discussion of the study area, please refer to Paper 1. The second part of the

chapter reviews general hydrochemistry concepts and factors that influence the

hydrochemical composition of natural waters and the dissolution and precipitation of

Fe in particular. Stable environmental isotopes are then discussed in relation to

recharge and nutrient sources and hydrological and biogeochemical processes. These

concepts are highly relevant to Chapters 4-6 (Papers 1-3).

2.1 Regional Setting

The area being studied is on the Fraser Coast of Queensland, adjacent to the Great

Sandy Strait, an estuarine/marine passage landscape between the large Fraser Island

sand island and the mainland (Figure 1). It is ca. 450 km2 in size and located

approximately 300 km north of Brisbane, the Queensland capital. Maryborough, the

closest large town, is located on the tidal Mary River and is approximately 25 km

northwest of Poona village (Figure 2). This coastal zone forms part of a

discontinuous belt of lowlands on the eastern seaboard of Australia.

Figure 2 shows the landuse, catchments and coastal villages within the study area.

For the purposes of this study the northern section of the area is referred to as the

Tuan catchment and contains the subcatchments of Kalah, Maaroom, Big Tuan and

Little Tuan Creek. The southern section of the area is referred to as Poona catchment

and contains the subcatchments of Poona and Buttha Creeks (Figure 2).

2.1.1 Landuse

Poona, Little Tuan and Boonooroo are small coastal villages with populations of

approximately 200 (Figure 2). These communities do not have town water supply

and residential water is obtained from rainwater tanks and/or groundwater bores.

There are short-term population increases in these coastal villages for vacation,

fishing and recreation.

14 Chapter 2 Background

Figure 1 Map of Australia and a section of the southeast coast of Queensland.

The dashed box shows the location of the study area on the Fraser Coast.

The red dots show rainfall data locations, Tuan Forestry Office,

Maryborough, Toolara and Rainbow Beach.

The main landuse in the area consists of mature Pinus plantations ranging from 16 to

30 years of age, which have native vegetation buffer zones adjacent to natural

waterways (see Figure 2). Since the 1950s, extensive areas within these coastal

catchments and lowlands, which were generally unsuitable or marginal for

agriculture, were acquired by the state government forestry department for Pinus

afforestation (Costantini and Loch 2002). According to the Tuan 1: 50,000 map

(FPQ 2007), pine forests were first established north of Big Tuan Creek in 1974.

Some small pine plots were established as early as 1948 in the study area near the

Tuan Forestry Office. There were also soft-wood plantations to the east of

Maryborough and at Tuan from the mid 1960s, but there were very few plots until

the 1970s.

Tuan Forestry

Office

Toolara

Rainbow Beach

Q

LD

Double Island Point

Wide Bay

Chapter 2 Background 15

Figure 2 Extent of the area of the study showing drainage systems, landuse,

coastal villages and catchments. Pine plantations are the dominant land-

use in this coastal region. Boonooroo, Little Tuan and Poona are all small

coastal villages. Tuan Forestry Office supplied some of the rainfall data

used to describe climate conditions during data collection time periods.

Kalah, Maaroom and Tuan catchments are generally referred to as the

Tuan or northern catchment and Poona and Buttha catchments are

generally referred to as the Poona or southern catchment in the text of

this thesis.

The Ramsar-listed Great Sandy Strait hosts the largest area of tidal swamps within

the southeast Queensland bioregion. A number of threatened species (flora and

fauna) exist in the marine areas and associated tidal wetlands in this area such as

Tuan Forestry

Office

Poona

Creek Buttha

Creek

Big Tuan

Creek Tuan

Catchment

Buttha

Catchment

Kalah

Catchment

Maaroom

Catchment

Poona

Catchment

Boonooroo

Little Tuan

Poona

Village

Great Sandy Strait


dugong, dolphins, migratory shorebirds, seasonal populations of humpback whales

and rare shrubs. In addition, the Great Sandy Region attracts significant tourism due

to its environmental significance. This coastal area is also popular for a range of

recreational activities (scuba diving, fishing and nature walks) (EPA 2005).

2.1.2 Climate

The climate of the area is subtropical, typical of southeast Queensland, with more

than 60% of the annual rainfall occurring during the summer wet season (December

to February) and comparatively dry winters (June to August). Mean annual rainfall at

Maryborough, located approximately 5 km from the northwest corner of the study

area is 1115.7 mm (Bureau of Meteorology 2009). Based on Bureau of Meteorology

(2009) data for Rainbow Beach located 40 km SSE of the study area on the coast

below Fraser Island (Figure 1), the wettest month of the year is February with a mean

rainfall of 212.1 mm and September the driest with a mean rainfall of 63.4 mm.

Mean annual rainfall is 1419.2 mm. The highest mean maximum temperature of

27.7°C occurs in January and lowest mean minimum temperature of 14.0°C occurs in

July. The closest rain gauge station is at Tuan Forestry Office within the study area

(Figure 2).

Daily rainfall measurements for all three stations are shown in Figure 3 and

demonstrate the variability in rainfall over the study area. There is an overall trend of

decreasing rainfall towards the northeast due to the dominance of southwesterly

winds along the coast of southeast Queensland. Note that Rainbow Beach data has

been plotted on the secondary axis. This location generally has the highest rainfall

measurements with a rainfall of 154.0 mm occurring during a storm event (with

subsequent flooding) on 25/08/2007 as compared with Tuan Forestry Office and

Maryborough that had 119.0 and 66.6 mm, respectively. Rainfall distribution during

the study was atypical with this heavy rainfall occurring in August (winter).

2.1.3 Geomorphology

The mainland coastal region is characterised by forested catchments that drain to the

coastal floodplains (Figure 2, Figure 4). In the Poona catchment and southern Tuan

catchment, coastal plains are found immediately adjacent to the shoreline.

Immediately inland of these coastal plains are low rolling downs, only 3-5 m high


occurring at elevations 10-20 m above sea level (ASL) and further inland again are

low rolling hills with ridges that reach a height of up to 10 m, and occasional incised

streams. The landscape then grades to more accentuated topography and ridges in the

southwest that are commonly up to 30 m in height where ephemeral streams are

more highly incised (Coaldrake 1961). The catchment divide in the southwest is the

Como Scarp (Cranfield 1994). In the northern Tuan catchment (northern Tuan,

Maaroom and Kalah catchments), gradients are lower towards the delta of the large

Mary River. Figure 5 shows the topographical gradients in the study area generated

in ArcGIS.

Figure 3 Daily rainfall for Tuan Forestry Office (blue), Maryborough (green) and

Rainbow Beach (red) from 01/08/2007 to 31/07/2008. FT1 – FT4 are

sample collection field trips and are shown as black dots to indicate

conditions at the time of sample collection. Note that Rainbow Beach is

plotted on the secondary axis.

Topographically, gradients in the study area are generally less than 1% and elevation

mostly below 50 m ASL (Figure 5). The drainage systems are overall shallow and

tidal in their lower reaches within the coastal plains. Tributaries in the headwaters

and upper parts of the catchment are ephemeral and can be highly incised. Extensive

intertidal banks occur for a distance of approximately of 4 km upstream from the

mouth of Poona Creek and for some distance up Big Tuan Creek.

FT1 FT2 FT3 FT4

0

100

200

300

400

500

600

0.0

20.0

40.0

60.0

80.0

100.0

120.0

140.0

160.0

180.0

200.0

Rai

nb

ow

Be

ach

Rai

nfa

ll (m

m)

Tuan

Fo

rest

ry O

ffic

e a

nd

Mar

ybo

rou

gh R

ain

fall

(mm

)

Date

Tuan Forestry Office

Maryborough

Rainbow Beach

Data Collection


Figure 4 View from the top of Poona Creek catchment eastward across the coastal

plain to the Great Sandy Strait and Fraser Island

Figure 5 Topography gradients and drainage system in the study area. Note the

flatter gradients in the northern areas of the Tuan catchment. The LiDAR

data sourced from FPQ only covers plantation areas.

Tuan

Catchment

Poona

Catchment


2.1.4 Geology

The study area comprises the following formations and unconsolidated sediments.

The distribution of these is shown in Figure 6, a GIS layer of the geology in the

region extracted from GSQ digital geology (Natural Resources Mines and Energy

2004) maps.

(1) Duckinwilla Group: lithofeldspathic-labile and sublabile-to-quartzose

sandstone, siltstone, shale, coal and a ferruginous oolite marker. This formation

is late Triassic (230 Ma) to early Jurassic (184 Ma) in age and occurs in

weathered form along the coast from Big Tuan Creek southwards and to the

south and west of the study area.

(2) Grahams Creek Formation: intercalated volcanics and volcaniclastic

sedimentary rocks (Cranfield 1993). This formation is late Jurassic (159 Ma) to

early Cretaceous (98 Ma) in age and occurs in weathered form and as small

pockets of unweathered material in a central zone parallel to the shoreline

within the study area.

(3) Elliot Formation: quartzose to sublabile sandstone, conglomerate, siltstone,

mudstone, shale. This formation is Eocene (55 Ma) to Oligocene (34 Ma) in

age and is mostly weathered, however, there are some unweathered outcrops

along Big Tuan Creek. This formation dominates the surficial geology in Tuan

and Boonooroo, but south of Big Tuan Creek occurs further inland alternating

with the Duckinwilla Formation.

(4) Holocene Beach ridges: sand, shelly sand, minor gravel. There are beach ridges

at Poona and Boonooroo adjacent to the Strait.

(5) Holocene Estuarine tidal flats: mud and sand. Estuarine tidal flats occur within

the estuaries of the creeks and for some distance from the coastline.

The Duckinwilla, Elliot and Graham‘s Creek formations have been highly weathered

since the Miocene (24 Ma) and most of the land surface in the study area is covered

by a deep lateritic1 profile. Both weathered Elliot and Graham‘s Creek formations

occur in two forms; as the duricrusted old land surface with dominant facies being

1 Laterization is the process whereby weathering conditions lead to the removal of silica and

alkalies, resulting in a soil or rock with high concentrations of iron and aluminium Parker, S. P.

(1997). Dictionary of Geology and Mineralogy. New York, McGraw-Hill..


ferricrete with silcrete and indurated palaeosols2 at the top of a deep weathering

profile and as undifferentiated coastal plain sediments, sand, silt, mud and minor

gravel. Duricrust is the case-hardened soil crust formed in semiarid climates by

precipitation of salts and can contain aluminous, ferruginous, siliceous, and

calcareous material. Ferricrete is the resulting conglomerate of surficial sand and

gravel held together by iron oxide resulting from this percolation of solutions of iron

salts (Parker 1997).

2.1.5 Soils

The soil profiles in the study area are highly variable and soil types range from ferric,

red and yellow kandosols within the more elevated catchment areas to aeric to

subaquic podzols on the coastal plain (Holzworth 1990). Higher topographic areas

often have very shallow topsoil overlying weathered bedrock while lower

topography areas often contain sediments that have been eroded from the higher

features. This is further complicated by the presence of aeolian sand dune deposits

which occur throughout the area (Hammond, unpub. data, 2007). Another common

feature in these soils in this area is a high proportion of Fe nodules. These can be in

the form of cemented horizons up to 50 cm thick, but mainly occur as uncemented,

ferric horizons (Löhr 2010; Löhr et al. 2010). According to Coaldrake (1961)

podzolisation, laterisation and gleying are the three most common pedogenic

processes throughout the coastal lowlands.

An important feature of this study area is the extensive seasonal waterlogging that

occurs in lower-gradient zones with these catchments (Wang et al. 2008).

Waterlogging in the coastal lowlands is commonplace following rainfall and is

attributed to podzol and podzolic soils forming shallow resistive layers (e.g. Bubb

and Croton, 2002). The hydrological connectivity of these perched shallow

groundwaters to the surface drainage systems is not yet fully understood. These

perched watertables can produce gleying in the upper part of the profile and have a

major influence on the mobilisation of Fe within these catchments (Löhr et al. 2010).

A common feature in gleyed soils is the watertable rising to within 30 cm of the

2 A paleosol is a soil horizon that formed on the surface during the geologic past, that is, an ancient

soil ibid..


surface several times during a normal wet season and may not drop below 2 m for up

to 3 months after a wet summer before receding to below 4 m during a dry season

(Coaldrake 1961).

Figure 6 Geology of the study area showing the location of data collection sites

and the boundaries of the Tertiary alluvium aquifer described in Laycock

(1969). Most of the area is covered by a deep weathering profile

overlying sandstone bedrock. See Figure 12 for a closer view of the sites

in the rectangle in the eastern central region of the figure.

Source: Natural Resources Mines and Energy (2004)

204B

134B

PCP

P1-P14 PCM


2.1.6 Surface water

Within much of the estate the drainage systems are little modified, and in low-lying

areas extensive areas of Melaleuca wetlands remain. In the more elevated parts of the

catchment, streams are more often ephemeral and incised into the bedrock. In the

coastal plain, streams are perennial but interaction between many tributary streams

and the main estuary is often restricted by downstream channel infilling.

The estuaries in the study region are tidally dominated. In Poona Creek, the estuary

head occurs approximately at Pappins Bridge (the Cooloola Road crossing), a

distance of 9 km following the main channel from the mouth of Poona Creek

(BMRG 2005) or approximately 5 km inland from the coast. According to the

Bureau of Meteorology (BoM) (2008), tidal peak and trough times at Elbow Point

(located approximately 10 km ENE of Poona Creek mouth on Fraser Island) occur

six minutes after those at Bundaberg located approximately 110 km north of Poona

village. Tides occurring at Bundaberg have microtidal (neap) to mesotidal (spring)

ranges with King Tides during 2008 falling on 23/01/08 and 14/12/08 (summer) and

03/07/08 (winter) of 3.45, 3.46 and 3.44 metres, respectively. Poona estuary has a

mixed tidal regime where a sequence of higher high, lower low, lower high and

higher low tides occurs approximately every 25 hours. At the mouth of Poona Creek,

spring tidal ranges are generally a little less than 2m (Larsen, unpub. data, 2008).

Poona, Big Tuan, Little Tuan and Maaroom Creeks all drain to Wide Bay in the

Great Sandy Strait.

2.1.7 Groundwater

There do not appear to be any continuous and/or substantial unconfined alluvial

deposit aquifers in the study area but rather shallow topsoils over semi-confining to

confining weathered bedrock in the elevated catchment areas and discontinuous clay

layers within the coastal plain. There are, however, some small pockets of

unconfined groundwater adjacent to the tributaries occurring within relict fluvial

channels or infilled meanders in the coastal plain.

Deeper confined aquifers in the area containing potable water occur in the beach

ridge sands adjacent to the Great Sandy Strait. These beach ridge aquifer systems,

however, are highly inhomogeneous with deeper confined aquifers and shallower

semi-confined and unconfined fresh and brackish waters with variable levels of


interaction with marine waters. In addition, an earlier study by Laycock (1969)

reports a Tertiary alluvial aquifer in the northern Tuan catchment which also contains

good quality potable waters. These data have been included in the study.

In the following sections, background information is provided in relation to coastal

hydrochemistry, in particular Fe related processes, and stable environmental

isotopes. Knowledge of these topics is essential in the investigation of the various

modes of surface water and groundwater interaction in this coastal plantation region.

2.2 Coastal Hydrochemistry

The subsurface can be thought of as a dynamic geochemical system consisting of (a)

solid phases (minerals, amorphous solids and organic matter), (b) a soil gas phase,

and (3) an aqueous solution phase (water with its dissolved constituents). The

solution phase in the subsurface is the primary medium of exchange and transport. At

the watertable and above in the unsaturated zone, gases dissolve into the water and

can be transported away from their point of origin. Along the entire flow path from

the earth‘s surface through aquifers and surface drainage systems, components of the

solid phases dissolve into and/or precipitate from these waters, which then facilitates

or retards the movement of dissolved components through the system (Deutsch

1997).

2.2.1 Water quality constituents

Solutes contained in natural water represent the net effect of a series of antecedent

chemical reactions that have dissolved material from another phase, have altered

previously dissolved components, or have eliminated them from solution by

precipitation or other processes. These chemical processes are influenced strongly by

biological activity in some environments and by a great many processes of a physical

nature (Hem 1992). Protecting groundwater and surface water from pollution

requires first identifying the sites where sudden or gradual changes in the

physicochemical properties of these waters have occurred (Kelly and Mares 1993).

Environmental hydrochemistry is focused on monitoring the dispersion of metals and

various organic compounds that have anthropogenic sources and has become

increasingly important in recent years for natural resource management. The


continued monitoring of these processes is fundamental to maintaining a healthy

environment (Faure 1998).

The chemistry of most natural ground and surface waters is a function of:

Rock and sediment type: different rock types have different weathering rates and

different ion ratios

Relief and aquifer geometry: high relief means high physical erosion, and

therefore the exposure of fresh rock to weathering. Aquifer geometry is

important for the water-rock volume ratio.

Climate: rainfall means dilution but larger amounts of water become available

for weathering. Temperature affects the rate and occurrence of chemical

reactions.

Vegetation: vegetation supplies acid to the soil, thus increasing the rate of

weathering, but also stabilises the soil and protects the underlying rock from

further weathering.

Time, as a function of other parameters

Major ions are solutes in ground and surface waters that can be found at quantities

larger than 1 mg/L and these are the major cations calcium (Ca2+

), magnesium

(Mg2+

), sodium (Na+), and potassium (K

+) and the major anions

bicarbonate/carbonate ( 33 /COHCO ), sulphate ( 2

4SO ), and chloride (Cl-).

Trace elements are elements with a concentration less than one milligram per litre.

Trace metals and other elements originate from the weathering of rocks, human

activity and direct dumping into the water system. Metal occurrence in rock forming

minerals is based on the type of crystallographic structure, for example, while quartz

and alkali-feldspar have low concentrations of heavy metals, magmatic minerals such

as biotite, pyroxene and olivine contain higher levels of heavy metals (Liaghati

2004). The concentrations of trace metals in natural waters vary as a function of

actual concentration in rock/pollutant and solubility as a function of water

composition, temperature, pH and, for species with different oxidation states, redox

potentials (Eh). The potential danger of elements is a function of their mobility, that

is of their chemical form, and that is a function of composition, pH and Eh. Their

toxicity is either intrinsic or a function of their concentration (Faure 1998; Drever

2002; Appelo and Postma 2005).


Atmospheric fall-out can also input trace metals and other pollutants to waterbodies.

Dust transported overland from the Saharan Desert (Olade 1987; Walsh and

Steidinger 2001; Garrison et al. 2006; Remoundaki et al. 2011) and Owen‘s Lake in

California, USA (Reheis 1997; Department of Water and Power LA 2000), for

example, can be sources of toxic trace metals such as lead and arsenic, in addition to

organic pollutants and microbes. Australia is the dominant source of mineral dust

aerosol in the Southern Hemisphere and the dust from central Australian soils is iron-

rich in character. This dust aerosol can be transported to coastal areas and to the

Indian Ocean, Tasman Sea and Pacific Ocean where it can influence marine

ecosystems after being deposited and dissolved in natural waters (Radhi et al. 2011).

For example, Gabric et al. (2010) used meteorological records, satellite ocean colour,

aerosol optical depth data and dust transport modelling to investigate the transport

and deposition of mineral dust from Australia over adjacent ocean regions. Their

results provided strong evidence for a large-scale natural dust fertilization even in the

Australian sector of the Southern Ocean and highlighted the importance of dust-

derived nutrients in the marine carbon cycle of the Southern Ocean.

Gaseous metals (which may form aerosols) in the atmosphere are derived from

perhaps six sources. These include: (1) volcanism; (2) release from biological

activity (Hg, As, Se); (3) sea surf fractionation during production of atmospheric sea

salt particles; (4) burning of fossil fuels - the combustion of leaded fuels can result in

a concentrations of Pb along roadsides (Langmuir 1997); (5) smelting of metal ores

can result, for example, in the emission of significant amounts of sulphur dioxide, a

source of acid rain (Pepper et al. 2006); and (6) incinerator combustion of urban

wastes (Langmuir 1997). An excess of metals in the atmosphere, whether due to

natural or anthropogenic causes, can be detrimental to human and ecosystem health.

Electrical Conductivity (EC) and Total Dissolved Ions (TDI)

Groundwater can be viewed as an electrolyte solution because nearly all its major

and minor constituents are present in ionic form. The ability of water to conduct

electricity is directly proportional to the amount of dissolved, charged species (ions)

which it contains (McNeil and Cox 2000). Electrical conductivity (EC) gives a

general indication of the total dissolved ionic constituents by determining the


capability of a water sample to conduct an applied current. The total dissolved ions

(TDI) in a sample in mg/L is related to conductivity by the following equation.

TDI = A×(EC) (1)

where A is a constant which, for groundwater, is typically somewhere between 0.55

and 0.75. The total concentration of the six major ions, Ca2+

, Mg2+

, Na+,

33 /COHCO , 2

4SO and Cl- is normally accounts for 90% of the TDI of groundwaters

(Freeze and Cherry 1979; Younger 2007). TDI greater than 2000 – 3000 mg/L is too

salty to drink and seawater typically has a TDI value around 35,000 mg/L.

Table 1 Typical EC and TDI ranges for waters of variable salinities

Category EC (µS/cm) TDI (mg/L)

Distilled water 1 0.67

Rainfall 30 20.1

Freshwater 0 – 1,500 0 – 1050

Brackish 1,500 – 15,000 1050 – 10,050

Saline 15,000 – 150,000 10,050 – 100,500

Brine > 150,000 > 100,500

Note: Here, an A value of 0.67 has been used to convert EC to TDS (Watling 2007).

Source: Freeze and Cherry (1979), Anderson and Cummings (1999), Waterwatch SA (2006)

There are expected differences between ground and surface water chemistry. For

example, dissolved iron concentrations in groundwater systems are typically two to

three orders of magnitude greater than those found in surface waters. This can be

due, in part, to the anoxic conditions in groundwater environments, which typically

increase the solubility of iron and also transform iron into a more bioavailable3 form

(Gibbes et al. 2006).

2.2.2 Iron

Iron is essential for the growth and metabolism of all aquatic organisms and is

involved in key metabolic processes: photosynthetic and respiratory electron

transport, nitrate and nitrite reduction, nitrogen fixation and sulphate reduction. Even

in regions once considered iron replete, iron exerts a considerable influence on the

3 Bioavailability is the degree and rate at which a substance is absorbed into a living system or is made

available at the site of physiological activity Merriam-Webster Incorporated (2012) Merriam-

Webster Online Dictionary. Retrieved January, 2012, from http://www.merriam-webster.com/.. In

this case, we are predominantly referring to Fe and other natural water nutrients such as nitrate and

phosphate and their availability for microbial and plant-related processes.


aquatic ecosystem (Coale et al. 1996; WBM Oceanics Australia 2001; Pointon et al.

2003).

The concentrations of trace metals in natural waters vary as a function of actual

concentration in rock/pollutant and solubility as a function of water composition,

temperature, pH and, for species with different oxidation states, redox potentials

(Liaghati 2004). In sedimentary environments, metals may occur: (a) adsorbed on

solids, (b) precipitated and co-precipitated on solids (e.g. Fe and Mn as metallic

coatings), (c) incorporated in solid biologic materials, and (d) incorporated in crystal

structures (Forstner and Wittmann 1983). A substantial input of metals to coastal

lowlands may occur as a result of weathering and erosion of geological formations.

The introduction of metals to the coastal environment can also be due to human

activities. Consequently, it is very important to consider both anthropogenic and

natural regional inputs when investigating trace metals (Preda and Cox 2001; Preda

and Cox 2002).

In general, water in flowing freshwater streams at near-neutral pH will not contain

significant concentrations of uncomplexed dissolved ferrous iron. Iron in these

waters will normally occur either as particulate ferric hydroxide or as some form of

organic complex (Hem 1992). In lakes and reservoirs where stratified conditions

exist, water at and near the bottom may become depleted in oxygen and be at low Eh.

In waters of this type, Fe(II) can be retained in solution to levels of many mg/L (Hem

1992).

Although dissolved Fe(III) is absent between pH 5 and 10, Fe(III) oxyhydroxides

occur in suspended form in ground and surface waters within this pH range

(Langmuir 1997). Colloidal forms of iron have been observed or postulated in fresh

and marine waters which account for iron concentrations much larger than the

equilibrium solubility of iron oxyhydroxides (Lofts et al. 2008). Forms of iron

consist largely of Fe(III) organic complexes or small hydroxide particles in

freshwaters (Davison and Vitre 1992) although organically complexed Fe(III) is far

more abundant. Hydrous ferric oxides (sometimes termed ferrihydrite) are usually

formed by oxidation of Fe(II) followed by subsequent Fe(III) hydrolysis and the rate

of these reactions may be increased due to bacterial Fe(II) oxidation activity.

Ferrihydrite present in waters may be sourced either from soils, or freshly-formed in

the water column (Allard et al. 2004), and generally precipitates out of solution.


Dissolved iron concentrations in groundwater systems are typically two to three

orders of magnitude greater than those found in surface waters. Generally, this is due

to anoxic conditions in groundwater environments which typically increase iron

solubility and transform iron into a more bioavailable form (Gibbes et al. 2006).

Groundwater with a pH 6 - 8 can be sufficiently reducing to carry as much as 50

mg/L of Fe(II) at equilibrium, where bicarbonate activity is less than 61 mg/L (Hem

1992).

Role of iron and nutrients in Lyngbya growth

The growth of Lyngbya, and algae generally, is promoted by high levels of nutrients

and iron and the presence of humic substances from land runoff that make the iron

bioavailable (Pointon et al. 2003). Nutrients such as nitrogen and phosphorus, plus

micronutrients such as iron all play a large part in regulating the metabolism, and

ultimately the growth, of cyanobacteria and algae.

Abal and Watkinson (2000) found that creeks and waterways adjacent to algal bloom

areas were large sources of iron and dissolved organic carbon during runoff events.

One theory is that the elevated level of iron in the runoff is due to the exposure of

acid sulphate soils, a result of coastal building development and other landuse

modifications in the area (Moreton Bay Catchment Water Quality Management

Strategy Team 1998; Pointon et al. 2003). Ahern et al. (2006a) investigated the

potential for groundwater from ten combinations of vegetation, soil and landuses to

stimulate Lyngbya growth in Deception Bay by measuring the photosynthetic

response of Lyngbya to diluted samples of groundwater under laboratory conditions.

Results showed that groundwaters from systems characterised by acid sulphate soils,

exotic pine plantations and Melaleuca vegetation significantly stimulated Lyngbya

photosynthesis (Ahern et al. 2006a).

Iron mobility in coastal zones

Oceanic waters have very low iron concentrations, generally being less than 0.1mg/L

(Armstrong 1957; Hem 1992; Anthoni 2006). Dissolved ferrous iron generally has a

terrigenous source and is transported to the coast where, under estuarine conditions,

the major proportion, if not all, precipitates out of solution via oxidation to ferric

oxyhydroxides. This occurs in both surface and groundwaters due to the differences


in dissolved oxygen (DO) concentrations, pH and Eh and between fresh and marine

waters. Spiteri et al. (2006) found that the pH gradient at the mixing zone of

freshwater and seawater in a subterranean estuary caused an approximately seven-

fold increase in the rate of oxidative precipitation of Fe(II) thereby reducing levels of

iron significantly before they could reach the marine environment.

Charette and Sholkovitz (2002) attributed iron oxide-coated sands in a subterranean

estuary on Cape Cod to the precipitation of groundwater-borne (non-colloidal)

dissolved ferrous iron and subsequent accumulation of iron oxides onto subsurface

sands at the groundwater-seawater interface – an ‗Iron Curtain‘. As naturally-

occurring iron oxides are strong adsorbers and concentrators of many dissolved

chemical species, such as phosphate (Spiteri et al. 2006), the occurrence of an ‗Iron

Curtain‘ has broad implications for transport of natural and anthropogenic materials

from aquifers into coastal waters (Charette and Sholkovitz 2002).

However, ground and river waters can still contribute significant quantities of

dissolved iron to marine environments (Krachler et al. 2005; Windom et al. 2006;

Roy et al. 2010). Terrigenous dissolved iron can be transported to the marine

environment via drainage systems and groundwater seepage often in organically

complexed form (Krachler et al. 2005). Due to the fact that inorganic Fe(III) species

in natural waters have very low solubility, iron is generally transported from

upstream soils in the form of low molecular weight colloidal fulvic-iron complexes

to marine waters (Krachler et al. 2005). Fe(III) forms strong complexes with most

ligands. In oxidised surface waters and sediments, dissolved iron is mobile below

about a pH of 3 - 4 as Fe(III) organic complexes. In many soils, as well as surface

and groundwaters, Fe(III) is mobile as ferric-organic (humic-fulvic) complexes up to

about pH 5 - 6 and as colloidal ferric oxyhydroxides between about pH 3 - 8

(Langmuir 1997).

Studies have shown that the input of fulvic acids4 can maintain iron in solution in

brackish to saline coastal waters. Krachler et al. (2005) studied the influence of

4 Fulvic acid, one of two classes of natural acidic organic polymer (the other is humic acid) that can

be extracted from humus found in soils, sediment, or aquatic environments. Its structure is best

characterized as a loose assembly of aromatic organic polymers with many carboxyl groups (COOH)

that release hydrogen ions resulting in species that have electric charges at various sites on the ion. It

is especially reactive with metals, forming strong complexes with Fe(III), Al(III) and Cu(II) in


natural metal chelators on the bioavailable iron input to the ocean by river water.

They observed the sequential destabilisation of different iron-binding colloids with

increasing salinity as a freshwater carrier was mixed with seawater at the continental

boundary. They found that, due to the supply of fulvic acids, approximately 20% of

the original Fe load (≈ 480 µg/L) from a sphagnum peat-bog was added to the

ocean‘s bioavailable iron pool. These results point to a natural mechanism of ocean

iron fertilisation by terrigenous fulvic-iron complexes originating from weathering

processes occurring in the upstream soils (Krachler et al. 2005). Windom et al.

(2006) estimated a submarine groundwater discharge flux of approximately 1.12×105

kg/day of dissolved Fe from the coastline of the Patos Lagoon in South America and

Roy et al. (2010) estimate a flux of 46.9 µg/L/day per metre of shoreline to the

Indian River Lagoon in Florida.

Suspensions of colloidal-sized Fe oxyhydroxides in surface waters can be

destabilized by increases in ionic strength (strong electrolyte concentrations) such as

occur when a stream enters an estuary (Langmuir 1997). Boyle et al. (1977)

duplicated these processes in the laboratory and confirmed the large-scale rapid

removal of iron from river water during estuarine mixing. The river-borne

‗dissolved‘ iron consisted almost entirely of mixed iron oxide-organic matter colloids

of diameter less than 0.45 µm, stabilized by dissolved organic matter. Precipitation

occurs on mixing due to seawater cation neutralization of negatively charged iron-

bearing colloids, allowing flocculation. Estuaries therefore become a kind of sink for

removal of iron. Boyle et al. (1977) estimated this flocculation results in an

approximate 90% reduction of input of dissolved iron to the ocean.

Another important process contributing to organic matter decomposition and Fe

geochemistry in drainage systems involves the reduction of Fe(III) oxyhydroxides in

the hyporheic zone bottom sediments of freshwater streams. Contrary to common

belief, groundwater and associated hyporheic zones are not sterile or devoid of life

(Hancock et al. 2005). Lovley and Phillips (1986) found the overall extent of

particular and leading to their increased solubility in natural waters Domenico, P. A. and F. A.

Schwartz (1990) Physical and Chemical Hydrogeology. New York, John Wiley & Sons, Appelo, C.

A. J. and D. Postma (2005) Geochemistry, Groundwater and Pollution. Amsterdam, A.A. Balkema

Publishers..


microbial Fe(III) reduction was governed by the inability of microorganisms to

reduce most of the Fe(III) in the freshwater stream sediments of the Potomac River.

Amorphous Fe(III) oxyhydroxides and poorly-ordered Fe(III) oxyhydroxides

(ferrihydrite Fe(OH)3) were considered readily reducible, while other Fe(III) forms

such as magnetite (Fe3O4) and siderite (FeCO3) persisted even after prolonged

incubation. The reductive dissolution of Fe oxides, a microbially mediated process,

can be represented by the following reaction.

(2)

where CH2O is a simplified representation of organic matter (Appelo and Postma

2005).

Waterlogging of soils can also contribute to the mobilisation of Fe to waterways.

Waterlogging often results in reducing conditions where Fe present in the soils or

sediments is reduced to its dissolved ferrous form and can then be transported via

seepage or rising watertables to ground and surface water systems. Fritsch et al.

(2009) found that reducing conditions restrict the production of organically

complexed Fe in subsoil B-horizons of waterlogged soils. Most of the Fe(II) released

from the dissolution of Fe-oxides was exported to the Negro River in the Amazon via

perched groundwater. However, significant amounts of Fe(III) organic complexes

and nano Fe-oxides were produced in topsoil A horizons due to shorter periods of

anoxia (Fritsch et al. 2009). Therefore, Fe in both forms can potentially be

transported to drainage systems due to rising watertables or groundwater seepage.

The inorganic oxidation of Fe(II) can be represented by the following reactions.

(3)

(4)

Iron bacteria obtain energy by oxidising soluble ferrous iron into insoluble ferric iron

which then precipitates out of solution forming slimy rust-coloured precipitates

and/or biofilms on creek bottoms and well casings which can produce negative water

quality issues (Queensland Government 2006). Biofilm results from the oxidation of

iron into its insoluble ferric state by the bacteria which is then deposited in the slimy

gelatinous extracellular polymeric material that surrounds the bacterial cells and can

promote microbially influenced corrosion (MIC) of underlying metallic surfaces


(Smith 2008; National Ground Water Association 2009a; Barrett 2010). These

bacteria are known to grow in waters containing as little as 0.1 mg/L iron (Langmuir

1997) but also require at least 0.3 mg/L of DO. The source of Fe-oxidising bacteria

in groundwater is often unknown but are assumed to be indigenous or disseminated

by contaminated surface water (i.e. sewage effluent (Tyagi et al. 1993; Maeda et al.

1999), leachate from garbage dumps (Yu et al. 2010), and other polluted waters) to

groundwater. Note Fe could also be disseminated into groundwaters from

uncontaminated surface waters, i.e. indigenous, not anthropogenic (Queensland

Government 2006; National Ground Water Association 2009a; Barrett 2010).

An oily sheen is sometimes associated with this rust-coloured biofilm that can be

observed floating on the surface of creeks and streams, a bi-product of the microbial

oxidation process. One theory is that anaerobic bacteria reduce ferric iron to ferrous

iron promoting ferrous iron movement through water to oxic zones where it oxidises

and precipitates. Rather than sinking to the bottom of the water body, these

precipitates float on the surface as the ―oily‖ colourful inorganic ferric sheen

(Thomas 2007).

Iron and sulphur

Total sulphide includes dissolved H2S and HS- and acid-volatile metallic sulphides

present in particulate matter. Hydrogen sulphide escaping into the air from sulphide-

containing wastewater causes odour nuisances (Parrott et al. 2009). The threshold

odour concentration of H2S in clean water is between 0.025 and 0.25 µg/L (Eaton

and Andrew 2005). H2S can attack metals directly and indirectly and has caused

serious corrosion of concrete sewers because it can be microbially oxidized to H2SO4

on pipe walls. Gaseous H2S is very toxic and can be fatal to humans and dissolved

H2S is toxic to fish and other aquatic organisms (Eaton and Andrew 2005).

Sulphide is often present in groundwater and is produced by the decomposition of

organic matter and bacterial reduction of sulphate. Sedimentary Fe(III)

oxyhydroxides are the source of iron for most precipitated Fe(II) sulphides

(Langmuir 1997). However, where sulphur is present and conditions are sufficiently

anaerobic to promote sulphate reduction, Fe(II) precipitates almost quantitatively as

sulphides (Langmuir 1997). Fe(II) forms a reasonably strong ion pair with the

bisulphide ion whereas other Fe(II) ion pairs are generally weak. Pyrite (FeS2) is by


far the most abundant sulphide mineral, occurring in most types of geologic

formation, particularly coals and peats (Langmuir 1997). The breakdown of these

minerals due to oxidation can result in the release of significant sulphate and iron

loads. Most coals also contain organically-bound sulphur in amounts usually

exceeding that present as FeS2 (Langmuir 1997).

Webb et al. (1998) investigated metal removal by sulphate-reducing bacteria from

natural and constructed wetlands. The biological processes involved in natural

wetlands centre on the complex anaerobic ecology within sediments and involve the

removal of metals by sulphate reducing bacteria (SRB) that generate hydrogen

sulphide and cause precipitation of metals from solution as insoluble metal sulphides

such as FeS2. The authors found that population compositions of SRB enrichments

were markedly different and consequently, rates of metal removal from solution were

significantly lower in the constructed wetlands than the natural wetlands.

Sulphate reduction by organic matter is catalysed by various strains of bacteria

according to the overall reaction

(5)

The importance of sulphate reduction in an aquifer depends on both availability of

reactive organic matter and sulphate supply (Appelo and Postma 2005).

Many of the processes described in the above section are discussed in Paper 3 of this

thesis in relation to Fe transport in the study area.

2.2.3 Macronutrients

Nitrogen and phosphorus are macronutrients and iron is a micronutrient required for

growth and photosynthesis of all marine plants. Some algae are less reliant on

nitrogen sources from the marine environment as they can fix their own nitrogen

(atmospheric N2). These algae often have higher iron requirements than non-

nitrogen-fixing organisms.

Understanding the temporal and spatial mechanisms of nutrient enrichment is

essential to controlling water quality (Slomp and van Cappellen 2004). Diffuse

nutrient pollution via runoff from agricultural areas or through submarine

groundwater discharge, is particularly difficult to control once in waterways due to

the complex relationships between nutrient sources, forms and their transport media


(Weiskel and Howes 1992; Kroeger et al. 2007). The major nutrients, nitrogen (N),

phosphorus (P) and carbon (C) can occur as dissolved inorganic species, organic

complexes, or associated with particulate material (Stutter et al. 2008).

The impact of these nutrients on aquatic ecosystems also depends on the timing of

the nutrient load. Climate is a very important influence on the accumulation and

transportation of nutrients. For example, the application of fertilizers and/or

pesticides immediately preceding high rainfall events will most likely result in much

higher loads being transported to waterways via runoff than if application occurs

during periods of low rainfall. Pointon et al. (2003) found that during prolonged dry

periods, DOC, nitrate and P accumulated in some surface soils due to mineralisation.

These nutrients were then mobilised in the ‗first flush‘ leachate produced by the first

significant rainfall following a dry period, potentially contributing significant pulsed

nutrient loads to marine areas.

The input of high levels of nutrients (usually N and P) can lead to eutrophication of

waters. During warm weather, eutrophic water bodies may exhibit surges of algal

growth that can interfere with the ecological balance (Hem 1992) through reduced

water clarity, associated loss of submerged plants such as seagrass and production of

algal toxins and deoxygenation. While N is transported in soluble form in natural

waters, P is often transported in association with soil particles and usually only from

specific areas with rapid hydrological connectivity with a watercourse (Pionke et al.

2000) reflecting the considerable variation in the forms and delivery of nutrients to

natural waterways (Withers and Sharpley 2008).

For example, Stutter et al. (2008) found substantial variability in nutrient forms in an

agricultural catchment area of the River Dee in Scotland both temporally and

spatially. Runoff from upland catchments was found to dilute concentrated inorganic

nutrient inputs from agricultural tributaries, and dissolved organic nutrients were

found to be dominant in the riverine waters. Storms resulted in large concentrations

of sediment, PO4-P (orthophosphate) and particulate P in the higher energy

headwater of the stream, whereas downstream the concentrations were lower but

were elevated for a longer time. In addition, greater nutrient fluxes, mean

concentrations and less variable hydrochemical values in a mesoscale stream within

the lower catchment area than in the headwaters of the river were attributed to

groundwater nutrient reserves in alluvial soils in the lower catchment. These are just


a couple of ways in which environmental conditions can influence the distribution

and forms of nutrients within catchments.

The concept of limiting nutrients is important when considering potential

eutrophication. In natural water bodies, it is rare that all required nutrients are

exhausted at the same rate. When one nutrient is depleted to levels limiting balanced

growth before other nutrients, it is called a limiting nutrient. Limiting nutrients

prevent or restrict growth by their absence. When returned to the specific nutrient-

limited environments, limiting nutrients allow productivity, which continues until a

limiting nutrient is again depleted. Nitrogen is a limiting nutrient in many terrestrial

and aquatic systems. As nitrogen and carbon availability is normally limited, plant

growth in lakes, bays and streams is also limited such that when fertilizers containing

N and P are added to agricultural areas, N and P-rich runoff to freshwater receiving

systems can result in their eutrophication (Cunningham 1994).

Nitrogen in soils is ultimately derived from two sources, atmospheric nitrogen and

geological materials. Contributions of nitrate from geological materials are not

considered to be important except on a localized basis. The majority of nitrogen in

the biosphere and hydrosphere is derived from atmospheric nitrogen gas via

biological nitrogen fixation, although in certain environments larger portions derive

from nitrate or ammonium deposition from anthropogenic sources (Macko and

Ostrom 1994).

Under aerobic conditions, NH4+ is oxidized by nitrification to nitrite.

(6)

Where anoxic conditions and an accessible organic substrate exist, microbially

meditated denitrification can occur via the following reaction.

(7)

(Clark and Fritz 1997). Denitrification can occur in soils, surface waters and

groundwaters and is the mechanism that completes the nitrogen cycle by returning

nitrogen to the atmosphere (Macko and Ostrom 1994).

The study region is generally nutrient poor with very little anthropogenic nutrient

input and as a result nitrate and phosphate concentrations are generally below


minimum detection limits. The occurrence of N and nitrates in the study area is

discussed in both Papers 1 and 3 and phosphate (or absence of it) in Paper 1.

2.2.4 Organic matter

Organic carbon compounds are complex and variable in composition and are most

commonly found in natural waters in the form of humic and fulvic acids originating

from decomposition of organic matter (Drever 2002). They are often found in

groundwater and runoff from coastal catchments. Organic matter (more specifically

in the form of dissolved organic carbon) is also regarded as a nutrient of concern in

relation to the growth of Lyngbya majuscula.

Organic materials are particularly important in this study as they play a major role in

metal geochemistry. Natural humic substances are strong complexants of iron and

may, through complexation within drainage systems and groundwaters, prevent the

hydrolysis of Fe(III) and subsequent precipitation of iron oxyhydroxides before

reaching the coast (WBM Oceanics Australia 2001) resulting in the transport of Fe to

the marine environment.

Typical ranges for dissolved organic carbon for different types of natural waters are

listed in Table 1. Dissolved organic carbon (DOC) in soils generally decreases with

depth. Usually, most dissolved organic carbon will be degraded through oxidation

and biodegradation before reaching the watertable, but groundwaters associated with

swamps or coal may have much higher DOC levels.

The availability of organic carbon is likely the main determinant of the trophic

complexity of groundwater ecosystems (Hancock et al. 2005). For the

biological/biogeochemical reduction of inorganic constituents, other constituents are

needed for oxidation. This is generally organic matter. Fe(III)/sulphate reduction and

Fe(II)/sulphur oxidation are catalysed by bacteria or extracellular enzymes that

derive energy by facilitating the process of electron transfer (Schlesinger 1997).

Lofts et al. (2008) used chemical speciation modelling to calculate activities of

Fe(III) for a range of UK surface waters of varying chemistry. They modelled the

organic complexation of Fe(III) in freshwater as a function of DOC concentration

and found it was possible to predict the Fe(III):DOM ratio expected at a given pH

due to organic and inorganic complexation. Where higher ‗dissolved‘ Fe:DOM ratios


occur at a given pH, the presence of Fe in other forms, particularly colloidal Fe(III)

and dissolved or complexed Fe(II) (Lofts et al. 2008) is suggested.

Table 2 Typical DOC ranges for different water types

Water category Typical range

mg C/L

Marshes and bogs 8 - 62

Soil solutions 2 – 52

Rivers and Lakes 2 - 15

Surface waters draining swamps and wetlands 5 - 60

Groundwaters 0 – 3

Rainfall 0 – 3.5

Seawater 0.3 – 2.0

Source: pp.108,118, Drever (2002)

Bacterial fermentation of organic matter in waterlogged sediments and soils can

result in the production of methane gas. Methane (and CO2) outgassing

(methanogenesis) from saturated sediments can be observed in the field as bubbles

rising to the surface of small ponds or waterlogged soils. If the bubbles are

flammable, they are more than likely methane. This process is carried out by

anaerobic bacteria known as methanogens. Methanogenesis depends on saturated soil

or sediment conditions and the redox potential needs to be low than -100mV for the

process to occur. This process can be represented by the following reaction involving

the fermentation of acetate although other substrates such as H2/CO2 and other C

compounds may also act as reactants (Freeze and Cherry 1979).

(8)

2.2.5 The role of microbes

Microbial transformations of elements in anaerobic soils play a large role in

biogeochemical cycling of elements, including nutrients. Heterotrophic respiration

may completely deplete oxygen in flooded soils. However, under anoxic conditions

anaerobic and facultative microbes can use alternative electron acceptors such as

nitrate, ferric iron, sulphate and carbon dioxide to produce energy and build biomass

(Schlesinger 1997). Microbes will successively use electron acceptors according to

availability and the order of energy yield resulting from electron acceptor utilization

(Schlesinger 1997) as shown in Figure 7.


Figure 7 Model for C and electron flow in groundwater with major potential

terminal-electron accepting processes (modified from Falkowski et al.

(2008) and Lin (2011))

When there is an accumulation of ferrous iron due to the reduction of ferric iron in

waterlogged soils and sediments this often results in a greenish, blue, grey

soil/sediment colour (Lovley 1993). These soils/sediments are referred to as being

―gleyed‖ and will often contain extractable Fe(III)-reducing bacteria. When

waterlogged soils drain and soils become oxic, dissolved ferrous iron will be

oxidised, resulting in formation of red, yellow or brown ferric oxides or ferric

hydroxide minerals (Vodyanitskii et al. 2006; Platova and Maslennikova 2009).

Sulphur- and iron-oxidising bacteria catalyse and accelerate reactions that may

otherwise be abiotically slow. Sulphur-oxidising bacteria may catalyse the release of

up to 200 times more Fe from pyrite than abiotic reactions (Kramarenko 1969). All

iron-oxidising bacteria are aerobic and are either autotrophs (obtain C from CO2

and/or carbonate species), heterotrophs (obtain from organic C), or facultative (get C

from either source). These bacteria favour pH between 5 - 8 and typically precipitate

hydrous ferric oxides (Schlesinger 1997). Iron oxidising bacteria typically occur

where Fe(II) emerges from groundwater or other sources and are common in

stagnant water, mines, springs, quiet parts of streams, marshes and lagoons,

reservoirs and water pipes, well screens and well casings. These bacteria can cause

substantial fouling of iron pipes in water supply systems and well screens (Langmuir

1997).

Where phosphorus occurs in coastal sediments, it is often bound with iron. Bacteria

can bind considerable amounts of P and N (Pointon et al. 2003), and as a result

microbial activity must be considered in the discussion of processes contributing to

nutrient transport.


2.2.6 Physicochemical parameters

Important water chemistry measurements that affect the form and therefore

mobilisation of Fe and other elements are pH (hydrogen ion activity), Eh (redox

potential) and DO (dissolved oxygen). These are generally measured in the field and

are known as physicochemical (or environmental) parameters. Changes in any of

these parameters can significantly alter the composition of ground and surface waters

(Hem 1992; Appelo and Postma 2005).

Hydrogen ion activity (pH)

pH is the negative log of the hydrogen ion activity and its main importance lies in the

fact that the dissociation of weak acids and bases is controlled by the pH of the

geochemical environment. For example, if pH = 6.0, the activity of [H2S] is 10 times

greater than [HS-]. Conversely, if pH = 8, the activity of [HS

-] is 10 times greater

than the activity of [H2S]. Consequently, if we know the pH of a solution, we should

be able to determine dominant ions in the solution , such as sulphur species H2S and

HS- (Faure 1998).

pH influences the form and species of Fe in solution, numbers of reducing and

oxidizing bacteria and can indicate the presence of humic/fulvic acids and therefore

the potential transport of nutrients and metals within hydrological systems. The pH

of soils and groundwaters can strongly influence the leaching ability and solubility of

nutrients. Iron in particular, but also most phosphorus minerals and compounds, are

more soluble under acidic conditions (Drever 2002; Appelo and Postma 2005). The

common causes of acidification are deposition of acidic compounds from the

atmosphere (‗acid rain‘), and oxidation of sulphide minerals; the latter commonly

being associated with mining activities (acid mine drainage). Acidification by

organic acids from the biodegradation of vegetation may also occur naturally in cool,

humid climates (Drever 2002).

Studies conducted in Australia have shown that soils under coniferous plant species,

such as those present in the study area, commonly have high concentrations or

organically-bound iron and low pH (Ahern et al. 2006b). A study carried out by

Pointon et al. (2003) showed extremely acidic pH values (< 3.6) and appreciable

concentrations of Fe (0.06-1.4 mg/L) in shallow groundwaters within Pinus forestry

compartments as well as high levels of DOC (100-200 mg/L). The authors concluded


these groundwaters could be a potential source of Fe due to the combination of Fe

and high DOC levels.

The composition of organic matter controls metal and proton binding properties.

Humic and fulvic acids contribute protons to the soil solution and affect the acidity-

alkalinity balance. Plants take up more cations than anions and thus ‗excrete‘ protons

to maintain charge balance. The concentration and chemical characteristics of the

organic complexes depend strongly on the types of terrestrial vegetation in

waterbody catchments (Krachler et al. 2005). Some tree species; conifers, for

example, increase rates of dry deposition of sulphate and nitrate compared to

grasslands. Consequently, planting Pinus can significantly increase the acidity input

to the ecosystem (Drever 2002). The growth of forest on a previously unforested area

is often accompanied by a progressive decrease in soil pH (Drever 2002). Studies

carried out in southeast Queensland approximately 200 km south of this study area

(Elimbah catchment) have found that leaf and organic matter from pine plantations

appear to lead to a decrease in groundwater pH. Wilson (2000) found that leaf and

cone litter from pine plantations may be responsible for high carbon dioxide

concentrations in soils, leading to carbonic acid formation and subsequent

dissociation with resultant acidification of groundwater.

Redox potential and dissolved oxygen

Like terrestrial animals, fish and other aquatic organisms need oxygen to live.

Oxygen is also needed by virtually all algae and all macrophytes, and for many

chemical reactions that are important to surface and groundwater system function. As

water moves past the gills of fish, microscopic bubbles of oxygen gas in the water,

called DO, are transferred from the water to their blood (Eaton and Andrew 2005).

Eh is used to describe relative electron activity and is analogous to pH which is used

to describe hydrogen ion (proton) activity. Examining the relationship between Eh,

pH, and the behaviour of specific ions or compounds in a given water is often useful

in hydrochemical analyses. Eh-pH diagrams can be constructed for a very wide range

of elements.

Figure 8 and Figure 9 indicate the predominant modes of occurrence of species of

iron and sulphur for various pH and Eh conditions. These diagrams are very


important in understanding processes that control the occurrence and mobility of

minor and trace elements (Freeze and Cherry, 1979).

Figure 8 Eh-pH diagram for the system Fe-O2-CO2-H2O at 25ºC ignoring ferrosic

hydroxide [Fe3(OH)8] and assuming pKsp=37.1 for amorphous Fe(OH)3.

Bicarbonate is fixed at 10-2.7

mol/kg. Aqueous/solid boundaries are drawn

for total dissolved iron concentrations of 10-5

mol/kg (solid line).

Source: Langmuir (1997)

Oxidation and reduction reactions mediate the behaviour of many chemical

constituents in ground and surface waters. The reactivities and mobilities of

important elements in biological systems; for example, Fe (Figure 8), S (Figure 9),

N, and C, as well as those of a number of other metallic elements, depend strongly on

redox conditions (Eaton and Andrew 2005). For example, the relative proportion of

Fe(II) and Fe(III) in a solution is a function of the redox potential of the system and

therefore a factor in the potential transport of this metal.


Figure 9 Eh-pH diagram for thermodynamically stable substances in the system S-

O2-H2O at 25ºC, showing the fields of predominance of the aqueous

species and of elemental sulphur for ΣS(aq) = 10-3

mol/kg.

Source: Langmuir (1997)

In natural systems, Eh, like pH, is an environmental parameter whose value reflects

the ability of the natural system to be an electron donor or acceptor relative to the

standard H2 electrode (Faure 1998). There is a tendency in groundwater toward

oxygen depletion and reducing conditions. Oxygen is usually consumed and not

replenished due to the groundwater being isolated from the atmosphere and oxygen-

consuming biological activity. Flood (1984) documented that the intertidal zone,

where wave and tidal-action occurs, has an aerobic surface but becomes anaerobic

several centimetres below the surface. This anaerobic state may increase the amount

of soluble Fe present in intertidal sediments. However, due to mixing with

atmospheric oxygen at the surface, rivers and lakes tend towards oxidising conditions

(Freeze and Cherry, 1979).


As discussed above, forms of carbon, microbial activity, pH, DO and redox

conditions all have an effect on the form and transport of Fe. This information relates

to Paper 3 where three micro-environments are used to illustrate these processes.

2.3 Environmental Isotopes

Stable isotopic data are used to investigate nutrient sources using graphical

techniques and known trends. In addition, typical isotope ratio ranges for specific

nutrients from the literature are referred to where relevant. C and S isotopes are

discussed in relation to the form and potential transport of Fe within these

catchments. Table 3 lists isotope ranges for various sources and associated

references. It should be noted, however, that stable isotopes are useful for processes

and origins but not applicable to providing quantitative recharge estimates because

they are non-conservative and are subject to fractionation by evaporation (de Vries

and Simmers 2002). The theory and interpretation of stable isotopes are discussed in

the following sections, including some examples from the literature.

2.3.1 Oxygen and hydrogen isotopes, δ18

O and δ2H

These naturally occurring isotopes can be used to detect the groundwater component

of streamflow during periods of storm runoff. For example, due to the differences in

concentrations of 18

O in rainfall and groundwater, the 18

O of rain can be used as a

tracer for rain that falls on a catchment (Freeze and Cherry 1979).

Isotope ratios of compounds in nature deviate slightly from the average values and

often do so in a predictable manner. There are characteristic patterns in 18

O and 2H

isotopes in precipitation that are related to latitude, temperature, land mass, altitude

and seasonality and, as a result, these data can provide information relating to

recharge sources, flow paths and mixing of natural waters (Freeze and Cherry 1979;

Clark and Fritz 1997). There are isotope ratio variations between different phases of

the same compound and different compounds of the same element. For example, the

oxygen isotope composition of rain and snow is determined by isotopic fractionation

during evaporation, condensation, and rainout (Mazor 1997; Mayer 2006).


Table 3 Isotope ranges for different sources and processes from the literature

Isotope Source Typical Range Reference δ13CDIC

(‰VPDB) Freshwater carbonates Hudson, Mississippi, Potomac Eastern Canadian rivers Mackenzie river, Canada

-17‰ to +5‰ -11‰ to -5‰ -10.9‰ to -3.5‰ -24.4‰ to-1.3‰

(Clark and Fritz 1997) (Sackett and Moore 1966) (Strain and Tan 1979) (Hitchon and Krouse 1972)

Groundwater DIC -22‰ to 0‰ (Clark and Fritz 1997)

Estuarine surface waters

-29‰ to +2‰

(Tan and Strain 1983) (Spiker and Schemel 1979)

Ocean DIC Marine end-member in estuaries Marine carbonate shells

-1‰ to +2‰ 0‰ to +3‰ Average of 1.5‰ to 2.0‰

(Sackett and Moore 1966) (Spiker and Schemel 1979) (Craig 1954)

Atmospheric CO2 -6.4‰ (1963) -8.4‰ (2009) –burning of fossil fuels depleted in 13C

(Craig and Keeling 1963) (Keeling et al. 2010)

C3 plant biomass -30‰ to -24‰, ave. = -27‰ (Vogel 1993) C4 plant biomass -16‰ to -10‰, ave. = -

12.5‰ (Vogel 1993)

C3 plant biomass -27‰ (Cerling 1984) C4 plant biomass -13‰ (Cerling 1984) Leaf and root litter (oak forest) -28.2‰ to -27.3‰ (Nadelhoffer and Fry 1988) 10 to 20 cm soils (oak forest) -23.6‰ (Nadelhoffer and Fry 1988) Soil respired CO2 (C3 plants) -22.2‰ (Cerling 1984) Soil respired CO2 (C3 plants)

Soil respired CO2 (C4 plants) -26‰ to -20‰ -12‰ to -6‰

Based on ca. 4‰ enrichment (Cerling 1984)

Soil respired CO2 (C4 plants) -8.5‰ Cerling (1984) Soil-respired CO2 (Canadian forested

watershed) -23‰ (summer) -25‰ (winter)

(Aravena et al. 1992a) (Aravena et al. 1992a)

Carbonate rocks ≈0‰ (Keith and Weber 1964) Methane -55‰ to -80‰

δ15N (‰ AIR)

See (Hubner 1986) for a range of δ15N values for various fertilizers, chemicals and some naturally occurring compounds as well as precipitation and atmospheric values. See (Letolle 1980) for δ15N values for different soils

Atmospheric N2 -1‰ to +1‰ (Letolle 1980) Peat and coal -2.8‰ to 1.9‰ (Hoering 1955) Rainfall -4‰ to +4‰ (Hoering 1955) Manure/septic effluent +10‰ to +20‰

+10‰ to +22‰ +9‰ to +19‰ +8.1‰ to 13.9‰ +6.7‰ to +18.2‰

(Mariotti et al. 1988) (Kreitler 1979) (Heaton et al. 1983) (Aravena et al. 1992b) (Kreitler 1979)

Soils – synthetic fertilizer Fertilizer nitrogen

-2‰ to +4‰ -4‰ to +4‰ 0‰ to 3‰ -7.4‰ to +1.9‰

(Aravena et al. 1992b) (Freyer and Aly 1974) (Mariotti et al. 1988) (Kreitler 1979)

Unfertilized cultivated fields +2‰ to +8‰ (Kreitler 1979) Plants (nitrogen fixation of atmospheric

N2 results in a depletion of 1 to 5‰ -10‰ to +8‰ -4‰ to +3‰

(Letolle 1980) (Fry 1991)

Tree tissues and fresh litter at surface Leaf and root litter (oak forest) 10 to 20 cm soils (oak forest) Groundwater under coniferous forest Soil organic matter at 20-40 cm depth (enrichment with depth) Soil organic matter Soil organic matter

-5‰ to +2‰ -3.8‰ to -1.6‰ +5.9‰ +1‰ to +4‰ +8±2‰ +2‰ to +10‰ +3‰ to +8‰

(Fry 1991) (Nadelhoffer and Fry 1988) (Nadelhoffer and Fry 1988) (Bottcher et al. 1990) (Nadelhoffer and Fry 1994) (Clark and Fritz 1997) (Heaton 1986)

Soil N2 -3‰ to +13‰ (Letolle 1980) Denitrification Variable enrichments of

remaining nitrate


Table 3 continued

Isotope Source Typical Range Reference δ34SSO4 Abiotic oxidation by O2 -5.2‰ ± 1.4‰ (Fry et al. 1988) (‰ VCDT) Oxidation by aerobic oxidisers

(bacteria) Up to a 20‰ depletion (Fry et al. 1988)

Oxidation by anaerobic oxidisers (bacteria)

ca. +2‰ (Fry et al. 1986)

Dissolution of Tertiary evaporites Tertiary or fresh-marine water interaction

+18‰ to +22‰ Ca/SO4 ≈ 1 → evaporite Ca/SO4 ≈ 0.36 → seawater

(Krouse 1980)

Reduction of sulphate by bacteria to H2S

Highly variable, typically ≈ +25‰

(Kaplan and Rittenberg 1964)

Modern seawater (marine sulphate)

+21‰ (Rees et al. 1978)

Coastal rainwater and seaspray +12‰ to +18‰ Generally lower than seawater due to mixing with biogenic sulphur

(Chukhrov et al. 1975)

Continental rainwater +2.2‰ to +6.0‰ Lower still due to

(Thode 1991)

Petroleum and coal -7‰ to +20‰ (Krouse 1980) Atmospheric sulphate, i.e.

petroleum and coal combustion, biological release of sulphur-bearing compounds

+2‰ to +9‰ Lower values dominated by biological sulphur whereas higher values dominated by fossil fuel S

(Nriagu and Coker 1978)

Cenozoic CaSO4 +10‰ to +18‰ (Krouse 1980) Devonian to Permian CaSO4 +10 to +24 (Krouse 1980) Biogenic pyrite <-50 to +5 (Krouse 1980) Shales -40 to +15 (Krouse 1980) Limestone -30 to +28 (Krouse 1980)

The isotopic composition of rain and snow, namely seasonal variation and mean

values for δ18

O and δ2H, provides information in relation to:

Transit time of water in the subsurface

Recharge area of groundwater

Mixing of different groundwaters

Occasionally, a crude groundwater age

Mixing of surface water in a river stretch

Mixing of groundwater and surface water (Mayer 2006)

In order to obtain this information a good understanding of the regional and temporal

variations in the isotopic composition of atmospheric deposition and the surface

water and groundwater in the study area are required (Clark and Fritz 1997).

The isotopic composition of 2H and

18O in water is expressed in per mil (‰)

deviations from SMOW (Standard Mean Ocean Water) and written as δ2H and δ

18O.

Global and local meteoric water lines (GMWL and LMWL), equations resulting

from the linear regression of δ2H and δ

18O data for water samples collected globally

and locally, respectively, can be used to assist in the interpretation of isotopic data.


The global meteoric water line was first defined by Craig (1961) and is based on

around 400 water samples of rivers, lakes, and precipitation from various countries

with the equation

δ2H = 8δ

18O + 10 (9)

When plotted this equation is known as the Global Meteoric Water Line (GMWL)

and gives the approximate compositions of rain/snow on earth (Johnson 2007).

Fractionation or separation of naturally occurring oxygen and hydrogen isotopes in

water occurs in the hydrologic cycle during evaporation and condensation.

Isotopically light water molecules evaporate before heavy ones. As a result, surface

water exposed to evaporation tends to be enriched in heavy isotopes relative to

meteoric water and will have a less negative or more positive 18

O/16

O ratio.

Data sourced from the Global Network of Isotopes in Precipitation (International

Atomic Energy Agency 2006) for Brisbane (approximately 200 km south of the

study area) have been used to construct the LMWL by linear regression and has the

following equation.

δ2H = 7.49δ

18O + 11.74 (10)

The slope of the Brisbane LMWL (BMWL), being relatively close to the GMWL

slope of 8, reflects the relatively high humidity in this region. In areas where there is

high humidity, kinetic evaporation effects are closer to equilibrium and the slope will

be closer to the GMWL. In areas of low humidity, kinetic nonequilibrium

evaporation effects will be more pronounced and the slope will become progressively

lower with decreasing humidity.

Lee and Kim (2007) used δ18

O and δ2H to determine seasonal contributions of

precipitation to groundwater recharge at a forested catchment area in Korea. The

stable isotopic signature upstream was found to be similar to most groundwater

indicating that these stream waters were mostly fed by groundwater discharge. There

was a distinct seasonal variation in δ2H values which made it a useful parameter for

evaluating relative contribution of wet and dry precipitation.

2.3.2 Stable isotopes of dissolved inorganic carbon, δ13

CDIC

Significant differences in the isotope ratios of carbon exist in the atmosphere, oceans,

and biosphere. Consequently, δ13

CDIC isotope data can reveal information about


carbon compound sources and/or processes these compounds have undergone. 13

CDIC

can be used to trace carbon sources and reactions for a multitude of inter-reacting

organic and inorganic species including CO2, dissolved inorganic carbon (National

Health and Medical Research Council (NHMRC)), DOC, methane and other

hydrocarbons (Clark and Fritz 1997). Telmer and Veizer (1999), Barbecot et al.

(2000) and Brunet et al. (2005) used 13

CDIC isotopes to identify sources of DIC in

natural waters, while Atekwana and Fonyuy (2009) used this technique to assess the

effects of variable acid mine drainage on DIC dynamics. δ13

CDIC results are reported

with respect to VPDB (Belemnitella Americana from the Cretaceous Pee Dee

Formation in South Carolina) and results are reported as per mil ‰ VPDB (Clark

and Fritz 1997).

There are many complex processes associated with the carbon cycle that can alter

natural water 13

CDIC composition. The coastal region under study primarily contains

siliceous sediments with little to no carbonate material within the shallow

groundwater aquifers and drainage system alluvium. Within such lithologies DIC

does not evolve substantially beyond conditions established in the soil (Clark and

Fritz 1997). As a consequence, processes affecting 13

CDIC composition at a majority

of these sites are related to the decay of plants at the surface and DOC. The microbial

oxidation of organic material in combination with root respiration is referred to as

soil respiration and results in higher CO2 partial pressures in soils than in the

atmosphere (Cerling 1984). δ13

CDIC for soil CO2 varies according to vegetation type.

The decay of C3 plants, common in temperate and high altitude regions, results in

soil CO2 with δ13

CDIC somewhere in the range -24 to -30‰ (average of 27‰) (Vogel

1993). C4 plants, which dominate tropical and temperate grasslands, will result in soil

CO2 with δ13

CDIC somewhere in the range -10 to -16‰ (average of -12.5 ‰) (Vogel

1993). However, CO2 diffusion through the air imparts an enrichment to soil CO2

(Clark and Fritz 1997) of approximately 4‰ (Cerling 1984), so the soil CO2

produced from the decay of these plant biomasses has ranges are closer to -26 to -

20‰ and -12 to -6‰ for C3 and C4 plants, respectively. Cerling (1984) suggested a

3-7‰ soil CO2 range enrichment compared with soil organic matter. For a soil CO2

concentration of 0.01%, Cerling (1984) calculated limits of -22.2‰ and -8.5‰ for

soil respired CO2 in soils dominated by C3 and C4 plants, respectively, whereas limits


of -27‰ and -13‰ were calculated for pure biomasses in soils dominated by C3 and

C4 plants, respectively.

DOC plays an important role in the geochemical evolution of groundwaters through

redox reactions (Clark and Fritz 1997). DOC oxidation in ground and surface waters

associated with denitrification and/or sulphate and Fe(III) reduction reactions leads

to dilution of DIC (refer to Equations 2 and 4) and consequently a depletion in

13CDIC. Microbes prefer lighter carbon isotopes leaving heavier isotopes in remaining

DOC. DOC can be flushed to ground and surface waters by rainfall and can also be

contributed to aquifers by buried peat layers.

2.3.3 Stable isotopes of dissolved organic nitrogen, δ15

NDIN

Nitrogen is a biologically active element and participates in a multitude of reactions

important to life, and can affect water quality. Isotope fractionation between various

N-bearing compounds such as organic N, N2, NH4+ and NO3

-, provides the basis for

15N as a tool in isotope hydrogeology. However, it should be noted that nitrate

fractionation is difficult to estimate and using δ15

N to trace origins of nitrate is

considered to be a semi-quantitative or qualitative technique (Macko and Ostrom

1994). The 15

N standard is the atmospheric N2 reservoir where δ15

NN2 = 0 ‰ AIR

and results are reported as per mil (‰) AIR (Clark and Fritz 1997).

15NDIN isotopes provide information about sources of inorganic nitrogen and the

processes that these inorganic forms have undergone. Nitrate is generally the most

abundant form of inorganic nitrogen in ground and surface waters and nitrate

concentrations in many aquifers increase as a result of atmospheric nitrogen

deposition typically as HNO3 in rainfall, synthetic fertilizers (nitrate, ammonium,

urea); manure, sewage, or soil nitrate; oxidation of organic N (nitrification). In

addition, nitrate concentrations in groundwater and surface water may be decreased

via denitrification, a microbially mediated process in which heavy 15

N and 18

O

isotopes of are preferentially retained in the non-reduced remaining nitrate.

Therefore, aqueous nitrate δ15

N values increase as total nitrate concentrations

decrease where this process occurs (Clark and Fritz 1997). Denitrification requires

the presence of denitrifying bacteria, a sufficient stock of oxidisable carbon or other

substrate and appropriate redox conditions (Macko and Ostrom 1994). Heaton (1986)


found that as little as a 20% nitrate removal by denitrification can result in an

increase in δ15

N by as much as 8‰ in the remaining nitrate.

At the soil surface, organic matter δ15

N

values are generally similar to, or slightly

greater than, values for plant litter, and increase to about +8 ± 2‰ at a depth of 20-40

cm (Nadelhoffer and Fry 1994). A survey by Fry (1991) of forests and other non-

cultivated ecosystems at a number of sites across North America illustrates the

overall pattern of progressive 15

N enrichment of plant litter, organic soil and mineral

soils in forests.

15N isotopes are most commonly used by scientists to trace sources of nitrates, often

associated with fertilizers and/or sewage. See, for example, Corbett et al. (1999),

Lertsirivorakul and Milne-Home (1999), Motzel et al. (2001), Mutchler et al. (2007),

Fox and Papanicolaou (2008), Petitta et al. (2009) and Hososo et al. (2010).

2.3.4 Stable isotopes of sulphate sulphur, δ34

SSO4

34SSO4 isotopes provide information about sources of sulphate and sulphide and

processes these sulphates have undergone. Sulphate concentrations in many aquifers

increase due to the influx of sea spray, atmospheric sulphur deposition, dissolution of

evaporites (gypsum, anhydrite), oxidation of pyrite (e.g. lowering of watertable

exposing ASS), sulphate from landfills or from industrial sources. δ34

SSO4 results are

reported with respect to Vienna Canyon Diablo Troilite (VCDT) (Clark and Fritz

1997).

Sulphate concentrations in groundwater and surface water can be decreased due to

bacterial sulphate reduction, i.e. the reduction of SO42-

to H2S. This results in an

increase in the heavier isotope, δ34

SSO4, which is preferentially retained, i.e. bacterial

sulphate reduction causes trends of increasing δ34

SSO4 values with decreasing

sulphate concentrations (Clark and Fritz 1997). Fractionation is considerably less

during oxidation of dissolved sulphide than sulphate reduction and also varies

depending on the mode of oxidation. For example, a δ34

SSO4 5‰ depletion in the

accumulated sulphate might occur when the oxidising agent is O2 at the surface or

near-surface, a 20‰ depletion if aerobic oxidizers (bacteria) are present, and in the

case of anaerobic oxidisers such as photosynthetic algae, the sulphate can be

enriched by approximately 2‰ (Clark and Fritz 1997). Negative δ34

SSO4 values can


indicate pyrite oxidation. Atmospheric sulphate produced by fossil fuel combustion

shows δ34

SSO4 values ranging from slightly negative to 10‰.

Dissolved sulphate resulting from dissolution of evaporites such as Tertiary-age

gypsum and anhydrite, fresh-saline water interaction and accumulation in soils by

evaporation will often have similar δ34

SSO4 values between 18 and 22‰ (Clark and

Fritz 1997). One technique to differentiate an evaporite source is calculation of the

molar ratio of calcium and sulphate. In pure water, a value close to one indicates

gypsum dissolution. However, calcite precipitation also affects this ratio due to the

common ion effect, resulting in a disproportionate increase in sulphate (Clark and

Fritz 1997).

A wide range of sulphur isotope ratios arise in natural surface waters regardless of

anthropogenic activities. Ground and surface waters with relatively high sulphate

contents due to presence of evaporite-bearing rocks such as gypsum and anhydrite

will have δ34

SSO4 values reflecting this source. However, 34

SSO4 in these waters may

be further enriched by the presence of sulphate-reducing bacteria either in shallow

sediments or anoxic water column. Conversely, lakes or surface waters with very low

sulphate concentrations may show no evidence of sulphur isotopic fractionation,

having δ34

SSO4 values similar to that of local rainwater (Thode 1991). The principal

source of sulphate in rainwater over the ocean is sea spray. δ34

SSO4 values for

rainwater sulphur over the ocean (+12 to +18‰) are appreciably lower than for

seawater (+21‰) due to mixing of atmospheric and biogenic sulphur (volatile

sulphur compounds such as dimethyl sulphate (DMS) and dimethyl sulphide

propyanate (DMSP) resulting from the decay of organic matter) carried from the

continents or the ocean itself. δ34

SSO4 values for rainwater sulphur are even lower

relative to seawater over the continents themselves, with previous studies in remote

continental areas showing values ranging from +2.2 to +6.0‰ (Thode 1991).

Dogramaci et al. (2001), Motzel et al. (2001), Kim et al. (2003), Harbison (2007) and

Ryu et al. (2007) are examples of studies where sources of sulphate and processes

contributing to δ34

SSO4 composition of natural waters are investigated. Robinson and

Gunatilaka (1991) used isotopic analyses of sulphur and oxygen to determine the

origin of dissolved sulphate and precipitated mineral sulphate in marine sabkhas in

Al-Khiran, Kuwait. These analyses confirmed that there was a minor contribution of


seawater sulphate in the tidal areas, but that a bulk of the marine sabkha water

sulphate and coexisting sulphate minerals were of continental origin.

δ13

CDIC, δ15

N and δ34

SSO4 data are used to determine sources and processes involving

C, N and S in Paper 3. In addition, these data are used to support process models

within the micro-environments described in this thesis.

53

3. METHODS AND APPROACHES

The following sections describe the data collection, sampling programme and

laboratory and interpretative methods for this study. Graphical borelogs for

groundwater sites have been included in the Appendix B where sufficient data were

available and site photos in Appendix C of this thesis. In order to assist the reader, a

conceptual geological cross-section and a map depicting data collection sites have

been included in Appendices D and E, respectively. See Table 4 for site names, water

sample type, site description, depth of borehole and screening interval. Table 2 in

Paper 1 also provides a description of these sites in relation to landuse and

vegetation, depth or borehole or depth of screening, distance from the closest estuary

of Great Sandy Strait, topographical height and water type.

3.1 Data Collection

3.1.1 Data Collection Sites

Location

To obtain a regional picture of water chemistry and transport processes in the region,

this study focuses on the mainland coastal zone including Kalah, Maaroom, Tuan,

Poona and Buttha catchments. This area has been chosen as an example of a low-

modification area with similar geomorphological and landuse characteristics to many

other coastal zones in southeast Queensland. Sites have been chosen in order to (a)

provide a description of the hydrochemistry of all shallow groundwater bodies, (b)

facilitate the investigation of interaction among and between subterranean and

surface waters, (c) cover all landuses in the study area, and (d) provide information

relating to processes in different hydromorphological settings. Figure 10 shows the

location of the data collection sites and topography (also see Appendix E) and Figure

11 shows the hydromorphological settings for data collection sites in the Poona

catchment.

Coastal Queensland is fortunate to have quite extensive groundwater resources.

Many rivers have well-developed alluvial tracts and deltas with extensive sand and

gravel aquifers. However, these usually develop where steeper seaward gradients

exist than those in this project study area. Large sand dune deposits occur both

54 Chapter 3 Methods and Approaches

onshore and as nearby islands, such as Fraser Island, and often contain substantial

freshwater aquifers. Streams with low seaward gradients tend to develop wide flat

alluvial deposits through which the streams meander to the sea. Although these

sediments have sand and gravel sections, the upper layers are usually very clayey and

this restricts direct recharge from rainfall (Hillier 1993). Exploratory drilling did not

reveal any continuous and/or substantial unconfined alluvial deposit aquifers in the

study area but rather shallow topsoils over semi-confining to confining weathered

bedrock and discontinuous clay layers and small pockets of unconfined and semi-

confined groundwaters adjacent to the tributaries occurring within relict fluvial

channels or infilled meanders in the coastal plain.

In order to investigate hydrochemical composition and processes at the fresh/saline

water interface, a particular area of focus for this study is an infilled meander aquifer

within the Poona catchment near the mouth of Poona Creek. A number of monitoring

wells (P2-P6, P8-P10) were installed in this aquifer which contains alluvial materials

hydrologically linked with the estuarine surface drainage system. The geology and

geomorphology of this site enables the investigation of transport and the mechanisms

affecting the transport of metals and nutrients potentially discharging to the Great

Sandy Strait through this subterranean estuary. Figure 12 shows a close-up of the

transect (P10, P9, P3, P6, P8, P4, P2, P5, going from south to north), in addition to

P7 on the north bank and P1 to the east. Later in the sampling programme four

shallow hand-augered monitoring wells (P11-P14) were installed in the supratidal

muds and sands adjacent to Poona Creek to monitor changes in hydrochemical

composition within the zone of fresh and saline water mixing between the transect

and the estuary. Figure 13 (also see Appendix D) shows a cross-sectional conceptual

model of this transect and these shallow monitoring wells between the forestry

compartments and the estuary and graphic borelogs for these sites are in Appendix B.

An additional monitoring well was drilled for this project in the Buttha Creek

catchment (B1).

Chapter 3 Methods and approaches 55

Table 4 Site names, sample type, site description and borehole depth or screening

interval

SITE ID Sample Type Sitea Description

Borehole depth/Screening interval (m bgs)

B1 GW close to Buttha Creek estuary Native bushland - grass trees, melaleuca, wallum 5.0-8.0

P1 GW close to Poona Creek estuary Mature pine forest 1.5-4.5

P2 Transect GW close to Poona estuary Native bushland - grass trees, melaleuca, wallum 6.0-9.0

P3 Transect GW close to Poona estuary Native bushland - grass trees, melaleuca, wallum




P7 GW screened in confining layer on north bank Native bushland - eucalypts 6.0-9.0


P9 Transect GW close to Poona estuary Native bushland- grass trees, melaleuca, wallum 3.5-6.5

P10 Transect GW close to Poona estuary Native bushland- grass trees, melaleuca, wallum 6.5-9.5

P11 Shallow supratidal flat GW (Poona) algal mats, grass, small salt-tolerant succulents 1.2

P12 Shallow supratidal flat GW (Poona) algal mats, grass, small salt-tolerant succulents 0.9

P13 Shallow supratidal flat GW (Poona) algal mats, succulents, mangrove stands 1.0

P14 Shallow supratidal flat GW (Poona) algal mats, succulents, mangrove stands 1.0

134B GW close to GSS Residential area - cultivated lawn and shrubs Unknown

204B GW close to GSS Residential area - cultivated lawn and shrubs 12.0

PCP GW close to GSS Caravan Park bore- cultivated lawn and shrubs 19.0

R+E GW close to GSS Residential area - cultivated lawn and shrubs 11.0

RF GW close to GSS Caravan Park bore - cultivated lawn and shrubs 6.0

C2d Confined GW (Tuan catchment) Mature pine forest 11.5-13.0

C3d Unsaturated zone GW (Tuan catchment) Native grassland 5.5-7.0

C4 Unsaturated zone GW (Tuan catchment) Mature pine forest 2.3-3.8

C5 Unsaturated zone GW (Tuan catchment) Native vegetation, grass trees, melaleuca 2.5-4.0

JL1 Confined fresh GW (Tuan catchment) Pine plantation 12.2

JL2 Confined brackish GW Pine plantation 10.7

JL4 Brackish GW Pine plantation 20.7

JL7 Confined fresh GW Poona National Park - Wallum heath communities

5.4

JL8 Confined fresh GW Native vegetation 5.2

JL9 Brackish GW Pine plantation 7.6

JL10 Confined fresh GW Poona National Park - Wallum heath communities communities

7.9

JL13 Confined fresh GW Native vegetation 6.1

JL20 Saline GW Residential 11.6

JL25 Confined fresh GW Residential 4.6

LRB SW Low flow, very small creek N/A

PB SW Moderate tidal flow N/A

PC9 SW Moderate flow, small creek N/A

PC10 SW Moderate flow, small creek N/A

PCM SW Strong tidal flow N/A

TCA SW Still pools/small flowing brooks N/A

TCB SW Moderate tidal flow N/A

WP11 SW Excavated still pool, low flow N/A




a) The site descriptions listed for the JL sites are for current conditions. At the time of the data collection for these sites (1968-1969), the pine plantations had not been established.


Figure 10 Location of data collection sites and topography. The dashed rectangle

shows the location of Figure 12. Please note map available in Appendix

D.

Source: Generated in ArcGIS using 5m resolution LIDAR data obtained from Forestry Plantations

Queensland for the purposes of this project in 2007.

Groundwater samples have also been collected from residential bores in the coastal

zone near Poona to investigate whether there is communication between these small

aquifers and the GSS. Three samples were collected from aquifers in Poona village

(PCP, 134B, 204B) (Figure 12), one from Boonooroo (RF) approximately 6 km

NNW of Poona village and one from an aquifer in Little Tuan (R+E) located

(m)


approximately 6 km NW of Poona village. Unsaturated zone groundwaters in four

monitoring wells drilled for another PhD project at QUT in the Tuan Creek

catchment (C2d, C3, C4, C5) were also included to investigate interaction between

the vadose zone and deeper confined aquifer waters (Figure 10).

Figure 11 Cross-section of Poona Creek catchment going from southwest to


and surface water data collection sites.

A number of surface water sites were included in order to investigate ground and

surface water interaction. There are nine surface water sites in the Poona catchment;

seven of which are fresh (LRB, PC9, PC10, WP11, WP12, WP19, WP31) and two

estuarine (PB, PCM). There is one estuarine (TCB) and one freshwater (TCA) site in

the Tuan catchment (Figure 10).

A number of sites from the Laycock study (Laycock 1969) have also been included

in order to provide a description of all shallow groundwaters in the region. These

sites (JL1, JL2, JL4, JL7, JL8, JL9, JL10, JL13, JL20, JL25) were selected based on

their proximity to the study area and their location in the Tertiary alluvium aquifer in

the northern Tuan catchment.

In total, eleven monitoring wells were drilled for this project in June 2007. The holes

for the monitoring wells were drilled using a hydraulic rotary drilling rig with

bentonite drilling mud. Cuttings samples were collected at 0.5 m intervals. Drillhole

depths varied (Table 4) and 3 m PVC slotted screens were placed at the bottom of the

borehole, gravel packed and sealed with bentonite. Wells were capped and housed

with a galvanised steel casing set in a concrete surface seal. Four shallow monitoring

wells (P11-P14) were later (mid-2009) installed by hand auger in muds and sands of

-15.00

-10.00

-5.00

0.00

5.00

10.00

15.00

20.00

25.00

0 2000 4000 6000 8000 10000 12000

Distance (m)

Limit of Tidal

Influence

COASTAL PLAIN

GREAT SANDY STRAIT

ELEVATEDCATCHMENT

Poona CreekEstuary Mouth

Incised bedrock

Alluvial deposit

aquifers

Beach

ridge

aquifer


the estuarine tidal flats between the transect and the estuary in order to further

investigate tidal intrusion in this area.

Figure 12 Poona Creek estuary and nearby monitoring wells.

Bores P1 – P14 were installed for the purposes of this project. Bores

134B, 204B and PCP are residential bores in Poona Village and PCM is

surface water site at the mouth of Poona Creek. The red dotted line

shows the transect for the conceptual hydrogeological model in Figure 13

and Appendix D. The grey lines (FPQ_CPTS) show the boundaries of

forestry compartments. The grey numbers inside these polygons are used

for identification of compartments by forestry management.

Notes: Teal colouring indicates intertidal and subtidal areas.

The location of this coastal section in the context of the study area is shown in Figure 10.

Source: Generated in ArcGIS using 5m resolution LIDAR data obtained from Forestry Plantations

Queensland for the purposes of this project in 2007

P7

PCM

P8 P6

P5

Forestry

Compartments

204B Poona Village

PCP

134B

Forestry

Compartments

P3 P9

P10

P1

P4

P2

P11

P13 P12

P14

Great Sandy Strait

(m)

Methods and Approaches 59

Figure 13 Conceptual model of geology, hydromorphology and location of monitoring wells at the transect adjacent to Poona Creek

estuary.

The red and blue dashed lines represent the approximate location of the upper and lower boundaries of the semi-confining

clay ‗layer‘ near the ground surface (see also Appendix D). Although present in all of the transect bore sediment profiles, the

quick recharge at these sites indicates that this layer is actually in the form of discontinuous lenses of variable thickness and

hydraulic conductivities allowing rainfall recharge to penetrate to this aquifer quickly. There was continual recharge to most

of these sites during a rainfall event which occurred in August 2007. This figure is also in Appendix D (modified from Lin

(2011)).

60 Methods and Approaches

Surficial geology and geomorphology

The transect (P2-P6, P8-P10) is within undifferentiated coastal plain materials of the

weathered Duckinwilla Group as are two other monitoring wells (P1 and P7) (Figure

6). Figure 13 (Appendix D), a cross-sectional view of this transect, shows some

important hydrogeological features such as a vertical semi-confining layer that

restricts seawater intrusion and discontinuous semi-confining clayey silts underlying

the soil profile that add to the variability in hydrochemistry of waters within the

transect. One monitoring well (B1) is located in weathered Graham‘s Creek

Formation which overlies the Duckinwilla Group formation to the southwest. The

weathered Grahams Creek Formation here is in the form of undifferentiated coastal

plain materials. The shallow monitoring wells (P11-P14) between the transect and

the estuary are located in Holocene estuarine tidal flats consisting of mud and sand.

One surface water data collection site (PCM) is located at the mouth of the Poona

Creek estuary. The hydrochemistry at this site is reflective of marine waters. The

surface water data collection site at Tuan Creek (TCA) is in weathered Elliot

Formation, as are the residential borehole sites at Boonooroo (RF) and Tuan (R+E).

Stream sites in the Poona catchment (PC9, PC10, WP11, WP12, WP16, LRB) all lie

in the Duckinwilla Group except for the site at Pappins Bridge (PB) which lies in

weathered Elliot Formation.

The three residential bore sites at Poona (PCP, 134B, 204B) are in Holocene beach

ridge sands (Figure 6). These beach ridges appear to contain a number of different

aquifers. There is a deeper confined aquifer in the Poona Village beach ridge at

containing fresh potable water (PCP) while groundwater from another borehole in

this beach ridge (204B) was brackish. Residential boreholes in Little Tuan and

Boonooroo villages are in the weathered Elliot formation and these groundwaters

were also brackish. It is likely that these boreholes are in semi- or unconfined

aquifers in contact with their respective estuaries and/or the Great Sandy Strait. All

boreholes from the Laycock (1969) study (JL1, JL2, JL4, JL7, JL8, JL9, JL10, JL13,

JL20, JL25) are screened in the Tertiary alluvial aquifer in the northern Tuan

catchment.


3.1.2 Sampling programme

In total, eight sampling runs were conducted over a period of 25 months from August

2007 to August 2009; the multiple sampling approach was used to determine if

seasonal variations were significant. Table 5 lists the sampling runs, sites and

analytes. The first field trip coincided with moderate (24-96 mm/day) to heavy (96-

384 mm/day) rain resulting in flooding conditions. Of the remaining 7 field trips,

FT3 and FT6 had very light (< 6 mm/day) to light rain (> 6 mm/day, < 24 mm/day)

and FT4 had very light rain. Otherwise, conditions were dry during the time of

collection and the previous several days leading up to sample collection. However,

there was evidence of recent rain in May of 2009 (FT6) but nil rainfall was recorded

at Tuan Forestry Office for this time, the closest rain gauge station to the study area

(Figure 1). However, 16.6 mm was recorded at Double Island Point (an ocean coast

site approximately 50 km southeast of the Tuan Forestry Office) for 31 May 2009,

demonstrating the variability in rainfall over this relatively small coastal region. Also

of significance to the distribution of regional rainfall are the southwesterly winds.

Figure 14 shows cumulative rainfall data for Maryborough, Tuan Forestry Office

(approximately 10 km from Poona village), Toolara located just south of the study

area, as well as at Rainbow Beach located approximately 40 km southeast of the

Poona village (Figure 1). There is an overall trend of decreasing rainfall with

distance travelling northwest from the coast. This is to give an idea of the variability

of rainfall in these coastal areas, although, due to its proximity to most sites, the TFO

data should adequately reflect conditions at the collection sites.

For all groundwater samples, bores were purged prior to physicochemical

measurements and collection of samples by use of a submersible pump or bailer. For

those boreholes with continuous recharge, a limit of 10 minutes was set on the

purging time.

62 Chapter 3 Methods and approaches

Table 5 Sampling runs, climatic conditions, sites and analytes

C = Cations (Mg, Na, Ca, K, Al, Fetotal, Fe(II)) for FT3-FT8. Samples from FT1 and FT2 were not

analysed for Fe(II)

A = Anions (Cl, SO4, S, Br, F, NO3, NO2, PO4) and alkalinity. Samples from FT1-FT3 were not

analysed for sulphide.

Notes:

1) Measurements were made in the field of pH, EC, T, Eh and DO for all samples collected except

for FT1 where DO was not measured

2) JL sites (not listed here) were analysed for EC and pH in the field and Na, Ca, Mg, Cl, SO4, F

and alkalinity.

3) We could not gain access to 134B on FT4 and 204B pump had ceased due to biofouling so we

were unable to collect either of these samples 4) Insufficient water was available at unsaturated zone groundwater sites, C5, for C, N, S isotope

samples

SITE FT1 FT2 FT3 FT4 FT5 FT6 FT7 FT8 Season Autumn Spring Summer Winter Autumn Summer Winter Autumn

Dates 24-25 /08/2007

20-21 /10/2007

18-19 /12/2007

15-17 /05/2008

08 /08/2008

03 /12/2008

31/05- 01/06/2009

05 /08/2009

Climate Storm/ flood

Dry Light rain Very light rain, dry Dry Dry Light rain Dry

B1 C, A, 18O, 2H C, A, 34S , 15N, 13C, DOC

P1 C, A, 18O, 2H 34S C, A, 15N, 13C, DOC C, A, DOC

P2 C, A C, A, 18O, 2H 34S C, A, 15N , 13C, DOC C, A, DOC C, A, DOC C, A, DOC C, A

P3 C, A C, A, 18O, 2H 34S C, A, 15N, 13C, DOC C, A, DOC C, A, DOC

P4 C, A C, A, 18O, 2H 34S C, A, 15N, 13C, DOC C, A, DOC C, A, DOC C, A, DOC

P5 C, A C, A, 18O, 2H 34S C, A, 15N, 13C, DOC C, A, DOC C, A, DOC C, A, DOC C, A


P7 C, A, 34S, 18O, 2H C, A, 34S, 15N, 13C, DOC




P11 C, A C, A C, A

P12 C, A C, A

P13 C, A C, A

P14 C, A C, A

134B C, A, 34S, 18O, 2H

204B C, A, 34S, 18O, 2H

PCP C, A, 34S, 18O, 2H C, A, 15N, 13C

R+E C, A, 34S, 18O, 2H C, A, 15N, 13C

RF C, A, 34S, 18O, 2H C, A, 15N, 13C

C2d C, A, 34S, 15N, 13C, 18O, 2H, DOC

C3d C, A, 34S, 15N, 13C, 18O, 2H, DOC

C4 C, A, 34S, 15N, 13C, 18O, 2H, DOC

C5 C, A, 18O, 2H

LRB C, A C, A, 18O, 2H 34S C, A, 15N, 13C, DOC C, A

PB C, A C, A, 18O, 2H C, A, 34S, 15N, 13C, DOC C, A C, A, DOC

PC9 C, A, 34S, 18O, 2H C, A, 34S, 15N, 13C, 18O, 2H, DOC

PC10 C, A C, A, 34S, 15N, 13C, 18O, 2H, DOC

PCM C, A C, A, 18O, 2H C, A, 34S, 15N, 13C C, A

TCA C, A, 34S, 15N, 13C, DOC C, A, DOC C, A

TCB C, A, 34S, 15N, 13C, 18O, 2H C, A, DOC C, A

WP11 C, A C, A, 18O, 2H 34S C, A, 34S, 15N, 13C, DOC C, A

WP12 34S C, A, 34S, 15N, 13C, 18O, 2H, DOC

WP16 C, A C, A, 18O, 2H 34S C, A, 34S, 15N, 13C, DOC C, A

WP31 C, A, 15N, 13C, 18O, 2H, DOC


Figure 14 Cumulative rainfall data for four sites (going from southwest to northeast

– Rainbow Beach, Toolara, Tuan Forestry Office, Maryborough), within

a 40 km radius of the study area during the data collection period.

3.2 Laboratory Methods

Major (Na, Mg, Ca, K) and minor (Fetotal, Al, Cu, Zn) cation concentrations were

determined using inductively coupled plasma atomic emission spectroscopy (ICP-

AES). Fetotal was also determined using an AQ2 discrete analyser for field trips 4 to

8. Fe(II) concentrations were determined by a manual spectrophotometric technique

using Ferrozine (FT3-FT8) as well as an automated technique using the AQ2 (FT4-

FT8). Anion concentrations were determined using ion chromatography (IC).

Sulphide concentrations were determined by spectrophotometry using the

colorimetric methylene blue method from Standard Methods for the Examination of

Water and Wastewater (Eaton and Andrew 2005). Concentrations of Fe3+

were

calculated by difference using the AQ2 measurements for total and ferrous iron.

Samples were also analysed for total dissolved organic carbon (DOC) using a

Shimadzu TOC-5000A Analyzer. Alkalinity was determined by titration with

hydrochloric acid within 24 hours of sample collection.

FT1FT2

FT3

FT4

FT5FT6

FT7FT8

0

500

1000

1500

2000

2500

3000

3500

4000

1/0

1/2

00

7

29

/01

/20

07

26

/02

/20

07

26

/03

/20

07

23

/04

/20

07

21

/05

/20

07

18

/06

/20

07

16

/07

/20

07

13

/08

/20

07

10

/09

/20

07

8/1

0/2

00

7

5/1

1/2

00

7

3/1

2/2

00

7

31

/12

/20

07

28

/01

/20

08

25

/02

/20

08

24

/03

/20

08

21

/04

/20

08

19

/05

/20

08

16

/06

/20

08

14

/07

/20

08

11

/08

/20

08

8/0

9/2

00

8

6/1

0/2

00

8

3/1

1/2

00

8

1/1

2/2

00

8

29

/12

/20

08

26

/01

/20

09

23

/02

/20

09

23

/03

/20

09

20

/04

/20

09

18

/05

/20

09

15

/06

/20

09

13

/07

/20

09

10

/08

/20

09

7/0

9/2

00

9

Cu

mu

lati

ve R

ain

fall

(mm

)

Date

Rainbow BeachToolaraTuan Forestry OfficeMaryboroughSample Collection

Rainfall magnitudes decrease overall travelling northwest from

the coastline at Rainbow Beach

SE

NW


3.2.1 Ferrozine method for determination of ferrous iron

Ferrozine has been tested as a reagent to determine ferrous iron concentration in a

number of studies and is now widely used to determine ferrous iron concentrations in

water samples. See, for example, Gibbs (1976), Sorensen (1982) and Hach Company

(2009). Ferrozine is a colorimetric reagent that forms a stable magenta complex with

Fe(II).

A solution of 0.1% wt/wt of Ferrozine and 50 mM N-2-hydroxyethyl piperazine-N’-

ethanesulfonic acid (HEPES) buffer was prepared as the reagent for the ferrous iron

assay. The ferrous iron standards, created using ferrous ammonium sulphate

hexahydrate (abbreviated to FAS and also known as Mohr‘s salt) were standardised

using potassium dichromate (K2CrO7) as FAS is not a primary standard (Ayres

1964). Triplicate solutions with concentrations of 0.5, 1.0, 2.0 and 4.0mg/L (4.0mg/L

being the maximum detection limit for the instrument) were used to construct a

calibration curve of absorbance against concentration using a Pharmacia LKB

spectrophotometer (Novaspec II) with a 1cm path length at a wavelength of 562 µm.

If the correlation coefficient for the calibration curve was over 0.95, it was deemed

acceptable and sample concentrations were determined from this curve based on

absorbance values given by the spectrophotometer. Samples that were close to the

maximum detection limit were diluted and reanalysed. This method is based on that

used by Faulkner et al. (1999).

3.2.2 Methylene blue method for determination of sulphide

The method used for this analysis is based on Method 4500-S2- D in Standard

Methods for the Examination of Water and Wastewater (Eaton and Andrew 2005).

The methylene blue method is based on the reaction of sulphide, ferric chloride, and

dimethyl-p-phenylenediamine to produce methylene blue and the intensity of the

blue colour is proportional to the sulphide concentration. Ammonium phosphate is

added after colour development to remove ferric chloride colour (Hach Company

2009). The procedure is normally applicable at sulphide concentrations between 0.1

and 20 mg/L. However, this range of concentrations depends on the path length

achievable with the spectrophotometer used. For this analysis, the spectrophotometer

did not have an adjustable path length and was fixed at 1 cm. Consequently, the

maximum detection limit was 8 mg/L. Samples were diluted sufficiently to fall


within this range. Triplicates of standards with sulphide concentrations of 0.5, 1.0,

2.0, 4.0, 5.0, 8.0 mg/L were used to construct the calibration curve using a Pharmacia

LKB spectrophotometer (Novaspec II) at a wavelength of 665 nm.

3.2.3 AQ2 methods

Total and ferrous iron concentrations were measured using an AQ2 Seal discrete

analyser. Ferrous iron concentrations were determined using the (AQ2 Method No:

UKAS-504-A Rev.2), a UK Blue Book Method based on phenanthroline method for

determination of Fe(II) from Eaton and Andrew (2005), which has a minimum

detection limit of 0.04 mg/L. 1,10-phenanthroline chelates ferrous iron at an acidic

pH to form an orange-red complex, which can be measured spectrophotometrically at

505 nm. Total Fe concentrations were determined using the AQ2 Method No:

UKAS-507-A Rev.2. The method for this is the same as that for determining ferrous

iron except that Fe(III) is reduced to Fe(II) using hydroxylamine hydrochloride prior

to reaction with phenanthroline.

3.2.4 Charge balance errors

The electroneutrality condition is often utilised to determine the accuracy of

hydrochemical analyses. Theoretically, the sum of the positive ionic (cationic)

charges in a solution should equal the negative ionic (anionic) charges. A charge

balance error can be calculated with the following equation:

(11)

where CBE is the charge balance error expressed in percent, z is the ionic valence, mc

is the molality of cation species, and ma is the molality of anion species (Freeze and

Cherry 1979).

Solutes present in concentrations above 100 mg/L generally can be determined with

an accuracy of better than ±5%. For solutes present in concentrations below 1 mg/L,

the accuracy is generally not better than ±10% and can be poorer. When

concentrations are near the detection limit of the method used, and in all

determinations of constituents that are near or below the mg/L level, both accuracy

and precision are even more strongly affected by the experience and skill of the

analyst (Deutsch 1997).


The following are just a few of the possible causes for charge balance errors to

exceed these percentage limits.

Species in significant concentrations have not been accounted for in the analysis.

It is common practice to analyse for the major cations and anions only when

performing analyses. This can lead to the exclusion of other ions at significant

concentrations in a sample. In addition, ionic species may occur in a form that is

more complicated to analyse. For example, solutions that are strongly coloured

commonly have organic anions that form complexes with metals, and the usual

analytical procedures will not give results that can be balanced satisfactorily

(Hem 1992)

The use of a fixed end point pH for alkalinity titrations (Hem 1992)

Instrument malfunction

Miscalculation by the analyst

Inadequate cleaning of equipment, sample collection bottles and instrumentation

Inadequate preservation of samples and/or delayed analysis

For the purposes of this study, the following criteria from Younger (2007) were used.

If a charge balance error value is less than 5%, then the analysis has been regarded as

sufficiently accurate for all uses. If a charge balance error lies in the range 5-15%,

then the analysis has been used with caution, while those analyses with CBE values

greater than 15% have been excluded from the dataset. Unfortunately, P1 and WP16

had consistently high CBEs and consequently have not been included in the

interpretation or discussion in the papers included in this thesis. These high CBEs are

most likely due to the presence of organic acids which have a negative charge not

accounted for when only analysing for inorganic constituents.

3.2.5 Isotope analysis

13CDIC, 34

SSO4 and 15

N isotope samples were sent to the Stable Isotope Laboratory at

the Institute of Geological and Nuclear Sciences (GNS) in New Zealand for analysis.

δ2H and δ

18O were sent to the Isotope Analysis Service, Land and Water, CSIRO,

Adelaide.

All δ34

SSO4 results were averages and standard deviations of duplicates and were

reported with respect to VCDT, normalized to internal standards with reported values

of -3.2‰, +3.3‰ and +8.6‰ respectively for δ34

SSO4. The analytical precision for


the GNS instrument was 0.6‰ for δ34

SSO4 on the sulphur elemental analyser (SEA).

Sulphate was precipitated out using BaCl2 to form BaSO4 precipitate and then

analysed for sulphur isotopic compositions using techniques given in Robinson et al.

(1991). Samples were filtered through 0.45µm filter, and the pH was adjusted to 4

with either 1:5 HCl or 1:1 NH4OH. Samples were heated to boiling on a hot plate

and 10mL 0.5 mol/L BaCl2 was added without stirring, and kept on hot plate for 2

hours. Samples were filtered onto 0.45µm nitrocellulose filters, and the filters

combusted in a platinum crucible. The BaSO4 was weighed out in duplicate in tin

capsules with equal amount of VO5 and run on a Sercon Sulphur Elemental Analyser

connected to a Europa Geo 20-20 mass spectrometer (Valerie Claymore, pers. comm.

2008).

δ13

CDIC results are reported with respect to VPDB (Belemnitella Americana from the

Cretaceous Pee Dee Formation in South Carolina) and results are reported as per mil

(‰) VPDB (Clark and Fritz 1997) and normalized to an internal standard of -22.7‰.

Analysis of waters for δ13

CDIC was done by CO2 evolution by phosphoric acid. The

analytical precision for these measurements was 0.2‰ (Valerie Claymore, pers.

comm. 2008).

Analyses for δ15

NDIN for this study were for total dissolved inorganic nitrogen. The

15N standard is the atmospheric N2 reservoir where δ

15NN2 = 0‰ AIR and results are

reported as per mil (‰) AIR and were normalized to an internal standard of 1.8 ‰.

The analytical precision for these measurements was 0.3‰ (Valerie Claymore, pers.

comm. 2008).

3.3 Data Analysis

The aims of this study require the analysis and interpretation of standard

hydrochemical and stable environmental isotope data to determine the distribution of

nutrients and/or trace metals throughout the study area and to investigate

hydrological links between subsurface and surface water bodies. Hydrochemistry and

stable environmental isotopes of both surface and subsurface waters, their analysis,

and interpretation are discussed in the following sections, including examples from

the literature.


As stated above, the overall aim of this project is to establish where hydrological

links exist between surface and subsurface water bodies and determine how solutes

are transported from the freshwater coastal catchment to the adjacent marine

environment via groundwaters. This will be achieved using graphical and statistical

methods which are described below.

3.3.1 Graphical methods

Traditional methods for the hydrochemical characterisation of waters in order to

investigate interaction between various water bodies include both graphical and

statistical methods. Graphical methods such as Piper and Stiff diagrams have been

used extensively to group waters visually and in some cases indicate mixing between

water bodies. These methods are used primarily in Paper 1. The classification of

ground and surface waters is based on the dominant cations and anions present and

these can be displayed graphically in a Piper diagram (Piper 1944). The relative

concentrations of the major ions in percent meq/L are plotted on cation and anion

triangles and projected to a point on a quadrilateral representing both cation and

anions. Stiff diagrams are another graphical method that is commonly used in the

classification of natural waters. Polygons are constructed with three parallel axes

relating to concentrations in meq/L of major ions (Stiff Jr 1951). Stiff diagrams are

easy to construct and provide a quick visual comparison of individual chemical

analyses. Scatterplots, Piper and Stiff diagrams are used to assess large datasets,

identify dominant processes and detect groupings of water samples. These methods

are described in numerous texts, for example, Freeze and Cherry (1979), Hem

(1992), Mazor (1997) and Drever (2002). Some useful examples of studies where

graphical methods are also employed in order to interpret and/or characterise

hydrogeochemical data are Sukhija et al. (1996), Gimenez and Morell (1997), Logan

et al. (1999), Sanchez Martos et al. (1999), Cruz and Silva (2000), Allen and Suchy

(2001), Kim et al. (2003) and Hodgkinson et al. (2007). See also Zaporozec (1972)

and Güler et al. (2002).

Aquachem (Rockware Inc. 2011) and AqQA (Rockware Inc. 2011) are fully-

integrated software packages developed specifically for graphical and numerical

analysis of aqueous geochemical datasets. Both programs feature a fully

customisable database of geochemical parameters and provide a comprehensive


selection of analysis tools such as charge balance calculations to check the quality of

the analysis. They also enable the easy generation of graphics that aid in

interpretation of water chemistry data such as Piper and Stiff diagrams which are

commonly used for interpreting and plotting aqueous geochemical data.

3.3.2 Hierarchical cluster analysis (HCA)

Multivariate analysis of hydrochemical data, more specifically hierarchical cluster

analysis (HCA) is used to support results from graphical methods in Paper 2 and is

also used to group waters in Paper 3 using a different set of parameters. Multivariate

analysis is a statistical tool often used in the interpretation of hydrochemical data

and, in some cases, the investigation of water origins and interactions of waters with

other water types. Multivariate analysis techniques have been widely used in

environmental studies to reduce the complexity of large scale datasets. These

techniques identify structure in the dataset, and reveal relationships between the data

components (Mencio and Mas-Pla 2008).

HCA is a common tool used to group similar objects, not only in the field of

hydrochemistry but in also in other scientific, sociological and finance-based fields.

It is semi-objective and efficient tool that can be used to group water samples and

assist in the interpretation of hydrochemical processes. HCA has advantages over

graphical methods for the following reasons: (a) the inclusion of more variables such

as pH makes it easier to differentiate between samples, and (b) the equal weighting

of variables ensures that all ions, regardless of magnitude, contribute to the

partitioning of samples (Güler et al. 2002; McNeil 2002; Thyne et al. 2004). HCA

also has the advantage of being a more objective method than graphical methods

where the assignment of samples to hydrochemical facies can be influenced by

researchers‘ assumptions and is often a highly subjective process.

The hierarchical cluster analysis itself consists of two steps. The first step is to find

the similarity or dissimilarity between every pair of objects in the dataset. For this

analysis, the Euclidean distance method is used to calculate the distance between all

pairs of objects and form a dissimilarity matrix. The second step is to group the

objects in to a binary, hierarchical cluster tree (Kaufman and Rousseeuw 1990;

Graham 1993; Mathworks Inc. 2011). In this study Ward‘s Method is used to link

pairs of objects that are close together into binary clusters and then link these clusters


to each other etc. until all data are linked together in a hierarchical tree. Ward‘s

Method utilises the inner squared distance between pairs and determines links using

a minimum variance algorithm (Ward 1963; Mathworks Inc. 2011) and is commonly

used by hydrochemists and geoscientists. This method is distinct from all other

methods because it uses an analysis of variance approach to evaluate the distances

between clusters. In short, this method attempts to minimize the Sum of Squares (SS)

of any two (hypothetical) clusters that can be formed at each step. Refer to Ward

(1963) for details concerning this method. In general, this method is regarded as very

efficient, however, it tends to create clusters of small size (StatSoft 2010).

All HCA in this thesis was carried out using Matlab 7.8.0 (R2009a) (Mathworks Inc.

2011). The Matlab Statistics Toolbox provides a function pdist that computes the

Euclidean distance between pairs of objects in an n×p data matrix (n is the number of

samples in this case and p is the number of parameters) and a linkage function

creates an agglomerative hierarchical cluster tree from the Euclidean distance matrix.

The Ward method can be specified (Mathworks Inc. 2011). Dendrograms can then be

generated for interpretation.

Generally, studies involving the use of graphical and statistical methods, more

specifically HCA, to characterise natural waters have been in study areas where there

is (a) a variation in landuse, (b) anthropogenic source input to waters, (b) a much

larger scale study area, (c) obvious lithological differences between aquifers, (d) a

focus on aquifers of different depths. HCA is used here in Chapter 6 (Paper 2) to

support and/or clarify the interpretation from Paper 1. Due to the limited variability

in major ionic proportions of samples in the area, partitioning samples using

graphical methods involved some uncertainty. The close clustering of samples on the

Piper diagram and similarity in the Stiff diagram shapes makes it difficult to

differentiate between hydrochemical groups. Many researchers have combined

various interpretative approaches to describe hydrological processes and

hydrochemical facies in the natural environment. Some examples of these types of

studies follow.

Meng and Maynard (2001) had a similar problem to the one addressed in Paper 2 of

this thesis in relation to limited hydrochemical variation in their study area, the

Botucatu aquifer in Sao Paulo. Bicarbonate was the predominant anion in all

groundwaters and the authors sought to obtain better separation of groups using the


multivariate statistical techniques, cluster analysis and principal components analysis

(PCA). Graphical techniques such as Piper diagrams were found to be of limited

value due to the tight clustering of samples. Cluster analysis was found to be more

successful and revealed three compositional regions, (a) a SiO2-dominated recharge

region, (b) an intermediate region dominated hydrochemically by the dissolution of

calcite, and (c) a basin interior where leakage from underlying bedrock supplied

concentrations of sodium and fluoride.

O‘Shea and Jankowski (2006) had the added disadvantage of dealing with samples

that not only had similar proportions of major ions but also similar magnitudes.

Sodium and bicarbonate concentration ranges were 245-333 mg/L and 570-739 mg/L

respectively for 25 samples collected in the lower Namoi River valley within the

Great Artesian Basin in New South Wales, Australia. After applying a number of

graphical techniques including Piper (1944), Durov (1948) and Chadha (1999)

diagrams, which had limited usefulness, PCA and cluster analysis were employed to

properly delineate the subtle differences in the chemical composition of the samples.

The combination of these graphical and statistical methods enabled the authors to

identify three main geochemical processes: ion exchange, precipitation, and mixing

between waters from different sources.

Güler et al. (2002) evaluated the use of graphical and multivariate statistical methods

for the classification of water chemistry data. The authors examine the efficacy of

these methods rather than provide an in-depth discussion of hydrochemical processes

and characterisation using water samples from a wide variety of climatic conditions,

hydrologic regimes and geological environments. Spatial variability was found to a

more dominant factor than temporal variation due to seasonal differences in the

study. They found that graphical techniques proved to have limitations compared

with cluster analysis for large datasets. However, they emphasized that the statistical

methods do not provide information about the chemistry of the groupings and as such

should be used in combination with graphical methods.

Thyne et al. (2004) described a sequential analysis method for hydrochemical data

for watershed characterisation which combines standard statistical methods (HCA

and principal components analysis), spatial techniques, and inverse geochemical

modelling. HCA is used to form clusters which are then analysed for spatial

coherence to confirm a geological basis for the cluster groupings. Principal


components analysis (PCA) was then used to determine the sources of variation

between parameters and inverse geochemical modelling (IGM) to quantitatively

describe the hydrochemical evolution in the catchment. The authors stated that the

advantage of this technique is the ability to use standard methods in a sequential

fashion where each step builds on the prior analysis, providing increasing confidence

and greater insight into the hydrochemical evolution of catchment, as are the aims of

Paper 2. The authors were able to identify the major processes controlling

hydrochemical variation, determine the location and chemical signature of

anthropogenic impact, and provide information about aquifer properties using this

sequential analysis.

Mencio and Mas-Pla (2008) investigated qualitative contributions of surface, ground

and wastewater flows using multivariate analysis of hydrochemical data, so that the

chemical quality of each sampling station could be attributed to a specific

hydrological pattern and, therefore, to a responsible human pressure. Multivariate

analysis was used to identify interaction between ground and surface waters as well

as the effect of wastewater discharge into streams. Gaining or losing stream

behaviour was based on hydraulic head distribution and surface, ground and

wastewater treatment plant samples were collected for hydrochemical analysis. The

results from the hydrological observations were supported by PCA and cluster

analysis and this joint analysis made it possible to observe the significance of the

interaction between streams and aquifers in anthropized Mediterranean Basins.

These examples show the efficacy of using HCA for the investigation of natural

water chemistry. In Paper 2, this method was found to be very useful in assigning

sites to hydrochemical groups and also indicated some important processes in

relation to solute transport in the study area.

Contribution of Co-Authors for Thesis by Published Paper

The authors listed below have certified* that:

1. they meet the criteria for authorship in that they have participated in the conception, execution, or interpretation, of at least that part of the publication in their field of expertise;

2. they take public responsibility for their part of the publication, except for the responsible author who accepts overall responsibility for the publication;

3. there are no other authors of the publication according to these criteria;

4. potential conflicts of interest have been disclosed to (a) granting bodies, (b) the editor or publisher of journals or other publications, and (c) the head of the responsible academic unit, and

5. they agree to the use of the publication in the student’s thesis and its publication on the Australasian Digital Thesis database consistent with any limitations set by publisher requirements.

In the case of this chapter:

Paper 1: Hydrochemical and isotopic characterisation of groundwaters to define aquifer type and connectivity in a sub-tropical coastal setting, Fraser coast, Queensland _________________________________________________________________________

Contributor Statement of contribution*

Larsen, G. (candidate)

Designed the project, carried out the field and laboratory work, interpreted results and wrote the manuscript

Cox, M.E. (principal supervisor)

Assisted with project design and field work and contributed to the manuscript

Principal Supervisor Confirmation I have sighted email or other correspondence from all Co-authors confirming their certifying authorship. _______________________ ____________________ ______________________

4. PAPER 1

Hydrochemical and isotopic characterisation of groundwaters to

define aquifer type and connectivity in a subtropical coastal

setting, Fraser Coast, Queensland

Genevieve Larsen, Malcolm E. Cox




Environmental Earth Sciences 64(7): 1885-1909

77

Hydrochemical and isotopic character of groundwaters to define aquifer type and connectivity in a subtropical coastal setting, Fraser Coast, Queensland

Abstract

Physicochemical parameters, major ion chemistry and isotope composition of surface and

groundwaters were determined in forested coastal catchments and adjacent coastal plains. Results

showed obvious characterisation related to physical and hydrological setting, and highly variable

spatial differences reflecting the complexities of these areas. All these coastal waters are dominated by Na and Cl and fall on a common dilution line; hydrochemical grouping is largely due to anionic

differences (Cl, SO4 and HCO3), although Na and Mg ratios also vary. Six major hydrochemical facies

were determined. For groundwaters, compositional differences are largely related to aquifer material

and level of confinement; for coastal groundwaters important factors are tidal effects and proximity to

the shoreline. Differentiation for surface waters is mainly by drainage morphology, flow regime plus

proximity to the coast. Connectivity between water bodies is reflected by minor baseflow to

catchment streams, including with floodplain wetlands, but mostly occurs in low-lying zones where

there is mixing of fresh and saline water within surface water and subterranean estuaries, or by

seawater intrusion enhanced by overuse. Oxygen and hydrogen isotopic data for confined and semi-

confined groundwaters along the coast indicates local recharge; fresh surface waters in the elevated

catchments are shown to be sourced further inland plus have experienced evaporation.

Keywords: hydrochemical characterisation, coastal aquifers, saltwater/freshwater

relations, stable isotopes, ground/surface water relations

Introduction

Globally, the impacts of anthropogenic activities on natural waters have become a

major issue (Hem 1992; de Vries et al. 2002) and more recently the potential impact

of climate change is gaining the attention of hydrological studies especially within

coastal zones. Changes in the amount and distribution of rainfall (Trewin 2007;

Taschetto et al. 2009), rising temperatures (Nicholls 2006) and associated increases

in sea level have and will significantly alter the hydrological and geomorphological

characteristics of these settings (Church 2006; Pepper et al. 2006; Ribbe 2006; Kim

et al. 2009; Gräwe et al. 2010). However, of fundamental importance is the physical

character of any setting (Drever 2002) and coastal settings, in particular, can be

hydrologically complex. Within coastal settings there can be substantial variations in

geology, morphology and drainage system form and dynamics. Possibly the most

significant feature of these settings is that they are at the interface between

freshwater catchments and the marine environment, and are often also influenced by

tidal processes. Typical of these settings are complex hydrological processes

involving recharge, discharge, and multiple mixing environments. Due to these

complexities, the links between groundwater and surface waters are usually not well

understood, especially because of variable scale sub-systems within an overall

―system‖.

The region of southeast Queensland is the fastest growing urban area in Australia,

and from 2006 to 2031 its population is expected to grow from 2.8 million to 4.4

million people. The region covers 22,890 km2, and stretches 240 km from the

78 Paper 1. Hydrochemical character of groundwaters

Queensland-New South Wales border in the south to Noosa in the north (Department

of Infrastructure and Planning 2010). This population growth will result in

substantial changes in landuse and impacts to a wide range of natural systems, of

note the hydrological and hydrochemical processes which support a variety of

ecosystems. In addition to this, there is the real potential of sea level rise which in

low-lying settings with tidal systems can be substantially impacted by storm surges.

To obtain some understanding of these processes in such settings with comparatively

low-level modification, we have chosen an area on the Fraser Coast in the southeast

Queensland region to conduct an integrated investigation of hydrological systems.

Although more sparsely populated than the Brisbane area to the south, the Fraser

Coast has many similar geomorphological features and is also under pressure from

urbanisation with around 1500 new dwellings and a population growth of 3 to 4%

each year (Department of Infrastructure and Planning 2008).

The focus of this study is the freshwater catchments and the adjoining low-lying

coastal plain that hosts tidal estuaries. The estuaries discharge to the marine

environment adjacent to the southern part of Fraser Island. The mainland freshwater

catchments host plantation forestry, which also extends to the coastal plains. Within

the coastal plains there are also areas of remnant native vegetation and small

residential communities located near estuary mouths. This Fraser Coast region is

typified by subtropical rainfall which results in highly seasonal stream flow. The area

is located adjacent to the Ramsar-listed Great Sandy Strait which is of high

environmental significance. A number of threatened species (flora and fauna) exist in

the marine areas and associated tidal wetlands such as dugong, dolphins, migratory

shorebirds, seasonal populations of humpback whales, and rare shrubs (EPA 2005).

Here we consider the hydrological and hydrochemical processes of these coastal

catchments to determine the character of the groundwaters, and the connectivity

between various water bodies. The aims of this study are to (a) establish the

chemistry of natural subsurface and surface waters of this typical setting as a baseline

for comparison of future monitoring, (b) investigate the dominant hydrological

processes contributing to the hydrochemistry of natural waters, (c) describe the

hydrogeological settings in which these waters occur, and (d) determine possible

solute transport pathways related to current and future landuse practices. The results

of this investigation will be of value to assess the future management of such

ecologically sensitive areas. A goal here is to determine the chemical character of the

surface and subsurface waters within this coastal setting utilising various

physicochemical parameters, major ion and nutrient concentrations and stable water

isotopes (δ18

O, δ2H). The approach of the study is to group waters into

hydrochemical facies, identify dominant hydrological processes, and confirm where

interaction exists between water bodies.

Background

Elevated nutrients and metals in surface and groundwaters can be due to both natural

and anthropogenic influences which can be complex in coastal settings.

Urbanisation, agricultural and other land modifications can impact on the quality of

both surface and groundwater bodies; introduced solutes can infiltrate to aquifers and

can be discharged to coastal waters (Church 1996; Moore 1999; Burnett et al. 2006;

Gallardo et al. 2006; Tirumalesh et al. 2007). Hydrological processes in coastal

settings typically occur at highly variable scales and interaction between different

water systems is common. This is especially the case when comparing upper

Paper 1. Hydrochemical character of groundwaters 79

catchment freshwater regimes with the tidal regimes of the estuaries. There are many

forms of mixing between groundwaters and surface waters in these settings which

include interaction between aquifers and rivers, estuaries, and bays and ocean

shorelines. In addition, there can be hydraulic connection between different aquifers

themselves. The pathways that solutes take are also frequently complex involving

aquifer to aquifer interaction (Bubb et al. 2002; Hodgkinson et al. 2007; Li et al.

2008) as well as exchange between ground and surface waters (Reay et al. 1992;

Smith et al. 2001; Taniguchi 2002; Mackay et al. 2005; Westbrook et al. 2005;

Soulsby et al. 2007; Bailly-Comte et al. 2009) and consequently the contamination of

one can lead to the contamination of the other (Hayashi et al. 1998; Pinder et al.

2006). As an example, nutrients such as nitrogen and phosphorus, and trace metals

such as copper and iron can infiltrate to aquifers as a result of agricultural practices

(Zekster et al. 1983; Church 1996; Cable et al. 1997; Ensign et al. 2001; Dowling

2002; Howarth et al. 2002; Shaffelke et al. 2002; Trojan et al. 2003; Nakano et al.

2007) or be sourced from a wide range of impacts resulting from urbanisation and

can eventually be discharged to coastal waters. These various solutes are also shown

to commonly enter surface waters via direct runoff and be delivered to the ocean via

estuaries (Crossland et al. 1997; Dyer 1997; Soicher et al. 1997; Iversen et al. 1998;

Stalnacke et al. 1999; Pointon et al. 2003; Withers et al. 2008).

Factors such as reduced rainfall, changes in vegetation, and groundwater over-

pumping can lead to a reduction in water levels in aquifers and surface systems. In

coastal settings, this reduction can result in landward movement of the seawater-

freshwater interface in both ground and surface water bodies (Mulligan et al. 2007;

Werner 2009) and processes in estuaries can often mirror changes in the adjacent

aquifer systems. In addition, significant rainfall events typically increase discharge

and runoff of dissolved and suspended nutrients and metals from anthropogenic and

natural sources to adjacent water bodies. These processes and other environmental

factors have been shown to contribute to the development in marine waters of

Lyngbya majuscula, a toxic blue-green algae (cyanobacterium) that is a major

environmental concern in southeast Queensland (Dennison et al. 1999; Pointon et al.

2003; Albert et al. 2005; BMRG 2005; Ahern et al. 2006a). Knowledge of potential

solute transport mechanisms and dominant hydrological processes can assist

decision-makers when planning current and future land management practices in

order to avoid such environmental impacts.

The small coastal villages of Poona, Boonooroo and Tuan within the study area are

all under increasing pressure from urban development. These villages are unsewered

and use septic systems for effluent disposal, and the increasing number is of some

concern to residents (BMRG 2005) due to potential contamination of aquifers. In

addition, the potential over-exploitation of local fresh groundwaters due to increasing

extraction is also of consideration. It is of note, that similar conditions to these were

the case around many coastal areas of Moreton Bay in southeast Queensland until

recently. There still exist areas using various combinations of groundwater,

reticulated water, septics and sewage systems with local area treatment plants.

Although there has been continuous water quality monitoring in some areas within

the Great Sandy Strait, a recent report (BMRG 2005) states that there has been no

continuous water quality monitoring (estuarine or freshwater) in the project area

prior to this study. In addition, no event monitoring water quality data exists for the

coastal streams in the Great Sandy Strait study area. A major aim of the study, in

addition to providing an initial assessment of water chemistry in the study area, is to


provide hydrochemical and process-related information during steady-state

conditions (i.e. fairly consistent climate conditions and not during high rainfall

events) as a guide for future monitoring of these coastal settings which are typical of

much of central and southern Queensland.

Study Area

General setting

The area being studied is on the Fraser Coast of Queensland, adjacent to the Great

Sandy Strait, a passage landscape between the large Fraser Island sand mass and the

mainland (Figure 1). The mainland coastal region is characterised by short, steep

catchments that drain to the coastal floodplains, with lower gradients in the north of

the area towards the delta of the large Mary River. For the purposes of this study the

northern section of the area is referred to as the Tuan catchment and contains the

subcatchments of Kalah, Maaroom, Big Tuan and Little Tuan Creek. The southern

section of the area is referred to as Poona catchment and contains the subcatchments

of Poona and Buttha Creeks (Figure 2). Maryborough, the closest large town, is

located on the tidal Mary River and is approximately 25 km northwest of Poona

village.

Fig. 1 Map of Australia and a section of the southeast coast of Queensland. The dashed box shows

the location of the study area on the Fraser Coast.

Q

L

D


Fig. 2 Fraser Coast study area showing catchments and drainage systems. Main types of landuse

are: plantation forestry (light grey) with forest compartments; native vegetation as buffer zones and

bushland (dotted); residential settlements (dark grey); and national park (striped). Elevation decreases

towards the east and northeast. The central dashed line is Cooloola Road.

Source: National Resources, Mines and Energy (2004)

Climate

The climate of the area is subtropical, typical of southeast Queensland, with more


to February) and comparatively dry winters (June to August). Mean annual rainfall is

1115.7 mm. Based on 1908-2006 data for Maryborough from the Bureau of

Meteorology (2009) the wettest month is February with a mean rainfall of 174.2 mm,

and August, the driest has a mean rainfall of 39.6mm. The maximum mean monthly

temperature of 30.7°C occurs in January and minimum mean monthly temperature of


8.6°C occurs in July. Table 1 lists climate conditions for data collection field trips.

Rainfall distribution during the study was, however, atypical with some heavy

rainfall occurring during winter months.

Table 1 Climate conditions for data collection dates

Field

Trip

DATE Rainfalla

(mm/day)

Rainfall

Classificationb

Max.

Temp.c

(°C)

Min.

Temp.c

(°C)

Evaporationd

(mm)

FT1 24/08/2007 42.4 Moderate Rain 19.6 14.8 4.4

FT1 25/08/2007 119.0 Heavy Rain 31.4 15.5 2.0

FT2 20/10/2007 0.0 No Rain 25.1 15.1 5.4

FT2 21/10/2007 0.0 No Rain 23.6 15.4 7.0

FT3 18/12/2007 19.6 Light Rain 27.0 21.1 7.2

FT3 19/12/2007 3.6 Very Light Rain 28.6 21.0 5.6



FT4 17/05/2008 0.0 No Rain 27.4 11.0 4.0

FT5 08/08/2008 0.0 No Rain 20.7 5.2 5.0

FT6 03/12/2008 0.0 No Rain 31.9 18.4 8.0

FT7 31/05/2009 0.0 (16.6)e No Rain 22.0 13.3 3.6

FT7 01/06/2009 10.0 Light Rain 22.7 13.6 3.8

FT8 05/08/2009 0.0 No Rain 23.9 8.0 5.6

Notes: a) Tuan Forestry Office data

b) Based on American Meteorological Society (2000)

c) Maryborough data

d) Bundaberg data

e) Previous day (30/05/2009) recorded at Double Island Point, evidence of recent rain at

sample collection sites

Surface water and drainage systems

In this area, the coastal bedrock was incised by river action during a period of

relative low sea level (glacial period) and these channels have been partially filled

with sediments during the succeeding base-level rise (interglacial period) (Lang et al.

1998; Neil 1998). According to Thom and Roy (1984) the last postglacial marine

transgression (PMT) began approximately 11,000 year BP and terminated

approximately 6500 years BP. Depending on location, this was followed by a near

constant relative sea level (RSL) or a falling trend from 1-3 m higher than present,

commencing approximately 5000 years BP. This coastal evolution is reflected by

Optically Stimulated Luminescence (OSL) dating of pebbly sand beds at Beachmere,

a similar setting on the northwestern margin of Moreton Bay, Queensland,

approximately 150 km south of the Poona village. These ages reveal that relative sea

level at Beachmere was approximately 1 m higher than present 1,700 ± 140 years

BP. Shortly after (1140 years BP) and up until approximately 140 years ago, there

was a linear rate of shoreline progradation of 0.40 m per year, an apparent increase

from around 0.16 m per year for the period 1700 – 1140 years BP (Brooke et al.

2008).

More than 70% of the study area has topographic gradients less than 1.5% while

gradients in the upper catchments increase to 10%. Elevations range from -0.6 m to

129 m ASL with most of the area being less than 60 m ASL. The smaller sub-


catchments such as Buttha, Poona, Little Tuan and Big Tuan, Maaroom and Kahlah

Creek (Figure 2) have poorly developed surface drainage systems and catchment

definition.

The estuaries of this area are tidally dominated. In Poona Creek, the largest estuary,

the estuary head occurs around Pappins Bridge (the Cooloola Road crossing), an

adopted middle thread distance (AMTD) of 10.5 km from the mouth (see Figure 2).

Upstream from this point there is a change of slope and the catchment profile

increases in gradient. At the mouth of Poona Creek, spring tidal ranges are generally

slightly less than 2 m (Larsen, unpub. data, 2008).

During and after rainfall-induced high flow events, runoff from the catchment into

streams and their lower order creeks can be substantial and can affect water quality

in the Great Sandy Strait (Shaffelke et al. 2002; Campbell et al. 2004; BMRG 2005).

In addition, heavy rainfall can produce significant seepage from shallow unconfined

aquifers adding to nutrients and trace metals discharged to estuarine and marine

environments. Many of the tributaries are small creeks of an ephemeral nature for

most of the year and consist of pools alternating with small flows.

Landuse and vegetation

Poona, Little Tuan and Boonooroo are small coastal villages with populations of

approximately 200. These communities do not have town water supply and

residential water is obtained from rainwater tanks and/or groundwater bores. There

are short-term population increases in these coastal villages for vacation, fishing and

recreation. The main landuse in the area consists of mature Pinus plantations

ranging from 16 to 30 years of age, which have native vegetation buffer zones

adjacent to natural waterways (see Figure 2). Since the 1950s, extensive areas within

these coastal catchments and lowlands, which were generally unsuitable or marginal

for agriculture were acquired by the state government forestry department for Pinus

afforestation (Costantini et al. 2002). According to the Tuan 1: 50,000 map (FPQ

2007), pine forests were first established north of Big Tuan Creek in 1974. Some

small pine plots were established as early as 1948 in the study area near the Tuan

Forestry Office. There were also soft-wood plantations to the east of Maryborough

and at Tuan from the mid 1960s, but there were very few plots until the 1970s.

Watercourses from the current areas of exotic pine plantations drain to the coastline

and the Great Sandy Strait. Riparian buffer zones have been retained throughout the

plantations, in which buffer widths of the zone mostly relate to stream order.

Plantation management practices tend to disrupt landscapes and drainage systems

when initially established, mostly by clearing, roads and drains, and then again after

25-30 years when harvested. After clearing, typical forestry practices are as follows

(M. Robinson, pers. comm. 2007): (a) herbicides to kill weeds in the plantation

compartment in preparation for planting; (b) pine seedlings planted in either straight

rows or mounds (the mound method helps reduce runoff); and (c) seedlings fertilised

with phosphorus. Unless required, plantation compartments are not given any further

fertilisation although further herbicide treatments are often carried out. After the

trees are harvested, the compartment is broadcast burnt. Hardwood stumps are then

heaped into windrows by dozer and burnt again (Bubb et al. 2002).

Remnant native vegetation within the buffer zones is typically grassy forest

containing various species of eucalyptus, and tufted native grasses such as Themeda

australis (Kangaroo grass) and Imperata cylindrical (blady grass) and low layered


forest containing paperbarks (Melaleuca quinquenervia), White Mahogany

(Eucalyptus acmenioides) and a ground layer consisting largely of sedges (Coaldrake

1961). Within the tidal zone of the coastal flats saltmarsh and mangrove areas occur

along the estuaries. Peripheral to the estuaries are freshwater wetlands supporting

Wallum banksias (Banksia aemula), melaleucas and grasstrees. These wetlands form

an important part of the overall freshwater drainage system; they often have

groundwater links, and in many cases are close to saline waters.

Hydrogeological Setting

This study largely addresses shallow groundwaters (<25 m depth) as those sampled

come from aquifers within weathered profile of the bedrock or unconsolidated

surficial formations such as alluvium or coastal deposits. The bedrock geology is

mainly comprised of the Duckinwilla Group and the Elliot and Grahams Creek

Formations (see Figure 3) (Natural Resources Mines and Energy 2004). These

formations have experienced deep weathering since the Miocene period (24 Ma) and,

as a result, much of the land surface in the study area is covered by a thick lateritic

profile.

Duckinwilla Group (Tiaro Coal Measures): Late Triassic to early Jurassic age

feldspathic to quartzose sandstone, siltstone, shale, coal and a ferruginous oolite

marker. This unit was previously defined to include both the Tiaro Coal Measures

and Myrtle Creek Sandstone (Cranfield 1989). In the area of this study, the upper

profile of the Tiaro Coal Measures comprises very thin sandstone-siltstone-shale

facies consisting of almost equal proportions of quartz, volcanic rock fragments,

feldspar (dominantly plagioclase), detrital muscovite, biotite and minor opaques set

in calcite cements with almost no matrix (Cranfield 1993). A weathered form of the

Tiaro Coal Measures dominates the surficial geology (see Figure 3) in the southern

half of the study area, although in places it is unconformably overlain by the

Grahams Creek Formation and Elliott Formation. These weathered materials are

made up of undifferentiated coastal plain sediments consisting of sand, silt, mud and

minor gravel. In many parts of coastal Queensland, catchments with low seaward

gradients have developed wide alluvial deposits forming aquifers that contain large

volumes of groundwater. Exploratory drilling in this area indicates that this particular

formation shows little potential as a groundwater source. Unconfined surficial and

semi-confined groundwaters in the Poona catchment coastal areas are generally

confined to (a) small pockets of alluvium within the drainage systems and only

within the coastal plain, or (b) meandering creek banks infilled as a result of channel

migration. Infill materials are eroded from the Duckinwilla Formation within the

low-lying coastal plain and do not occur in the elevated catchment west of Pappins

Bridge. Both lithological logs and hydraulic behaviour of boreholes drilled adjacent

to the Poona Creek estuary show this site is on an infilled meander bank; at this point

the stream channel is migrating northward. Figure 3 shows the location of these

monitoring wells.

.


Fig. 3 Geology of the area and sample sites. Broken lines to the north indicate boundaries of the Tertiary alluvial aquifer identified by Laycock (1969) and Wang (2007) study area boundaries. Bores

labelled ―JL‖ are from Laycock (1969), those labelled ―C‖ are from Wang (2008). Inset shows

enlargement of bore transect and Poona town bores, at mouth of Poona Creek

Source: Natural Resources Mines and Energy (2004)

Grahams Creek Formation: Late Jurassic to Early Cretaceous age intercalated

volcanic and volcaniclastic sediments. The volcanic rocks are of andesitic to rhyolitic

composition (Ellis 1968; Cranfield 1993). The Grahams Creek Formation is observed

as weathered material adjacent to the shoreline within the southern part of the area,

and also as small pockets of unweathered material within some catchments (Figure

3). The weathered Grahams Creek Formation occurs in the form of undifferentiated

coastal plain sediments of sand, silt, mud and minor gravel.

Tertiary Alluvium: In an earlier report, Laycock (1969) describes an extensive

Tertiary alluvium aquifer in the northern catchment. Laycock‘s study focused on the

Tiaro and Pialbo forestry areas in the north of the project area. A sand-gravel aquifer

was indicated by lithological and hydrochemical data collected in 1969 (Laycock


1969). Further investigation was carried out in 1975 to determine the potential for the

supply of good quality water from this aquifer (Laycock 1975). This aquifer occurs

at a depth of 4-15 m and comprises fine to coarse grained sand and gravel, which in

all cases is overlain by impermeable clays (ferricrete and fine saprolite layers of the

weathered Elliot Formation profile). Potentiometric contours and isopachs of the

sand-gravel aquifer derived from lithological logs indicate a paleochannel (probably

an old Mary River channel) in the north of the area, striking southeast towards

Boonooroo (Figure 3). At the time, groundwater EC measurements indicated a

variable salinity distribution, however, it was also observed that high pumping rates

often resulted in saltwater intrusion particularly in bores located near the tidal

reaches of streams. Laycock concluded that the alluvial aquifer, although extensive,

is extremely variable in grain-size composition. As a result the success rate for site

selection for high yielding bores is likely to be low and best prospects appeared to be

along the direction of the paleochannel (Laycock 1975). Data for 10 sites included in

the 1969 report have been included in the dataset for this project; Figure 3 shows the

indicated boundaries of this formation.

Elliot Formation: Eocene to Oligocene quartzose to sublabile sandstone,

conglomerate, siltstone, mudstone and shale (Natural Resources Mines and Energy

2004). Sandstone forms the bulk of this formation and is generally white or

yellowish, fine to medium grained, well sorted, and lithic sublabile to quartzose, with

angular clasts and white clay matrix. The Elliot Formation dominates the surficial

geology of the northern section of the area, and overlies the Duckinwilla Group in

the southern section. This unit is comparatively thin with logs from Cranfield (1982)

indicating depths of 7.5, 10.0 and 24.3 m to the Tiaro Coal Measures in boreholes

within the Poona catchment. A fluviatile depositional environment is suggested for

the Elliot Formation (Cranfield 1982).

The Elliot Formation occurs in two forms: a duricrusted old land surface with

dominant facies being ferricrete with silcrete and indurated palaeosols at the top of a

deep weathering profile and as undifferentiated coastal plain sediments of sand, silt,

mud and minor gravel (Natural Resources Mines and Energy 2004). The weathered

Elliot Formation dominates the northern parts of the study area, occurring in its

duricrust form. In the southern parts, it occurs more often as undifferentiated

unconsolidated sediments overlying the Tiaro Coal Measures of the Duckinwilla

Group.

Wang (2008) used a combination of XRD analysis, and aqueous and soil

geochemical measurements, to develop a regolith profile typical of lithology of the

weathered Elliot Formation found within the northern Tuan catchment. This type of

profile is widespread at this latitude and results from intense weathering over long

periods. Hydrologically, the infiltration of water is restricted at three levels: the top

of a ferricrete or mottled saprolite layer, the top of a deeper fine saprolite layer

containing soluble salts, and the unweathered bedrock. A thin coarse saprolite layer

overlies the bedrock and contains freshwater. Data indicate that there is no vertical

migration of soluble salts from the fine saprolite layer to the groundwaters within the

coarse saprolite. A number of monitoring wells were established for the Wang (2008)

project and four of these have been included in the dataset for this area: C2d (13m),

C3 (7m), C4 (3.8m) and C5 (4m). See Figure 3 for the locations of these bores.

Quaternary Alluvium: Surficial Quaternary alluvium occurs more extensively in the

northern Tuan catchment than in the Poona catchment, where it is mostly derived


from weathering of the Elliot Formation and is confined to drainage systems (Natural

Resources Mines and Energy 2004).

Beach Ridges: These are Holocene in age and consist of sand, shelly sand and minor

gravel. There appears to be good quality freshwater locally within this formation,

however, there is also evidence of some saline intrusion (discussed below).

Estuarine Tidal Flats: These Holocene estuarine tidal muds and sands occur along

the coast in this section of the Great Sandy Strait, and for several hundred metres

upstream of the mouth of Poona Creek. These sediments are sometimes areas of

significant fresh and marine water interaction.

Soils: Much of the area is covered by deep weathering profiles overlain by shallow

topsoil. This is typical of coastal lowlands along the seaboard of eastern Australia,

and soils are nutrient poor and generally deficient in nitrogen and phosphorus

(Coaldrake 1961). The soil profiles in the study area are highly variable. Higher

topographic areas often have very shallow topsoil such as humus podzolics, red

earths and yellow earths overlying deep weathering profiles while lower topography

areas often contain sediments that have been eroded from the higher features. This

profile is further complicated by the presence of aeolian sand dune deposits which

occur throughout areas of medium elevation (A. Hammond, unpub. data, 2007).

Investigations for acid sulphate soils were conducted in 2003 within the Poona

catchment and were identified in two shoreline forestry compartments . One of these

(compartment 9B) had possible actual acid sulphate soils (AASS) while the other

(compartment 13A) showed potential acid sulphate soils (PASS) at depth in the

Tewan Creek drainage line (Malcolm et al. 2004). See Figure 3 for these locations.

Waterlogging: Widespread waterlogging occurs in much of this region and has been

of some concern to plantation management, notably the effects on catchment water

balance (Bubb et al. 2002). This is of high significance during management of

harvesting. Highly variable groundwater responses were recorded within bores at

different depths and these suggested that there are localised recharge areas within the

forestry compartments where the aquitards causing the waterlogging may be

discontinuous or have a considerably higher hydraulic conductivity than had been

observed previously. This type of waterlogging is also evident in the Poona and Tuan

coastal zones. Wang (2008) further investigated waterlogging in this region and

confirmed that it was due to groundwater perched on layers of ferricrete and mottled

saprolite within the weathered Elliot Formation.

Site Locations

To test coastal zone processes, a transect of five monitoring bores (P2, P4-P6, P8)

was established on a meander at the mouth of the Poona Creek estuary. An additional

monitoring well, B1, was drilled just north of Buttha Creek (see Figure 3). The holes

were drilled using a hydraulic rotary drilling rig with bentonite drilling mud. Cuttings

samples were collected at over 0.5 m intervals. Drillhole depths varied (Table 2) and

3 m PVC slotted screens were placed at the bottom of the borehole, gravel packed

and sealed with bentonite. Wells were capped and housed with a galvanised steel

casing set in a concrete surface seal. Four shallow monitoring wells (P11-P14) were

later (mid-2009) installed by hand auger in muds and sands of the estuarine tidal flats

between the transect and the estuary in order to further investigate tidal intrusion in

this area.


Table 2 Description of sample locations

SITE ID Sample

Type Site

a Description

AMTDb (km) (SW)

or Depth (m bgs) (GW)

Distancec from

estuary/strait (m)

Topographical height

(m AHD)

Water Type

B1 GW Native bushland, ghost gums, paperbarks, banksia 5.0-8.0 100 (Buttha) 4.3 Na-Mg-Cl

P2 GW Transect - Native vegetation between pine plantation and estuary 6.0-9.0 320 (Poona) 2.3 Na-Cl

P4 GW Transect - Native vegetation between pine plantation and estuary 9.0-12.0 390 (Poona) 3.4 Na-Cl-HCO3

P5 GW Transect - Native vegetation between pine plantation and estuary 3.0-6.0 300 (Poona) 1.5 Na-Mg-Cl



P11 GW Supratidal flats – algal mats, small salt-tolerant succulents and grass 1.2 180 (Poona) 1.1 Na-Mg-Cl


P13 GW Supratidal flats – algal mats, small salt-tolerant succulents and grass, mangrove stands 1 240 (Poona) 1.1 Na-Mg-Cl


134B GW Residential bore – cultivated lawn and shrubs Unknown 143 < 3.5 Na-Mg-Cl

204B GW Residential bore – cultivated lawn and shrubs 12.0 214 < 3.5 Na-Cl

PCP GW Caravan Park bore – cultivated lawn and trees 19.0 100 < 3.5 Na-Cl-HCO3

RE GW Residential bore – cultivated lawn and shrubs 11.0 290 3.27 Na-Mg-Cl

RF GW Caravan Park bore – cultivated lawn and shrubs 6.0 180 2.84 Na-Mg-Cl

C2d GW Mature pine forest 11.5-13.0 9100 21.5 Na-Cl-HCO3

C3d GW Native grassland opposite timber mill 5.5-7.0 9000 22.1 Na-Cl

C4 GW Mature pine forest 2.3-3.8 8500 16.8 Na-Cl

C5 GW Native vegetation, grass trees, melaleuca, wallum 2.5-4.0 8700 14.5 Na-Mg-Cl

JL1 GW Pine plantation 12.2 8700 14.6 Na-Cl

JL2 GW Pine plantation 10.7 55 (Big TCd) 3.5 Na-Cl


Notes: SW = Surface water, GW = Groundwater a) The site descriptions listed for the JL sites are for current conditions. At the time of the data collection for these sites (1968-1969), the pine plantations

had not been established.

b) AMTD = Adopted Middle Thread Distance

c) Brackets in this column contain estuary names. Otherwise, distances are from the Great Sandy Strait.

d) TC = Tuan Creek.

Table 2 continued

SITE ID Sample

Type Site

a Description

AMTDb (km) (SW)

or Depth (m bgs) (GW)

Distancec from

estuary/Strait (m)

Topographical height

(m AHD)

Water type

JL4 GW Pine plantation 20.7 8600 16.5 Na-Cl-SO4

JL7 GW Wallum heath communities – Poona National Park 5.4 4000 7.8 Na-Cl

JL8 GW Native vegetation 5.2 140 (Little TC) 7.5 Na-Cl-HCO3

JL9 GW Pine plantation 7.6 8400 14.8 Na-Cl-SO4

JL10 GW Wallum heath communities – Poona National Park 7.9 7100 < 9.0 Na-Mg-Cl

JL13 GW Native vegetation 6.1 4600 7.8 Na-Cl

JL20 GW Residential 11.6 450 < 4.0 Na-Cl

JL25 GW Residential 4.6 780 (Little TC) 3.8 Na-Cl

LRB SW Low flow, very small creek 12.8 N/A 8.7 Na-Mg-Cl

PB SW Moderate tidal flow 10.5 N/A 2.7 Na-Mg-Cl

PC9 SW Moderate flow, small creek 16.4 N/A 15.9 Na-Mg-Cl


PCM SW Strong tidal flow 0.0 N/A 0.0 Na-Mg-Cl

TCA SW Still pools/small flowing brooks 16.8 N/A 18.6 Na-Mg-Cl

TCB SW Moderate tidal flow 8.5 N/A 1.5 Na-Mg-Cl

WP11 SW Excavated still pool, low flow 9.0 N/A 3.2 Na-Mg-Cl




Figure 3 shows the locations of all sampling sites included in this study. Table 2 lists

all sites, site descriptions, adopted middle thread distance (AMTD) from creek

mouths for surface waters (SW) or depth of sampling or screening interval for

groundwaters (Lau et al.), distance of groundwater sites from estuary or the Strait,

topographical heights and water type computed for a representative dataset.

Poona Estuary Transect: This transect of bores (P2, P4-P6, P8) was established for

detailed hydrochemical and water level measurements of the groundwaters adjacent

to the estuary. The transect is within fluvially derived sediments of the weathered

Duckinwilla Group (Tiaro Coal Measures). Bores P11-P14 lie within the muds of

sands of the supratidal flats between this transect and the estuary.

Poona Catchment Sites: One monitoring well (B1) is located in the duricrust of the

weathered Grahams Creek Formation which overlies the Duckinwilla Group

formation to the southwest. Surface water site PCM is located in the tidal muds and

sands at the mouth of Poona Creek. Stream sites in the Poona catchment (PC9, PC10,

WP12, WP19, WP16, WP31, LRB) are within the Duckinwilla Group except for the

sites at WP11 and Pappins Bridge (PB) which are within weathered Elliot Formation.

The surficial geology at the residential bore sites at Poona (PCP, 134B, 204B)

consists of Holocene beach ridge sands.

Tuan Catchment Sites: Surficial geology at the residential borehole sites at

Boonooroo (RF) and Tuan (R+E) consists of the duricrust of the weathered Elliot

Formation while the surface water data collection site at Tuan Creek (TCA) is in the

Elliot Formation. The geology at TCB, located in the Big Tuan Creek estuary,

consists of mixed mafic and felsic rocks of the Grahams Creek Formation (Natural

Resources Mines and Energy 2004).

According to the 1969 Laycock report, the boreholes JL1, JL2, JL7, JL9 and JL10 lie

within Tertiary alluvium consisting of varying amounts of clays, sands and gravels

overlain by Tertiary Elliot Formation which occurs as a thin veneer of white siltstone

or clay and underlain by Maryborough Formation bedrock. Bores JL13, JL20 and

JL25 have a similar profile but also have a superficial layer of coastal deposits. Bore

JL8 also lies within this Tertiary alluvium but is overlain by organic silts and clay,

occurring east of where the sediments of the near-horizontal Elliot Formation merge

with these coastal deposits. Bore JL4 occurs within the Maryborough Formation

itself where it is not overlain by the Elliot Formation or Tertiary Alluvium (Laycock

1969).

Both Laycock (1969) and Wang et al. (2008) studied the northern area, however,

Wang et al. (2008) focused on vadose zone hydrology. All boreholes except C2d

(13.0m) and C3d (7m) had depths of only around 2 to 4.6 metres while the Laycock

study focused on the Tertiary alluvial valley occurring at variable depths and

thicknesses between 4 to 15 m. Practically all of the shallow bores drilled for the

Wang project occur within weathered Elliot Formation, which is reflected in the

regolith profiles described. Although C2d is south of the estimated boundary for this

Tertiary alluvial valley, a thin layer containing gravels and coarse sands that was

intercepted at between 10.5 and 12.5 m depth within this borehole could be part of

the peripheral thinning of the Tertiary alluvial valley (Figure 3).


Methods

Data Collection

Surface and groundwater samples were collected from Poona, Little Tuan, Big Tuan

and Boonooroo catchments, all predominantly pine plantation areas. There are a total

of 29 groundwater sites including residential boreholes and sites included from the

Wang (2008) and Laycock (1969; Laycock 1975) studies and 10 surface water sites.

The sites from the Wang study were resampled in May 2008 (FT4). The selection of

sites is to provide representative samples from the main geological landform settings

of the area.

In total, eight sampling runs were conducted over a period of 25 months from August

2007 to August 2009; the multiple sampling approach was used to determine if

seasonal variations were significant. The first field trip coincided with moderate (24-

96 mm/day) to heavy (96-384 mm/day) rain resulting in flooding conditions. Of the

remaining 7 field trips, FT3 and FT6 had very light (< 6 mm/day) to light rain (> 6

mm/day, < 24 mm/day) conditions (FT3) and one during very light rain (FT4).

Otherwise, conditions were dry during the time of collection and the previous several

days leading up to sample collection. However, there was evidence of recent rain in

May of 2009 (FT6) but nil rainfall was recorded at Tuan Forestry Office for this

time, the closest rain gauge station to the study area (Table 1). However, 16.6 mm

was recorded at Double Island Point (an ocean coast site approximately 50 km

southeast of the Tuan Forestry Office) for 31 May 2009, demonstrating the

variability in rainfall over this relatively small coastal region. Also of significance to

the distribution of regional rainfall is the presence of the Fraser Island landmass.

Field Methods

Physicochemical parameters (EC, pH, Eh, DO and T) were measured in situ at all

sites with a TPS 90FL field meter. Samples for dissolved ion analysis were collected

in 250 mL polyethylene bottles and samples for the determination of δ18

O and δ2H in

35 mL McCartney bottles. Samples for cation analysis by ICP-OES were filtered in

the field using 0.45 µm pore diameter polycarbonate filter papers and acidified to pH

< 2 using 50% nitric acid for preservation; anion bottles were not acidified and filled

to eliminate air space. Collected samples were kept on ice or refrigerated for

transport and storage; isotope samples were kept in containers in the dark to avoid

evaporation. For all groundwater samples, bores were purged prior to

physicochemical measurements and collection of samples by use of a submersible

pump or bailer. For those boreholes with continuous recharge, a limit of 10 minutes

was set on the purging time.

Analytical Methods

Inductively coupled plasma optical emission spectroscopy (Varian Liberty 200 ICP-

OES and Varian Vista-MPX ICP-OES) was used to determine concentrations of the

cations, Al, Mn, Fetotal, Mg, Ca, Na, Zn, Cu and K. Samples were analysed for anion

concentrations of F-, Br

-, Cl

-, SO4

2-, PO4

3- and NO3

- by ion chromatography (IC

Dionex DX300) and alkalinity by titration with hydrochloric acid within 24 hours of

collection. For samples collected on field trips 6, 7 and 8, an AQ2 SEAL discrete

analyser was used to colorimetrically determine alkalinity (AQ2 Method No: EPA-

100-A Rev.2) and concentrations of chloride (AQ2 Method No: EPA-105-A Rev. 4).


For stable isotope determinations of δ2H and δ

18O, samples were sent to the Isotope

Analysis Service, CSIRO, Adelaide, and the results are reported in ‰ VSMOW.

Isotope analysis was not included in the earlier Laycock project, and many of these

bores could no longer be located.

Assessment of chemical analyses showed that some ground and surface water

samples had a high ionic imbalance. The presence of significant amounts of humic

and fulvic acids is the most likely cause for these charge balance errors which is a

common problem for certain samples in these coastal settings. As a consequence, a

relatively relaxed limit of |15%| charge balance error is utilised in this study in order

to obtain a good spatial coverage. Aside from P11-P14 and the Laycock sites, the

dataset used here is from the fourth field trip (FT4) in 15-17 May 2008 when

conditions were mostly dry with occasional light showers. The shallow monitoring

wells (P11-P14) were not installed until 2009 and for these 5 August 2009 (FT8) data

is used (Table 1). The Laycock samples included in this study were collected and

analysed in 1968; the Wang study sites were re-sampled during the May 2008 (FT4)

data collection.

Graphical Methods

Scatterplots, Piper (Piper 1944) and Stiff (Stiff Jr 1951) diagrams are used to assess

large datasets, identify dominant processes and detect groupings of water samples.

These methods are described in numerous texts, for example, Freeze & Cherry

(1979), Hem (1992), Mazor (1997) and Drever (2002). Some useful examples of

studies where graphical methods are also employed in order to interpret and/or

characterise hydrogeochemical data are Sukhija et al. (1996), Gimenez & Morell

(1997), Logan et al. (1999), Sanchez Martos et al. (1999), Cruz & Silva (2000),

Allen & Suchy (2001), Kim et al. (2003) and Hodgkinson et al. (2007).

Environmental Stable Isotopes

There are characteristic patterns in 18

O and 2H isotopes in precipitation that are

related to latitude, temperature, land mass, altitude and seasonality and, as a result,

these data can provide information relating to recharge sources, flow paths and

mixing of natural waters (Freeze et al. 1979; Clark et al. 1997). The isotopic

composition of 2H and

18O in water is expressed in per mil (‰) deviations from

SMOW (Standard Mean Ocean Water) and written as δ2H and δ

18O. Global and local

meteoric water lines (GMWL and LMWL), equations resulting from the linear

regression of δ2H and δ

18O data for water samples collected globally and locally

respectively, can be used to assist in the interpretation of isotopic data. The global

meteoric water line used was first defined by Harmon Craig (1961) and is based on

around 400 water samples of rivers, lakes, and precipitation from various countries

with the equation

δ2H = 8δ

18O + 10

Data sourced from the Global Network of Isotopes in Precipitation (International

Atomic Energy Agency 2006) for Brisbane (approximately 200 km south of the

study area) has been used to construct the LMWL by linear regression and has the

following equation.

δ2H = 7.49δ

18O + 11.74


The slope of the Brisbane LMWL (BMWL), being relatively close to the GMWL

slope of 8, reflects the relatively high humidity in this region. In areas where there is

high humidity, kinetic evaporation effects are closer to equilibrium and the slope will

be closer to the GMWL. In areas of low humidity, kinetic nonequilibrium

evaporation effects will be more pronounced and the slope will become progressively

lower with decreasing humidity.

Results and Discussion

Major ion concentrations, physicochemical parameters, isotope ratios and charge

balance errors for all samples are summarised in Table 3.

Coastal rainfall has relatively high proportions of sodium and chloride compared to

inland precipitation due to prevailing southeasterly winds and cyclic salt content of

the rainfall. As a consequence, sodium and chloride are the dominant cations and

anions in all samples in this coastal region (McNeil et al. 2005). Other major ions are

low relative to sodium and chloride although in some cases bicarbonate and sulphate

exceed 10% of the total ion sum. The samples have been typed based on major ions

in Table 2. Excluding data collected in August 2007 during storm conditions, major

cation and anion concentrations are relatively consistent over time for the majority of

sites. The main cause of variability in the data is mixing of estuarine and fresh

ground and surface waters. To assist in the characterizing of samples, Na

concentrations were plotted against Cl concentrations (Figure 4) and illustrate

concentration ranges and grouping of waters and various hydrological processes such

as evaporation and saline-fresh water mixing in both surface and subsurface waters.

Overall, groundwater is indicated to occur in three hydrogeological settings in this

region, (a) zones within weathered bedrock, (b) Tertiary alluvial valley in the north,

and (c) Quaternary unconsolidated materials of the tidal coastal strip which can be

further subdivided into (i) coastal plain alluvial deposits, (ii) tidal sands and muds,

and (‗iii) coastal beach ridge sands. Surface waters can be separated into two readily

differentiable groups, (a) freshwaters within the elevated catchments and streams

within the coastal plains disconnected from the main tidal channel, and (b) estuarine

water within the main tidal drainage channels of the coastal plains.

(a) Weathered bedrock

Many of the unconfined groundwaters in the weathered Elliot Formation of the Tuan

catchment (Wang et al. 2008) had variable salinities relating to the brackish waters

within the mottled saprolite. The kaolinised pallid zone of deep weathering profiles is

widely accepted as a major repository of soluble salts and the major source of these

salts is most likely coastal rainfall and marine aerosols rather than bedrock

weathering (Wang et al. 2008). These salinities are highly variable spatially,

however, and EC values at C3, C4 and C5 were much higher than other

groundwaters sampled in this area. The EC distribution suggests relict salinity or

tidal influence although these sites are some distance from the coast. Certainly, C5

has a much higher EC than at any of the other sites, being close to 10,000 µS cm-1

,

and groundwater here may be subject to some degree of saline intrusion. The site is

located at the boundary of Poona National Park, a low-lying coastal plain covered by

extensive wallum heath communities and mangroves, and where the surficial

geology consists mainly of sands and some degree of saline intrusion. Some degree

of saline intrusion could reasonably be expected in this type of environment.


Table 3 Physico-chemical and isotopic data

SITE ID

pH

EC µS/cm

Na+

mg/L Mg

2+

mg/L Ca

2+

mg/L K

+

mg/L Cl

-

mg/L SO4

2-

mg/L HCO3

-

mg/L TDI

mg/L δ

2H

‰ VSMOW δ

18O

‰ VSMOW CBE

a

%

B1 4.2 515 77 20 0.4 0.3 165 22 <0.1 293 -15.7 -4.1 1.4

P2 5.1 825 138 19 2.5 4.1 291 52 4 526 -19.7 -4.2 -6.5

P4 5.2 237 40 3 0.7 1.0 60 13 32 159 -19.4 -4.0 -3.7

P5 5.6 2102 221 91 12 13 652 53 13 1131 -37.9 -6.6 6.1

P6 5.6 241 54 3 2.1 1.9 61 7 36 167 -17.5 -4.0 6.3

P8 5.6 569.0 115 7 1.2 3.6 136 4 79 354 -14.8 -3.6 6.0

P11 7.0 73300 16534 4020 412.8 571.6 31218 3330 535 56622 n.a.b n.a. 6.2

P12 7.2 44200 9592 2311 294.8 344.0 16847 2309 336 32037 n.a. n.a. 8.8

P13 6.3 68400 14398 3760 399.6 500.0 28096 3857 473 51491 n.a. n.a. 4.8

P14 6.8 57400 12008 2998 393.2 426.4 27608 5583 282 49311 n.a. n.a. -5.9

134B 5.0 387 50 18 5.4 0.0 111 23 6 218 -16.5 -4.1 7.1

204B 6.4 1396 153 23 28.3 2.6 426 108 49 814 -12.3 -3.6 -14.9

PCP 7.5 716 117 12 12.7 0.0 127 26 137 404 -15.8 -3.9 3.4

R+E 4.4 1932 316 90 16.7 7.2 695 47 34 1216 -16.5 -3.9 2.1

RF 5.3 1744 232 156 12.5 2.7 660 31 7 1113 -18.2 -4.4 10.6

C2d 6.0 680 147 14 2.1 0.0 214 46 138 563 -19.2 -4.3 -9.5

C3d 3.1 4040 841 64 3.3 0.9 1492 43 <0.1 2457 -19.1 -4.3 -1.2

C4 2.7 3680 707 81 0.5 0.2 1221 195 <0.1 2209 -21.3 -4.4 -1.5

C5 4.2 9370 1752 446 5.4 1.1 3468 392 <0.1 6075 -21.8 -4.5 3.4

JL1 7.0 1140 233 13 6.0 n.a. 298 64 117 672 n.a. n.a. -0.8

JL2 6.4 1000 181 14 11.0 n.a. 304 42 5 554 n.a. n.a. 0.2

JL4 4.2 1640 291 17 8.0 n.a. 365 170 37 870 n.a. n.a. 0.0

JL7 5.1 825 156 9 5.0 n.a. 230 25 49 450 n.a. n.a. -0.3

Table 3 Physicochemical measurements, major ion concentrations, water isotope ratios and charge balance errors for all samples


Notes: a) JL sites were sampled in the period 1968-69. P11, P12, P13 and P14 were all sampled August of 2009. The remaining sites were sampled in May of

2008 except for 204B and 134B where samples could not be retrieved at that time due to biofouling and lack of access. Subsequently data from the

December 2007 dataset were used for these two sites.

b) CBE = charge balance error

c) n.a. = not analysed

Table 3 continued

SITE ID

pH

EC µS/cm

Na+

mg/L Mg

2+

mg/L Ca

2+

mg/L K

+

mg/L Cl

-

mg/L SO4

2-

mg/L HCO3

-

mg/L TDI

mg/L δ

2H

‰ VSMOW δ

18O

‰ VSMOW CBE

a

%

JL8 7.8 222 37 4 3.0 n.a. 55 4 37 128 n.a. n.a. -3.6

JL9 8.0 2060 343 24 10.0 n.a. 392 170 171 1024 n.a. n.a. -0.1

JL10 7.8 669 124 7 3.0 n.a. 196 14 20 354 n.a. n.a. -0.3

JL13 7.0 774 169 8 4.0 n.a. 220 18 49 424 n.a. n.a. 5.2

JL20 6.9 23400 4966 450 160.0 n.a. 8780 468 220 14933 n.a. n.a. 0.0

JL25 7.0 630 122 5 3.0 n.a. 184 14 24 340 n.a. n.a. -0.2

LRB 6.1 143 24 6 1.7 1.1 35 4 11 89 -26.4 -4.8 13.8

PB 6.7 26300 5257 1298 185.5 194.5 10805 45 37 19433 -19.6 -3.8 1.3

PC9 6.4 95 12 3 1 1 23 9 10 62 -29.5 -5.0 -2.1

PC10 7.2 81 16 4 0.9 0.6 31 8 10 73 -27.3 -4.6 -3.0

PCM 7.8 48000 10898 2682 381.4 410.3 22833 3149 124 40576 7.7 1.0 0.8

TCA 5.3 591 103 28 2.0 0.4 215 21 4 408 n.a. n.a. 12.4

TCB 6.5 32600 6112 1569 216.7 261.6 14977 2895 96 26136 -24.4 -4.9 -8.0

WP11 6.4 129 22 5 0.7 0.9 40 <0.05 2 78 -16.7 -3.9 5.2

WP12 6.1 124 21 6 1.5 0.3 38 3.2 7 81 -27.2 -4.8 10.9

WP31 6.9 108 21 5 1.9 1.0 39 4.4 18 93 -28.6 -4.5 1.1


Shallow bores C3, C4 and C5 are strongly acidic (2.7 – 4.2) due to input of organic

acids from the soil layer whereas C2d, screened within a thin layer of coarse sands

and gravels, has a much higher pH of 6.0. This appears to confirm that downward

flow of water is restricted by fine (saprolite) clay layers within the weathering

profile, as reported in Wang et al. (2008).

Drilling carried out for this project did not reveal any substantial unconfined alluvial

aquifers in the Poona or Buttha catchments within the coastal plain, but more

typically shallow soil profiles overlying semi-confining to confining weathered

bedrock. There were no boreholes drilled in the elevated areas of the Poona

catchment. Much of the elevated catchment is covered by bedrock of the Duckinwilla

Formation and pockets of weathered Elliot Formation are likely to have a similar

profile to that found in boreholes, C3, C4 and C5 described and possibly contain

small amounts of fresh groundwater. Overall, however, these weathered profiles are

poor water-bearing zones.

Monitoring well B1, screened in weathered materials within the Poona catchment,

had a pH value of 4.2 due to organic acids leached from leaf litter at the surface or

from organic materials at depth. Based on EC variation over time (assuming saline

intrusion will lead to variation with tidal condition) and depth and topographical

differences, it appears that B1 located 100 m from the Buttha Creek estuary could

experience some saline intrusion.

(b) Tuan Catchment Tertiary alluvial valley

In the northern section, the Tertiary alluvial valley aquifer contains a substantial

volume of good quality freshwater. All of these groundwaters from the Laycock

1969 study have pH in the near-neutral to weakly basic range. Most of the samples

occurring within the Tertiary alluvium aquifer in this northern area plot closely

together in the Na vs Cl plot (Figure 4), expected for samples with similar lithology

and rainfall recharge (fresh confined groundwaters). The EC and pH measurements

within the Tertiary alluvium relative to the shallow unconfined waters (C3d, C4, C5)

suggests that there is little to no infiltration of soluble salts through the profile to this

aquifer.

(c) Quaternary unconsolidated materials of the tidal coastal strip

There are three formations along the coastal strip containing Quaternary

unconsolidated materials. There are the alluvial deposits adjacent to the drainage

system within the coastal plain, the supratidal tidal muds and sands adjacent to the

lower estuary, and the beach ridge sands located at Poona and Boonooroo.

(i) Coastal plain alluvial deposits

In the low-lying coastal plain of the Poona catchment there are small pockets of

semi-confined groundwater adjacent to the tributaries occurring within relict fluvial

channels or infilled meanders, such as the one where monitoring bores P2, P4-P6 and

P8 are located. Preliminary analysis of sediment samples collected from these

boreholes show layers with varying amounts of organic matter and sands alternating

with clean aeolian sands. Semi-confining silt/clay layers were also present in some of

these boreholes underlying the soil profile. A gravel and sand layer of high hydraulic


conductivity was present in five of the boreholes at several metres depth in this

transect.

Fig. 4 Log-log plots of sodium ion versus chloride ion concentrations in mg/L for all waters

sampled, relative to the saltwater dilution line. Figure A is higher salinity waters and Figure B is lower

salinity waters. These figures display the wide range of waters in these coastal settings

B1

P2

P4

P6

P8PCPC2d

134B

JL1

JL2

JL4

JL7

JL8

JL9

JL10

JL13

JL25204B

LRB

PC9

PC10

TCA

WP11

WP12

WP31

10

100

20 200

Sod

ium

(mg

/L)

Chloride (mg/L)

Groundwaters

Surface waters

FRESH CONFINED

GROUNDWATERS

FRESH SURFACE WATERS

FRESH SEMI-CONFINED GROUNDWATERS

Saltwater Dilution Line

40 60 80 100 140 400

300

200

50

30

20

B1

P2

P4

P5

P6

P8PCP

R+E

RF

C2d

C3dC4

C5

134B

JL1JL2

JL4

JL7

JL8

JL9

JL10

JL13

JL20

JL25

P11

P12

P13

P14

204B

LRB

PB

PC9PC10

PCM

TCA

TCB

WP11WP12WP31

10

100

1000

10000

100000

20 200 2000 20000

Sod

ium

(mg

/L)

Chloride (mg/L)

Groundwaters

Surface waters

A

B


40 60 100 400 600 1000 4000 8000 40000 80000

50000

20000

5000

2000

500

200

50

20

P5

R+E

RF

C3dC4

C5

JL4

JL9

JL20

P11

P12

P13

P14

204B

PB

PCM

TCB

130

1300

13000

320 3200 32000

Sod

ium

(mg

/L)

Chloride (mg/L)

Groundwaters

Surface Waters

EVAPORATED ESTUARINEGROUNDWATERS

MIXED FRESH-SALINE

GROUNDWATERS

BRACKISH UNSATURATED ZONE GROUNDWATERS

SALINE INTRUDED GROUNDWATER

FRESH-SALINE INTERFACESURFACE WATERS


640 960 1600 6400 9600 16000

26000

9100

5200

2600

910

520

260

A

A

B

B


All of these transect groundwaters are fresh except for P5 which is generally brackish

due to tidal influence. However, during the flooding conditions of August 2007, the

EC of both P2 and P5 were significantly elevated. P5 had an EC of nearly 17,000 µS

cm-1

and P2 exceeded 1000 µS cm-1

. This elevated EC is most likely due to a storm

surge raising water levels in the estuary, so increasing the reach of the intrusion of

saline estuarine waters inland. However, the significant drop in EC between P2 and

P5 which are only 20 m apart, demonstrates typical small scale variations and the

existence of a confining layer between these two sites. In addition, the fact that P8,

only 40 m south of P2 did not have an elevated EC at this time shows further vertical

confinement within this transect. These transect groundwaters all have acidic pH

(5.1-5.6). Many are within sediments that contain few reactive minerals, being

mainly composed of quartz sand and consequently these groundwaters often have pH

values related to rainfall, typically around 5.6, and, in the more acidic cases, show

the input of organic acids.

Sites R+E at Tuan and RF at Boonooroo have comparatively high EC values at 1932

and 1744 µS cm-1

respectively. The magnitudes and time-series variation of these EC

values indicate that these aquifers are subject to saline intrusion. These two bores are

shallow (< 11 m) and at low elevation very close to estuarine creeks. As would be

expected based on the EC measurements, the ion concentrations (Figure 4) for these

two bores also indicate saline intrusion. Samples obtained during the drilling of the

R+E residential borehole indicate a paleochannel infilled with pebbles at around 10

m depth, and highly transmissive conditions for the interaction of fresh and estuarine

waters. It is possible that these features represent the coastal extent of the Tertiary

alluvial valley. Local residents in Boonooroo, Tuan and Poona report that many

bores in the area have become increasingly saline over the last 10 years as use of

groundwater has increased.

(ii) Tidal sands and muds

Unconfined groundwaters in monitoring wells P11-P14, located in the supratidal flats

adjacent to Poona Creek estuary, are all saline due to tidal intrusion with EC

exceeding 70,000 µS cm-1

at times. The salinities here often exceed those at PCM

(Poona Creek estuary mouth) due to evaporation from the watertable which is

generally less than 1 m below the ground surface (Figure 4). This evaporative

process leads to enrichment of Na and Cl and other ions such as sulphate relative to

the saline surface waters intruding the sediments. There is also variation over time

due to varying magnitudes in tidal flux and freshwater input. The shallow

groundwaters within the supratidal flats adjacent to Poona Creek estuary (P11-P14)

had circum-neutral values reflecting the mixing between acidic groundwaters,

rainfall and basic marine waters.

(iii) Coastal beach ridge sands

The beach ridge aquifer groundwaters (134B and PCP) have low EC of around 400

to 700 µS cm-1

. Both are fresh and have fairly consistent measurements over time

and appear to be confined. Residential borehole PCP was the only fresh groundwater

with a near-neutral pH (6.5) in the Poona catchment. Bore 204B has an EC of 1396

µS cm-1

indicating saline intrusion and is approximately 12 m deep. Borehole PCP is

19 m deep within beach ridge sands, while the depth of 134B is unknown but is

thought to be of the same order. This variation in salinity may be related to depth and


reflect that the beach ridge sands contain a deeper confined fresh aquifer and an

upper semi-confined aquifer prone to saline intrusion.

Surface Waters

All surface waters in the Tuan and Poona catchments are fresh except for the

estuarine sites, PCM, PB and TCB; surface water sites PB and TCB are both

brackish to saline depending on tidal conditions. Many surface waters had a pH value

close to that of rainfall except for estuarine waters, PB, TCB and PCM, where pH

values reflect the mixing of fresh and saline waters due to tidal flux. However, an

electrical conductivity (EC) of only 59 µS cm-1

was measured at PB in August of

2007 when flooding occurred. Similarly, a brackish EC of 7790 µS cm-1

and a much

lower pH of 5.5 was measured at PCM at this time due to fresh flood waters mixing

with marine waters. At other times EC measurements at this bore were saline and pH

values were basic as would be expected for marine waters.

Site TCA has significantly higher concentrations of Na and Cl (and therefore higher

TDI) than all other fresh surface waters. These higher concentrations may be a result

of limited drainage from this site, due to the ephemeral nature of the creeks and flat

gradients in this region. Upstream waters are being transported to this low-lying site

but are not being drained from it unless there is substantial rainfall. In addition,

evaporation from the water surface raises the concentration of inorganic solutes in

these surface waters.

Hydrochemical Facies

The Piper ternary diagram (Piper 1944) was used to support the assignment of

groundwaters to different hydrochemical facies and to better define processes. The

use of this plot shows partitioning between the different waters and revealed six

chemical groups (Figure 5).

Representative Stiff diagrams (Stiff Jr 1951) are shown for the hydrochemical facies

groups in Figure 6. These plots show quite a lot of similarity between groups and, as

a result, have been further subdivided based on water type, location and geology.

These graphical methods were found to be only useful to a point and then a priori

knowledge and observations were used to partition sites according to hydrochemical

character and processes.

Isotopes

Mean values for all samples analysed for δ18

O and δ2H are -4.27‰ and -20.94‰

respectively. These values are very close to the mean isotopic composition of global

precipitation of -4.0‰ and -22.0‰ and are typical of precipitation for which the

water vapour has been sourced from seawater; the influence of other processes that

alter the isotopic concentrations within these reservoirs appears to be limited. In this

region, a moderating maritime effect on temperature due to the coastal location

means variation is minimal compared to areas further inland. This condition is

reflected in the isotope data. Excluding PCM, a marine water that is significantly

enriched compared to the other surface waters, the δ18

O and δ2H data have standard

deviations of 0.42‰ VSMOW and 4.62‰ VSMOW and ranges of 1.43‰ (-5.03 to -

3.6‰) and 13.8‰ (-29.5 to -15.7‰) respectively. Groundwater samples have an

even smaller spread of 0.65‰ (-4.45 to -3.6‰) for δ18

O and 6.1‰ (-21.8 to -15.7‰)

for δ2H. Considering that measurement precision for these two isotopes is 0.15‰ for


δ18

O and 1‰ for δ2H, it is clear that the groundwater sample ratios, in particular, fall

within a relatively narrow range.

Fig. 5 Piper diagram showing generalised groupings based on lithology, salinity and level of

confinement. Circles are surface waters and triangles are groundwaters. See Table 4 for details of

samples and groups

LEGEND

Na-Mg-Cl GW Na-Mg-Cl SW Na-Cl GW Na-Cl-HCO3 GW Na-Cl-SO4 GW


Fig. 6 Representative Stiff diagrams for hydrochemical facies showing relative distributions of

major ions. The predominance of Na-Cl ions in this coastal setting is evident and there is a great deal

of similarity between hydrochemical facies. Due to this similarity, facies have been further subdivided

based on water type, location and geology. See Table 4 for site assignments

Table 4 Assignment of sites to hydrochemical facies based on Stiff diagrams and aquifer types and processes

Aquifer/ Surface Water Type Group

No. Samples

Evaporated Estuarine GWs I P11, P12, P13, P14

Estuarine SWs II PCM, TCB, PB

Saline-intruded GWs (Na-Cl) IIIA JL2, JL20, 204B, P2

Saline-intruded GWs (Na-Mg-Cl) IIIB R+E, RF, P5, B1, C5

Unsaturated zone brackish GWs IV C3, C4

Fresh Tertiary alluvium confined GWs VA JL1, JL7, JL10, JL13, JL25, JL4, JL9, C2d

Fresh coastal sediments semi/confined GWs VB P4, P6, P8, JL8, PCP, 134B

Fresh Tuan catchment SWs VIA TCA

Fresh Poona catchment SWs VIB WP11, WP12, LRB, WP31, PC10, PC9

Mg

Ca

Na

SO4

HCO3

Cl

I Evaporated Estuarine

Groundwaters

P13

II Estuarine

Surface Waters

PB

IIIA Na-Cl

Saline-intruded Groundwaters

JL20

IIIB Na-Mg-Cl


P5

IV Unsaturated Zone

Brackish Groundwaters

C3

VA Tertiary Alluvial Aquifer

Confined Fresh Groundwaters

JL7

VB

Quaternary Coastal Sediment Fresh

Semi- confined to Confined Groundwaters

P4

VI Fresh Surface Waters

LRB


To put this isotopic data into a regional perspective, a comparison is made with

groundwater and surface water data from other coastal areas in southeast Queensland

(Figure 7). These locations are the Pimpama coastal plain at the southern end of

Moreton Bay located approximately 250 km south of the study area (Harbison et al.

2009) and the Bell‘s Creek catchment located approximately 150 km south of the

study area (Ezzy 2005) in northern Moreton Bay (inset of Figure 6). Similar to this

study area, groundwaters within the Pimpama coastal plain were found to be of

relatively local origin. In addition, the Pimpama data also showed processes such as

mixing between freshwater and seawater, transpiration and evaporation (Harbison et

al. 2009). Data from the Bell‘s Creek catchment study showed clear differences

between waters within surficial alluvial and sand-rich coastal aquifers and bedrock

groundwaters due to delayed recharge. These data also showed where bedrock

discharge was contributing to groundwaters with alluvial aquifers (Ezzy 2005).

Although there is some limited evidence for evaporative and saline-freshwater

mixing processes reflected in the isotopic data for this project, isotopic ratios

excluding PCM all group at the bottom end of these datasets. The groundwaters

sampled for this study are all relatively shallow and generally within surficial

sediments with local recharge. Consequently isotopic ratios reflect those of rainfall

and group closely together. In addition, as along much of the coast of Queensland

winds are predominantly from the southeast, as rainfall passes over Fraser Island to

reach the mainland, rain-out effects deplete 18

O and 2H isotope concentrations.

Within this closely spaced group, however, there is an overall trend where sites

recharged from rainfall further inland are more depleted in 18

O and 2H than those that

are closer to the coast, i.e. there is a depletion in isotopes with distance from the

shoreline.

Of note, nearly all groundwaters (including semi-confined and confined aquifers)

appear to cluster along the Brisbane Meteoric Water Line (BMWL) (Figure 7). The

proximity of the groundwaters to the LMWL indicates that secondary processes such

as evaporation are not occurring prior to infiltration. It is most likely that the shallow

groundwaters (P2, P3, P6, P9, C4, C5) are recharged directly by meteoric waters and

have little to no interaction with other waters, except where there is limited tidal

influence. Shallow groundwaters from bores C4 and C5 in the northern catchment

are slightly depleted compared to the transect groundwaters, reflecting their location

further from the shoreline. Coastal residential boreholes, 204B, PCP, 134B and R+E

appear to have local rainfall recharge based on isotopic ratios, although bore RF is

somewhat more depleted perhaps indicating recharge from further inland.

There is overall grouping of fresh surface waters (LRB, PC9, PC10, WP12, WP31)

which are isotopically depleted in comparison with shallow groundwaters. This is

likely a result of these waters recharging at higher elevation in the catchment

(downwind). This rainfall would be isotopically lighter compared to coastal rainfall.

In addition, the fresh surface waters all plot below the LMWL. This may be the result

of kinetic evaporation effects which leads to a disproportionate enrichment in 2H and

18O, i.e. the waters are more depleted in

2H than

18O relative to the LMWL resulting

in displacement below the LMWL. Isotopic ratios for these surface waters confirm

that there is no interaction with marine waters. A sample of ponded water, WP11, has

isotopic ratios that are strongly elevated by comparison and similar to those for semi-

confined groundwater values, suggesting a significant groundwater input, but not

necessarily evaporation.


Fig. 7 δ2H vs δ18O plot for all waters. (A) shows the range and distribution of isotope data for the

study area with a regional context including data from Harbison and Cox (2002) and Ezzy (2005). The common saline water intrusion into coastal Quaternary unconsolidated aquifers is evident in these

earlier studies. (B) shows the Fraser Coast isotope data in relation to PCM and VSMOW. (C) detail of

the samples from this study. Surface waters distribution indicates evaporation effects

C5

C4P2

P4C2d

C3

P6

B1P8

RF134B R+E

PCP

204B

PC9

WP31

PC10WP12

LRB

TCB

PB

WP11

-30

-28

-26

-24

-22

-20

-18

-16

-14

-12

-5.2 -5.1 -5 -4.9 -4.8 -4.7 -4.6 -4.5 -4.4 -4.3 -4.2 -4.1 -4 -3.9 -3.8 -3.7 -3.6 -3.5 -3.4 -3.3

δ2H

(‰V

SMO

W)

δ18O (‰ VSMOW)

BMWLGroundwatersSurface Waters

BMWL: δ2H = 7.49δ18O + 11.74

Recharge to surface waters from inland rainfall and evaporation effects

General trend of depletion with distance of recharge downwind of predominant south-easterly winds

C5

C4

P2 P4C2d

C3 P6

B1

P8

RF

134BR+EPCP

204B

PC9WP31

PC10

WP12LRB

TCB

PB

WP11

PCM

-30

-25

-20

-15

-10

-5

0

5

10

-5.2 -4.7 -4.2 -3.7 -3.2 -2.7 -2.2 -1.7 -1.2 -0.7 -0.2 0.3 0.8 1.3

δ2H

(‰V

SMO

W)

δ18O (‰ VSMOW)

BMWL

Groundwaters

Surface Waters

BMWL: δ2H = 7.49δ18O + 11.74

VSMOW

A

B

C

-30

-25

-20

-15

-10

-5

0

5

10

15

20

-5 -4.5 -4 -3.5 -3 -2.5 -2 -1.5 -1 -0.5 0 0.5 1 1.5 2 2.5 3 3.5 4

δD

(‰V

SMO

W)

δ18O (‰ VSMOW)

BMWL

Fraser Coast GW

Fraser Coast SW

Bells Creek Catchment Weath. Bedrock GW

Bells Creek Catchment Alluvial GW

Bells Creek Catchment Bedrock GW

Pimpama SW

Pimpama Shallow Coastal GW

Pimpama Bedrock GW

BMWL: δ2H = 7.49δ18O + 11.74

Fraser Coast Surface and Groundwaters

A

B


Site PCM is located at the estuary mouth and has water chemistry typical of marine

waters and is highly enriched in 18

O and 2H compared with all other Fraser Coast

samples (see Table 3). The level of enrichment indicates that there is limited fresh

stream water mixed with these estuarine waters reflecting the hydrology (tidally

dominated estuary) and geomorphology (flat gradients and intermittent streams) of

the area. This slight enrichment δ18

O (0.96‰) compared with SMOW δ18

O of 0.5‰

(Clark et al. 1997) is due to evaporation at the ocean surface. Surface water sites PB

and PCM show a correlation between δ18

O and δ2H with salinity as would be

expected for estuarine samples (Zhang et al. 1990; Fry 2002). Isotopic ratio data for

mixed saline-fresh waters are typically placed along a line between freshwaters on

the LMWL and SMOW (being Standard Mean Ocean Water) or in this case PCM.

This is not the case at the surface water site TCB where there is interaction between

marine and freshwaters. Depths at TCB are often greater than three metres and water

was sampled from depths less than a metre so it is possible that if the water column

was stratified at the time of collection, with fresh upstream waters flowing on top of

the more dense saline tidal flow, only the overlying more isotopically depleted

freshwater has been collected. This would explain the proximity of TCB isotopic

ratios to those of the other fresh surface sites.

Nutrients

Waters collected for this study were also analysed for nitrate and phosphate. From all

116 samples analysed, only 11 showed nitrate concentrations above 1 mg/L (1.2 –

3.8 mg/L) and of those only one had a concentration greater than 5 mg/L. A

deficiency of nutrients such as nitrogen and phosphorus is typical of the soils and

sediments in these coastal lowlands on the southeast coast of Queensland, unless

there is significant artificial input due to agricultural practices or urbanisation, which

is reflected in their nutrient concentrations. The maximum nitrate concentration

detected was 8.3 mg/L, well below the Australian drinking water quality guideline of

50mg NO3ˉ/L (National Health and Medical Research Council (NHMRC) 2003), and

was for a residential bore sample. This addition of nitrate is most likely a result of

leaching of organic fertilizers or septic tank effluent (based on δ15

N data not included

here).

Dissolved phosphate was only detected in four water samples from one data

collection period and ranged from 0.42 to 5.20 mg/L. These sites appear randomly

distributed and phosphate concentrations were below MDL for all other data

collections. No fertilisation operations had been carried out in the adjacent

plantations for at least the preceding 11 months, so it is unlikely that these results

were due to forestry practices. However, as phosphorus has a strong tendency toward

forming ionic complexes and compounds of low solubility with many metals,

phosphate introduced to the system often precipitates out of solution and, therefore,

dissolved concentrations are generally very low.

The above only applies to data collected specifically for this study. Samples from the

Laycock study of the northern alluvial valley were not analysed for nitrate or

phosphate concentrations.

Summary

This study has focused on the setting of coastal catchments and the adjoining

floodplain. The study has shown that there is complex interaction between different


water bodies and with different chemical types, and that a wide range of processes

occur within this area. To clarify the occurrence of surface and groundwaters in this

regional setting and the controls over them, the results from the study have been

summarised into (a) hydrochemical and hydrological processes, (b) hydrochemical

facies, and (c) hydrological interaction.

(a) Hydrochemical and Hydrological Processes

The main processes identified are summarised below:

Coastal rainfall is a dominant influence on the water chemistry of the fresh

ground and surface waters. This influence is reflected in the fact that all

samples have Na and Cl as dominant ions irrespective of location or lithology.

Saline intrusion is a dominant factor in the chemical character of many of the

coastal groundwaters and some surface waters and, for these sites, elevates the

concentrations of all major ions. Ionic concentrations at C5 indicate that saline

intrusion may be occurring in sandy aquifers of low-lying areas some distance

inland through the sandy sediments of Poona National Park.

Another major contributor to salinity of unconfined groundwaters is the soluble

salts within the saprolite layers in the Tuan catchment area, inland from the

coastal zone.

Natural deficiencies of nutrients, such as nitrate and phosphate, in the soils and

sediments of this region results in low or negligible concentrations of these

nutrients in all waters.

The lithology of sediments and bedrock materials throughout the area is

generally siliceous which means that little dissolved calcium or bicarbonate is

contributed to the system through water/rock interaction. Any elevated

bicarbonate contributed to groundwaters is most likely sourced from shell

material within the coastal sediments or, in the case of surface waters, from a

catchment source.

Topography is a major influence on surface water chemistry. The lower

gradient in the northern Tuan catchment reduces the flushing capacity of creeks

and thereby increases the dissolved ion concentrations. In addition, the reach of

tidal intrusion along the creek is limited by the elevation at or near site PB just

east of Cooloola Road. This is reflected in the significant reduction in TDI

between PB and LRB which, although only 2.3 km apart (AMTD) drops from a

TDI of 19433 to 89 mg/L. The change in topographical height is 6m.

Drainage system morphology is also an important influence on the chemistry of

surface waters here. Streamflow is limited during drier months when a drop in

water levels results in the drainage system becoming a series of pools rather

than a continuous and connected drainage network. In addition, the substantial

reduction in TDI between PB and WP11 (and WP12) indicates that there is

significant constriction at some point along this tributary. Although WP11 is

closer to PCM than PB in relation to AMTD and the topographical height

difference is only 0.7 m, TDI drops from 19433 to 81 mg/L. This indicates

there is negligible interaction with marine waters at this site, a result of

downstream channel infilling.


Isotopic data indicate that the presence of the large Fraser Island sand mass

leads to significant rain-out effects depleting 18

O and 2H in rainfall before it

reaches the mainland and, as a consequence, the shallow groundwaters and

surface waters here are depleted in 18

O and 2H isotopes.

Isotopic ratios of the groundwaters and surface waters for this coastal region

broadly reflect the distance of rainfall recharge inland.

Isotopic ratios at the Poona Creek estuary mouth confirm that there is little

discharge from the catchment during dry conditions.

Most surface water isotopic ratios indicate there is little to no input by

groundwaters to the drainage system. The exception is WP11, located within

the floodplain, which appears to have a significant groundwater contribution.

Isotopic data indicates that most groundwaters are recharged locally, except

possibly for RF which may be recharged from further inland.

Major ion chemistry, pH and EC of estuarine surface water samples collected

during a flood event (FT1) indicate substantial discharge to the Strait from the

drainage system.

Groundwater data collected during the flood event also showed the effect of

storm surges on some coastal groundwaters where elevated TDI concentrations

reflected an increase in marine water input due to the forcing of marine water

inland.

(b) Hydrochemical Facies

Ground and surface waters within this coastal area can be broadly classified into a

number of facies or groups based on the chemical character, which reflects both

setting and hydrological processes. These groups are derived from the previous

graphical methods, in addition to lithology, spatial distribution and time-series

variation of physicochemical parameters and ionic concentrations (Table 4). Means

and ranges are shown in Table 5 for pH, EC, sulphate, bicarbonate and TDI; the

other major ions, Na, Cl, Mg and Ca are not included in Table 5 as they all strongly

correlate with TDI.

Group I. Evaporated Estuarine Groundwaters: These Na-Mg-Cl type

groundwaters have the highest concentrations of ions; they are unconfined with

shallow watertables within the muds and sands of the supratidal flats adjacent to

Poona estuary. Tidal flux is a dominant influence on their chemical character and Na,

Cl, Mg, SO42-

, Ca, and HCO3- concentrations are often elevated relative to intruding

estuarine surface waters due to evaporative processes. Circum-neutral pH values

reflect mixing between draining acidic groundwaters and marine surface waters.

Nitrate and phosphate concentrations are below detection limits.

Group II. Estuarine Surface Waters: These Na-Mg-Cl surface waters have

variable major ion concentrations, pH (weakly acidic to basic) and EC (brackish to

saline) values depending on distance from the coastline, tidal conditions and rainfall.

Nitrate and phosphate concentrations are below detection limits.

Group IIIA. Saline-intruded Groundwaters: These Na-Cl type waters are very

similar to Group IIIB except for having lower proportions of magnesium; host

lithologies are variable. The location and depth of bores is important: bore 204B lies


within beach ridge sands perhaps underlain by weathered Duckinwilla Formation

undifferentiated coastal plain sediments; bores JL2 and JL20 lie within the Tertiary

alluvium aquifer in the Tuan catchment, JL2 is adjacent to Big Tuan Creek and JL20

is close to Boonooroo Point not far from the strait. Generally, waters within this

Tertiary alluvial aquifer appear to have less magnesium content than the other coastal

aquifers in the Poona catchment. The higher magnesium elsewhere is most probably

sourced from the mafic volcanics of the Grahams Creek Formation. The magnitude

of ionic concentrations varies significantly among these waters and is related to a

combination of the intervening geology, tidal conditions, rainfall and proximity to

the coast.

Group IIIB. Semi-confined Saline-intruded Groundwaters: These Na-Mg-Cl type

groundwaters have variable major ion concentrations and pH and EC values relate to

magnitude of intrusion, a function of distance from the estuary/strait, geology, tidal

conditions and rainfall. Tidal processes are a major factor in determining the

frequency of saline intrusion at some sites. For example, P5 has a salinity flux related

to a semi-diurnal tidal cycle, whereas P2 is only intruded during highest astronomical

tides or storm surges and as such may only have a major rise in TDI due to saline

intrusion 2-3 times a year. Lithologies are variable: bore P2 is within the

undifferentiated coastal plain materials of the weathered Duckinwilla Formation and

P5 within the muds and sands of the supratidal flats adjacent to Poona Creek estuary.

B1 lies within duricrusted old land surface of the Grahams Creek Formation adjacent

to Buttha Creek and R+E within a pebble-filled paleochannel adjacent to the mouth

of Big Tuan Creek; this may represent the coastal extent of the Tertiary valley. These

sites are well distributed along the coastal strip, however, all sites except C5 are

located within 450 metres of an estuarine creek or the Great Sandy Strait. It is still

uncertain as to whether saline intrusion is occurring within the region of C5. Stiff

diagram groupings indicate that C5 is of a very similar character to the semi-confined

saline-intruded groundwaters of Group IIIB, however, water isotopes (δ18

O and δ2H)

do not indicate saline intrusion. Nitrates are practically non-existent within these

waters except at one site where the source is most likely organic fertilizer.

Group IV. Brackish Shallow Groundwaters: These Na-Cl waters occur within the

unsaturated zone saprolite layers of the weathering profile in the Tuan catchment and

are removed from any direct marine influence. These waters have relatively high Na

and Cl concentrations due to the soluble salts present in these clays. Spatially, EC

and ion concentrations within these shallow groundwaters is highly variable. Waters

are often strongly acidic due to the input of organic acids from surficial leaf litter.

Nitrates and phosphates are negligible.

Group VA. Fresh Tertiary Alluvium Confined Groundwaters: These fresh Na-Cl

and Na-Cl-SO4 type waters occur within the extensive aquifer of the Tertiary

alluvium in the Tuan catchment to the north. The exception is JL4 which, according

to Laycock (1969), is screened within the Maryborough Formation. For these waters,

pH is neutral to weakly basic and major ion concentration, EC, TDI and pH values

all indicate they are confined, and are much fresher and less acidic than the Group IV

waters within the overlying saprolite layers of weathered Elliot Formation. Of note,

C2d may be screened within the peripheries of the Tertiary alluvial valley.

Group VB. Fresh Unconsolidated Coastal Sediment Semi-confined to Confined

Groundwaters: These fresh Na-Cl-HCO3 and Na-Mg-Cl waters occur within the

undifferentiated coastal plain sediments within the transect near Poona Creek estuary


Table 5 Physico-chemical character of hydrochemical facies

GROUP pH EC (µS/cm) Sulphate (mg/L) Bicarbonate (mg/L) TDI (mg/L)

Mean Range Mean Range Mean Range Mean Range Mean Range

I 6.8 6.3 - 7.2 60825 44200 - 73300 3770 2309 - 5583 406 282 - 535 47365 32037 - 56622

II 7.0 6.5 - 7.8 35633 26300 - 48000 2029 45 - 3142 86 37 - 124 28715 19433 - 40576

IIIA 6.6 6.4 - 6.9 8599 1000 - 23400 206 42 - 468 91 5 - 220 5434 554 - 14933

IIIB 4.8 4.2 - 5.6 2748 515 - 9370 99 22 - 392 10 0 - 34 1725 293 - 6075

IV 2.9 2.7 - 3.1 3860 3680 - 4040 119 43 - 195 <0.1 <0.1 2333 2209 - 2457

VA 7.3 6.0 - 8.0 1052 630 - 2060 65 14 - 170 76 20 - 171 587 340 - 1024

VB 6.1 5.0 - 7.8 395 222 - 716 13 4 - 26 54 6 - 138 238 128 - 404

VIA 5.3 – 591 – 21 – 4 – 408 –

VIB 6.5 6.1 – 7.2 113 81 - 143 5 0 - 9 10 2 - 18 79 62 - 93


mouth (P4, P6, P8), the beach ridge sands adjacent to the Strait (PCP and 134B) and

the Tertiary alluvium and coastal sediments at JL8 near Little Tuan Creek. Most of

these waters have a higher proportion of bicarbonate than other groundwaters in this

region. The bicarbonate is likely to be from minor shell material within these coastal

sediments. The pH is weakly acidic to weakly basic (5.0-7.8). This range in values

reflects the varying contributions of bicarbonate, organic acids and rainfall to these

waters.

Group VIA. Fresh Tuan Catchment Surface Waters: This Na-Mg-Cl water

(TCA) is located in the Tuan catchment and has a much higher TDI than surface

waters located in the Poona Catchment. This is most likely due to a build-up of

dissolved ions in this shallow pool due to limited drainage as discussed previously.

This water is acidic (pH = 5.3) due to rainwater recharge and significant input of

organic acids.

Group VIB. Fresh Poona Catchment Surface Waters: These Na-Mg-Cl waters are

located within the drainage system of the Poona Creek catchment. There is little

variability in the TDI of these waters which are fresh and have water chemistries

reflecting that of coastal rainfall. Upper catchment sites have higher bicarbonate

concentrations than lower catchment sites (WP11, WP12). This bicarbonate could be

a result of interaction with sediments and/or rocks forming creeks beds and banks in

the upper catchment or be sourced from further inland. Isotopic data indicates rainfall

recharge is from further inland. In addition, the weathered bedrock in this area is

generally siliceous containing little to no carbonate material. This suggests an inland

bicarbonate source. Isotopic data also indicate that there is some degree of

evaporation occurring at these surface water sites.

These creeks are generally very shallow except for where water points (artificial

ponds for fire fighting – WP11, WP12, WP31) have been excavated and at times will

dry out completely. These ponds may act as sinks (similar to TCA) for dissolved

inorganic and organic materials stratifying the water column while any rainfall

maintains a freshwater layer on top. These were all composite samples and as such

do not show variation throughout the profile.

(c) Hydrological Interaction

One of the goals of the study was to establish the potential connectivity between

different water bodies. This aspect is summarised here.

There is only limited contribution of alluvial groundwaters to the drainage

system (i.e. baseflow) in the middle and upper Poona catchment. This is largely

due to the low volume of alluvial material within the upper drainage system

plus the bedrock geology typically consists of a deep weathering profile

containing discontinuous clay layers. These layers are very low permeability

and often cause waterlogging within the shallow overlying soil profile.

Overland flow and runoff through the soil profile during rainfall represent the

more dominant input to the poorly developed drainage system in the upper

catchment.

The alluvial sands and gravels of meanders in the low-gradient sections of

catchments provide potential pathways for solutes from the plantations to the

estuary. Some of the shallow groundwaters adjacent to the Poona Creek estuary

clearly show tidal influence and therefore a zone of mixing between marine and


inland waters. These settings, however, are hydrogeologically complex at a

local scale. Confining layers locally produce perching, and appear to limit

interaction between fresh groundwaters and marine waters within the transect.

There are several small coastal communities that use groundwater from limited

freshwater aquifers within unconsolidated Quaternary sediments. The water

chemistry in some residential bores indicates hydrological connectivity

between the aquifers and the marine environment. This connectivity may

permit nutrient and/or metal discharge into the adjacent Great Sandy Strait.

Interaction between unconfined and confined groundwaters in the Tuan

catchment appears to be negligible, with deeper confined waters maintaining

lower TDS and higher pH values relative to the brackish waters contained

within the weathered Elliot Formation. The Tertiary paleovalley is semi-

confined to confined and does not appear to receive recharge locally, however,

chemistry indicates it is connected to marine waters near the shoreline.

Conclusions

Assessment of this coastal region and its catchments identified three fresh

groundwater regimes, (a) zones within weathered bedrock, (b) Tertiary alluvial

paleovalley in the north, and (c) Quaternary unconsolidated materials of the tidal

coastal strip. The study has shown variable interaction between surface waters and

groundwaters, and also between different groundwaters including saline waters. This

mixing is especially the case in low gradient sections of the catchments and the

coastal plain. Hydrological processes contributing to the hydrochemistry of these

sites have been identified and hydrochemical facies described. Based on the sites

monitored, interaction between these hydrochemical facies is shown to be minimal

except in the coastal zone where saline-fresh water mixing occurs at a number of

locations. The potential impacts of this are two-fold. Where interaction between

marine and fresh groundwaters occurs there is the potential for dissolved species to

be transported to the Great Sandy Strait, especially during times of high rainfall; also,

there is the potential for groundwater supplies to be degraded by saline intrusion

which is already a concern in the coastal villages of this area.

Water analysis determined only one example of anthropogenic nutrient input to the

natural waters in the area which was most likely sourced from organic fertilizers in a

residential area. Other than potential issues related to planting or harvesting,

plantation forestry practices appeared to have had comparatively low impact on the

natural waters in this region during the time of the study.

This study confirms dynamic settings with complex hydrological systems at various

scales and with multiple processes operating and has defined the types of ground and

surface waters that exist, their host materials and their potential connectivity. The

information from this study not only provides a necessary foundation for future

hydrochemical monitoring in this study area but also for much of the coastline in

southeast Queensland which has similar geomorphological, hydrological and landuse

characteristics. A sound understanding of regional ground and surface water

hydrochemistry, hydrochemical processes and possible transport pathways for

solutes to marine waters is essential for the future management of coastal

environments, particularly in ecologically sensitive areas subject to increasing

pressure from urbanisation.


Acknowledgements

This work was supported by grants from Forestry Plantations Queensland and the

Australian Research Council Grant #LP0669786. The authors would also like to

thank Dr Ken Bubb, Lin Chaofeng, Pavel Dvoracek, Bill Kwiecien, Martin Labadz,

Stefan Löhr, Shane Russell and Dr James Smith for assistance with laboratory and

field work and for general support during the course of this project.


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5. they agree to the use of the publication in the student’s thesis and its publication on the Australasian Digital Thesis database consistent with any limitations set by publisher requirements.


Paper 2: Cluster analysis to support graphical methods in the characterisation of ground and surface waters in a subtropical coastal zone, Fraser coast, Queensland _________________________________________________________________________





Assisted with project design and field work and contributed to the manuscript

Principal Supervisor Confirmation I have sighted email or other correspondence from all Co-authors confirming their certifying authorship. _______________________ ____________________ ______________________ Name Signature Date

5. PAPER 2

CLUSTER ANALYSIS TO SUPPORT GRAPHICAL METHODS

IN THE CHARACTERISATION OF GROUND AND SURFACE

WATERS IN A SUBTROPICAL COASTAL ZONE, FRASER

COAST, QUEENSLAND

Genevieve Larsen, Malcolm E. Cox




Prepared for submission to Hydrogeology Journal

Abstract

Hierarchical cluster analysis (HCA) is used to partition water samples into

hydrochemical facies in an area of limited hydrochemical, mineralogical, and

physiographic variability. Results from the HCA and from conventional graphical

methods, Piper and Stiff diagrams, are compared. Although samples were overall

partitioned to the same facies using both methods, there are some important

differences. HCA results indicate (a) ground-surface water interaction and

unsaturated zone-semi-confined groundwater interaction not indicated using

graphical methods, (b) different aquifer types at four sites, (c) an anomalous or

unique site, and that (d) further investigation is required to confirm the sources of

salinities at a number of sites. Temporal data were also analysed. Results indicate (a)

confinement of aquifers at two sites, (b) groundwater baseflow at two surface water

sites, and that (c) seasonal variation in proportions of ions is minimal for nearly all

waters except when extreme climatic conditions such as heavy rainfall or drought

exist.

The HCA method was found to be very useful in supporting, augmenting and

rejecting interpretation based on graphical methods and is particularly helpful where

there is limited hydrochemical variability among samples. However, the results from

HCA do not provide direct information concerning dominant hydrochemical

processes and so should be used in combination with graphical methods in the

characterisation of natural waters. In addition, it was found in a couple of cases that

group assignments using HCA were inappropriate. Knowledge of geology, climate

and other environmental influences should always used in conjunction with both

graphical and statistical methods to investigate hydrochemical processes and

characterise natural waters.

Keywords: hierarchical cluster analysis, surface water/groundwater interaction,

hydrochemical processes, major ion chemistry, subtropical coastal catchment,

seasonal variation

125

INTRODUCTION

Coastal catchment areas can include estuaries, surface drainage systems such as

rivers and tributary creeks as well as semi-confined, confined and unconfined

aquifers all of which are hydrologically linked to some degree. Where there are high

levels of both dissolved and suspended constituents such as nutrients, metals and/or

sediments in a coastal drainage system, invariably levels of these constituents will

also be elevated in the estuary and subsequently adjacent marine waters. A major

factor in the degradation of catchment water quality is landuse. Deforestation of

adjacent land for agriculture and the paving of nearby areas for roads and building

developments often leads to increased runoff directly into rivers, creeks and drains

(Dyer 1997; Pointon et al. 2003). Drainage systems often interact with subsurface

waters and consequently the contamination of one can lead to the contamination of

the other. Over-exploitation of coastal groundwater for residential or agricultural use

can result in saline intrusion and septic sewerage systems can cause contamination of

aquifers. A challenge is to understand the hydrological processes and the

connectivity between different waters in these settings. The chemical characterisation

of natural ground and surface waters is an important first step in determining possible

transport pathways for contaminants within catchments. Samples with similar

chemical characteristics can have similar hydrologic histories, recharge areas,

infiltration pathways, and flow paths in terms of climate, mineralogy and residence

times (Güler et al. 2002).

Overview of hydrochemical characterisation methods

Traditional methods for the hydrochemical characterisation of waters in order to

investigate interaction between various water bodies include both graphical and

statistical methods. Graphical methods such as Piper (1944) and Stiff (1951)

diagrams have been used extensively to group waters visually and in some cases

indicate mixing between water bodies [See Sukhija et al. (1996), Gimenez and

Morell (1997), Logan et al. (1999), Sanchez Martos et al. (1999), Cruz and Silva

(2000), Allen and Suchy (2001), Kim et al. (2003) and Hodgkinson et al. (2007) for

examples]. Hierarchical cluster analysis (HCA) is a more recent tool in the field of

hydrochemistry. It is semi-objective and efficient tool that can be used to group

126 Paper 2. HCA to support graphical methods

water samples and assist in the interpretation of hydrochemical processes. HCA is

advantageous in hydrological applications for two reasons: (1) the inclusion of more

variables such as pH makes it easier to differentiate between samples, and (2) the

equal weighting of variables ensures that all ions, regardless of magnitude, contribute

to the partitioning of samples. This approach also has the advantage of being more

objective than graphical methods where the assignment of samples to hydrochemical

facies can be influenced by researchers‘ assumptions and is often a highly subjective

process. As suggested by Kumar et al. (2009), it is also useful for investigating the

strength and extent of groundwater-surface water interaction and general

hydrochemical processes prior to using more expensive tools such as modelling and

isotope analysis.

However, Cormack (1971) stated many computer packages that aim to assist in the

classification of data can be ineffective and often waste valuable time. Users of such

methods should be careful not to accept results blindly but integrate/support/augment

them with other forms of information and interpretation tools. In aqueous

geochemistry, a good knowledge of geology, geomorphology and other factors such

as vegetation is essential for the interpretation of hydrochemical character and

processes. Graphical methods are valuable when determining dominant

hydrochemical processes within catchments and can also provide information in

relation to hydrochemical evolution along pathways. Dreher (2003) also discussed

the dangers involved when transforming data in order to achieve normal distribution

and equal weighting for HCA. This manipulation of data may lead to the loss of

information and misrepresentative datasets.

Generally, previous studies involving the use of graphical and statistical methods,

and specifically HCA, to characterise natural waters have been where there are clear

differences between hydrochemical facies, e.g. (a) a variation in landuse, (b)

anthropogenic source input to waters (Frohlich et al. 2008; Koh et al. 2009; Kumar et

al. 2009; Zhang et al. 2009; Yidana 2010) (c) a much larger scale study area

(Daughney et al. 2005; Frohlich et al. 2008), (d) obvious lithological differences

between aquifers (McNeil et al. 2005; Koh et al. 2009; Yidana 2010), and/or (e) a

focus on aquifers of different depths (McNeil et al. 2005; Irawan et al. 2009). These

factors all contribute to distinct variations in the hydrochemistries of ground and

Paper 2. HCA to support graphical methods 127

surface waters. These noticeable hydrochemical differences also make it easier to

determine when mixing between source waters or end-members occurs.

An earlier paper, Larsen and Cox (2011) [see Paper 1 in this thesis], used graphical

methods. Piper and Stiff diagrams were used to investigate hydrological and

hydrochemical processes to determine the character of the groundwaters and surface

waters, and connectivity between various water bodies. The current study expands on

that paper where HCA is used to support the interpretation based on graphical

analyses.

The use of graphical and multivariate statistical methods for the classification of

water chemistry data were evaluated by Güler et al. (2002). These authors examined

the efficacy of these methods rather than provide an in-depth discussion of

hydrochemical processes and characterisation using water samples form a wide

variety of climatic conditions, hydrologic regimes and geological environments.

They found that graphical techniques proved to have limitations compared with

cluster analysis for large datasets. However, they emphasized that statistical methods

do not provide information on the chemistry of the groupings and as such should be

used in combination with graphical methods. Thyne et al. (2004) describe a

sequential analysis method for hydrochemical data for watershed characterisation

which combines standard statistical (HCA and principal components analysis),

spatial techniques, and inverse geochemical modelling. Using these methods in a

sequential fashion, the authors were able to identify the major processes controlling

hydrochemical variation, determine the location and chemical signature of

anthropogenic impact, and provide information about aquifer properties using this

sequential analysis.

Many other researchers have also combined various interpretative approaches to

describe hydrological processes and hydrochemical facies in the natural environment

[See, for example, Irawan et al. (2009), Koh et al. (2009), Menció and Mas-Pla

(2008), Meng and Maynard (2001) and O‘Shea and Jankowski (2006)]. Meng and

Maynard (2001) had a similar problem to the one addressed in this current paper in

relation limited hydrochemical variation in the study area as did O‘Shea and

Jankowski (2006). These two authors had the added disadvantage of dealing with

samples that not only had similar proportions of major ions but also similar

magnitudes.


There is always a level of uncertainty involved with scientific studies of any type as

there is in establishing the character of waters and assigning those waters to groups

with other waters of similar type. Waters in this study area also have very limited

variability in major ionic composition making the allocation of samples to

hydrochemical facies using traditional graphical methods a difficult task. The aim of

this paper is to augment and support and/or reject the interpretation based on

graphical methods put forward in a previous paper (Larsen et al. 2011) [see Paper 1

in this thesis]. The graphical methods used previously were found to have limitations

and prior knowledge and assumptions based on observations were used to partition

sites according to hydrochemical character and processes. HCA is used here as a

semi-objective tool to reveal whether or not the assumptions leading to these group

assignments were valid.

BACKGROUND

The current study is part of an integrated project developed in response to concerns

regarding the effects of landuse practices on the natural environment in this region.

This component of the project focuses on hydrological and hydrochemical processes

in surface and subsurface water bodies in order to determine hydrological links and

potential transport mechanisms for dissolved metals and nutrients from coastal

catchments to the marine environment.

These catchments host plantation forests and are adjacent to the Ramsar-listed Great

Sandy Strait, a passage landscape between Fraser Island and the mainland (see

Figure 1). This region is formed of a low-lying coastal plain with tidal creeks which

drain elevated catchments within the bedrock ranges. Groundwater occurs within

complex systems of mostly semi-confined and confined aquifers with variable

connectivity to the shallow drainage system. Shallow aquifers are generally semi-

confined by discontinuous clay layers that have very low hydraulic conductivities.

Recharge rates vary with location and appear to be dependent on the proximity of

shallow aquifer sites to discontinuities in these clay layers (Bubb et al. 2002).

Although natural waters in the area can have highly variable physicochemical

properties, based on their major dissolved ions they tend to be of Na-Cl or Na-Mg-Cl

type. Waters within these coastal regions are typically Na and Cl dominated due to

both the presence of cyclic salts in the local rainfall, direct mixing of brackish-saline


waters (McNeil et al. 2005) and soluble salts within the sediment profile (Wang et al.

2008). Further, mineralogical, and physiographic variability is relatively limited in

the study area. These features limit the ability to group waters into hydrochemical

facies, an important step in determining connectivity between different waters, and

possible mechanisms/pathways for the transport of nutrients and/or metal loads from

the coastal zone to marine areas.

After applying most of the conventional graphical methods, such as scatterplots,

Piper and Stiff diagrams (Larsen et al. 2011), we compare the hierarchical cluster

analysis (HCA) approach to augment the interpretation. The main aim of this current

paper is to use HCA to confirm or reject interpretation previously obtained using

graphical methods.

CHARACTER OF STUDY AREA

The study area is described in relation to landuse and vegetation, geology, climate

and surface water and groundwater occurrence in Larsen and Cox (2011). Here,

general features of the study area are described briefly.

The study area covers an area of approximately 470 km2 and includes the catchments

of Kalah, Maaroom, Big Tuan, Little Tuan, Poona and Buttha Creeks (Figure 2).

Maryborough, the closest town to the study area, is located approximately 27 km

northwest of Poona village in the central coastal zone or 5km west of the northwest

corner of the study area.

The climate in the study area is subtropical, typical of SE Queensland, with more


to February) and comparatively dry winters (June to August).

This coastal region is of high environmental significance with a number of

threatened species (flora and fauna), such as dugong, dolphins, migratory shorebirds,

seasonal populations of humpback whales and rare shrubs, exist in the marine areas

and associated tidal wetlands in the adjacent Great Sandy Strait (EPA 2005).


Figure 1 Map of Australia and a section of the southeast coast of Queensland. The

dashed box shows the location of the study area on the Fraser Coast. Dots

indicate location of meteorological data collected for this study.

Landuse and vegetation

Landuse in the area studied consists mainly of mature Pinus plantations ranging from

16 to 30 years of age with native vegetation buffer zones adjacent to natural

waterways (see Figure 2). Poona, Little Tuan and Boonooroo are small villages with

populations of approximately 200. These communities do not have town water

supply and residential water is obtained from rainwater tanks and/or groundwater

bores. There are also frequent visitors to these coastal villages for vacations, fishing

and recreation.

Q

LD

Tuan Forestry

Office

Double Island Point


Figure 2 Fraser Coast study area showing catchments and drainage systems. Main

types of landuse are: plantation forestry (light grey) with forest

compartments; native vegetation as buffer zones and bushland (dotted);

residential settlements (dark grey); and national park (striped). Elevation

decreases towards the east and northeast. The dashed and dotted line

going from the north-west corner to the southern boundary of the figure

is Cooloola Road, the road taken to reach the study area whether from

Tin Can Bay to the south or from Maryborough to the north-west. The

red dashed line shows the location of the cross-section shown in Figure 3.

Source: National Resources, Mines and Energy (2004)

Geology

The bedrock geology is important and can influence the chemical character of the

groundwater. The geology in the study area mainly comprises the following three


formations: (1) late Triassic to early Jurassic quartz-rich sandstone, siltstone, shale,

coal and a ferruginous oolite marker, known as Duckinwilla Group, (2) late Jurassic

to Early Cretaceous intermediate to acid volcanics and volcaniclastic rocks known as

the Grahams Creek Formation, and (3) Eocene to Oligocene quartzose to sublabile

sandstone, conglomerate, siltstone, mudstone and shale of the Elliot Formation

(Natural Resources Mines and Energy 2004). These formations have experienced

deep weathering since the Miocene period (24 Ma) and most of the land surface in

the study area is covered by a thick lateritic profile.

Overlying the Tertiary units in the coastal areas are the coastal deposits, a sequence

of unconsolidated poorly sorted generally fine-grained sediments deposited under

marine or estuarine conditions and exposed as a result of relative land emergence in

recent times. Quaternary alluvial deposits, consisting of sands, silts and minor gravel

eroded from the weathered bedrock are also present adjacent to the drainage system

within the Poona catchment but are generally restricted to the coastal plain and

absent in the elevated catchment. Quaternary alluvium occurs more extensively in

the northern Tuan catchment where it is mostly derived from the Elliot Formation

and is generally confined to the drainage systems. At a couple of sites, these

materials appear to form a paleovalley and may have some connection with a

Tertiary alluvial formation in the Tuan catchment.

Tertiary alluvium occurs at a depth of 4-15m in the northern part of the study area

(Tuan catchment) and comprises fine to coarse grained sand and gravel, which in all

cases is overlain by impermeable clays (weathered Elliot Formation). This formation

is the focus of studies by Laycock (1969; 1975) and is discussed below.

The soil profiles in the study area are highly variable. Higher topographic areas often

have very shallow topsoil such as humus podzolics, red earths and yellow earths

overlying deep weathering profiles while lower topography areas often contain

sediments that have been eroded from elevated regions. This is typical of coastal

lowlands along the seaboard of eastern Australia, and soils are nutrient poor and

generally deficient in nitrogen and phosphorous (Coaldrake 1961). Löhr et al. (2010)

investigated the occurrence of iron in soils within the Poona catchment. They found

extensive areas of high Fe soils containing a large proportion of ferricrete and Fe-

concretions, most of which was in the form of sparely soluble Fe-oxides. Iron is

widespread throughout this study area although readily extractable Fe concentrations


are low overall. However, anoxic conditions and the input of organic matter in

waterlogged soils and stream sediments enable the transformation of Fe-oxides into

more readily available forms (Löhr et al. 2010).

Hydrological settings

The drainage systems within these catchments are an integrated system of tributaries

attached to a trunk stream, which transport surface water to the Great Sandy Strait in

direct and indirect ways. These surface water bodies are very shallow and ephemeral

in nature, and have tidally dominated estuaries with maximum tidal ranges

approaching 2 m at the mouth of Poona Creek. Inflow from the creeks to the estuary

is considered to be insignificant except during and after high rainfall events when

runoff from the catchment can be substantial and can affect water quality in the Great

Sandy Strait (Shaffelke et al. 2002; Campbell et al. 2004; BMRG 2005). For most of

the year, however, many of the tributaries consist of still pools alternating with small

flowing creeks and are ephemeral in their upper reaches.

This study largely considers shallow groundwaters (<25m depth) from

unconsolidated surficial formations such as alluvium or coastal deposits and aquifers

within the weathered profile of the bedrock. More than 70% of the study area has

topographic gradients less than 1.5% while gradients in the remaining area rarely

exceed 10%. The low-lying coastal plain contains a complex system of variable size

unconfined, semi-confined and some confined aquifers. In the southern coastal area,

the estuary contains alluvial materials and meandering channels infilled as a result of

channel migration. Figure 3 shows a cross-section from the southwest of the

catchment to the Great Sandy Strait.

Earlier work by Larsen and Cox (2011) [see Paper 1 in this thesis] showed that

groundwater occurs in three hydrogeological settings in this region, (a) zones within

weathered bedrock, (b) Tertiary alluvial valley in the north, and (c) Quaternary

unconsolidated materials of the tidal coastal strip. This coastal strip can be further

subdivided into (i) coastal plain alluvial deposits, (ii) tidal sands and muds, and (iii)

coastal beach ridge sands. Surface waters here can be separated by physicochemical

properties into two readily differentiable groups, (a) freshwaters within the elevated

catchments and streams within the coastal plains disconnected from the main tidal


channel, and (b) estuarine water within the main tidal drainage channels of the

coastal plains.

Figure 3 Cross-section of Poona Creek catchment going from southwest to


and surface water data collection sites. See Figure 2 for the location of

this cross section.

HYDROCHEMICAL CHARACTER

In this subtropical coastal environment, waters are predominantly Na-Cl or Na-Mg-

Cl type. Refer to Table 1 for site descriptions, pH, major ion concentrations, depth of

boreholes and water types. These ions account for a significant proportion of the

dissolved species of nearly all shallow ground and surface waters here. These salts

are contributed by rainfall, oceanic spray, saline intrusion within shallow coastal

aquifers and drainage systems, as well as soluble salts within clay layers present

throughout the area. Alkalinity is variable and pH values typically reflect rainfall,

input of marine waters to the system and levels of organic acids within soils and/or

organic layers at depth local to the site. Lithologies in the area are predominantly

siliceous with very little, if any, calcareous material available for dissolution and

consequently dissolved calcium and bicarbonate concentrations are generally low.

This is reflected in pH values throughout the area which are predominantly slightly

acidic.

For surface waters, topography is an important influence on hydrochemistry. Lower

gradients in the northern Tuan catchment reduce the flushing capacity of creeks and

increase total dissolved ions (TDI) also by allowing greater tidal intrusion than in the

Poona catchment. The morphology of the streams and estuaries in the region is also

an important influence. When stream flow is limited during drier months, the lower

-15.00

-10.00

-5.00

0.00

5.00

10.00

15.00

20.00

25.00

0 2000 4000 6000 8000 10000 12000

Distance (m)

Limit of Tidal

Influence

COASTAL PLAIN

GREAT SANDY STRAIT

ELEVATEDCATCHMENT

Poona CreekEstuary Mouth

Incised bedrock

Alluvial deposit

aquifers

Beach

ridge

aquifer


water levels can lead to the isolation of pools within the drainage system,

significantly altering hydrological processes contributing to the hydrochemistry at

some sites. Except for the first round of data collection, during which a flood event

occurred, physicochemical and ionic concentrations showed little variation except

where tidal flux was a dominant influence on water chemistry. Tidal influence results

in semi-diurnal variation in the proportions of fresh catchment-derived waters and

saline marine waters at some sites and, consequently, major ion concentrations vary

depending on tidal condition.

Isotopic data indicate local recharge from rainfall at most surface sites, and that there

is little to no input by groundwaters to the Poona catchment drainage system, except

possibly at a surface water site in the coastal plain (WP11) (Larsen et al. 2011). This

finding confirms that there is little if any discharge to the strait under steady-state

conditions, and implies quick residence times and, consequently, limited water-rock

interaction as reflected in the major ion concentrations.

In Larsen and Cox (2011), a Piper ternary diagram and Stiff diagrams were used

assign waters to hydrochemical facies. Representative stiff diagrams are shown in

Figure 4 and illustrate the similarity in proportions of the major ions among groups.

These graphical methods were found to have limitations and prior knowledge and

observations were used to partition sites according to hydrochemical character and

processes. Table 2 lists the hydrochemical facies grouping determined using these

graphical methods. An important question to answer is whether the assumptions

leading to these group assignments are valid.

On a much broader scale, a study by McNeil et al. (2005) used a two-stage K-means

clustering method to characterise 34,000 surface water samples distributed

throughout Queensland. This study found that regional chemical trends were

consistent with geology and climate, where the overall pattern of water types was

dominated by lithological and atmospheric salts, either recent, or accumulated and

recycled. The available data for the fresh surface waters in the vicinity of the coastal

catchments investigated here indicated low salinity, sodium chloride waters derived

from oceanic spray. The upper catchment freshwaters from this study area also fall

within this group.


Table 1 Site descriptions, pH, major ion concentrations, depth of boreholes and water types for all samples

Table 1 Site descriptions, pH, major ion concentrations, depth of boreholes and water types

for all samples

SITE ID Sample

Type Site

a Description pH

Na+

mg/L Mg

2+

mg/L Ca

2+

mg/L Cl

-

mg/L SO4

2-

mg/L HCO3

-

mg/L Depth (GW)

in m Water Type*

B1 GW Native bushland 4.2 77 20 0.4 165 22 <0.1 5.0-8.0 Na-Mg-Cl

P2 GW Transect 5.1 138 19 2.5 291 52 4 6.0-9.0 Na-Cl

P4 GW Transect 5.2 40 3 0.7 60 13 32 9.0-12.0 Na-Cl-HCO3

P5 GW Transect 5.6 298 129 16.8 652 53 13 3.0-6.0 Na-Mg-Cl



P11 GW Supratidal flats 7.0

16534 4020 412.8 31218 3330 535 1.2 Na-Mg-Cl

P12 GW Supratidal flats 7.2 9592 2311 294.8 16847 2309 336 0.9 Na-Mg-Cl

P13 GW Supratidal flats 6.3 14398 3760 399.6 28096 3857 473 1 Na-Mg-Cl

P14 GW Supratidal flats 6.8 12008 2998 393.2 27608 5583 282 1 Na-Mg-Cl

134B GW Residential bore 5.0 50 18 5.4 111 23 6 Unknown Na-Mg-Cl

204B GW Residential bore 6.4 153 23 28.3 426 108 49 12.0 Na-Cl

PCP GW Caravan Park bore 7.5 117 12 12.7 127 26 137 19.0 Na-Cl-HCO3

R+E GW Residential bore 4.4 316 90 16.7 695 47 34 11.0 Na-Mg-Cl

RF GW Caravan Park bore 5.3 232 156 12.5 660 31 7 6.0 Na-Mg-Cl

C2d GW Mature pine forest 6.0 147 14 2.1 214 46 138 11.5-13.0 Na-Cl-HCO3

C3d GW Native grassland 3.1 841 64 3.3 1492 43 <0.1 5.5-7.0 Na-Cl

C4 GW Mature pine forest 2.7 707 81 0.5 1221 195 <0.1 2.3-3.8 Na-Cl

C5 GW Native vegetation 4.2 1752 446 5.4 3468 392 <0.1 2.5-4.0 Na-Mg-Cl

JL1 GW Pine plantation 7.0 233 13 6.0 298 64 117 12.2 Na-Cl

JL2 GW Pine plantation 6.4 181 14 11.0 304 42 5 10.7 Na-Cl

SITE ID Sample

Type Site Description pH

Na+

mg/L Mg

2+

mg/L Ca

2+

mg/L Cl

-

mg/L SO4

2-

mg/L HCO3

-

mg/L Depth (GW)

in m Water Type

JL4 GW Pine plantation 8.0 291 17 8.0 365 170 37 20.7 Na-Cl-SO4

JL7 GW Poona National Park 7.9 156 9 5.0 230 25 49 5.4 Na-Cl

JL8 GW Native vegetation 7.8 37 4 3.0 55 4 37 5.2 Na-Cl-HCO3


JL10 GW Poona National Park 7.8 124 7 3.0 196 14 20 7.9 Na-Mg-Cl

JL13 GW Native vegetation 7.0 169 8 4.0 220 18 49 6.1 Na-Cl

JL20 GW Residential 6.9 4966 450 160.0 8780 468 220 11.6 Na-Cl


LRB SW Low flow, very small creek 6.1 24 6 1.7 35 4 11 Na-Mg-Cl

PB SW Moderate tidal flow 6.7 5257 1298 185.5 10805 1590

37 Na-Mg-Cl

PC9 SW Moderate flow, small creek 6.4 11.74 2.97 0.77 22.59 9.33 9.76 Na-Mg-Cl

PC10 SW Moderate flow, small creek 7.2 16 4 0.9 31 8 10 Na-Mg-Cl


Table 1 continued

* Water-types are determined by computing the percentages of ion concentrations. Aquachem (Schlumberger Water Services 2011) was used for this purpose.

Any ions have a percentage of total dissolved ions (TDI) greater than 10% are included in the water type with the highest percentage cation, followed by the

next highest percentage cation if there is one, then the anions etc.

SITE ID Sample

Type Site Description pH

Na+

mg/L Mg

2+

mg/L Ca

2+

mg/L Cl

-

mg/L SO4

2-

mg/L HCO3

-

mg/L Depth (GW)

in m Water Type


JL7 GW Poona National Park 7.9 156 9 5.0 230 25 49 5.4 Na-Cl

JL8 GW Native vegetation 7.8 37 4 3.0 55 4 37 5.2 Na-Cl-HCO3


JL10 GW Poona National Park 7.8 124 7 3.0 196 14 20 7.9 Na-Mg-Cl

JL13 GW Native vegetation 7.0 169 8 4.0 220 18 49 6.1 Na-Cl



LRB SW Low flow, very small creek 6.1 24 6 1.7 35 4 11 Na-Mg-Cl

PB SW Moderate tidal flow 6.7 5257 1298 185.5 10805 1590

37 Na-Mg-Cl

PC9 SW Moderate flow, small creek 6.4 11.74 2.97 0.77 22.59 9.33 9.76 Na-Mg-Cl

PC10 SW Moderate flow, small creek 7.2 16 4 0.9 31 8 10 Na-Mg-Cl

PCM SW Strong tidal flow 7.8 10898 2682 381.4 22833 3149 124 Na-Mg-Cl

TCA SW Still pools/small flowing brooks 5.3 103 28 2.0 215 21 4 Na-Mg-Cl

TCB SW Moderate tidal flow 6.5 6112 1569 216.7 14977 2895 96 Na-Mg-Cl

WP11 SW Excavated still pool, low flow 5.2 22 5 0.7 40 <0.05 2 Na-Mg-Cl

WP12 SW Excavated still pool, low flow 6.1 21 6 1.5 38 3.2 7 Na-Mg-Cl

WP31 SW Excavated still pool, low flow 6.9 21 5 1.9 39 4.4 18 Na-Mg-Cl


Figure 4 Representative stiff diagrams for hydrochemical facies showing relative

distributions of major ions from Larsen and Cox (2011). The

predominance of Na-Cl ions in this coastal setting is evident and there is

a great deal of similarity between hydrochemical facies. The shaded sites

are those where grouping is different using cluster analysis.

Table 2 Assignment of sites to hydrochemical facies based on Stiff diagrams and

aquifer types and processes

Aquifer/ Surface Water Type Group No.

Samples

Evaporated estuarine groundwaters I P11, P12, P13, P14

Estuarine surface waters II PCM, TCB, PB

Saline-intruded groundwaters (Na-Cl) IIIA JL2, JL20, 204B, P2

Saline-intruded groundwaters (Na-Mg-Cl) IIIB R+E, RF, P5, B1, C5

Unsaturated zone brackish groundwaters IV C3, C4

Fresh Tertiary alluvium confined groundwaters

V JL1, JL7, JL10, JL13, JL25, JL4, JL9, C2d

Fresh coastal sediments semi/confined groundwaters

VI P4, P6, P8, JL8, PCP, 134B

Fresh Tuan catchment surface waters VIIA TCA

Fresh Poona catchment surface waters VIIB WP11, WP12, LRB, WP31, PC10, PC9

Note: Sites referred to in the discussion are highlighted in bold.

Mg

Ca

Na

SO4

HCO3

Cl


Groundwaters

P13

II Estuarine

Surface Waters

PB

IIIA Na-Cl


JL20

IIIB Na-Mg-Cl


P5

IV Unsaturated Zone


C3



JL7

VB



P4


LRB

Mg

Ca

Na

SO4

HCO3

Cl


Groundwaters

P13

II Estuarine

Surface Waters

PB

IIIA Na-Cl


JL20

IIIB Na-Mg-Cl


P5

IV Unsaturated Zone


C3



JL7

VB



P4


LRB


METHODS

Data Collection

Physicochemical parameters (EC, pH, Eh, DO and T) were measured at all sites and

samples were collected for cation and anion analysis using standard preservation and

collection techniques according to Eaton and Andrew (2005). Detailed information

relating to analytical techniques and sample collection is given in Larsen and Cox

(2011).

Hierarchical Cluster Analysis (HCA)

HCA is a multivariate classification procedure that detects natural groupings in data

and is used in a wide range of disciplines. The aim of the analysis is to arrange the

samples so that those within a cluster possess an intrinsic similarity that is relatively

distinct from that of the other clusters (McNeil 2002). Broadly speaking, we can say

that a cluster analysis has been successful if it brings to light previously unrecognised

groupings in a set of data or helps to formalize its hierarchical structure (Chatfield et

al. 1980). The output of the analysis is a number of groups of samples that have

similar characteristics that may be significant in a geologic/hydrological context, as

well as from a statistical point of view (Güler et al. 2002; Thyne et al. 2004). HCA

also has the advantage of being a more objective method than graphical methods

where the assignment of samples to hydrochemical facies can be influenced by


Some researchers stress the use of normalisation of data before performing cluster

analysis. However, methods in the literature vary. While Güler et al. (2002), Thyne

et al. (2004), Güler and Thyne (2006), O‘Shea and Jankowski (2006) and Zhang et

al. (2009) state that it is a requirement for HCA, Meng and Maynard (2001), McNeil

(2002) and McNeil et al. (2005) and Mencio and Mas-Pla (2008) do not mention

normalisation of data. However, Meng and Maynard (2001) did use the Cosine Theta

method and McNeil et al. (2005) converted their data to percentages so that the

relative proportions of the variables are considered in the analysis and not their

absolute magnitudes. Many texts simply do not mention normalisation in relation to

cluster analysis (Chatfield et al. 1980; Kaufman et al. 1990; Johnson et al. 1992;

Graham 1993) though they stress this requirement for other statistical techniques. In


their reply to a comment made by Dreher (2003) in relation to issues involved with

the normalisation and standardisation of data, Güler and Thyne (2003) stated

―Ultimately, we would encourage users to try several variations (raw, transformed,

transformed and standardized) and compare the results‖. After comparing the results

using a variety of combination of raw, transformed and standardised data, meq/L%

for ionic concentrations and standardisation of variables in the dataset was found to

provide the best results in relation to expected relationships between samples for this

study. Fresh surface waters and fresh groundwaters were generally grouped

separately as were fresh and estuarine waters.

It is also important to ensure that there is equal weighting of the selected variables

otherwise variables such Na and Cl can overwhelm the analysis (McNeil 2002) in

this coastal environment. The equal weighting of variables ensures that all ions,

regardless of magnitude, contribute to the partitioning of samples and reveals

differences/similarities between samples that may not be detected using graphical

methods alone. For this reason, data is usually standardised in some way.

Standardisation of variables is achieved by conversion of data to z-scores where for

each data value, the mean is subtracted and the results divided by the standard

deviation for each variable. The result is a normalized distance function.

All hierarchical cluster analyses here were carried out using Matlab 7.8.0 (Vers.

R2009a) (Mathworks Inc. 2011). The HCA cluster analysis itself consists of two

steps. The first step is to find the similarity or dissimilarity between every pair of

objects in the dataset. For this analysis, the Euclidean distance method is used to

calculate the distance between all pairs of objects and form a dissimilarity matrix.

The second step is to group the objects in a binary, hierarchical cluster tree. Here, we

use Ward‘s Method to link pairs of objects that are close together into binary clusters

and then link these clusters to each other until all data are linked in a hierarchical

tree. Ward‘s Method utilises the inner squared distance between pairs and determines

links using a minimum variance algorithm (Mathworks Inc. 2011) and is commonly

used by hydrochemists and geoscientists. This method is distinct from all other

methods because it uses an analysis of variance approach to evaluate the distances

between clusters. In short, this method attempts to minimize the Sum of Squares (SS)

of any two (hypothetical) clusters that can be formed at each step. Details concerning


this method are found in Ward (1963). In general, this method is regarded as very

efficient, however, it tends to create clusters of small size (StatSoft 2010).

The first dataset used for the HCA is identical to the one used for the graphical

methods in Larsen and Cox (2011). The data were all collected at the same time

(FT4: 15-17/08/2008) except for residential borehole waters, 134B and 204B (FT3:

18-19/12/2007) and shallow supratidal monitoring well waters, P11-P14 (FT8:

05/08/2009). We could not gain access to 134B during FT4 and the 204B pump had

ceased due to biofouling. Monitoring wells, P11-P14, were not installed until 2009.

The second, third and fourth datasets are temporal data, which are analysed to

investigate the effects of the seasonal/climatic variation on the hydrochemistry of

these ground and surface waters. Table 3 shows the data collection field trip dates,

rainfall, rainfall classification, maximum and minimum temperatures and

evaporation. The sample collections were timed to adequately cover seasonal

variation in the study area, with a range of temperatures and rainfall. To make

interpretation of these temporal datasets easier, the data are separated into fresh (EC

< 1500µS/cm), brackish (1500µS/cm < EC < 15000µS/cm) and saline (EC >

15000µS/cm) groups.

RESULTS AND DISCUSSION

Representative dataset

When selecting variables, exclusion of one of a pair of highly correlated variables is

normally recommended to ensure that multiple-collinearity is minimal. Inclusion of

dependent variables, such as EC in addition to Na and Cl concentrations may well

skew the results towards those parameters (Chatfield et al. 1980; McNeil 2002).

Correlation analysis was performed on the representative dataset of major ionic

concentrations and pH. All correlation coefficients were below |0.5| except for Mg

and Na which had a correlation coefficient equal to -0.82 and a p-value of 1.23x10-10

and Cl and HCO3 which had a correlation coefficient equal to -0.79 and a p-value of

2.25x10-9

. However, in order to make a better comparison with the graphical results,

all major ions should be included. The resulting set of parameters included in the

analysis was Na, Mg, Ca, Cl, SO4, HCO3 and pH. A cut-off at dissimilarity = 4.5 was

used for each dendrogram to determine the grouping of samples (Figure 5). This fits


well with the already perceived grouping of samples. For example, Tertiary alluvium

aquifer groundwaters are grouped at this level as are fresh surface waters and saline

ground and surface waters. The cluster analysis groups are shown in Figure 5. Table

4 lists and describes the resulting hydrochemical facies groups. Table 5 lists the

means and ranges for pH, TDI, SO4 and HCO3 for each group in Table 4.

Table 3 Climate conditions for data collection dates

Field

Trip

(FT)

DATE Rainfalla

(mm/day)

Rainfall

Classificationb

Max.

Temp.c

(°C)

Min.

Temp.c

(°C)

Evaporationd

(mm)

FT1a 24/08/2007 42.4 Moderate Rain 19.6 14.8 4.4

FT1 25/08/2007 119.0 Heavy Rain 31.4 15.5 2.0

FT2 20/10/2007 0.0 No Rain 25.1 15.1 5.4

FT2 21/10/2007 0.0 No Rain 23.6 15.4 7.0

FT3 18/12/2007 19.6 Light Rain 27.0 21.1 7.2




FT4 17/05/2008 0.0 No Rain 27.4 11.0 4.0

FT5 08/08/2008 0.0 No Rain 20.7 5.2 5.0

FT6 03/12/2008 0.0 No Rain 31.9 18.4 8.0

FT7 31/05/2009 0.0 (16.6)e No Rain 22.0 13.3 3.6

FT7 01/06/2009 10.0 Light Rain 22.7 13.6 3.8

FT8 05/08/2009 0.0 No Rain 23.9 8.0 5.6

Notes: a) Tuan Forestry Office data (rain gauging station within the study area – Figure 1)

b) Based on American Meteorological Society (2000)

c) Maryborough data (Figure 1).

d) Bundaberg data (Figure 1)

e) Previous day (30/05/2009) recorded at Double Island Point, evidence of recent rain at

some coastal sample collection sites

Table 4 Hierarchical cluster groups for representative dataset

Aquifer/ Surface Water Type Group No. Sites

Estuarine GWs and SWs 1&2 PCM, PB, P11, P12, P13, TCB, P14, P2

Brackish and fresh GWs and SW with GW input 3A P5, RF

Brackish and fresh GWs 3B B1, C5, TCA, WP11, R+E

Unsaturated zone brackish GWs 4 C3, C4

Tertiary alluvium GWs – seawater dilution 5A JL2, JL20

Tertiary alluvium GWs – soluble salts 5B JL1, JL7, JL13, PCP, JL10, JL25

Fresh semi-confined to confined GWs 6 P6, P8, P4, C2d, JL8

Fresh SWs and unconfined GW 7 LRB, WP31, WP12, 134B, PC9, PC10

Tuan catchment brackish GWs 8 JL4, JL9

Saline-intruded GW – local processes 9 204B

Note: Sites referred to in the discussion are highlighted in bold.


Overall, all sites have been allocated to similar groups to those determined using

graphical methods. In general terms, saline waters (Group 1 & 2), unsaturated zone

brackish groundwaters (Group 4), Tuan catchment Tertiary alluvium aquifer

groundwaters (Groups 5A and 5B), Poona catchment fresh semi-confined to confined

waters (Group 6) and fresh surface waters (Group 7) have been grouped together. For

the graphical methods surface and groundwaters in Group 1 & 2 were separated by

choice; here, they have been left in the same group. This illustrates that these waters

have very similar pH and proportions of major ions and that processes such as ion

exchange, sorption and co-precipitation are minimal within the sediments of the

supratidal flats (see Figure 2) indicating that major ions behave conservatively some

distance from the estuary (approximately 300 m). Group 1 & 2 also has a very large

range in ion concentrations. This range reflects seawater dilution along the flow path

between fresher subterranean and surface waters and the marine environment at these

sites. In addition, there is a further concentration of ions by evaporation within the

shallow groundwaters of the supratidal flats. This is confirmed by HCO3/Cl ratios

within this group which are all in the range 0.003 to 0.017 indicating that water-rock

interaction is a minor process and has little influence on the major ionic composition

of these waters. Based on data from Anthoni (2006), seawater HCO3/Cl ratios are

typically around 0.07 while a typical freshwater ratio is around 1.502.

There are, however, a number of important differences between the graphical and

HCA results, which are indicated by shading in Figures 4 and 5 and bold typeface in

Table 4. These differences are summarised as follows.

Table 5 Physico-chemical character of hydrochemical facies using HCA

GROUP pH TDI

(mg/L)

Sulphate

(mg/L) Bicarbonate (mg/L)

Mean Range Mean Range Mean Range Mean Range

1&2 6.7 5.1 - 7.8 34517 526 - 56622 2846 52 - 5583 236 4 - 535

3A 5.5 5.3 - 5.6 1122 1113 - 1131 42 31 - 53 10 7 - 13

3B 4.7 4.2 - 5.3 1616 85 - 6075 97 4 - 392 8 0 - 34

4 2.9 2.7 - 3.1 2333 2209 -2457 119 43 - 195 0 –

5A 6.7 6.4 - 6.9 7801 557 - 15045 255 42 - 468 113 5 – 220

5B 7.4 7.0 – 7.9 466 352 - 732 27 14 - 64 66 20 - 137

6 6.0 5.2 – 7.8 286 159 - 563 15 4 - 46 64 32 - 138

7 5.7 4.8 – 7.2 103 62 - 218 9 3 - 23 10 6 - 18

8 8.0 – 1000 889 - 1111 170 – 104 37 - 171

9 5.7 – 814 – 108 – 49 –

Note: EC, Na, Cl, Ca and Mg are highly correlated with TDI and so are not included here.


Groups 1 & 2 (P2): Semi-confined groundwater, P2, located near the Poona estuary

has been grouped with estuarine ground and surface waters confirming saline/fresh

water interaction at this site. Water level data also showed a small tidal effect at this

site (Larsen, unpub. data, 2008).

Group 3B (B1, C5, TCA, WP11, R+E): Fresh surface waters WP11 and TCA

(Figure 2) have been included in a group with two brackish and one fresh

groundwater, two of which are thought to be seawater-intruded. The graphical

interpretation pointed toward a groundwater contribution at these two sites as did

δ18

O and δ2H data for WP11 (see Larsen and Cox, 2011).

Groundwater contribution to inland Tuan catchment fresh surface water site, TCA,

was not indicated by the graphical methods although ion concentrations are much

higher at TCA than at other fresh surface water sites. This was originally thought to

be a result of poor drainage from the site in combination with evaporation. Results of

the cluster analysis, however, indicate that it is at least in part due to the input of

shallow brackish groundwaters, which have been observed elsewhere in this region.

Figure 5 Dendrogram for representative dataset generated using Euclidean

distance and Ward linkage methods. Groups/sites discussed in the text

are shaded.

19 72223 32115242520 5 6 118282930 2 4262716 81013 912111417

24681012

Sa

mp

le In

de

x

Dissimilarity

DENDROGRAM - ALL SITES

JL9 JL4 JL2 JL20 JL10, JL25 PCP JL7, JL13 JL1 JL8 P8 P6 C2d, P4 204B PC9 PC10 WP31 LRB, WP12 134B C4

C3 RF P5 WP11 R+E TCA B1, C5 P2 TCB, P14 PCM P11, P12, P13, PB


Using the graphical methods, uncertainty existed as to whether the high levels of ions

such as Na and Cl (relative to other fresh surface waters) at an unsaturated zone

groundwater C5, semi-confined groundwater in close proximity to the Buttha Creek

estuary B1 and TCA were due to seawater-intrusion or the accumulation of dissolved

salts within the sediment profile. As well as groundwaters directly affected by

seawater intrusion, the continual cycle of water and solute input as rainfall and the

concentration of solutes in the subsurface by partial evaporation and plant

transpiration of water can result in groundwaters very similar in character to diluted

seawater (Herczeg et al. 2001; Poulsen et al. 2006). Consequently, it can be quite

difficult to identify sources of salts in some ground and surface waters from

‗snapshot‘ sampling in such a coastal location. However, direct seawater intrusion to

an aquifer should be reflected in higher δ18

O and δ2H ratios relative to rainfall. This

difference is due to mixing between the relatively 18

O and δ2H depleted meteoric

waters and the enriched 18

O and δ2H marine waters, however, both C5 and B1 have

isotopic ratios reflecting local rainfall (Larsen et al. 2011). This similarity indicates

that the source of dissolved salts is from surface accumulation of salts from

atmospheric aerosols. However, B1 water samples may have been collected from

freshwaters overlying more saline waters intruding from the estuary. In this case,

isotope measurements will not indicate seawater intrusion. Groundwaters and surface

within the zone of mixing between saline and freshwaters will often have a variation

in ionic concentrations with depth due to density differences (Freeze et al. 1979).

Whether or not seawater intrusion is occurring at this site needs to be confirmed with

temporal measurements of EC and water levels. Samples were collected at B1 on two

occasions and although there is some difference between ion concentrations, this is

too small a dataset to be conclusive. Depth sampling should be included in any future

work.

Group 5A (JL2, JL20): Semi-confined Tuan catchment groundwaters, JL2 and

JL20, have now been grouped with other Tertiary alluvial aquifer waters. These two

sites both have Na/Cl ratios indicating seawater dilution (typically around 0.86 using

meq/L (Anthoni 2006)) of 0.92 and 0.87 respectively and are located in close

proximity to estuaries. Na/Cl ratios close to and greater than 1.0 indicate soluble salt

(present in clay layers throughout the area) dissolution for the remaining Tertiary

alluvium aquifer sites (Group 5Aa). For this reason JL2 and JL20 have been assigned


to a separate group (Group 5Ab). This highlights the fact that results from statistical

analyses should not be accepted blindly and should only be used in conjunction with

careful observation and interpretation of the data using other methods and

process/source indicators, especially in areas of limited chemical variability.

Group 5B (PCP): Poona Village fresh groundwater site, PCP, is a residential bore

located in beach ridge sands in Poona village whereas the remaining groundwaters in

this group are all located in the Tertiary alluvial aquifer in the Tuan catchment to the

north. The inclusion of PCP with these waters seems to be coincidental. Their

similarity lies in the fact that these waters are all fresh and are confined and that there

is very little water-rock interaction occurring. This is reflected in the HCO3/Cl ratios

for this group which are all below 0.13.

Group 6 (C2d, JL8): In Larsen and Cox (2011), the authors hypothesised that

confined fresh groundwater C2d was screened within the periphery of the Tuan

catchment Tertiary alluvial aquifer, i.e. it was grouped with Group 5B groundwaters.

The grouping of C2d with fresh coastal plain groundwaters indicates that this

hypothesis is incorrect.

JL8 is located adjacent to Little Tuan Creek estuary and is described in Laycock

(1969) as being located in coastal deposits of undifferentiated interbedded sand and

silt which has been deposited under marine conditions overlying the Tertiary alluvial

aquifer. The geomorphology at this site is similar to that at fresh coastal plain

transect groundwater sites P4, P6 and P8 in the Poona catchment and all are located

in close proximity to the creek estuary where occasional surface water/groundwater

interaction may occur. Although some distance apart, the similar settings and

processes occurring at these sites has resulted in similar water chemistries. All of the

waters in the group have HCO3/Cl ratios between 0.3 and 0.4 indicating some degree

water-rock interaction, or in this case water-sediment interaction, most likely due to

the presence of shell material within these sediments. The weathering of these

carbonate shells and dissolution of HCO3 will increase the HCO3/Cl ratio.

Group 7 (134B): Fresh groundwater sample 134B is grouped with fresh surface

waters. 134B was previously thought to be located in a confined freshwater aquifer.

Based on the cluster analysis, it appears that this aquifer could well be a shallow


unconfined or, at most, semi-confined freshwater aquifer. This sample was collected

during light rainfall and most probably reflects recent rainfall recharge.

Group 8 (JL4, JL9): As above, the main differences between these groundwaters

(JL4, JL9) which are also geographically close to each other and other groundwaters

within the Tertiary alluvium aquifer in the Tuan catchment (JL2, JL7, JL10, JL13,

JL20, JL25) is that they have lower percentages of magnesium and higher

percentages of sulphate.

Based on graphical methods, JL4 and JL9 were grouped with confined groundwaters

within the Tertiary alluvium aquifer in the Tuan catchment. The higher

concentrations of ions indicate that there may be some interaction between

unconfined/unsaturated zone waters such as those at C3-C5, indicating semi-

confined rather than confined conditions at these sites.

Group 9 (204B): Residential groundwater 204B is anomalous. Based on

physicochemical measurements, Fe concentrations and isotope ratios of 15

N, 13

C and

34S to be discussed in a future paper [see Paper 3 in this thesis], this site is known to

have local hydrochemical processes occurring in relation to iron and sulphur

oxidising bacteria and as such has a unique chemical composition.

The effect of the inclusion of pH can be seen in differences between the pH ranges

for the graphical and cluster groups. Overall, the pH ranges are smaller for the HCA

cluster groups than for the graphical method groups. The average pH ranges using

the graphical and HCA methods were 1.51 and 1.11 respectively, which is significant

considering the logarithmic nature of pH.

Temporal data

Figure 6 and Tables 6 to 8 show the results for temporal datasets.

Freshwaters only

Overall, surface waters and groundwaters are grouped separately. The exceptions are

coastal plain surface waters WP11 and TCA (see Figure 6 and Table 6); WP11 is

quite variable and has been assigned to three different groups. WP11FT1 was

collected during flood conditions and has been grouped with upper catchment

freshwaters LRB, PC9 and PC10 in Group 2 including LRBFT1 also collected during

flood conditions. At other times, WP11 water is grouped with groundwaters


indicating groundwater contribution as discussed above. The variability at WP11

reflects the complex processes occurring at this site involving variable groundwater

and rainfall contributions and timing of sampling.

TCA also shows some variability and has been assigned to two different groups. The

grouping of WP11 and TCA with a number of groundwaters in Group 5 indicates that

both these surface water sites had a significant groundwater contribution at this time

(FT4). There was very little rainfall leading up to FT4 (05/05/2008), with cumulative

rainfall being less than 0.7 mm in the preceding two weeks. It is likely that the

surface waters at these two sites were predominantly groundwater baseflow at this

time.

Semi-confined groundwater P6FT1 is a unique site indicating flood conditions and

significantly altered the major ionic chemistry at this site with heavy rainfall

infiltrating to this small sand and gravel aquifer very quickly.

C2d and P8 temporal data are all within the same groups indicating very little

seasonal variation. This indicates that these bores are located in confined aquifers.

Confined aquifers commonly have physicochemical and hydrochemical characters

that reflect the seasonal average.

Overall, seasonal differences are minimal except possibly where substantial

groundwater input occurs such as at WP11 and TCA during drier periods or when

heavy rainfall occurs.

Saline waters

The grouping together of supratidal flat groundwaters (P11-P14) and estuarine

surface waters (PCM, PB, TCB) (Figure 6 and Table 8) shows the conservative

nature of major ions in the shallow waters of muds and sands adjacent to the Poona

Creek estuary. There is minimal precipitation or sorption of major ions within these

sediments. Within the drainage system, there is a straightforward dilution along the

flow path upstream. Processes affecting ion concentration magnitudes, however,

include rainfall contribution, tidal condition and evaporation effects within the waters

of the supratidal flats. Table 9 shows the ranges of Na and Cl for estuarine waters

due to tidal flux. PCMFT1 is unique here as it was collected during flood conditions

and the sample is a mixture of fresher inland water being discharged to the Great

Sandy Strait, and marine waters. The Na/Cl ratio for this sample is also much higher


than for marine waters, indicating an inland source.

Figure 6 Dendrograms of temporal data for fresh, brackish and saline datasets.

P6FT1, PCMFT1 and P5FT1 (shaded) are anomalous sites due to flood

conditions.

SUMMARY

Overall, the previously established hydrochemical facies and assignment of settings

to them is supported. However, there are a number of important findings based on

the representative dataset cluster analysis results.

1) The hypothesis that confined fresh groundwater C2d was located on the

periphery of the Tertiary alluvial aquifer in the Tuan catchment appears to be

5

6

7

8

12

14

13

4

1

9

2

10

3

11

12345678

Sam

ple

In

dex

Dissimilarity

Time-series Data: Brackish water only

1015 1 8 9171112162120223023 3192425 4141318 5 62628 7 22729

1234567891011

Sam

ple

In

dex

Dissimilarity

Time-series data: Fresh water only

6

12

5

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Dissimilarity

PCMFT1

P12FT7

PCMFT2

PBFT4

PCMFT4

TCBFT6

P12FT8

P11FT7

PBFT2

PBFT7

P13FT7

TCBFT4

P13FT8

Time-series Data: Saline waters only

PC9FT4 PC10FT4 TCAFT6 LRBFT4 PC9FT3 PC10FT3 LRBFT2, WP11FT1 LRBFT1 P6FT1 WP11FT2 P4FT2 C2dFT4 P8FT7 P8FT6 P6FT2 C2dFT0, P8FT4 WP11FT6 TCAFT4 P6FT7 P6FT4 P6FT6 P4FT6 P2FT7 P2FT6, P2FT8, WP11FT4 P4FT7 P2FT2 P2FT1 B1FT2, B1FT4 P4FT4 P2FT4

C5FT4

C5FT0

C4FT4

C4FT0

C3FT4

C3FT0

P5FT1

P5FT7

P5FT8

P5FT6

R+EFT4

P5FT4

R+EFT3

P5FT2

Time-series Data: Brackish waters only

C5FT4

C5FT0

C4FT4

C4FT0

C3FT4

C3FT0

P5FT1

P5FT7

P5FT8

P5FT6

R+EFT4

P5FT4

R+EFT3

P5FT2

Time-series Data: Brackish waters only


incorrect. This supports the estimated boundary for this aquifer put forward in

Laycock (1969).

2) Interaction between ground and surface waters is indicated at WP11, TCA and

possibly JL8 where adjacent alluvial aquifers supply groundwater baseflow to

these sites during times of low rainfall. This has implications for solute transport

within the catchment.

Table 6 Hierarchical cluster groups for temporal data: Freshwaters

Group No. Description SW Sites GW Sites

1 Inland SWs

PC9FT4 PC10FT4 TCAFT6 LRBFT4

2 Upper catchment surface waters, one coastal plain SW collected during heavy rainfall

PC9FT3 PC10FT3 WP11FT1 LRBFT1, LRBFT2

3 GW collected during flood conditions P6FT1

4 One coastal plain surface water Confined and semi-confined groundwaters

WP11FT2

C2dFT0, C2dFT4 P4FT2 P6FT2 P8FT4, P8FT6, P8FT7

5 One coastal plain surface water, one inland surface water Three semi-confined coastal groundwaters

WP11FT4, WP11FT6 TCAFT4

P2FT6, P2FT7, P2FT8 P4FT6 P6FT4, P6FT6, P6FT7

6 Semi-confined groundwaters B1FT2, B1FT4 P2FT1, P2FT2, P2FT4 P4FT4, P4FT7

Notes: Samples with the suffix FT1 were collected during flood conditions.

Sites highlighted in bold are discussed in the text.

Table 7 Hierarchical cluster groups for temporal data: Brackish waters

Group No. Source of dissolved ions GW Sites

1 Cyclic salts? C3FT0, C3FT4, C4FT0, C4FT4, C5FT0,C5FT4

2 Storm surge P5FT1

3 Seawater intrusion P5FT6, P5FT7, P5FT8

4 Seawater intrusion R+EFT3, R+EFT4 P5FT2, P5FT4


Table 8 Hierarchical cluster groups for temporal data: Saline waters

Group No. GW/SW SW Sites GW Sites

1 Surface water – Flood conditions PCMFT1

2 Supratidal groundwater P12FT7

3A Saline estuarine SWs and Supratidal GWs

PCMFT2, PCMFT4 PBFT4 TCBFT6

P11FT7 P12FT8

3B Saline estuarine SWs and Supratidal GW

PBFT2 TCBFT4

P11FT8 P13FT7, P13FT8

Table 9 Ranges for Na and Cl for saline estuarine ground and surface waters

Site Na range (g/L) Cl range (g/L)

P11 Supratidal muds and sands groundwater 10.5 – 15.5 18.8 – 31.2




PB Surface water 0.4 – 13.5 0.9 – 10.8

TCB Surface water 6.1 – 7.5 15.0 – 22.7

3) In three cases, JL4, JL9, JL8, results indicate that these aquifers are not confined

as stated in Laycock (1969). The level of confinement of aquifers has

implications for water quality within the aquifers themselves and for ground and

surface waters that they are in communication with.

4) A unique site, 204B, was identified. Based on the graphical methods, this site

was considered to be similar in character to seawater-intruded groundwaters JL2

and JL20 and P2. This site is a residential borehole in communication with the

Great Sandy Strait and as such a potential source of solutes. Its unique chemistry

requires that it be treated separately from these other seawater-intruded

groundwaters.

5) There appears to be little to no ion exchange, precipitation, adsorption or other

processes that might affect major ionic proportions occurring and the major ions

are behaving conservatively within the supratidal flats adjacent to the estuary.


The important findings based on the results from HCA using temporal data are:

Confinement of aquifers at two sites, C2d, P8, is indicated. The confinement of

P8 confirms the complexity of the geology at the transect of monitoring wells

adjacent Poona Creek estuary. Discontinuous clay layers at varying orientations

in the vicinity of the transect have an important influence on confinement in this

aquifer and consequently interaction between waters.

Seasonal variations in proportions of ions within fresh ground and surface waters

are minimal except where groundwater contribution may be increased during

extended dry periods, such as at surface water sites TCA and WP11.

Seasonal variations in proportions of ions within brackish and saline waters are

minimal regardless of tidal conditions due to direct mixing between fresh coastal

rainfall and saline waters except during extreme weather conditions or where

storm conditions lead to a substantial rainfall recharge, e.g. PCMFT1.

Cluster groups from brackish water analysis appear to confirm different sources

of salts for inland and coastal groundwaters. Identification of sources of ions

within waters is important when considering hydrological processes and potential

transport.

CONCLUSIONS

Processes

The HCA results have highlighted a number of important processes and

characteristics including (a) groundwater contribution to surface waters, (b) aquifer

type in relation to level of confinement, (c) the conservative behaviour of major ions

within the subterranean estuary near the mouth of Poona Creek, and (d) an

anomalous site. In addition, temporal HCA confirms that there is little seasonal

variation in the proportional ion concentrations of most waters except where there is

ground/surface water interaction or high rainfall events. This new information does

not so much contradict the results using the graphical methods but rather reveals new

processes/characteristics of waters that were previously obscured.

However, the problem of the similarity among samples is not solved completely.

There are still ‗incorrect‘ or inappropriate assignments where group samples are

located in very different sediment profiles and are known to have different processes


occurring and/or sources of solutes. Clearly, as in the case of the graphical methods,

results from HCA should be carefully examined before final interpretation.

Methodology

Multivariate statistical methods are very useful in the process of hydrochemical

characterisation and investigation of hydrological processes particularly in areas

where there is limited variability in ionic concentration proportions. The hierarchical

cluster analysis methodology outlined here makes the partitioning of samples a more

objective process, allows the inclusion of additional variables and ensures that all

variables are considered equally. Unlike graphical methods, however, the results

from HCA are not directly useful for identifying dominant processes and factors

contributing to the character of natural waters. Using both methods in combination

with ionic ratios and other process/source indicators will lead to more accurate and

detailed interpretation of hydrochemical processes occurring in natural waters as

shown in the discussion of Group 5 waters above. Familiarity with geology, climate,

vegetation, hydrochemical processes and other environmental influences is essential

to achieve a proper characterisation of waters. Although the cluster analysis is

helpful in supporting the assignment of samples to particular hydrochemical facies

and, in some cases, revealing new information relating to aquifer types and

interaction between different waters, it would have been unwise to use this technique

blindly.


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5 they agree to the use of the publication in the student’s thesis and its publication on the Australasian Digital Thesis database consistent with any limitations set by publisher requirements.


PAPER 3: Sources, distribution and transport of iron and nutrients within the groundwaters and surface waters of a sub-tropical coastal setting, Fraser coast, Queensland, using hydrochemical and isotopic data _________________________________________________________________________





Assisted with project design and field work. Contributed to the manuscript

Smith, J.J. (associate supervisor)

Assisted with laboratory methods and field work. Contributed to the manuscript

Principal Supervisor Confirmation I have sighted email or other correspondence from all Co-authors confirming their certifying authorship. _______________________ ____________________ ______________________ Name Signature Date

6. PAPER 3

SOURCES, DISTRIBUTION AND TRANSPORT OF IRON AND

NUTRIENTS WITHIN THE GROUNDWATERS AND SURFACE

WATERS OF A SUBTROPICAL COASTAL SETTING, FRASER

COAST, QUEENSLAND, USING HYDROCHEMICAL AND

ISOTOPIC DATA

Genevieve Larsen, Malcolm E. Cox, James J. Smith




Abridged version prepared for submission to Biogeochemistry

Abstract

This study was part of an integrated project developed in response to concerns

regarding current and future land practices affecting water quality within coastal

catchments and adjacent marine environments. Two forested coastal catchments on

the Fraser Coast, Australia, were chosen as examples of low-modification areas with

similar geomorphological and land-use characteristics to many other coastal zones in

southeast Queensland. For this component of the overall project, organic , physico-

chemical (Eh, pH and DO), ionic (Fe2+

, Fe3+

), and isotopic (δ13

CDIC, δ15

NDIN δ34

SSO4)

data were used to characterise waters and identify sources and processes contributing

to concentrations and form of dissolved Fe, C, N and S within the ground and surface

waters of these coastal catchments. Three sites with elevated Fe concentrations are

discussed in detail. These included a shallow pool with intermittent interaction with

the surface water drainage system, a monitoring well within a semi-confined alluvial

aquifer, and a monitoring well within the fresh/saline water mixing zone adjacent to

an estuary. Conceptual models of processes occurring in these environments are

presented. The primary factors influencing Fe transport were; microbial reduction of

Fe3+

oxyhydroxides in groundwaters and in the hyporheic zone of surface drainage

systems, organic input available for microbial reduction and Fe3+

complexation,

bacterial activity for reduction and oxidation, iron curtain effects where saline/fresh

water mixing occurs, and variation in redox conditions with depth in ground and

surface water columns. Data indicated that groundwater seepage appears a more

likely source of Fe to coastal waters (during periods of low rainfall) via tidal flux.

The drainage system is ephemeral and contributes little discharge to marine waters.

However, data collected during a high rainfall event indicated considerable Fe loads

can be transported to the estuary mouth from the catchment.

165

Introduction

Transport of nutrients and metals from both natural and anthropogenic sources may

occur through shallow groundwater, surface runoff, surface streams and tidal

movement. Solute pathways can be complex, involving ground and surface water

mixing, including interaction between groundwater aquifers and rivers, estuaries,

bays and ocean shorelines. Within these systems, processes affecting the dissolution,

oxidation and complexation of Fe; biochemistry of sulphur species (reduction and

oxidation); and amounts and forms of organic and inorganic carbon compounds all

potentially influence transport of dissolved Fe loads to the marine environment.

In addition to causing general water quality degradation and contributing to

eutrophication of natural water bodies (Norton et al. 2000), nutrients such as

phosphorus, iron and humic substances all play a part in regulating the growth of

algae and cyanobacteria such as Lyngbya majuscula, a potentially toxic blue-green

algae. Lyngbya majuscula can smother seagrass meadows and deplete oxygen during

breakdown decreasing fish and coral populations (Moreton Bay Catchment Water

Quality Management Strategy Team 1998). These blooms also pose a threat to

human health and to the recreational and commercial values of coastal waterways

(Albert 2001; Ahern et al. 2006a; Ahern et al. 2006b; Queensland Government

2010). The occurrence of these algae in coastal waters is of worldwide concern (Lin

et al. 2004; Al-Shehri et al. 2007; Titlyanov et al. 2008; Paerl et al. 2009), and

particularly in Queensland, Australia, where these blooms have increased in

frequency, duration and intensity over the past 16 years (Ahern et al. 2006a; Ahern et

al. 2007; Queensland Government 2010). Seasonal Lyngbya blooms have been

reported in close proximity to the study area for this project as well as nearby

locations on the Southeast Queensland coast at Noosa Main Beach, 80 km south of

the study area (BMRG 2005), and in the Deception Bay/Pumicestone Passage region,

150 km south of the Poona catchment (Dennison et al. 1999).

Iron is essential for the growth and metabolism of all aquatic organisms and is

involved in key metabolic processes: photosynthetic and respiratory electron

transport, nitrate and nitrite reduction, nitrogen fixation and sulphate reduction. Even

in regions once considered iron replete, iron exerts a considerable influence on the

aquatic ecosystem (Coale et al. 1996; WBM Oceanics Australia 2001; Pointon et al.

2003). Gross and Martin (1996) demonstrated the dependence of L. majuscula on

166 Paper 3. Distribution and transport of Fe and nutrients

iron for growth under laboratory conditions and concluded that the occurrence of

blooms of this cyanobacterium could be reduced by treatments that would reduce the

availability of iron. Bell and Elmetri (2007) concluded that L. majuscula growth is

often limited by the bioavailability of Fe with the principal reason the lack of supply

of suitable organic ligands, chelators, not the lack of Fe per se. Ahern et al. (2006b)

found that although inorganic Fe (FeCl3) did stimulate L. majuscula filament growth,

organically-chelated iron (FeEDTA) was far more effective. These studies emphasize

the importance of the input of humic substances to waterbodies in addition to Fe

loads for development of L. majuscula blooms.

The focus of this study were the Tuan and Poona freshwater catchments and the

adjoining low-lying coastal plain located on the Fraser Coast, Queensland.

Catchment estuaries discharge to the marine environment adjacent to the southern

end of Fraser Island. The mainland freshwater catchments host plantation forestry,

which also extends to the coastal plains. Within the coastal plains there are also areas

of remnant native vegetation and small residential communities located near estuary

mouths. The area is located adjacent to the Ramsar-listed Great Sandy Strait, which

is of high environmental significance. A number of threatened species (flora and

fauna) exist in the marine areas and associated tidal wetlands such as dugong

(Dugong dugon), Bottlenose (Tursiops truncatus) and Indo Pacific Humpback

(Sousa chinensis) dolphins, migratory shorebirds, seasonal populations of humpback

whales (Megaptera novaeangliae), and rare shrubs (EPA 2005).

Elevated nutrients and metals in ground and surface waters may arise from both

natural and anthropogenic influences. Studies in the region have shown that although

urban and industrialised land-uses have a strong influence over metal release, natural

processes exert the dominant influence (Eyre et al. 1993; Kawaguchi et al. 1997;

Preda et al. 2002). Within Australia, numerous baseline metal studies have been

undertaken within estuaries, bays and floodplains adjacent to major population

centres which relate to either natural or anthropogenic events (see review in Cox and

Preda, 2005). A common finding is an association between elevated metals and

industrial activities on a local basis, but natural processes on a broader scale. These

studies often focus on one discipline such as geology, inorganic chemistry, organic

chemistry or microbiology. Very few identify potential interactions and linkages

between chemistry, physics, biology and geology in what is essentially a trans-

Paper 3. Distribution and transport of Fe and nutrients 167

disciplinary topic. In particular, biological factors are often overlooked (Warren et al.

2001).

This study was part of an integrated project developed in response to concerns

regarding the effect of land-use practices on the natural environment in this region.

In Larsen and Cox (2011) and Larsen (2012), graphical methods and hierarchical

cluster analysis of major ion concentration data were used to; identify the

hydrological and hydrochemical processes in the study area, determine the character

of the groundwaters and surface waters, and investigate the connectivity between

various water bodies.

The primary aim of this paper was to provide hydrochemical and process-related

information under steady-state conditions (the term ‗steady-state conditions‘ is used

here to refer to climate, i.e. periods of low rainfall where there is little variation in

hydrochemical and hydrodynamic conditions) as a guide for future monitoring of

these coastal settings, which are typical of much of central and southern coastal

Queensland. More specifically, the aims of this paper are to (a) characterise iron and

nutrients in ground and surfaces waters within the study area, and (b) identify and

investigate micro-processes potentially affecting the transport of iron to the marine

environment.

Ground and surface waters within the study area are characterised in relation to Fe,

S, C and N using dissolved organic carbon , physicochemical (Eh, pH, dissolved

oxygen [DO]), ionic (Fe[II], Fe[III], S2-

) and isotopic signature (δ13

CDIC, δ15

NDIN and

δ34

SSO4) data. After the initial regional characterisation of waters, sites of interest are

examined in more detail and specifically in relation to processes affecting the

mobilisation and transport of Fe. For two of these sites, cultivable bacterial numbers

were also available for Fe reducing bacteria (FeRB), Fe oxidising bacteria (FeOB),

sulphate reducing bacteria (SRB) and sulphur oxidising bacteria (SOB). This paper

provides new information relating to the input of nutrients to coastal waters under

low-modification conditions in these types of coastal settings. This study not only

indicates current areas of concern that require careful monitoring but provides a good

foundation for future monitoring after further development.

This study integrates hydrogeological, inorganic and organic chemical, isotopic and

microbiological information (where these data were available) and field observations


in addition to established knowledge relating to hydrological and hydrogeological

processes in the area. An interdisciplinary approach is utilised to develop and support

conceptual models of processes affecting the mobilisation and transport of Fe within

the Tuan and Poona catchments.

Background

Study Area

General setting

For a more detailed description of the study area in relation to geology, hydrology,

hydrogeology and major ion chemistry, see Larsen (2012) and Larsen and Cox

(2011). Table 1 describes flow regime and associated vegetation/land-use, borehole

depth, distance from the estuary mouth or Strait, topographical height and water type

for the sites described here.

The study area is on the Fraser Coast of Queensland, adjacent to the Great Sandy

Strait, a passage landscape between the large Fraser Island sand mass and the

mainland (Figure 1). The setting area encompasses a number of small catchments

and the low-lying coastal plain. More than 70% of the study area has topographic

gradients less than 1.5% while gradients in the upper catchments increase to 10%,

with lower gradients to the north of the area towards the large Mary River delta.

These Tuan and Poona catchments have poorly-developed surface drainage systems

and catchment definition. Maryborough, the closest large town, is located on the tidal

Mary River approximately 27 km northwest of Poona village which is located in the

central coastal zone. See Figure 2 for the location of data collection sites and

topography.

Both Big Tuan Creek and Poona estuaries are tidally dominated. At the mouth of

Poona Creek, Spring tidal ranges are generally slightly less than 2 m (Larsen, unpub.

data, 2008). For most of the year many of the tributaries are small creeks that are

ephemeral in their upper reaches and contribute very little, if any, discharge to the

Strait. However, during and after rainfall-induced high flow events, run-off from the

catchment into streams and their lower-order creeks can be substantial, potentially

affecting water quality in the Great Sandy Strait (Shaffelke et al. 2002; Campbell et

al. 2004; BMRG 2005). In addition, heavy rainfall can produce significant seepage


from shallow unconfined aquifers, potentially adding to nutrient and trace metal

loads discharged to receiving estuarine and marine environments.

Figure 1 Map of Australia and a section of the southeast coast of Queensland. The

dashed box shows the location of the study area on the Fraser Coast.

The main land-use in the area consists of mature Pinus plantations ranging from 16

to 30 years of age. Watercourses from the current areas of exotic pine plantations

drain to the coastline and the Great Sandy Strait. Riparian buffer zones have been

retained throughout the plantations, in which buffer widths mostly relate to stream

order. Remnant native vegetation within the buffer zones is typically grassy forest

containing various eucalyptus species, and tufted native grasses such as Themeda

australis (Kangaroo grass) and Imperata cylindrica (blady grass) and low layered

forest containing paperbarks (Melaleuca quinquenervia), white mahogany

(Eucalyptus acmenoides) and a ground layer consisting largely of sedges (Coaldrake

1961). Within the coastal flats tidal zone, saltmarsh and mangrove areas occur along

the estuaries. Freshwater wetlands peripheral to estuaries support Wallum banksias

(Banksia aemula), tea trees (Melaleuca) and grasstrees (Xanthorrhoea). These

Q

LD


wetlands form an important part of the overall freshwater drainage system; often

with groundwater links, and in many cases close to saline waters.

Poona and Little Tuan are small coastal villages with populations of approximately

200 within the study area and are under increasing pressure from development. These

villages are unsewered, increasingly using septic systems for effluent disposal,

creating concern among residents (BMRG 2005) due to potential aquifer

contamination. In addition, potential over-exploitation of local fresh groundwaters

due to increasing extraction is also of concern, with encroachment of the saline/fresh

water interface potentially significantly influencing nutrient mobilisation and

transport. Until recently, similar conditions to these were observed around many

coastal sections of Moreton Bay in southeast Queensland. Indeed, there still exist

developed coastal areas using various combinations of groundwater, reticulated

water, septics, and sewage systems using local area treatment plants.

The subtropical climate of the area is typical of southeast Queensland, with more


to February) and comparatively dry winters (June to August).

Hydrological setting

The hydrogeological setting is described in some detail in Larsen and Cox (2011).

Overall, groundwater is indicated to occur in three hydrogeological settings in this

region, (a) zones within weathered bedrock, (b) Tertiary alluvial valley in the north,

and (c) tidal coastal strip Quaternary unconsolidated materials which can be further

subdivided into (i) coastal plain alluvial deposits, (ii) tidal sands and muds, and

coastal beach ridge sands. Surface waters can be separated into two readily

differentiable groups, (a) freshwaters within the elevated catchments and streams

within the coastal plains disconnected from the main tidal channel, and (b) estuarine

water within the main tidal drainage channels of the coastal plains.


Figure 2 Location of data collection sites (triangles indicate surface water sites

and circles, groundwater sites), drainage system and topography.

Catchments have been delineated using ArcGIS.

Source: 5m resolution LIDAR data from FPQ

Kalah catchment

Maaroom catchment

Big Tuan catchment

Poona catchment

Buttha catchment


Table 1 Description of sample locations

Notes: a) The landuse/vegetation descriptions listed for the JL sites are current (2011). At the time of the data collection for these sites (1968-1969), the pine

plantations had not been established, b) AMTD = Adopted Middle Thread Distance from estuary mouth, c) Brackets in this column contain estuary

names. Otherwise, distances are from the Great Sandy Strait, d) TC = Tuan Creek, e) Water type is defined as those ions within the sample that

constitute more than 10% of the total. This are listed in descending order of percentages, starting with cations and followed by anions.

SITE ID Sample

Type Sitea Description

AMTDb (km) (SW) or Depth (m bgs) (GW)

Distancec from estuary/strait (m)

Topographical height (m AHD)

Water Type

B1 GW Native bushland, ghost gums, paperbarks, banksia 5.0-8.0 100 (Buttha) 4.3 Na-Mg-Cl

P2 GW Transect - Native vegetation between pine plantation and estuary 6.0-9.0 320 (Poona) 2.3 Na-Cl


P5 GW Transect - Native vegetation between pine plantation and estuary 3.0-6.0 300 (Poona) 1.5 Na-Mg-Cl







134B GW Residential bore – cultivated lawn and shrubs Unknown 143 < 3.5 Na-Mg-Cl

204B GW Residential bore – cultivated lawn and shrubs 12.0 214 < 3.5 Na-Cl

PCP GW Caravan Park bore – cultivated lawn and trees 19.0 100 < 3.5 Na-Cl-HCO3

RE GW Residential bore – cultivated lawn and shrubs 11.0 290 3.27 Na-Mg-Cl

RF GW Caravan Park bore – cultivated lawn and shrubs 6.0 180 2.84 Na-Mg-Cl

C2d GW Mature pine forest 11.5-13.0 9100 21.5 Na-Cl-HCO3

C3d GW Native grassland opposite timber mill 5.5-7.0 9000 22.1 Na-Cl

C4 GW Mature pine forest 2.3-3.8 8500 16.8 Na-Cl

C5 GW Native vegetation, grass trees, melaleuca, wallum 2.5-4.0 8700 14.5 Na-Mg-Cl

LRB SW Low flow, very small creek 12.8 N/A 8.7 Na-Mg-Cl

PB SW Moderate tidal flow 10.5 N/A 2.7 Na-Mg-Cl



PCM SW Strong tidal flow 0.0 N/A 0.0 Na-Mg-Cl

TCA SW Still pools/small flowing brooks 16.8 N/A 18.6 Na-Mg-Cl

TCB SW Moderate tidal flow 8.5 N/A 1.5 Na-Mg-Cl





Hydrochemistry

Major ions and pH

Hydrochemical characterisation and processes are also described in detail in Larsen

and Cox (2011) and Larsen (2012). When compared with many other studies of this

type, mineralogical and physiographic variability is relatively limited in the study

area due its size and location. As the environment is subtropical and coastal, waters

are predominantly of Na-Cl or Na-Mg-Cl types. These ions account for a significant

proportion of the ionic content of nearly all shallow ground and surface waters and

are contributed by rainfall, oceanic spray, saline intrusion within shallow coastal

aquifers and drainage systems, and soluble salts within clay layers present

throughout the area. pH values (2.7 to 7.8) are variable and relate to rainfall, input of

marine waters to the system, levels of organic acids within soils, and/or organic

layers at-depth local to the site (Larsen et al. 2011). Lithologies in the area are

predominantly siliceous with very little, if any, calcareous material available for

dissolution and consequently dissolved calcium and bicarbonate concentrations

(mean = 1.7 mg/L Ca2+

and 26.1 mg/L HCO3- for non-saline intruded samples) are

generally low (Larsen et al. 2011). This is reflected in predominantly slightly acidic

pH values throughout the study area (see Table 2).

Iron transport and sources

As part of this integrated project, Löhr et al. (2010) investigated processes

controlling the distribution and phases of Fe in soils and sediments of the Poona

catchment. Although the catchment has extensive areas of high-Fe soils, which

contain a large proportion of ferricrete and Fe-concretions, readily-extractable Fe

concentrations were low. However, two processes were identified that contributed to

elevated Fe concentrations at some sites. These were (a) anoxic conditions due to

water-logging reducing iron oxides in clay-rich soils on lower slope positions, and

(b) accumulation of Fe-rich sediment and organic detritus in streams resulting in the

release of Fe under resultant sediment anoxic conditions and subsequent

complexation with organic material (Löhr et al. 2010).

Water-logging is a common feature in lower-gradient zones with this study area

(Bubb et al. 2002; Wang et al. 2008) and is an important process contributing to the

mobilisation of iron within these catchments. Iron in the form of concretions and


ferricrete in the study area are likely to release Fe where they occur in waterlogged

soils (Löhr et al. 2010) where anoxic conditions result in the reduction of Fe3+

oxides

to dissolved mobile loads of ferrous iron. Whereas there appears to be very little

interaction between groundwaters and surface waters in the Poona catchment aside

from small alluvial aquifers in the coastal plain (Larsen et al. 2011), these water-

logged areas could play a significant role in the mobilisation of Fe within these

catchments (Löhr et al. 2010), with potential transport to marine environments.

During floods or heavy rainfall, the water table rises, Fe is brought to the surface,

and is transported overland and through the soil profile to study area streams and

creeks. In addition, run-off from roads, where Fe concretions are often used as a road

base, will add to the Fe load within the drainage system (Löhr et al. 2010).

Methods

Data collection

A total of 32 sites were sampled for this project including 22 groundwater and 10

surface water sites. A transect of monitoring wells was drilled specifically for this

study adjacent to Poona Creek estuary in order to investigate hydrochemical

processes and Fe transport at the saline/fresh interface. Figure 3 shows a cross-

sectional view of this transect. In this paper, monitoring wells P5, P6 and P11-P14

and surface water sites TCA, TCB, PB and PCM are discussed in relation to

processes affecting iron transport and potential for Fe transport to marine waters

under steady state conditions (Figure 2). The main focus of this study is the

freshwater upper catchment surface water site TCA and monitoring wells P5 and P6

(Figure 2). See Figure 4 for a close-up map view of transect groundwaters including

P5 and P6. The remaining sites are discussed in relation to transport of Fe from these

sites.


Figure 3 Cross-section of lithology and monitoring wells near the Poona Creek estuary. Note the locations of P5, P6 and P11-P14 in

bold which are discussed in this paper. The red and blue dashed lines represent the approximate location of the upper and

lower boundaries of the semi-confining clay ‗layer‘ near the ground surface (see also Appendix D). Although present in all

of the transect bore sediment profiles, the quick recharge at these sites indicates that this layer is actually in the form of

discontinuous lenses of variable thickness and hydraulic conductivities allowing rainfall recharge to penetrate to this aquifer

quickly. There was continual recharge to most of these sites during a rainfall event which occurred in August 2007. This

diagram is modified from Lin (2011).


Aside from P11-P14 monitoring wells located in the supratidal flats adjacent to

Poona Creek, the data used here is from one field trip in May 2008 There was limited

rainfall leading up to this data collection period, with cumulative rainfall < 35 mm in

the preceding six weeks with a maximum daily rainfall of 8 mm occurring 26 days

before data collection. The shallow monitoring wells P11-P14 were not installed

until 2009, and for these August 2009 data was used. Isotope analyses for these four

sites were not performed due to financial constraints. Only a limited number of

cultivable bacterial number analyses were carried out (Table 3). These data are from

related but different project carried out by Lin (2011).

Field methods

In total, eleven monitoring wells were drilled for this project in June 2007. The holes

for the monitoring wells were drilled using a hydraulic rotary drilling rig with

bentonite drilling mud. Cuttings samples were collected at 0.5 m intervals. Drillhole

depths varied (Table 1) and 3 m PVC slotted screens were placed at the bottom of the

borehole, gravel packed and sealed with bentonite. Wells were capped and housed

with a galvanised steel casing set in a concrete surface seal. Four shallow monitoring

wells (P11-P14) were later (mid-2009) installed by hand auger in muds and sands of

the estuarine tidal flats between the transect and the estuary in order to further

investigate tidal intrusion in this area.

Physico-chemical parameters, electrical conductivity (EC), pH, redox (Eh), dissolved

oxygen (DO) and temperature (T), were measured in situ at all sites with a calibrated

TPS 90FL field multimeter. Samples for dissolved ion analysis were collected in 250

mL high density polyethylene (HDPE) bottles. Samples for cation analysis by ICP-

OES were filtered in the field through 0.45 µm pore size polycarbonate filters and

preserved by acidification to pH < 2 using 50% nitric acid (Eaton et al. 2005); anion

bottles were not acidified and filled to eliminate head-space. Samples were kept on

ice or refrigerated during transport and storage; isotope samples were kept in tightly

closed containers in the dark. For all groundwater samples, bores were purged prior

to physico-chemical measurements and collection of samples by using a submersible

pump or bailer. For microbial sampling, the bailer was disinfected with ethanol and

rinsed with distilled water. For boreholes with continuous recharge, a 10 minute

minimum purge time was used before sampling.


To preserve the samples for sulphide analysis, zinc acetate was added to precipitate

the sulphide as zinc sulphide. Sodium hydroxide was then added to a pH > 9

according to sampling and storage for sulphide analysis stated in APHA method

4500-S2-

A (Eaton et al. 2005).

Figure 4 Location of data collection sites discussed in relation to Fe transport

processes near the Poona Creek estuary mouth (triangles indicate surface

water sites and circles, groundwater sites), drainage system and

topography.

Analytical methods

Alkalinity was determined by titration with hydrochloric acid within 24 hrs of

collection. Sulphide concentrations were determined by spectrophotometry using the

colorimetric methylene blue method 4500-S2-

D (Eaton et al. 2005). A Pharmacia

LKB spectrophotometer (Novaspec II) with a 1 cm path length was used for these

analyses. Total and ferrous iron concentrations were measured using an AQ2 Seal

discrete analyser. Ferrous iron concentrations were determined using AQ2 Method

No: UKAS-504-A Rev.2, a UK Blue Book Method based on the phenanthroline

method for determination of Fe2+

from American Public Health Association (2005)

with a MDL of 0.04 mg/L. Phenanthroline chelates ferrous iron at an acidic pH to

form an orange-red complex which can be measured spectrophotometrically at 505

nm on an AQ2 discrete analyser. Total Fe concentrations were determined using

AQ2 Method No: UKAS-507-A Rev.2. This method is the same as used for


determining ferrous iron except Fe3+

is reduced to Fe2+

using hydroxylamine

hydrochloride prior to reaction with phenanthroline. Fe3+

concentrations were

calculated by difference using the AQ2 measurements for total and ferrous iron.

Samples were also analysed for DOC using a Shimadzu TOC-5000A Analyzer.

The Fe3+

portion of the total Fe concentration is assumed to be in the form of either

nano-oxyhydroxide particles or colloidal organically bound Fe. Although

percentages and forms of suspended iron in surface waters are variable (see Allard et

al. (2004)), many studies, e.g. Boyle et al. (1977) and Björkvald et al. (2008), have

found colloidal organically bound Fe3+

to be the dominant form of ‗dissolved‘ iron in

areas with high DOC input. Lofts et al. (2008) hypothesise that the degree of binding

of Fe3+

to aquatic DOM may be related to the total concentration of DOM and found

that organic complexation of Fe3+

in freshwaters can be modelled as a function of

DOC concentration without the need to invoke distinct organic ligands. In addition,

speciation modelling of Fe in soil waters in the Poona catchment suggest that more

than 95% of Fe is bound to dissolved organic matter (Löhr 2010). This, in addition to

high DOC concentrations at these sites would seem to suggest that most of the

colloidal Fe3+

is organically-complexed. Further analysis of surface and ground

waters is required to confirm this. Although these Fe3+

organic complexes and Fe3+

oxyhydroxides are in fact colloidal and not truly dissolved, they will be treated here

as ‗dissolved‘ loads that can potentially be transported within the catchment and to

marine waters.

15NDIN,

13CDIC and

34SSO4 isotope samples were analysed by the Stable Isotope

Laboratory at the Institute of Geological and Nuclear Sciences (GNS) in New

Zealand. All δ34

SSO4 results are averages of duplicates (n=2) and are reported with

respect to Vienna Canyon Diablo Troilite (VCDT), normalized to internal standards

with reported values of -3.2‰, +3.3‰ and +8.6‰ respectively. The analytical

precision for the GNS instrument was 0.6‰ for δ34

SSO4. δ13

CDIC results are reported

with respect to the Vienna Pee Dee Formation Belemnitella Americana (VPDB) and

results are reported as per mil ‰ VPDB (Clark et al. 1997) and normalized to an

internal standard of -22.7‰. The analytical precision for δ13

CDIC measurements was

0.2‰. Analyses for δ15

NDIN for this study were for total dissolved inorganic nitrogen

(DIN). The 15


NN2 = 0‰ AIR and

results are reported as per mil (‰) AIR and were normalized to an internal standard


of 1.8 ‰. The analytical precision for these measurements was 0.3‰ (Valerie

Claymore, pers. comm. 2008).

Interpretation methods

Graphical techniques and hierarchical cluster analysis (HCA) are employed to assist

in characterising water in relation to Fe, S and C. Stable environmental isotopic data

were used to investigate dissolved inorganic carbon (National Health and Medical

Research Council (NHMRC)) and sulphate sources and their ability to indicate

processes affecting the form and potential transport of Fe within these catchments.

Known trends in addition to typical isotope ratio-ranges for specific nutrients from

the scientific literature are used to determine sources and processes.

δ13CDIC

There are many complex processes associated with the carbon cycle that can alter

natural water 13

CDIC composition. The coastal region under study primarily contains

siliceous sediments with little to no carbonate material within the shallow

groundwater aquifers and drainage system alluvium. Within such lithologies DIC

does not evolve substantially beyond conditions established in the soil (Clark et al.

1997). As a consequence, processes affecting 13

CDIC composition throughout most of

the study area are related to decay of plants at the surface and DOC. Microbiological

processes such as iron- and sulphate- reduction lead to oxidation of DOC, and the

addition of this low ratio HCO3 to the DIC pool results in an overall depletion in

13CDIC. Microbes prefer lighter carbon isotopes leaving heavier isotopes in remaining

DOC. DOC can be flushed to ground and surface waters by rainfall and also

contributed to aquifers by buried peat layers. Literature ranges from Craig (1954),

Sackett et al. (1966), Cerling (1984), and Clark and Fritz (1997) are used to assist in

the interpretation of sources of DIC.

δ15NDIN

Nitrogen is a biologically active element and participates in a multitude of reactions

important to life, and can affect water quality. Isotope fractionation between various

N-bearing compounds such as organic N, N2, NH4+ and NO3

-, provides the basis for

15N as a tool in isotope hydrogeology. However, it should be noted that nitrate

fractionation is difficult to estimate and using δ15

N to trace origins of nitrate is

considered to be a semi-quantitative or qualitative technique (Macko et al. 1994).


The 15


NN2 = 0 ‰ AIR and

results are reported as per mil (‰) AIR (Clark et al. 1997).

15N isotopes provide information about sources of nitrates and the processes that

these nitrates have undergone. Although these 15

N isotopic data are for total

dissolved inorganic nitrogen we will assume that the inorganic nitrogen pool is

primarily in the form of nitrate. Nitrate concentrations in many aquifers increase as a

result of atmospheric nitrogen deposition typically as HNO3 in rainfall, synthetic

fertilizers (nitrate, ammonium, urea); manure, sewage, or soil nitrate; oxidation of

organic N (nitrification). In addition, nitrate concentrations in groundwater and

surface water may be decreased via denitrification, a microbially mediated process in

which heavier 15

N is preferentially retained in the non-reduced remaining nitrate.

Therefore, aqueous nitrate δ15

N values increase as total nitrate concentrations

decrease where this process occurs (Clark et al. 1997).

At the soil surface, organic matter δ15

N

values are generally similar to, or slightly

greater than, values for plant litter, and increase to about +8 ± 2‰ at a depth of 20-40

cm (Nadelhoffer et al. 1994). A survey by Fry (1991) of forests and other non-

cultivated ecosystems at a number of sites across North America illustrates the

overall pattern of progressive 15

N enrichment of plant litter, organic soil and mineral

soils in forests. Literature ranges from Hoering (1955), Kreitler (1979), Letolle

(1980), Aravena et al. (1992b) and Clark and Fritz (1997) are used to assist in the

interpretation of sources of DIN.

δ34SSO4

34SSO4 isotopes provide information about sources of sulphates and the

biogeochemical processes these sulphates have undergone. Sulphate concentrations

in many aquifers increase due to the addition of sea spray, atmospheric sulphur

deposition, dissolution of evaporites (gypsum, anhydrite), oxidation of pyrite (e.g.

lowering of water table exposing acid sulphate soils), sulphate from landfills or from

industrial sources. Sulphate concentrations in groundwater and surface water can be

decreased due to bacterial sulphate reduction, i.e. the reduction of SO42-

to H2S. This

results in an increase in the heavier isotope, δ34

SSO4, which is preferentially retained,

i.e. bacterial sulphate reduction causes trends of increasing δ34

SSO4 values with

decreasing sulphate concentrations (Clark et al. 1997). Literature ranges from Nriagu


et al. (1978), Chukhrov et al. (1975) and Fry (1988) are used to determine sources of

sulphate.

Carbonate speciation

A carbonate speciation tool, GWCarb v1.0 (Taulis 2010), was used to determine the

proportions of dissolved inorganic carbonate species at the sites of interest.

Alkalinity titrations only provide the bicarbonate concentration for the sites here (as

they are all slightly acidic). Carbonate speciation also calculates the concentration of

CO2 for these samples which is important when considering sources of DIC and

relating these sources to δ13

CDIC signatures.

Results and Discussion

Fe in solution, whether in organically-chelated form or dissolved Fe2+

, is

considerably more mobile than particulate ferric oxyhydroxides or other Fe

complexes and consequently is transported more easily through ground and surface

waters. Factors such as redox, pH and DO, presence of DOC (for organic

complexation of Fe2+

and as a substrate for microbial reduction), FeRB and FeOB,

and indirectly SRB and SOB, can all affect the form of Fe in natural waters. Sites

TCA, P6 and P5 are discussed here in relation to these characteristics and associated

processes. All three sites had appreciable levels of ferrous and ferric iron. These

environments have hydrological and morphological features which are common

within drainage systems and shallow aquifers along the coast of southeast

Queensland. In addition, processes affecting Fe transport and concentrations within

the supratidal flats adjacent to Poona Creek estuary and estuarine surface water sites

PB, TCB and PCM are discussed in the context of transport to marine waters.

Physico-chemical, Fe species, sulphide, bicarbonate and DOC concentrations, 13

CDIC

and 34

SSO4 isotope ratios, and cultivable bacterial count numbers for the sites

described below are listed in Tables 2 and 3. Data collection sites are shown in

Figures 2 and 4 and transect groundwater sites are shown in Figure 3.

General Characterisation

Physicochemical parameters

Overall redox conditions are oxidising in surface waters and unsaturated zone

groundwaters (C3, C4, C5). The exception is TCA1, a shallow intermittent stream


located ca. 10 km inland from the coast, where reducing conditions exist near the

bottom of the stream. Oxidising conditions in groundwaters were mainly due to

saline/fresh water mixing at sites close to the Poona Creek estuary (P11-P14, P5 and

possibly B1); otherwise conditions were reducing (Eh < 0 mV).

Groundwater DO concentrations were generally low, the exceptions being again at

P5 and in the unsaturated groundwaters at C4 and C5. Comparatively free flowing

surface waters (LRB, PC9, PC10) overall had higher DO concentrations than surface

waters at water points (ponds excavated for forestry operations; WP11, WP12,

WP16). The highest DO concentration of 8.0 mg/L was measured at PCM, a surface

water site located at the estuary mouth and typical of marine waters. Estuarine

surface water samples at TCB and PB had concentrations of 3.4 and 4.8 mg/L,

respectively, reflecting marine and fresh water mixing. Lowest DO concentrations

for surface waters were measured at TCA at 0.1 and 0.2 mg/L near the bottom

sediments (TCA1) and at 0.4m above bottom (TCA2) in the water column

respectively (see Table 3).

Although DOC was not measured for 12 of the 30 sites investigated in this study, of

those measured, overall DOC concentrations in surface waters (10.0–30.7 mg/L) fall

within the general range for surface water draining swamps and wetlands where the

major DOC component is humic and fulvic acids (Drever 2002). Surface water

concentrations were higher than for groundwaters (2.7 – 10.0 mg/L) where most

organic material is often retained in soils and sediments above the watertable (Drever

2002). However, a number of groundwaters were still above the typical range of 0 –

3 mg/L (Drever 2002). P2 and P5 at 10.0 mg/L and 40.3 mg/L, respectively, are

located close to the supratidal area where swamp-like conditions exist, whereas the

lithological profile at fresh alluvial aquifer transect waters P4, P6 and P8 includes a

peat layer at depth which contributes to DOC concentrations.


Table 2 Physico-chemical, ionic and isotopic data for all sites excluding P5, P6, P11-P14, TCA, TCB and PCM

SITE ID pH Eh mV

DO mg/L

TDI mg/L

Fe2+

mg/L

Fe3+

mg/L

δ13

C ‰ VPDB

DOC mg/L

HCO3-

mg/L δ

15N

‰ AIR NO3

-

(mg/L) δ

34S

‰ VCDT H2S

d

mg/L

B1 4.2 +210 1.5 293 6.7 1.6 -19.7 3.7 0 1.4 <MDLb 14.1 1.8

P2 5.1 -50 1.1 526 14.0 2.0 -20.9 10.0 4 1.1 0.6 18.8 1.1

P4 4.9 -70 0.1 173 3.5 0.4 -19.2 7.2 32 2.2 3.7 20.1 1.8

P8 5.6 -87 0.1 354 5.9 0.8 -17.5 8.3 79 5.8 0.3 10.7 0.7

134B 5.0 -39 —a 218 0.7 4.2 -18.3 — 6 2.5 <MDL 28.3 —

204B 6.4 -62 0.5 814 6.3 17.6 — — 49 — <MDL -1.1 —

PCP 7.5 +183 — 404 0.2 0.6 -14.3 — 137 2.4 0.7 26.4 <MDL

R+E 4.4 -9 — 1216 0.3 1.0 -16.3 — 34 22.4 8.3 15.0 <MDL

RF 5.3 +1.1 — 1113 6.0 3.7 -18.4 2.7 7 -1.2 <MDL 17.9 <MDL

C2d 6.0 +113 0.6 563 0.9 0.0 -19.0 5.2 138 1.3 <MDL 17.9 0.5

C3d 3.1 +299 1.0 2457 3.7 0.0 -18.0 3.1 0 -0.7 <MDL 18.9 0.1

C4 2.7 +420 5.0 2209 0.1 0.0 -19.2 — 0 1.2 0.1 11.1 0.4

C5 4.2 +261 4.0 6075 3.9 0.0 — — 0 — <MDL — —

LRB 6.1 +253 2.3 89 1.7 0.0 -17.3 14.0 11 3.1 3.8 19.5 0.1

PC9 6.4 +208 2.3 62 2.3 0.4 -17.3 13.5 10 3.0 0.6 15.2 0.1

PC10 7.2 +250 3.0 73 1.6 0.0 -18.6 21.1 10 3.2 <MDL 10.4 0.1

WP11 5.2 +267 0.6 78 1.3 0.4 -19.5 16.9 1 1.4 <MDL 9.9 0.1

WP12 6.1 +173 0.4 81 1.3 0.1 -18.4 19.4 7 4.0 1.2 8.3 0.1

WP31 6.9 +249 1.6 93 1.7 0.2 -16.7 25.6 18 3.6 <MDL <MDL — Notes: a) The dash indicates that there is not result for this analyte

b) <MDL = below minimum detection limits

c) DO = Dissolved Oxygen, TDI = Total Dissolved Ions, DOC = Dissolved Organic Carbon

d) Analytical method measured S2-

. This concentration has been recalculated based on the assumption that all S2-

present in the sample is in the form of dissolved hydrogen sulphide gas (H2S).


Table 3 Physico-chemical, ionic and isotopic data for P5, P6, P11-P14, TCA, TCB and PCM during dry conditions and P5, P6, PB

and PCM during a high rainfall event

SITE ID P5 P5e P6 P6e TCA1d TCA2

d P11 P12 P13 P14 PB PBe PCM PCMe TCB

pH 5.6 5.3 4.9 5.2 5.3 5.3 7 7.2 6.3 6.8 6.7 5.5 7.8 5.5 6.5

Eh (mV) 52 -35 -50 8 -76 22 36 46 74 55 100 167 159 267 102

DO (mg/L) 4.2 — 0.1 — 0.1 0.2 0.7 0.3 0.8 1.9 4.8 — 8 — 3.4

TDIg (mg/L) 1209 6890 131 324 422 396 56622 32037 51491 49311 19433 38 40577 3569 26136

Fe2+ (mg/L) 38.4 31.4f 5.7 10.6f 29.8 — 0.7 2.4 5.7 5.6 0.4 2.4f 0.1 0.3f 0.2

Fe3+ (mg/L) 17.4 — 0.6 — 9.1 — 0.7 0.7 0.9 6.6 0.1 — 0 — 0

δ13C (‰ VPDB) -17.7 — -20 — -19.4 — — — — — -11 — -1.4 — -11.5

DOC (mg/L) 40.3 — 7.8 — 22.1 — — — — — 10 — — — 26

HCO3- (mg/L) 13 132 13 166 4 — 535 336 473 282 37 11 124 4 96

δ15N (‰ AIR) -1.4 — 6.8 — 7.4 — — — — — —h — —h — —h

NO3- (mg/L) <MDL <MDL 1.8 <MDL <MDL — <MDL <MDL <MDL <MDL 0.3 — <MDL <MDL <MDL

δ34

S (‰ VCDT) 19.3 — 19 — 32.6 — — —. — — 21.2 — 20.1 — 21.3

H2S

c 0.9 — 4.3 — 0.3 — 1.6 <MDL

b <MDL <MDL <MDL — <MDL — <MDL

FeOBg (CFU/mL) 102 — 104 — — — — — — — — — — — —

FeRBg (CFU/mL) 104 — 108 — — — — — — — — — — — —

SOBg (CFU/mL) 105 — 103 — — — — — — — — — — — —

SRBg (CFU/mL) 103 — 103 — — — — — — — — — — — —

a) The dash indicates that there is not result for this analyte

b) <MDL = below minimum detection limits

c) Analytical method measured S2-

. This concentration has been recalculated based on assumption that S2-

present in the sample was in the form of dissolved hydrogen sulphide gas (H2S).

d) TCA1 sample was taken at the bottom of the water column. TCA2 was taken at approximately 0.4m from the bottom of the stream.

e) Subscript e = sample collected during high rainfall event.

f) Only total Fe measured (analysis of high rainfall event samples). Samples for TCA and TCB were not taken during high rainfall event.

g) DO = Dissolved Oxygen, TDI = Total Dissolved Ions, DOC = Dissolved Organic Carbon, FeOB = Fe oxidising bacteria, FeRB = Fe reducing bacteria, SOB = Sulphur oxidising bacteria,

SRB = Sulphate reducing bacteria

h) Insufficient volume to obtain δ15

N


Iron

Tables 2 and 3 list ferrous and ferric iron concentrations for all sites. All surface

waters had total Fe concentrations below 3 mg/L with the exception of TCA at 38.9

mg/L. Groundwater concentrations were variable. Monitoring well P5 had the

highest concentration at 55.8 mg/L, P2 was the second highest with 16.0 mg/L and

B1, P4, P6, P8 all had total Fe concentrations between 3 and 9 mg/L. Unsaturated

groundwaters C3 and C4 had Fe < 1 mg/L while coastal semi-confined groundwaters

134B, 204B and RF have much higher concentrations at 4.9, 24.0 and 7.3 mg/L

respectively.

A plot of Fe2+

/Fetotal ratios versus Eh is shown in Figure 5. The plot shows an overall

grouping of samples according to hydrological type. Most sites can be broadly

grouped into either coastal unconfined to semi-confined fresh and brackish

groundwaters, confined and semi-confined fresh transect groundwaters, supratidal

and coastal groundwaters, estuarine surface waters, fresh surface waters and

unsaturated groundwaters. Again, the surface water exception was TCA with very

similar values to the fresh transect groundwaters.

Higher concentrations of ferric iron at R+E, RF and 204B (1.0, 3.7 and 17.6 mg/L,

respectively) were most likely a result of saline intrusion where changes in pH, DO,

Eh resulted in oxidation of ferrous iron within these aquifers, while subsequent

complexation with organic matter maintains the Fe3+

in suspended colloidal form.

Higher proportions of Fe2+

within the transect groundwaters P2, P4, P6, and P8 were

due to reducing conditions and low DO at these sites.

Cluster Analysis

Figure 6 shows the hierarchical cluster analysis (HCA) dendrogram including all

sites for variables, Fe2+

, Fe, Eh and pH. Table 4 shows the tabulated results of the

cluster analysis using a cut-off of 2.5 including ranges of Fe2+

, Fe, Eh and pH for

each group. Cluster analysis revealed three unique sites, 204B, P5 and TCA.

Although P5 (Group 2A) and TCA (Group 2B) were still grouped at a cut-off of 2.5

and there are many similar processes occurring at these sites, they will be treated

separately as they are located in very different environments; TCA is a fresh surface

water site and P5 an estuarine groundwater site. In addition to P6, P5, TCA, P11-

P14, PCM and TCB are discussed in detail in relation to processes affecting Fe, C


and S forms and potential Fe transport to the marine environment in the following

section. Overall, however, sites are grouped as expected with fresh surface waters,

unsaturated brackish groundwaters, fresh transect groundwaters, and evaporated

estuarine groundwaters grouped together.

Group 1 consists solely of Poona village residential groundwater 204B. This

borehole has been seawater-intruded possibly due to the over-exploitation of this

small local aquifer. Fe oxidising bacteria were evident when this sample was

collected. The water was reddish-brown in colour with a brown slime build up on the

pipe and fixtures. This biofouling subsequently clogged the pump and collection of

further samples was not possible. A negative δ34

SSO4 value at this site indicated

sulphur oxidation as discussed earlier in this paper. Sulphur and iron oxidising

bacteria are commonly found together. The origin of these Fe-oxidising bacteria is

unknown. However, the oxidising conditions provided by seawater-intrusion to the

site may well maintain and assist in the development of these bacteria. This site also

has a very high Fe3+

concentration (17.6mg/L) indicating it is likely that DOC is

available for Fe3+

complexation.

Figure 5 The ratio of ferrous iron to total iron versus redox potential Eh

Group 3 consist of unsaturated zone groundwaters (C3, C4, C5), a seawater-intruded

groundwater (B1) and a surface water with a significant groundwater contribution

B1

P2

P4

P5

P6P8

P11

P12

P13

P14

134B

204BR+E

RF

C3dC5LRB

PB PC9

PC10

TCA

TCB

WP11

WP12 WP31

0.00

0.20

0.40

0.60

0.80

1.00

1.20

-120 -70 -20 30 80 130 180 230 280 330

Fe(I

I)/F

eto

tal

Eh (mV)

Fe(II)/Fetotal vs Eh

Groundwaters

Surface Waters

Transect confined and semi-confined fresh

groundwaters

Supratidal and coastal estuarine groundwaters

Fresh surface waters

Unsaturated zone brackish groundwaters

Estuarine surfacewaters

Coastal unconfined to semi-confined fresh and brackish groundwaters


(WP11). This group has variable Fe2+

, overall low Fe, high positive Eh and acidic to

slightly acidic pH (2.7-5.2). The unsaturated zone groundwaters do not appear to

have any hydrological interaction with marine waters or the underlying aquifer

(Larsen et al. 2011) so it is unlikely they will contribute Fe to the Strait, whereas as it

is possible that B1 with quite high Fe2+

(6.7 mg/L) and Fe3+

(1.6 mg/L) and being

located 100 m from the Strait could make some contribution to Fe loads via

organically complexed Fe3+

. It is unclear what level of interaction occurs between

WP11 and the Poona Creek estuary. Although it is located closer to the estuary

mouth than PB – an estuarine surface water site – total dissolved ion (TDI) and major

ion concentrations measurements indicate fresh waters and only appear to have

seasonal variation related to increased groundwater contribution (Larsen 2012).

Figure 6 Hierarchical cluster analysis results for Fe

2+, Fe, pH and Eh. Sites

discussed in relation to micro-processes are shaded.

Group 4 consists primarily of fresh alluvial groundwaters, P2, P4, P6 and P8. These

waters have appreciable levels of Fe2+

and lower but still significant levels of Fe3+

.

Due to their location adjacent to the Poona Creek estuary, and occasional tidal

intrusion during highest astronomical tides or storm surges, it is possible these waters

contribute to Fe loads being transported to the Strait. Although Fe concentrations are

comparatively low at R+E, there is interaction between waters at this site and the

121726 9 7 8102511131914201523 2 3 5 62124 129182728 41622

0123456789

Sa

mp

le In

de

x

Dissimilarity

Dendrogram: pH, Eh, Fe(II), Fe(III)

204B TCA

P5 C4 C3

WP11 C5 B1

RE

134B P8 P6 P4 P2 PCP PCM

WP31 PC10

WP12

PC9 LRB

RF P14 P12 P11

P13 C2d TCB PB


marine waters of the strait so it is possible this site could also contribute to Fe loads

entering the strait. It is unclear whether there is interaction between the unconfined

waters at 134B and estuarine waters but it seems unlikely based on the low major ion

concentrations at this site. Processes occurring at P6 are described in more detail in

the following section.

Group 5 primarily consists of fresh surface waters. All of these waters have low Fe2+

,

very low if any Fe, positive Eh and slightly acidic to circum-neutral pH. In addition,

during times of low rainfall these sites are hydrologically disconnected from the

Strait. These waters would appear to contribute little, if any, iron to the marine

environment under steady-state conditions. PCP located in a well-confined beach

ridge sand aquifer in Poona Village (Larsen et al. 2011) had very low concentrations

of Fe and does not appear to interact with estuarine waters. PCM, an estuarine

surface water site is discussed in more detail in the following section.

Group 6 has variable concentrations of Fe2+

and Fe, positive Eh ranging from 36 to

113 mV and circum-neutral pH values. PB and TCB are both estuarine surface waters

that have small Fe2+

concentrations and 0.1mg/L of Fe3+

at PB only. P11-P14 located

in the supratidal flats between P5 and the Poona Creek estuary have appreciable

levels of Fe2+

and Fe. These loads could be transported to the strait due to tidal flux

through groundwater seepage to estuarine waters. These sites are discussed further in

relation to P5 in the following section.

C2d is located in a well-confined aquifer over 9 km from the strait and has very low

levels of Fe. RF, however, has similar hydrological characteristics to R+E and could

well contribute Fe loads to the Strait waters.

Carbon

Bicarbonate levels were below MDL (1 mg/L) for semi-confined groundwater B1,

and unsaturated zone groundwaters C3 andC4 indicating that the DIC at these sites

consists mainly of soil CO2. Although there is a mixture of C3 and C4 plants at these

sites, δ13

CDIC values at -19.7, -18.0 and -19.0‰ VPDB, respectively, are closer to the

range for C3 (-26.0 to -20‰ VPDB) than C4 plants (-12 to -6.0‰ VPDB) (Cerling

1984) suggesting that DIC in these waters is dominated by soil-respired CO2 from C3

plants.


Table 4 HCA Groups using Fe2+

, Fe3+

, Eh and pH

Aquifer/ Surface Water Type

Group No. Sites Fe2+ Fe3+ Eh pH

Residential Bore 1 204B 6.3 17.6 -62 6.4

Fresh surface water 2A TCA 32.6 9.1 -76 5.5

Estuarine groundwater 2B P5 38.4 17.4 52 5.6

Vadose zone groundwaters Saline-intruded GW SW with GW contribution

3 C4, C5, C3 B1 WP11

0.1 – 6.7 0.0 – 1.6 210 – 420 2.7 – 5.2

Coastal GWs Fresh alluvial GWs

4 134B, RE P8, P6, P4, P2

0.3 – 14.0 0.4 – 4.2 -87 – -9 4.1 – 5.6

Fresh beach ridge aquifer Estuarine SW Fresh SWs

5 PCP PCM WP12, PC9, WP31, PC10, LRB

0.0 – 2.3 0.0 – 0.6 159 – 253 5.4 – 7.5

Evaporated estuarine GWs Coastal GW Fresh confined GW Estuarine SWs

6

P11, P12, P13, P14 RF C2d TCB, PB

0.2 – 6.0 0.0 – 6.6 36 – 113 6.0 – 7.2

Note: GW = Groundwater, SW = Surface water


PCP, at -14.3‰ VPDB, is enriched relative to all other fresh ground and surface

water sites and this is most likely due a marine carbonate shell source (HCO3- = 137

mg/L) within the beach ridge sands contributing to the DIC pool where this site is

located. According to Craig (1954), marine carbonate shell typically has an average

of 1.5 to 2.0‰. Estuarine sites PB and TCB (-11.0 and -11.5‰ VPDB) are enriched

compared to all other samples due to the mixing of marine DIC (marine DIC = -1 to

+2‰ VPDB (Sackett 1966)) with fresher upstream waters depleted in 13

CDIC such as

WP11 (-19.5‰ VPDB) or WP12 (-18.4‰ VPDB).

All fresh surface water sites are substantially depleted (-19.5 to -16.7‰ VPDB)

relative to marine DIC. This may be due to dilution of the DIC pool by low ratio

bicarbonate; a by-product of bacterial reduction of iron and sulphate, as mentioned

previously. It is unlikely, however, that this process is occurring where the water

column is oxygenated (DO = 0.4 to 3.0 mg/L and Eh = 62 to 93 mV) and flowing

freely such as at PC9 or PC10 (see Tables 1 and 2). Clark and Fritz (1997) give a

range of -17‰ to +5‰ for freshwater carbonates. Although the values for PC9,

PC10, WP12 and WP31 (-18.6 to -16.7‰ VPDB) fall slightly below this range, this

is the most likely the dominant source of DIC at these sites. Stable water isotopes for

these sites (δ18

O=-5.0 to -4.5‰ VSMOW, δ2H=-29.5 to-26.5‰ VSMOW) were

depleted in comparison with coastal zone shallow groundwaters indicating upstream

recharge (Larsen et al. 2011). There is also a trend of increasing bicarbonate with

distance inland (Larsen et al. 2011). These two factors strongly suggest an inland

source of freshwater HCO3-. However, stable water isotopic ratios at WP11 (δ

18O=-

3.9‰ VSMOW, δ2H=-16.7‰ VSMOW) were strongly elevated by comparison and

similar to those for semi-confined coastal groundwater values, suggesting a

significant groundwater input. This would explain the greater depletion in 13

CDIC at

WP11 (19.4‰ VPDB), a still pool excavated for forestry practices in the coastal

plain. Groundwater input to this surface water could very well be depleted due to

microbial reduction depleting 13

C in the DIC pool and/or soil CO2.

Groundwaters P2, P4, and P6 are all significantly depleted at -20.9, -19.2 and -

20.0‰ VPDB, respectively. This is most likely due to microbial-related processes

mentioned above and discussed in more detail in the following section.

Groundwaters, P5, P8 and R+E were comparatively slightly elevated at -17.7, -17.5

and -16.3‰ VPDB, respectively, which is most likely due to the presence of a minor


seawater DIC contribution related to tidal flux slightly enriching a 13

C in a DIC pool

predominantly sourced from organic C.

Nitrogen

Nitrate values were below the minimum detection limit for nearly all samples. Only

four of the 29 samples analysed, only five had nitrate concentrations > 1 mg/L (1.2 –

8.3 mg/L), six had nitrate concentrations > minimum detection limit (MDL=0.05

mg/L) and less than 1.0 mg/L, and 18 had nitrate concentrations < MDL. These low

nitrate concentrations indicate it is unlikely δ15

NDIN measurements of these samples

were related to the input of synthetic fertilizers, although many samples are in the

range given for synthetic fertilizers of -4.0 to +4.0‰ AIR (Aravena et al. 1992b). In

addition, forestry practices no longer include N treatments so, except for sites located

within residential areas where synthetic fertilizers may be used to fertilize gardens or

lawn, N is most like sourced from elsewhere such as from soil organic nitrogen, soil

N2 or rainfall. Soil organic N has a range of ca. +3 to +8‰ AIR (Heaton 1986) or +2

to +10‰ AIR according to Clark and Fritz (1997), soil N2 a range of -3 to +13‰

AIR (Letolle 1980) and a rainfall (in the form of HNO3) a range of ca. 0 and +4‰

AIR (Hoering 1955).

R+E, a residential bore in Poona village, had the highest δ15

NDIN (22.4‰ AIR) and

nitrate value (8.3 mg/L) with nitrate most likely sourced from either organic

fertilizers (manure) or septic tank effluent. Kreitler (1979) gives a range of +10 to

+22‰ AIR for manure and septic tank effluent. Transect boreholes P6 (6.8‰ AIR)

and P8 (5.8‰ AIR) had δ15

NDIN indicative of a soil organic N source as does TCA

(7.4‰ AIR). There was quite a lot of vegetation in, and close to, surface waters and

streambed sediments at TCA and bores P6 and P8 both have a peat layer within their

screened profiles, both likely sources of organic N in these waters. It is also possible,

however, that denitrification has resulted in the enrichment of rainfall-sourced N

15NDIN as conditions are reducing at all three sites with Eh values of and -50, -87 mV

and -76mV for P6, P8 and TCA respectively.

Groundwaters, B1, P2, P4, 134B, PCP, C2d, C3, C4 and RF all have ratios in the

range 0 to +3‰ AIR indicating rainfall- or soil- sourced N2. Soil-sourced N2 is more

than likely within the unsaturated zone groundwater C2d, C3 and C4 where nitrate

values are below MDL or negligible. As PCP is located in the residential area,


measurable nitrate (0.7 mg/L) may indicate synthetic fertilizers. A below MDL

concentration at 134B makes synthetic fertilizer source unlikely even though it is

located in Poona village underneath well tended lawns and gardens. Nitrate

concentrations and location make synthetic fertilizer a highly unlikely source at B1

and RF. Location also makes it high unlikely that P2 and P4 have a synthetic

fertilizer source. However, it is possible that there is an organic N source from a peat

layer at depth at these two monitoring wells. Hoering (1955) found peat and coal

samples generally had δ15

NDIN in the range -2.8 to 1.9‰ AIR.

There was no result for tidally-influenced groundwaters PCM, PB and TCB as

insufficient volume was provided for δ15

N analysis. 250 mL samples yielded < 0.1%

nitrogen which was too small for the δ15

N analytical system (Valerie Claymore, pers.

comm., 2009). Seawater generally contains approximately 0.5 ppm nitrogen

(dissolved inorganic nitrogen compounds such as nitrate and ammonium without N2).

However, this varies with depth and is much lower at the surface, being

approximately 0.1 µg/L (Millero 1996; Lenntech B.V. 2011).

All remaining surface water sites except WP11 had values between 3 to 4‰

indicating a rainfall N and/or soil organic N from the sediments along the beds of

these streams. WP11 (1.4‰ AIR) has interaction with ground and soil waters (Larsen

2012) and this potentially results in the input of soil N2. Overall, these results are

ambiguous and a dual isotope approach utilising δ18

ONO3- in addition to δ15

N analyses

would be recommended for future work. Further analysis of nitrogen species such as

NH4+ and organic N would also be helpful. However, the data here do indicate that

sources of N are generally non-anthropogenic.

Sulphur Species

Sulphate concentrations were highly correlated with TDI and were sourced primarily

from atmospheric deposition of marine sulphate and direct intrusion of marine

waters. Atmospheric sulphate produced by fossil fuel combustion shows δ34

SSO4

values ranging from +2 to +9‰ VCDT (Nriagu et al. 1978). Due to the location of

the study area and winds originating predominantly from the ocean, such a source is

unlikely and this is reflected in the data.

P2 and P4 δ34

SSO4 values, at 18.8‰ VCDT and 20.1‰ VCDT, respectively, indicate

a coastal rainfall and/or seaspray source. Coastal rainfall and seaspray are generally


in the range +12 to +18‰ VCDT and values can be higher (Chukhrov et al. 1975)

the closer the site is to the coast. These sites are located only 1.5 km from the mouth

of Poona Creek so values could reasonably be expected to be at the top end of this

range. The extra enrichment may be due to the effects of sulphate reduction. Sulphate

reducing bacteria enrich the remaining sulphate by reducing the lighter sulphur

isotopes to H2S. Enrichments due to this process are highly variable. H2S values were

P2 and P4 were 1.1 and 1.8 mg/L, respectively and there was also a strong odour of

H2S at these sites during data collection.

The elevated values at PCP (26.4‰ VCDT) and 134B (28.3‰ VCDT) indicate that

sulphate reducing bacteria are also present at these sites although no odour was

detected at the time of collection. Sulphate reduction at 134B is supported by the

reducing conditions (-39 mV) measured at the site and communication from a nearby

resident who mentioned that she often smelt rotten egg gas when the residents at

134B were watering their lawn. Unsaturated groundwater C4 (11.1‰ VCDT) and

fresh surface water sites PC9 (15.2‰ VCDT) and PC10 (10.4‰ VCDT) appear to

have varying contributions of rainfall/seaspray- and soil- sourced sulphate. The

lowest value at saline-intruded residential groundwater sites 204B of -1.1‰ VCDT is

most likely due to the presence of sulphur oxidising bacteria (SOB). Bacteria oxidise

the lighter isotopes of sulphur to form sulphate and consequently the sulphate pool is

depleted. This is supported by an SO4/Cl ratio of 0.25 (seawater has a typical SO4/Cl

ratio of 0.14) and the fact that biofilms from FeOB were also observed at this site.

FeOB and SOB are often found together in ground and surface waters. Oxidation by

aerobic oxidisers can lead to a depletion in 32

S up to 20‰ VCDT (Fry et al. 1988).

Processes and environments

TCA, P6 and P5 are all discussed here in relation to micro-processes involving Fe, S

and C. All three sites had unique physicochemical and morphological characteristics

and as such were considered as micro-environments within the context of broader-

scale regional processes. In addition, processes occurring within the supratidal flats

adjacent to Poona Creek estuary are discussed in relation to P5.

TCA (Tuan Creek A) is located in a shallow (depth generally less than 1 m) stream

ca. 9 km inland from the mouth of Tuan Creek estuary or 16.4 km adopted middle

thread distance (AMTD) along the creek channel from the estuary mouth. Much of


the adjacent terrain is made up of a duricrusted old land surface with dominant facies

being ferricrete and silcrete overlying weathered sandstone bedrock (Wang et al.

2008; Larsen et al. 2011). Immediately adjacent to the stream is a native vegetation

riparian zone with pine plantation compartments at ca. 20 m distance, although some

smaller pine trees were located quite close to the stream. Unlike surface waters

sampled in the Poona catchment, data for this site indicated some groundwater

baseflow contribution (Larsen 2012). Table 2 lists physico-chemical data at the

bottom and 0.4m from the bottom of the water column at TCA. Figure 7 shows the

sites discussed here on an Eh vs pH diagram and Figure 8 shows a conceptual

process model for TCA.

TCA had a total Fe concentration of 38.9 mg/L. DO is slightly lower and Eh values

go from oxidising (+22 mV) to reducing (-76 mV) with depth indicating an oxic-

anoxic interface in the water column. A redox gradient exists with reducing

conditions close to and in the hyporheic zone and increasingly oxidising conditions

closer to the water table. Water in flowing freshwater streams at near-neutral pH will

generally not contain significant concentrations of uncomplexed dissolved Fe2+

. Iron

in such waters will normally occur as either particulate ferric hydroxide or chelated

as some form of organic complex (Hem 1992). However, in lakes, ponds and

reservoirs where stratified conditions exist, water at and near the bottom may be

depleted in oxygen and at low Eh. In waters of this type, Fe2+

can be retained in

solution to levels of many mg/L (Hem 1992). Fe3+

reduction occurs between ca. -100

and +100 mV while sulphate reduction will generally occur with an Eh between ca. -

100 and -200 mV. Methane production will occur at Eh < -200 mV (Langmuir 1997).

Pine needles and other vegetation within stream bottom sediments of the stream

provide ample DOC (22.05 mg/L) for organic complexation of Fe. As inorganic Fe

species in natural waters have very low solubility (dissolved Fe2+

is absent between

pH 5 and 10) iron is generally transported from upstream soils in the form of low

molecular weight colloidal fulvic-iron complexes to marine waters (Krachler et al.

2005). Humic substances (or organic ligands) are strong natural chelators that can

form soluble iron complexes, limiting the hydrolysis of Fe3+

and subsequent

precipitation of ferric oxides (Liu et al. 2002). Colloidal forms of iron have been

observed or postulated in fresh and marine waters which account for iron


concentrations much higher than the theoretical equilibrium solubility of iron

oxyhydroxides (Lofts et al. 2008).

As discussed in the background section, iron is predominantly sourced from high Fe

soils within the catchment. Reducing conditions due to water-logging mobilise Fe2+

within the soil profile. This Fe2+

and other forms of Fe (particulate and dissolved)

within the soil profile are then transported to the drainage system via overland flow

during rainfall events and groundwater seepage. A percentage of the Fe2+

transported

will again be oxidised, hydrolysed to Fe3+

oxyhydroxides, drop out of solution and

settle in the bottom sediments (hyporheic zone). A second process mobilises such

iron in these surface water bodies where anaerobic microorganisms in the hyporheic

zone release dissolved ferrous iron from the precipitated Fe3+

oxyhydroxides. As

discussed above, physico-chemical measurements at this site indicate variable redox

conditions in the water column where reduction of Fe3+

oxyhydroxides is occurring

in bottom sediments, but when the dissolved iron rises in the water column, some of

it is again oxidised to Fe3+

. A proportion of this will again precipitate out as Fe3+

oxyhydroxides while the remaining Fe3+

will be either be stabilised by organic matter

or remain in solution as nano-sized oxyhydroxide particles and remain in the water

column as transportable colloidal sized particles. In this way, Fe loads undergo a

cyclic biogeochemical process of oxidation and reduction as they are transported to

the drainage systems and within surface waters.

The high concentrations of both ferrous (29.8 mg/L) and ferric (9.1 mg/L) iron

suggest that there is considerable microbial reduction of ferric oxyhydroxides, abiotic

and microbial oxidation and subsequent organic complexation of Fe3+

occurring at

this site. Both FeOB and FeRB speed up the rate of oxidation and reduction of Fe

and although there are no CBN data available for this site, the presence of these

bacteria, in large quantities, is supported by observation. In addition to the presence

of Fe3+

oxyhydroxide precipitates, observed as a rust-coloured biofilm on the shallow

sediments at this site, an oily inorganic ferric sheen was also observed at various

places along the stream, a bi-product of the microbial oxidation process. Iron bacteria

obtain energy by oxidising soluble ferrous iron into insoluble ferric iron which then

precipitates out of solution forming slimy rust-coloured precipitates and/or biofilms

on creek bottoms and well casings which can produce negative water quality impacts

(Smith 2008; National Ground Water Association 2009a; Barrett 2010). An oily


sheen floating on the surface of creeks and streams is produced when anaerobic

bacteria reduce ferric iron to ferrous iron promoting ferrous iron movement through

water to oxic zones where it oxidises and precipitates. Rather than sinking to the

bottom of the water body, these precipitates float on the surface as the ―oily‖

colourful inorganic ferric sheen (Thomas 2007). DOC provides an oxidisable carbon

substrate for microbial sulphate and Fe reduction and the oxic/anoxic interface

provides appropriate redox conditions for oxidising and reducing bacteria.

TCA had a sulphide concentration as H2S of 0.3 mg/L. There was also a strong smell

of sulphur at the site suggesting the presence of H2S gas. Sulphide is often present in

groundwater and is produced by the decomposition of organic matter and bacterial

reduction of sulphate (National Ground Water Association 2009b). The importance

of sulphate reduction in an aquifer depends on both availability of reactive organic

matter and sulphate supply (Appelo et al. 2005). In addition, outgassing of ignitable

methane was observed emitting from the bottom sediments indicating the redox

values are further decreasing with depth in the water column and in the bottom

sediments and bacteria are reducing different elements according to electron tower

theory (Schlesinger 1997).

TCA had the highest δ34

SSO4 value at 32.6‰ VCDT of all samples by a large margin,

most likely due to the presence of sulphate reducing bacteria in the shallow

sediments at this location. As discussed in the methods section, the SRB

preferentially take up the lighter sulphur isotopes from the sulphate increasing the

isotopic ratio of the remaining sulphate (Clark et al. 1997). In combination with a

sulphate/chloride ratio of 9.9% (as compared with a seawater ratio of ca. 14%), this

strongly suggests pyrite precipitation likely due to the presence of sulphate and Fe

reducing bacteria in the shallow sediments. Where oxidized sulphur is present and

conditions are sufficiently anaerobic to promote sulphate reduction, Fe2+

precipitates

almost quantitatively as sulphides (Langmuir 1997). TCA1 and TCA2 are both

plotted in Figure 7, a stability field diagram for dissolved and solid forms of iron as a

function of pH and Eh. TCA1 plots almost on the borderline between the FeS2 and

Fe2+

fields and TCA2 which also has suboxic conditions plots in Fe2+

field.

Conversely, when the water table drops, moving the oxic/anoxic interface closer to

the bottom, it is also possible that this newly formed pyrite will then be oxidised and


again release ferrous iron and sulphate into solution, followed by bacterial reduction

of sulphate, precipitation again of pyrite and so forth.

Using an open system approach, carbonate speciation results are 4.0 mg/L HCO3- is

86.5% of total dissolved inorganic carbon (CT) and 0.5 mg/L CO2 at 13.5% CT.

Freshwater carbonates generally lie in the range -17 to +15‰ and seawater DIC that

might be input with rainfall and seaspray in small concentrations is generally in the

range +1 to -1‰ (Clark et al. 1997). The depletion in 13

CDIC at TCA (-19.4‰) is

most likely predominantly due to the dilution of the DIC pool by low ratio

bicarbonate, a by-product of microbial reduction of Fe and sulphate due to much

higher percentage of bicarbonate in the sample. CO2 concentrations higher than

atmospheric pressure in surface waters are generally related to the decay of organic

matter (Langmuir 1997). δ13

CDIC values for soil CO2 from the decay of C3 plant

biomass is generally in the range of -30 to -24‰ and for C4 plant biomass, -16 to -

10‰ (Vogel 1993). As there is a mixture of C3 (pines, eucalypts) and C4 (grasses)

plant materials adjacent to and within this stream, it is difficult to ascertain whether

this plant derived CO2 is further depleting or enriching 13

CDIC. Further study of the

percentage of C3 and C4 plant material within these streams and possibly laboratory

experiments could determine this. Please note also that these C3 and C4 categories

are based on family and not on species as found in various references – Florabank

(2011), Florabase (Western Australian Herbarium 2011) and Grass Genera of the

World (Watson et al. 1992 onwards).

Transport of Fe via surface water drainage system (PB, PCM, TCB)

Surface water site PCM is located at the mouth of Poona creek where waters are

marine in character with a total dissolved ion (TDI) concentration of 40576 mg/L

(Figure 2). Both PB and TCB are located in the coastal plain and are estuarine. TDI

values for these sites are 19433 and 26136 mg/L respectively.


Figure 7 Stability field diagram for dissolved and solid forms of iron as a function of pH and Eh at 1 atm and 25ºC (from

Elder,(1988)).


Oceanic waters have very low iron concentrations; generally less than 0.1mg/L

(Armstrong 1957; Hem 1992; Anthoni 2006). Dissolved ferrous iron generally has a

terrigenous source and is transported to the coast where, under estuarine conditions,

most precipitates out of solution via oxidation to ferric oxyhydroxides. Precipitation

occurs on mixing due to seawater-cation neutralisation of negatively charged iron-

bearing colloids, allowing flocculation. Estuaries therefore become a kind of sink for

removal of iron (Boyle et al. 1977). Boyle et al. (1977) estimated this flocculation

results in an approximate 90% reduction of input of dissolved iron to the ocean.

However, even though most dissolved and organically-complexed iron sourced from

catchments will precipitate out of solution before entering marine waters, river and

ground waters can still contribute significant quantities of dissolved iron to marine

environments (Krachler et al. 2005; Windom et al. 2006; Roy et al. 2010). Studies

have shown that the input of fulvic acids can maintain iron in solution in brackish to

saline coastal waters, most often in organically complexed form (Krachler et al.

2005; Windom et al. 2006).

Similar settings and processes occurring at TCA are likely to be occurring at many

other locations along the upper Poona and Big Tuan catchment drainage systems and

may lead to some input of Fe to the estuary. However, the likelihood that significant

Fe loads will be transported from settings such as TCA to the marine environment

under steady-state conditions is low. Fe concentrations at TCB (8.5 km AMTD from

the estuary mouth) in Big Tuan Creek were low (0.22 mg/L dissolved Fe2+

) so it

appears unlikely significant loads are entering the Strait via this drainage system. No

Fe was detected at TCB so it would appear colloidal-sized Fe3+

oxyhydroxides were

not present this far downstream from TCA and any Fe2+

present will most likely be

oxidised and precipitate out as pH, DO and Eh increase before it enters the marine

waters of the Strait. It also appears unlikely that there is much Fe entering the Strait

via Poona creek under steady-state conditions as Fe levels are low at 0.39 mg/L Fe2+

at PB (10.5 km AMTD from the estuary mouth) and at the estuary mouth (PCM)

levels were below the minimum detection limit of 0.05 mg/L.


Figure 8 Schematic representation of presumed processes involving Fe, S and C at TCA, a shallow surface water site in the

Tuan catchment. Red and green boxes indicate sources and processes related to sulphur and carbon species,

respectively. Blue font shows forms and processes relating to Fe.


Although PB and TCB are estuarine, pH and Eh measurements at these sites still plot

in the Fe2+

stability field of Figure 7. Consequently most of the dissolved Fe at these

sites, and in the case of TCB all of the dissolved Fe, was Fe2+

. However, a low level

of Fe3+

(0.11 mg/L) was detected at PB indicating that either colloidal ferric

oxyhydroxides or Fe3+

organic complexes were present. PCM (PCMe in Table 2)

showed Fe concentrations above the detection limit with a total Fe concentration of

0.3 mg/L during a high rainfall event. Total Fe at PB (PBe in Table 2) was also

highest on this occasion at 2.4 mg/L. Otherwise, Fe concentrations at PCM were

below detection limits and, at PB, below 0.5 mg/L. These data point towards heavy

rainfall as being a major influence on Fe being transportation to the Strait.

Unfortunately no data was collected from the Tuan catchment sites during high

rainfall events for comparison with steady-state data.

13CDIC was more enriched in surface waters with tidal influence (PCM, PB and TCB)

than at TCA. PCM, located at Poona Creek estuary mouth and have marine water

character had a δ13

CDIC value of -1.37‰ VPDB, close to the range for seawater DIC

of ca. -1‰ to +2‰ (Sackett et al. 1966). Estuarine surface waters PB (-11.0‰) and

TB (-11.5‰) values are both reflective of a mixing of seawater DIC and lower ratio

bicarbonate from fresh upstream waters. Estuarine surface waters, PCM (20.1‰), PB

(21.2‰) and TCB (21.3‰) δ34

SSO4 values were all very close to typical seawater

δ34

SSO4 value of 21‰ VCDT suggesting the sulphate at these sites is predominantly

sourced from marine waters. Interestingly, Fry (2002) found that isotopic

compositions of sulphate were quite constant through most of the salinity range in

estuaries. This constancy arises because the mixing dynamics so markedly favour the

dominant seawater source of sulphate in seawater as compared with much lower <

concentrations in freshwater. This is unlike freshwater-marine mixing models for

δ13

CDIC which generally have close to linear gradient for δ13

CDIC vs salinity.

Consequently the ground and surface water estuarine sites in the study area have

values very close to that of marine sulphate.

P6

Monitoring well P6 is located within the transect of boreholes located near the Poona

Creek estuary (Figures 3 and 4). Cutting samples were collected during drilling at 0.5

m intervals. These cuttings indicated a soil layer down to a depth of 2.0 m below


ground surface (bgs), a semi-confining clay/silt layer from 2 to 5 m, a sand, silt and

gravel layer from 5 to 10 m and a peat layer at about 10 to 11 m. A graphic borelog

for P6 is shown in Figure 9. The peat layer in the sediment profile has a strong

influence on the chemistry at this site. Orange mottles were also observed in the

gleyed confining clay/silt layer indicating oxidation of Fe. When water-logged soils

or sediments are exposed to oxygen, dissolved ferrous iron will be oxidised, resulting

in formation of red, yellow or brown ferric oxides or ferric hydroxide minerals

(Vodyanitskii et al. 2006; Platova et al. 2009). The processes discussed below are

illustrated in Figure 10.

Figure 9 Graphical borelogs for monitoring wells P6 and P5. The scale to the left

of the image indicates depth below ground surface in metres.

Dissolved iron concentrations in groundwater systems are typically two-to-three

orders-of-magnitude greater than those found in surface waters. Generally, this is due

to anoxic conditions in groundwater environments which increase iron solubility and

transform iron into more bio-available forms (Gibbes et al. 2006). Groundwater with

a pH 6 - 8 can be sufficiently reducing to carry as much as 50 mg/L of Fe2+

at

equilibrium, where bicarbonate activity is less than 61 mg/L (Hem 1992).

Microbial activity is an important influence on the hydrochemistry of this aquifer.

Cultivable bacteria numbers (CBN) in colony forming units per mL (CFU/mL)

collected in December 2008 were 1x108 for FeRB, 1x10

4 for FeOB, 1x10

3 for SOB

and 1x103 for SRB (Lin 2011). FeRB are reducing Fe

3+ oxyhydroxides to dissolved

Fe2+

as evidenced by the comparatively high Fe2+

(5.7 mg/L) (Table 2). The SRB

CBN indicates that SRB are present in this aquifer and H2S concentration of 4.1

P

6

P

5


mg/L, the highest concentration measured of all samples by 2.5 mg/L (Table 2),

indicates that these SRB are reducing sulphate to H2S. There was also a strong H2S

odour detected during sampling. The presence of SOB and FeOB as well as SRB and

FeRB suggests oxidation and reduction cycling is occurring along the water column

as illustrated in Figure 10.

Figure 10 Schematic of presumed processes involving Fe, S and C at P6 fresh water

monitoring well located near Poona Creek estuary

The availability of organic carbon is likely the primary determinant of groundwater

ecosystem trophic complexity (Hancock et al. 2005). For the biological/

biogeochemical reduction of inorganic constituents, other substrates are required for

oxidation. This is generally organic matter (Schlesinger 1997). Most DOC will be

degraded through oxidation and biodegradation before reaching the water table, but

groundwaters associated with swamps or coal may have much higher DOC levels

(Drever 2002). The peat layer at the bottom of the lithological profile at P6 provides


the organic carbon substrate (DOC = 7.76 mg/L) these bacteria require to reduce Fe

and sulphate.

Peat layers commonly contain pyrite (FeS2) which is by far the most abundant

sulphide mineral, occurring in most types of geologic formation, particularly coals

and peats (Langmuir 1997). Due to the strong affinity and low solubility of pyrite

and the microaerophilic reducing conditions (Table 2) at this depth (ca. 10 m below

ground surface), it is unlikely that this peat layer is contributing Fe to solution.

However, precipitation of FeS2 could reasonably be expected due to the presence of

H2S and Fe2+

and, as can be seen in Figure 7, P6 plots in the pyrite stability field. A

small amount of Fe detected (0.6 mg/L) (Table 2) at this site could be present as

either colloidal Fe3+

oxyhydroxides or as organically-complexed Fe transported via

vertical percolation or horizontally through the aquifer.

Carbonate speciation (open system) for this site is 13 mg/L HCO3 (95.6% of total

carbon [CT]) and 0.5 mg/L CO2 (4.4% CT). δ13

CDIC (-20.0‰ VPDB) for this site are

depleted compared to freshwater carbonates (-17 to +5‰ VPDB). This is again most

likely due to the high numbers of reducing bacteria diluting the DIC pool with low

ratio bicarbonate as the percentage of CO2 is much smaller compared to the

percentage HCO3. Again, there was a mixture of C3 and C4 plants on the ground

surface at P6 so it cannot be determined what range the δ13

CDIC signatures for the

dissolved CO2 at this site might fall into.

Although P6 had a strong odour of H2S (4.1 mg/L) and the highest level of H2S

measured of any ground or surface water, a δ34

SSO4 of 19.0‰ VCDT is very close to

that of coastal rainfall. The slight enrichment compared with the typical range for

coastal rainfall (ca. 12 to 18‰ VCDT) may be due to of sulphate reduction.

However, a greater enrichment than this is more typical. SRB (1x103 CFU/mL) and

SOB (1x103 CFU/mL) were found in equal amounts by Lin (2011) and so it is likely

that these two processes are in some kind of equilibrium.

P5 and P11-P14 (estuarine groundwaters)

Monitoring well P5 (Figures 3 and 4) had the highest concentrations of all ground

and surface waters sampled (38.35mg/L Fe2+

and 17.40 mg/L Fe, Table 2). A graphic

borelog for this site is shown in Figure 9. This site is located ca. 300 m from Poona


Creek estuary on the boundary of the supratidal area where swamp-like conditions

exist. The semi-confining clay layer along the transect (Figure 3) appears to dip

downward here from P2 limiting tidal intrusion further inland. At P5 this is overlain

by ca. 3 m of humic silty sands and a thin layer of topsoil consisting of sands and

organic materials (Figure 9). This site is at the landward boundary of the zone of

mixing between fresh inland and tidally intruding marine waters. As observed in the

clay layer at P6, red-orange mottling was also observed in the silty clay samples

collected during drilling after exposure to oxygen indicating the presence of Fe. The

processes discussed below are illustrated in Figure 11 (high tide conditions) and

Figure 12 (low tide conditions).

Similar to P6, there is a cycle of oxidation and reduction of Fe. Hydrological

conditions, however, are very different at this site as P5 is essentially at one end of a

transitional region between fresh inland and estuarine groundwaters. Due to density

differences, waters will be increasing fresh towards the water table and increasingly

saline with depth. Consequently there is a variation in DO and pH with depth. DO,

Eh and pH will decrease downward from the water table and then increase again as

the groundwater becomes more saline. So the level of activity of reductive and

oxidising processes varies at different depths due to tidal intrusion. DO and pH are

still low enough to support reducing bacteria and high enough to support microbial

and abiotic oxidation of Fe2+

at different depths in the water column.

However, levels of Fe are much higher than for P6. This is most likely due to ‗iron

curtain‘ effects. Flocculation of Fe3+

oxyhydroxide-organic matter colloids occurs in

both ground and surface waters where marine and fresh waters mix (Charette et al.

2002; Spiteri et al. 2006). As ferric oxyhydroxides such as ferrihydrite are strong

adsorbers and concentrators of many dissolved chemical species, such as phosphate

(Spiteri et al. 2006), the occurrence of an ‗Iron Curtain‘ has broad implications for

transport of natural and anthropogenic materials from aquifers into coastal waters

(Charette et al. 2002).

Redox and pH conditions not only vary with depth but laterally towards the estuary

and over time (Figure 13). Due to tidal flux, pH and Eh will vary cyclically at P5 and

P11-P14 depending on tidal conditions. At high tide, pH and Eh will be elevated due

to the intrusion of higher pH and DO marine waters and abiotic and biotic oxidation

processes will be dominant over most of the water column. Consequently, the


dissolved Fe2+

in the fraction of the water column with high enough Eh and pH will

become oxidised and either precipitate out of solution or bond with organic materials

within the sediment profile. When the tide starts to ebb, a greater fraction of the

water column is dominated by reducing conditions and lower pH. FeRB reduce Fe3+

oxyhydroxides that have precipitated out of the water column to Fe2+

. With the

flooding tide, a fraction of this Fe2+

is again oxidised are subsequently oxidised with

the flood tide and either precipitate again, remain in solution as colloidal ferric

oxyhydroxides or complex with organic materials and so on. As the tide ebbs it is

likely that some of the dissolved Fe will be transported towards the estuary with

outgoing waters that are lower in pH thereby maintaining the stability of dissolved

Fe(II) and organically complexed Fe3+

. However, based on the data (Table 3), a good

proportion of this Fe is immobilized at P5 and remains there due to the iron curtain

effects discussed above. So there will be a variation in pH and Fe concentrations

spatially and temporally between the estuary and P5 which will move inland and

estuary-ward depending on tidal conditions.

Monitoring well P5 has a very high DOC (40.3 mg/L) sourced from organic

materials throughout the sediment profile, so it is likely that a major percentage of Fe

is occurring in organically-complexed form. These organic materials also provide a

carbon substrate for Fe-reducing bacteria. Cultivable bacteria numbers in CFU/mL

from Lin (2011) were 1x104 for FeRB and 1x10

2 for FeOB. δ

13CDIC for P5 (-17.7‰

VPDB) was enriched compared to P6 (-20.0‰ VPDB) most likely due to the

presence of seawater DIC. Based on carbonate speciation (open system) there is

HCO3- is 95.1%CT (13.0 mg/L) and CO2 is 4.9%CT (0.5 mg/L) of DIC. As with both

TCA and P6, the larger influence on the depletion of 13

CDIC is probably the

conversion of DOC to lower ratio HCO3- by Fe and sulphate reducing bacteria.

However, at this site there is a variable input of ocean DIC due to tidal flux and

consequently the δ13

CDIC signature is slightly enriched compared to TCA and P6.


Figure 11 Fe-related processes at P5 during high tide conditions. Redox and pH

conditions vary both with depth and laterally towards the estuary. The

wavy lines represent that part of the water column which is dominated by

intruding subterranean estuarine waters and is overlain by fresher waters.

Saline intrusion further inland is limited by the semi-confining layer

dipping from south to north.

The δ34

SSO4 (19.3‰ VCDT) isotopic ratio at P5 indicates an ocean DIC or coastal

rainfall source (ocean water DIC ca. 21‰ VCDT). Based on the location and the

existence of tidal intrusion at this site, it is likely to be a mixture of the two. H2S was

0.9 mg/L and cultivable bacteria numbers in CFU/mL from Lin (2011) were 1x105

for SOB and 1x103 for SRB. Complex microbial processes relating to sulphur are

occurring here. However, the dominant sulphate source would most likely be ocean

DIC, simply due to concentration differences as found by Fry (2002).

Transport of Fe via the subterranean estuary (P11 – P14)

Although the iron curtain effect is most obvious at P5, this site represents the

landward boundary of a transitional zone between fresh and marine waters. Although

the iron curtain effects result in the accumulation of high levels of Fe, a proportion of

this Fe is still being transported with the outgoing tide towards the estuary. Shallow


groundwaters, P11, P12, P13 and P14 (Figures 2 and 3) in the supratidal flats

between P5 and the estuary had 0.73, 2.44, 5.71, 5.56 mg/L Fe2+

and 0.71, 0.66,

0.92, 6.64 mg/L Fe respectively (Table 2). Sediments retrieved during the installation

of these bores (maximum depth 1.2 m) also exhibited gleying as a result of an

accumulation of ferrous iron due to the reduction of ferric iron in the water-logged

sediments (Lovley 1993). These soils/sediments often contain extractable Fe-

reducing bacteria (Vodyanitskii et al. 2006; Platova et al. 2009).

Figure 12 Fe-related processes at P5 during low tide conditions. Redox and pH

conditions vary both with depth and laterally towards the estuary.

Figure 13 shows the concentrations of Fe2+

, Fe and pH for P5 and P11-P14 with

distance from P5. Although tidal intrusion at these sites results in the input of DO

and high levels of dissolved ions elevating Eh and pH (compared with P6, for

instance), organic acids produced from organic materials in the sediment profile

maintain pH at a level that plots these sites in the Fe2+

field of the Eh/pH diagram

(Figure 7). Flood (1984) documented that the intertidal zone, where wave and tidal-

action occurs, has an aerobic surface but becomes anaerobic several centimetres

below the surface. This anaerobic state may increase the amount of soluble Fe


present in intertidal sediments. This appears to be the case within the waters of these

supratidal flats.

It should also be noted that these P11-P14 are highly evaporated so concentrations of

Fe are elevated relative to non-evaporated waters. Average TDI for marine waters at

the mouth of Poona Creek (PCM) was 34,100 mg/L whereas average TDI for sites

P11-P14 groundwaters ranged from 30,800 to 53,400 mg/L depending on tidal

condition. Marine waters are typically around 30,000 to 40,000 mg/L (Water Quality

Association 2012). This evaporation of water increases the concentration of all ions

and gives the impression that Fe loads being transported to the supratidal flats are

higher than they really were.

Figure 13 Fe2+

, Fe and pH for monitoring wells P5, P11-P14 with distance from P5.

As samples were taken at different times, tidal conditions were variable.

This explains why there is an increase instead of a decrease and vice

versa at some points in the data with increasing proximity to the estuary.

However, Fe measurements do illustrate the significant reduction in iron

concentrations with proximity to the estuary due to increasing pH.

Surface water site PCM located at the mouth of Poona Creek has been

assumed to be similar in character to the estuary directly across from the

transect.

Whether or not Fe is being transported through these groundwaters to the estuary is

unclear. Organically-complexed Fe will become progressively unstable with

increasingly saline conditions as will any remaining dissolved Fe2+

. Again, Fe

P5

P13

P11P12

P14

PCM

4.0

4.5

5.0

5.5

6.0

6.5

7.0

7.5

8.0

8.5

0.0

5.0

10.0

15.0

20.0

25.0

30.0

35.0

40.0

45.0

-10.0 40.0 90.0 140.0 190.0 240.0 290.0

pH

Fe(I

I), F

e(I

II) i

n m

g/L

Distance from P5 (m)

Fe(II), Fe(III) and pH for P5, P11, P12, P13, P14

Fe(II) Fe(III) pH

ESTU

AR

Y


measurements at PCM were below detection limits indicating that these Fe loads are

not being transported to the estuary mouth and then to the marine waters of the Strait.

However, further investigation is required including the analysis of shoreline

sediments. It is possible that Lyngbya majuscula acquires iron when a) Fe3+

oxyhydroxides are released into the water column as Fe2+

with the onset of anoxia

and/or b) Fe is taken up from amorphous Fe oxides accumulating on the Lyngbya

exterior (WBM Oceanics Australia 2001) as well as from organically-complexed Fe

which require lower pH than is typical of marine waters for stability. In this way,

particulate concentrations of Fe in the bottom sediments of marine waters are

potentially a major influence on the growth of Lyngbya.

Summary and conclusions

Organic (DOC), physicochemical (Eh, pH and DO), ionic (Fetotal, Fe2+

), and isotopic

(δ13

CDIC, δ15

N and δ34

SSO4), microbial data and field observations have revealed

sources, forms and processes relating to the occurrence, transport and mobilisation of

dissolved Fe, C, S within the waters of these types of coastal regions. As well as

providing a general characterisation of ground and surface waters of this area, three

sites or micro-environments within the Poona and Tuan coastal catchments on the

Fraser Coast in southeast Queensland were used to illustrate various processes

contributing to the mobility and transport of Fe. In summary, this study as revealed

the following general characteristics and processes occurring within the waters of

these coastal catchments.

Characterisation and processes

Overall, cluster analysis of Fe2+

, Fe3+

, Eh and pH data revealed expected groupings

of waters related to geomorphology and hydrological settings. Following are general

features of waters in the study area that are of relevance to iron transport.

Although readily extractable Fe from Fe-concretions and ferricrete in soils and

sediments within these catchments was not high (Löhr et al. 2010), microbially-

mediated reduction and oxidation and the presence of significant levels of DOC

(groundwaters have 3.7 to 40.3 mg/L DOC and surface waters have between 13.5

and 25.6 mg/L) appear to be the main contributors to high dissolved Fe

concentrations in the study area.


The presence of DOC within these catchments enables Fe mobilisation via

organic complexation and also provides a carbon substrate for microbial reduction

of Fe3+

oxyhydroxides and therefore contributes to the mobilisation of dissolved

Fe2+

.

Organic materials accumulated along the banks and bottom sediments at

freshwater stream sites such as TCA, results in the high levels of DOC

available for these processes.

A peat layer at depth in monitoring well P6 provides a carbon substrate for

high levels of sulphate and Fe reducing bacteria, resulting in considerable

dissolved Fe2+

and H2S gas concentrations.

In the case of P5 and P11-P14, organic materials not only provide ligands for

Fe organic complexation and a carbon substrate for microbial Fe reduction, but

also supply fulvic acids that keep pH low enough that these dissolved Fe loads

remain stable even where marine waters dominate.

Microbial activity (and related Eh and DO concentrations) is an important factor

in determining the form of Fe in these waters. Reducing conditions encourage

microbial reduction of Fe and sulphate (therefore enabling transport) while

oxidising conditions encourage the oxidation and subsequent precipitation of Fe.

Both of these processes were occurring as cyclic Fe and S reduction and oxidation

at the sites studied here. A concurrent study by Lin (2011) showed that cultivable

bacterial numbers were high for both oxidising and reducing bacteria at fresh

groundwater site P6 and the tidally intruded brackish groundwater site P5 within

the transect near Poona Creek estuary. These results emphasise the importance of

the role of microbial activity in determining the form of nutrients and ions in these

waters. The form of these nutrients and ions affect their chemical properties and

also their mobility and potential for transport..

There are two processes which immobilise Fe within these catchments.

a) Iron curtain effects at P5 where pH and DO increase sufficiently to

precipitate the major proportion of Fe loads that have been transported to this

site. Physico-chemical conditions lead to an accumulation via oxidation

followed by precipitation of Fe3+

oxyhydroxides (iron curtain effects) at the

boundary of the supratidal flats of the Poona Creek estuary as shown.


b) Precipitation of pyrite where H2S and dissolved Fe2+

are available. This

process is very likely to be occurring at both P6 and TCA.

Isotopes

Isotopic data has indicated various nutrient sources within the catchment and in some

cases provide further evidence for some of the micro-processes occurring at some

sites. These are summarised as follows.

δ13

CDIC isotopic data indicate that groundwater DIC is generally sourced from

either soil CO2 and/or low ratio bicarbonate resulting from the microbial

conversion of organic carbon. There is a slight enrichment in some groundwaters

due to a minor contribution of ocean DIC due to tidal flux. One confined fresh

groundwater site had comparatively elevated δ13

CDIC ratio due to a DIC

contribution from marine carbonate shell material within the sediment profile.

Freshwater carbonates sourced from further inland are the most likely source of

DIC in fresh surface waters in the upper catchment and at sites in the coastal

plain. The greater depletion of 13

CDIC at WP11 could be explained by groundwater

contribution from adjacent alluvial sediments.

δ15

NDIN data indicate that nitrogen sources are predominantly soil N2, organic N

and rainfall. The exception is one residential borehole where the presence of

either organic fertilizer or septic tank seepage is indicated. Denitrification may be

occurring at two ground and one surface water sites where conditions are

reducing. Overall, however, many of these results are inconclusive and a dual

isotope approach including δ18

ONO3

-, in addition to analysis for NH4

+ and organic

N, is recommended for any future samples collected if N is specifically of interest.

δ34

SSO4 indicated sulphur oxidation processes at the residential borehole 204B.

These processes were supported by observations in the field. δ34

SSO4 at estuarine

surface water sites are close to that of typical seawater. Otherwise sulphate

sources appear to be a mixture of rainfall and/or seaspray sulphate. Sulphate

reduction is indicated at a number of sites; most markedly at TCA, followed by

134B and PCP. Sulphate reduction was not indicated at a number of sites even

though H2S was present and, in a couple of cases, SRB, due to the much larger

input of marine sulphate from rainfall and seaspray sources.


Isotopic data showed various sources and processes affecting the form of nutrients

in the study area. δ34

S isotopic data indicate sulphate reduction processes at a

surface water site in the Tuan catchment (δ34

SSO4=32.6 ‰ VCDT). δ34

SSO4 at

estuarine surface water sites are close to that of typical seawater showing the

dominance of marine sulphate. The depletion of the δ13

CDIC signature (ca. -19.0 to

-20.0 ‰ VPDB) at P6 and TCA is due to dilution of the DIC pool by low ratio

bicarbonate, a bi-product of the microbial reduction of sulphate and Fe where low

ratio organic carbon from organic materials is converted to bicarbonate. P5 is

enriched in comparison due to the input of ocean DIC. Significant enrichment at

estuarine surface water sites are due to marine and fresh water mixing.

Fe transport

Based on the data collected for this study, the surface water drainage system is

contributing very little if any dissolved Fe loads to the Strait under steady-state

conditions. Although high Fe concentrations were detected at TCA, this site is nearly

17 km inland and often disconnected hydrologically from the estuary. As dissolved

Fe concentrations were below minimum detection limits in the marine waters at

Poona Creek estuary mouth during steady-state conditions, it appears that these

dissolved loads are not transported any significant distance downstream unless high

rainfall occurs. However, total Fe data collected during storm conditions at PB and

PCM suggest that substantial rainfall can transport significant Fe loads to marine

waters.

Groundwater seepage and interaction is indicated to be a more likely source of

dissolved Fe loads during times of low rainfall partly because reducing conditions

are more prevalent in groundwater aquifers than in surface water systems. Although

the iron curtain at P5 forms a barrier to Fe loads transported from further inland, a

small percentage of this Fe is still transported through the supratidal flats resulting in

concentrations as high as 6.6 mg/L only 85 m from the estuary. The input of fulvic

acids from DOC within these estuarine muds and sands maintains pH at a level

where both dissolved Fe2+

and some forms of organically complexed Fe are stable.

This Fe could potentially be transported to the drainage system on outgoing tides

although much of it will precipitate out of solute quickly due to the increase in pH.


In addition, high levels of dissolved Fe3+

(most likely in organically complexed

form) at saline-intruded residential borehole, 204B, could be a source of Fe to the

Strait as could other small coastal aquifers at Boonooroo and Tuan where over-

exploitation of groundwater has resulted in the fresh/saline interface moving

landward.

This study has focused on two catchments on the subtropical Fraser Coast which are

geomorphologically representative of much of coastal southeast Queensland.

Examination of this environment and the identification of isotopic and

hydrochemical processes and solute sources has provided insight into mechanisms

for Fe transport within this region and by analogy many similar settings. The

complexity of these processes effecting Fe concentrations is an important feature of

these environments. These factors need to be considered in order to obtain an

accurate picture of Fe transport and mobility in these coastal catchments when

considering the potential for transport of Fe loads to marine waters in order to avoid

algal blooms and other detrimental impacts.

Acknowledgements

This work was supported by grants from Forestry Plantations Queensland and the

Australian Research Council. The authors would also like to thank Lin Chaofeng,

Pavel Dvoracek, Bill Kwiecien, Martin Labadz, Stefan Lӧhr, and Shane Russell for

assistance with laboratory and fieldwork in the course of this project and Tanya

Scharaskin, Melody Fabillo and Peraj Karbaschi for help with researching C3 and C4

plant species.

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221

7. DISCUSSION

This study has focused on a number of catchments on the subtropical Fraser Coast

which are geomorphologically representative of much of coastal southeast

Queensland. Examination of this environment and the identification of hydrological

and hydrochemical processes and solute sources has provided insight into

mechanisms for solute transport within this region and by analogy many similar

settings. This information can be related to both landuse and environmental condition

and provides valuable information relating to the potential impacts on water quality

in these coastal zones. The research program was based on three components, each of

which addressed different aspects of the research problem. Collectively, these studies

enable a better understanding of the controls on the distribution and mobilisation of

solutes in the ground and surface waters of the region.

Paper 1 showed that there is complex interaction between different water bodies and

that a wide range of processes have been identified within the area from

interpretation based on graphical methods. Paper 2, which applied another analytical

approach, supported these findings overall, but showed that some

assumptions/hypotheses previously made required reassessment, and provided new

insight into hydrochemical processes and interaction between different water bodies.

Paper 3 was focused on solute transport and investigated sources of nutrients and

processes that control the transport of Fe. This later study considered variable scale

subsystems within the overall coastal zone and addressed hydrological and aqueous

biochemical and geochemical complexity.

Groundwater in the study area primarily occurs in (a) a regional Tertiary alluvial

aquifer in the northern part (Tuan catchment), (b) alluvial materials within and

adjacent to the drainage systems, (c) beach ridge sand aquifers and alluvial sediments

close to the coast, and (d) estuarine supratidal areas. The weathered sedimentary

rocks of the Elliot and Duckinwilla Formations which form the local bedrock are of

low permeability and show little potential as a source of groundwater. The results

show that although there is a large range in the magnitude of major ion

concentrations, there is limited variability in major ionic proportions among most

samples due to local rainfall recharge, short residence times and the siliceous

222 Chapter 7 Discussion

sediments of the region. However, waters are highly variable in relation to physico-

chemistry and Fe concentrations, spatially, with depth, and temporally in some

waters.

The main mechanism for solute transport to the drainage system in the elevated

catchment areas is overland flow; this is because of the low volume of alluvial

material and discontinuous clay layers which produce waterlogging both in the

elevated catchment and coastal plain areas. However, ground and surface water

interaction does occur in the coastal plain between pockets of alluvial and marine

sediments and the drainage system. Interaction also occurs between groundwaters in

beach ridge sand aquifers in the coastal villages and the Strait. These are both

potential pathways for solute transport. Statistical analyses showed ground and

surface water interaction does occur at two surface water sites examined in the Tuan

catchment. Interaction between the drainage system and adjacent shallow aquifers

appears to be more widespread in the Tuan catchment due to the lower relief and

larger volumes of alluvial material adjacent to the drainage systems compared with

the Poona catchment. HCA results also showed semi-confined conditions at four

sites that had previously been thought to be confined. These findings have potential

implications for confirming interaction between aquifers as well as between aquifers

and surface waters and therefore solute transport.

Isotopic results showed various sources and processes affecting the form of nutrients

in the study area. δ34

S isotopic data show that sulphate is predominantly sourced

from rainfall, seaspray and, in three cases, soils. These data also indicate oxidation of

sulphur in a residential bore subject to saline intrusion (δ34

SSO4=-1.1‰ VCDT) and

sulphate reduction processes at a surface water site in the Tuan catchment

(δ34

SSO4=32.6‰ VCDT) as well as two groundwater sites in Poona Village. Slightly

enriched values, in addition to the presence of H2S, at two fresh alluvial groundwater

sites also indicate possible sulphate reduction.

δ13

CDIC data indicated various sources of DIC such as soil CO2 in the case of

unsaturated groundwater, marine carbonate at one confined groundwater site,

freshwater carbonates for fresh surface water sites and provided further evidence for

ground and surface water interaction for a surface water site in the coastal plain. The

depletion of the δ13

CDIC signature (ca. -19.0 to -20.0‰ VPDB) at two surface water

and three groundwater sites appears to be due to dilution of the DIC pool by low

Chapter 7 Discussion 223

ratio bicarbonate, a by-product of the microbial reduction of sulphate and Fe where

low ratio organic carbon from organic materials is converted to bicarbonate.

Otherwise, isotopic data indicated saline/fresh water mixing at estuarine surface

waters where δ13

CDIC was more enriched (> -12‰ VPDB) and δ34

SSO4 values close to

that expected for seawater (ca. 21‰ VCDT).

A concurrent study by Lin (2011) showed that cultivable bacterial numbers were

high for both oxidising and reducing bacteria at one freshwater (FeRB = ca. 1x108,

FeOB = ca. 1x104 for, SOB = ca. 1x10

3, SRB = ca. 1x10

3) and one tidally intruded

(FeRB = ca. 1x104, FeOB = ca. 1x10

2, SOB = ca. 1x10

5, SRB = ca. 1x10

3) site

within the transect near Poona Creek estuary. These findings based on isotopic and

cultivable bacterial count data emphasise the importance of the role of microbial

activity in determining the form of nutrients and ions in these waters. The form of

these nutrients and ions affects their chemical properties and also their mobility and

potential for transport. However, S reduction indicated by H2S, DOC and CBN data

and the presence of H2S odour at some sites was not reflected in the δ34

SSO4 ratios

Generally, δ34

SSO4 ratios at these sites are more reflective of coastal rainfall and/or

seaspray or marine sulphate. As discussed in Paper 3, Fry (1989) found that marine

34SSO4 was dominant in estuaries over very large salinity ranges and very close to

head waters simply due to concentration differences.

For many sites, δ15

NDIN data indicated rainfall- and/or soil- N2 due to the absence of

anthropogenic N input and the nutrient-poor nature of the study area. δ15

NDIN values

enriched relative to other ground and surface waters (δ15

N = -1.4‰ AIR to -3.6‰

AIR) indicate possible denitrification at three sites; one fresh surface water site in the

Tuan catchment (δ15

N = 7.4‰ AIR) and two transect groundwaters (δ15

N = 5.8 ‰

AIR, 6.8‰ AIR). Septic tank effluent or organic fertilizer is indicated for one

residential borehole (δ15

N = 22.4 ‰ AIR). Many of these results, however, are

inconclusive due to the overlapping ranges of synthetic fertilizer, rainfall N2 and soil-

respired N2 and a lack of concurrent δ18

ONO3 analysis.

Interpretation of physicochemical, organic, isotopic and Fe species data identified

important processes affecting the transport of Fe within different waters. The main

features contributing to the mobilisation and transport are microbial reduction of Fe

oxyhydroxides, supply of organic material as a substrate for microbial reduction and

for organic material of Fe(III), redox conditions and the variability of redox


conditions with depth. Although readily extractable Fe in soils and sediments of

these catchments is not high (Löhr et al. 2010), microbially-mediated reduction and

high DOC leads to relatively high dissolved Fe concentrations in some waters.

Highest surface water Fe(II) and Fe(III) concentrations measured were 29.8 and 9.1

mg/L at one surface water site in the Tuan catchment and highest groundwater Fe(II)

and Fe(III) concentrations were 38.4 and 17.4 mg/L, respectively, at the saline/fresh

water interface near the Poona estuary. The complexity of these processes effecting

Fe concentrations is an important feature of these environments. These factors need

to be considered in order to obtain an accurate picture of Fe transport and mobility in

these coastal catchments.

Based on the available data, there is no confirmation that the surface water drainage

system is contributing any significant dissolved Fe loads to the Strait under steady-

state conditions. Even though very high levels of Fe were detected at a freshwater

stream site in the Tuan catchment, this site is some distance inland and often

hydrologically disconnected from the estuary. A significant rainfall event would be

necessary in order for Fe and other nutrients to migrate from this site to the Great

Sandy Strait. Levels of Fe measured at the mouth of the larger Poona Creek estuary

at PCM of 0.26 mg/L and further upstream at PB of 2.39 mg/L during a high rainfall

event that occurred on 25/08/2011 (119 mm recorded at Tuan Forestry Office)

indicate that significant loads of Fe are transported to the Strait with flood waters.

Groundwater seepage and interaction is indicated to be a more likely source of

dissolved Fe loads during times of low rainfall partly because reducing conditions

are more prevalent in groundwater aquifers than in surface water systems.

Physicochemical conditions lead to an accumulation via oxidation followed by

precipitation of Fe oxyhydroxides (iron curtain effects) at the boundary of the

supratidal flats of the Poona Creek estuary. This accumulation is produced by an

increase in pH in this zone of mixing between estuarine and fresh inland waters as

observed in other studies (Charette and Sholkovitz 2002; Spiteri et al. 2006). Due to

the cyclic nature of tidal flux increasing and decreasing pH and Eh levels, there is a

cycle of reduction-dissolution and oxidation-precipitation of Fe over time. Although

this iron curtain forms a barrier to Fe loads transported from further inland, a

significant amount of this Fe is transported through the supratidal flats resulting in

concentrations as high as 6.6 mg/L only 85 m from the estuary. The input of fulvic


acids from DOC within these estuarine muds and sands maintains pH at a level

where both dissolved Fe(II) and some forms of organically complexed Fe(III) are

stable. This Fe could potentially be transported to the drainage system on outgoing

tides. As dissolved Fe concentrations were below minimum detection limits in the

marine waters at Poona Creek estuary mouth during steady-state conditions, it

appears that these dissolved loads are not transported any significant distance

downstream unless high rainfall occurs.

7.1 Implications for further landuse development

Saline intrusion occurring in small local coastal aquifers, a source of water for

village residents, is also of environmental and economic concern. Due to the lack of

historical temporal data, it cannot be assumed that this seawater intrusion is due to

over-exploitation by residents for household/garden use. However, communication

with local residents indicates that these bores have become increasingly saline as

more bores are established and used. In addition, the presence of iron-oxidising

bacteria at one residential borehole is of some concern and has led to the clogging

and subsequent breakdown of the borehole pump. The origin of these Fe-oxidising

bacteria is unknown, however, the oxidising conditions provided by seawater-

intrusion to the site may well maintain and assist in the development of these

bacteria.

Only one site tested, a residential borehole, showed high levels of macronutrients, in

this case nitrate, and is thought to be due to septic tank effluent or organic fertilizer.

This is of concern as, during times of high rainfall, these solutes are likely to be

transported to the Strait where they could potentially degrade water quality and

contribute to the growth of Lyngbya. It is well established that elevated levels of

nutrients have been found in coastal ground and surface waters associated with

nutrient input from populated coastal areas, particularly from septic tank effluent

(Valiela et al. 1992; Weiskel and Howes 1992; Thorburn et al. 2003; Cole et al.

2006).


7.2 Implications for plantation forestry

Although the effects of forestry practices have not been assessed directly in this

overall study, the findings provide a good foundation for further monitoring and

research. It has also identified areas of interaction and potential pathways for the

transport of solutes from forestry compartments to the groundwaters, the drainage

system, and then to the Great Sandy Strait.

The findings relating to the form and transport of Fe are particularly relevant. Large-

scale harvesting and site preparation can lead to increases in water levels (Haydon

and Jayasuriya 1992; Bubb and Croton 2002; Lin and Wei 2008) and associated

increases in nutrient concentrations to drainage systems and aquifers (Blackburn and

Wood 1990; Ensign and Mallin 2001; Costantini and Loch 2002). The raising of

watertables will not only potentially increase discharge to the Strait but will alter

physicochemical conditions throughout the water column of ground and surface

waters. How this affects Fe loads and form should be monitored carefully post-

harvest using the results produced in this study as a baseline comparison.

7.3 Recommendations for further sampling and analysis

7.3.1 Surface waters

Many studies have found that high rainfall events result in the transport of large

quantities of sediments (Campbell and McKenzie 2004) and macro- and micro-

nutrients to marine waters (Xu et al. 2008; Gorman et al. 2009) (Gorman et al. 2009;

Xu et al. 2008) and in some cases has been shown to initiate algal growth (Devlin et

al. 2001; Vargo 2009; Brodie et al. 2010). Likewise, the current data suggest that, in

general, the bulk of Fe loads would be transported from the drainage system to

marine waters during high rainfall events and most of this with the first flush of flood

waters. First flush measurements are quite difficult to obtain but essential to the

accurate quantification of nutrients being transported within and out of catchments.

Event mean concentrations (EMCs) would also provide very useful information.

EMCs are mean concentrations of a particular constituent over the quick flow

component of an event hydrograph, i.e., EMC = Total constituent load during the

event/Total quick flow during the event in mg/L (Jordan 2010). The EMC is an


important factor in predicting the total pollutant load, which has made the EMC a

critical parameter for estimating the contribution of runoff to receiving waters

(Marsalek 1978; Irish et al. 1998). See Maniquiz et al. (2010) for an example.

However, substantial finance, equipment and time is needed for the determination of

these EMC values. It requires continuous flow, physico-chemical and hydrochemical

measurements over storm events.

7.3.2 Groundwaters

Of particular interest here, is the transport of Fe through the supratidal sediments

adjacent to the Poona Creek estuary. Measurements should be taken concurrently at

P5 and P11-P14 for a variety of tidal conditions and at a number of locations in the

estuary adjacent to the transect. Transport during high rainfall events is also

important here and is further complicated by storm surges as demonstrated by the

elevated TDI at P2 and P5 during a flood event (Paper 1). A study of the interaction

of storm surges and rainfall recharge from inland and its effects on Fe transport

would be of considerable interest.

Nitrogen would appear to be less important in forested areas as indicated by overall

low or below MDL concentrations of nitrate and the absence of anthropogenic N

input but should certainly be considered when looking at nutrient transport and

processes within the residential areas due to the potential important of organic and

inorganic fertilizers and the presence of septic tanks. Another area of focus in the

potential transport of nutrient loads from residential loads. Results indicate that

nitrates are infiltrating an aquifer at one site where saline intrusion is evident. High

rainfall may result in the submarine groundwater discharge of these nitrates to

marine waters. Further hydrochemical and isotopic sampling would be appropriate

and at more sites within these coastal villages. Again, event sampling at these sites as

well as nearby estuarine waters is suggested.

7.3.3 Effects of forestry practices

As no harvesting or fertilizer treatments were carried out near the locations of the

sites examined here, it would be very useful to design a future study to coincide with

these practices. Data collection and nutrient analysis before, during and post

fertilisation in adjacent ground and surface waters would be appropriate. As stated


above, N appears to be relatively unimportant in these forested areas as current

fertilisation consists of only phosphorus treatments. Logically, nutrient analysis

should focus on P. However, phosphorus has a strong tendency toward forming ionic

complexes and compounds of low solubility with many metals, phosphate introduced

to the system is often more often found in particulate form and, therefore, dissolved

concentrations are generally very low (Boyd 2000). Examination of creek bottom,

aquifer and shoreline sediments to determine particulate concentrations should be

carried out in addition to analysis for dissolved fractions.

229

8. CONCLUSIONS

The results of this study provide a better understanding of the ways in which solutes

can be transported from catchment areas to marine waters in these coastal settings.

Although the area has been modified over the last 40 years by plantation forestry,

between the harvest periods it is relatively benign from the viewpoint of hydrological

processes and can be considered as a coastal setting of limited modification. This is

shown to be the case relative to the intense modification that accompanies heavily

urbanised areas, such as in southeast Queensland. One of the aims of the study was to

identify the character of the setting and indicative hydrochemical processes that

reflect the baseline conditions. The conclusions from this study are therefore relevant

to many other catchments in this region, as they remain in a relatively low

modification state, and have similar geomorphological and hydrological

characteristics.

Following are the main findings from the study in relation to groundwater

occurrence, sources of solutes, processes affecting solute concentrations and solute

transport within these coastal catchments.

8.1.1 Groundwater occurrence

The Tertiary alluvial aquifer is an extensive paleovalley of around 8 km width in

the northern region of the study area has overall good quality water suitable for

household and agricultural use. The existence of this aquifer was established in

1969 by Laycock (Laycock 1969) but currently the groundwater is little used due

to the establishment of pine plantations.

Coastal plain alluvial sediment groundwaters have variable major ionic and

concentrations and physicochemical parameters and range from fresh to saline.

The main control on the magnitude of major ion concentrations in these waters

under steady-state conditions is the degree of saline/fresh water mixing, which is a

function of proximity to the coast and the intervening geology.

Beach ridge aquifers also have variable major ionic compositions and

physicochemical parameters and appear to be complex systems with deeper

confined and semi- to unconfined aquifers at shallower depths. Shallow aquifers

appear to be saline-intruded while the deeper confined aquifer remains fresh.

230 Chapter 8 Conclusions

8.1.2 Sources of solutes in ground and surface waters

Sources of inorganic major ions in ground and surface waters (Na, Mg, Ca, Cl,

SO4, HCO3) are rainfall, marine waters, accumulated soluble salts within

sediments and soils, and carbonate shell material in some aquifer sediments.

Where higher proportions of magnesium occur in waters, this is most likely

sourced from the intermediate composite volcanic rocks of the Graham‘s Creek

Formation.

Almost all waters have low bicarbonate concentrations. Higher concentrations

generally reflect the mixing of marine and fresh inland waters.

δ13

CDIC isotopic data indicate that at some sites DIC is sourced from soil CO2.

One confined fresh groundwater site had comparatively elevated δ13

CDIC ratio due

to a DIC contribution from marine carbonate shell material within the sediment

profile. Freshwater carbonates sourced from further inland are the most likely

source of DIC in fresh surface waters in the upper catchment and at sites in the

coastal plain where groundwater contributions are not significant such as at

WP12.

The depletion of the δ13

CDIC signature (ca. -19.0 to -20.0 ‰ VPDB) at P2, P4, P6

and TCA is most probably due to dilution of the DIC pool by low ratio

bicarbonate, a by-product of the microbial reduction of sulphate and Fe where low

ratio organic carbon from organic materials is converted to bicarbonate. P5 is

enriched in comparison due to the input of ocean DIC. Significant enrichment at

estuarine surface water sites are due to marine and fresh water mixing.

Organic carbon is sourced from surface organic materials as well as from a peat

layer at depth in the shallow alluvial aquifer adjacent to the Poona Creek estuary.

Almost all waters have negligible nitrate concentrations.

δ15

NDIN data indicate that nitrogen sources are predominantly soil-respired N2,

organic N and rainfall. The exception is one residential borehole where the

presence of either organic fertilizer or septic tank seepage is indicated.

Denitrification may be occurring at two ground and one surface water sites where

conditions are reducing. Overall, however, many of these results are inconclusive

and a dual isotope approach including δ18

ONO3, in addition to analysis for NH4+

and organic N, is recommended for any future samples collected if N is

specifically of interest.

Chapter 8 Conclusions 231

δ34

SSO4 indicated sulphur oxidation processes at the residential borehole 204B.

These processes were supported by observations in the field. δ34

SSO4 at estuarine

surface water sites are close to that of typical seawater. Otherwise sulphate

sources appear overall to be a mixture of rainfall and/or seaspray sulphate.

Sulphate reduction is indicated at a number of sites; most markedly at TCA,

followed by 134B and PCP. Sulphate reduction was not indicated at a number of

sites even though H2S was present and, in a couple of cases, SRB, due to the

much larger input of marine sulphate from rainfall and seaspray sources.

8.1.3 Processes/characteristics affecting hydrochemical composition

Saline/fresh water mixing, absence of nutrients such as N and P, low levels of

bicarbonate and high proportions of silicate materials, limited water-rock

interaction and short residence times of waters are all factors effecting the major

ionic composition of shallow ground and surface waters in the study area.

Discontinuous clay layers throughout the area not only cause waterlogging, but in

some cases limit interaction between marine and fresh groundwaters.

Drainage system morphology and topography are also important influences on the

flow regime and chemistry of surface waters.

Hydrochemical and isotopic data indicate negligible discharge of water and

therefore solutes from the drainage system under steady-state conditions.

High rainfall events result in significant discharge from the drainage system as

well as increased interaction between coastal groundwaters and marine waters due

to storm surges leading to detectable concentrations of Fe at the estuary mouth.

Seasonal variation in proportions of major ions are minimal except when

groundwater contribution to surface waters is increased during extended dry

periods or when storm conditions lead to a substantial rainfall recharge, storm

surges and drainage system discharge.

Most groundwaters in the catchment are recharged locally.

Surface waters in the elevated catchment areas appear to receive recharge from

further inland and are subject to evaporation.

The input of fulvic acids from organic materials within sediments and at the

ground surface results in slight acidic waters at some sites.


Microbial activity is an important factor in determining the form of S and Fe in

these waters. Sulphur and Fe oxidation but predominantly sulphate and Fe(III)

reduction processes catalysed by bacteria are occurring in many waters throughout

these catchments. This has implications for transport of Fe as oxidation generally

leads to precipitation therefore immobilising Fe whereas reduction results in

higher dissolved Fe increasing mobility. The reduction of sulphate can lead to

pyrite precipitation also immobilising Fe. However, the oxidation of pyrite will

again release Fe(II) and SO4 into the water column. The dominance of one process

over the other will vary spatially and temporally and should be considered when

assessing the transport of Fe loads.

8.1.4 Solute transport

Primary mechanisms for solute transport in the Poona Catchment are:

Overland flow and runoff to drainage systems in the upper catchment.

Interaction between fresh groundwaters and saline marine groundwaters in the

coastal plain

Fresh groundwaters and surface waters in the coastal plain

Beach ridge aquifers in residential areas and the Great Sandy Strait

Primary mechanisms for solute transport in the Tuan Catchment are:

Groundwater and surface water interaction for some distance inland between

alluvial materials and the drainage system

Groundwaters in beach ridge aquifers and alluvial sediments in residential

areas and the Strait

The main factors affecting the mobilisation and transport of Fe are:

Microbial reduction of Fe oxyhydroxides in groundwaters and in the hyporheic

zone of surface drainage systems.

The presence of DOC provides a carbon substrate for microbial reduction of

Fe(III) oxyhydroxides and sulphate and organic ligands for organic-

complexation of Fe(III), thereby enabling Fe mobilisation in these waters.

Saline/fresh water mixing leads to an accumulation of Fe close to marine

waters (‗iron curtain‘ effects).

Chapter 8 Conclusions 233

pH and Eh vary with depth in some groundwaters. This is important because

pH and redox conditions determine whether Fe is reduced and dissolved, or

oxidised and precipitated.

In summary, it appears unlikely that the surface water drainage system is

contributing any significant dissolved Fe loads to the Strait under steady-state

conditions. However, total Fe data collected during storm conditions at estuarine

surface water sites suggest that substantial rainfall can transport significant Fe loads

to marine waters. Groundwater seepage and interaction appears to be a far more

likely pathway for dissolved loads from residential and forested areas to the drainage

system and potentially to the Strait during times of low rainfall. Significant dissolved

Fe(II) and Fe(III) concentrations have been measured within groundwaters very close

the estuary in the Poona catchment.

Other significant outcomes of the study are:

Hierarchical cluster analysis is a very useful tool for the grouping of waters, as

an indicator of mixing between waters, and in the clarification of aquifer types in

relation to degree of confinement

High levels of organically complexed Fe(III) in addition to dissolved Fe(II)

reinforces the importance of analysing for Fe species. The form of Fe in ground

and surface waters has major implications for stability and transport

Stable isotopes are a valuable tool in supporting these process models. However,

the merit in using the different isotopes is variable in this setting. Both δ13

C and

δ34

S were very useful and appropriate to the study area. However, the δ15

NDIN

isotopes were less useful do to the nutrient-poor nature of the area and the

absence of anthropogenic input in nearly all waters sampled. It was difficult to

determine sources of N due to overlapping ranges for various sources. δ18

ONO3 is

commonly used to differentiate between sources of N and is recommended for

any further sampling involving N.

This integrated hydrochemical study has established the distribution and sources of

key solutes of environmental significance within these catchment waters. It has

determined under what conditions transport of these solutes is likely to occur, and

has also identified small-scale processes that can contribute to the form and

subsequent mobilisation of Fe. Such processes are characteristic of these coastal


settings. With any future development of these coastal zones by increased population

and associated modification it is important to consider the connection between

landuse and shallow alluvial aquifers of the coastal plain. Many residential activities

will potentially impact on marine waters through groundwater interaction (and

decrease the amount of potable water for residential use), and the flushing of nutrient

loads from the catchment to the marine environment during high rainfall events.

These activities that affect the form of Fe and potentially lead to its mobilisation in

catchments (such as increasing the input of DOC to waterways and/or decreasing pH

and Eh of waters) should be considered from a management strategy, so as not to add

to loads already input to marine waters by natural processes.

The area studied is adjacent to the Great Sandy Strait, a Ramsar-listed wetland of

international significance; it is the largest and least disturbed wetland area in

southern Queensland, and supports many vulnerable species and is adjacent to the

World Heritage listed Fraser Island. The environmental integrity of this area has

substantial value, both economically and inherently. Increasingly there is awareness

of water quality issues by many governmental and community groups in southeast

Queensland, Australia-wide, and globally, particularly in relation to algal blooms and

impacts of urbanisation. Determination of potential transport of nutrients and Fe is of

high value. In addition to contributing to the general degradation of water quality,

excess nutrients and Fe discharging to the Great Sandy Strait can also contribute to

the growth of Lyngbya and result in significant environmental and economic losses

to this area. This thesis provides important information relating to nutrient sources

and hydrochemical processes in these types of coastal catchments and will be a

useful reference for further research and monitoring with the aim of preventing water

quality degradation and associated negative impacts such as algal blooms.

235

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APPENDIX A

Conference abstracts

Appendix A: Conference abstracts 253

Australian Earth Sciences Convention Abstract

Using physico-chemical, ionic and multi-isotope data to establish hydrochemical facies and potential contaminant pathways in a coastal pine plantation catchment, Fraser Coast, Queensland Genevieve Larsen, Queensland University of Technology, Associate Professor Malcolm Cox, Queensland University of Technology

In addition to the discharge from surface drainage systems, water in coastal aquifers is often discharged to the sea. This groundwater input is an often overlooked yet possibly significant process in the geochemical and nutrient budgets of marine near-shore waters. Nutrient and/or metal rich waters can also take indirect routes to protected marine areas. There are many forms of ground and surface water mixing including interaction between rivers and aquifers, oceans and aquifers and hydraulically connected aquifers (Cable et al. 1997; Moore 1999). The chemical and isotopic character (hydrochemical facies) of surface and sub-surface coastal waters within a forested coastal plantation catchment, Fraser Coast, Queensland, are described using graphical and statistical methods. A number of well-established interpretation methods, including scatter plots, Piper and Stiff diagrams and cluster analysis, are used in order to (a) understand dominant hydrological processes; (b) group sites by similar characteristics (hydrochemical facies); and (c) identify sites of potential interaction between surface and subsurface water bodies.

Overall, soils and sediments in the study area are highly siliceous and nutrient poor. Results indicate only isolated anthropogenic nutrient inputs to groundwaters most likely the result of the application of organic fertilizers or septic tank effluent in a residential area. Waters are predominantly Na-Mg-Cl type. Major ion concentrations are contributed by rainfall, tidal flux within shallow coastal aquifers and drainage systems, and soluble salts and evaporites within discontinuous clay layers present throughout the area.

The analysis and interpretation of isotopic, physico-chemical and ionic data indicate seven hydrochemical facies within the ground and surface waters in this region. These generally correlate spatially both geographically and to some extent with depth in the lithological profile. The groups can be differentiated based on level of tidal intrusion, level of confinement, recharge areas and lithology and to some extent organic input and microbiological activity.

The similarity in hydrochemical character between many of the surface and shallow ground waters sampled indicates significant groundwater baseflow contribution to the drainage systems making this a potentially significant pathway for nutrients from the surrounding plantation areas. In addition, shallow groundwaters adjacent to the Poona Creek estuary clearly show tidal influence. The differences in major ion concentrations, Na, Cl and Mg, within groundwater samples in the northern catchment of the study area indicate that there is little to no interaction between more saline unconfined groundwaters and a deeper confined coarse saprolite aquifer. However, two coastal residential bore samples indicate marine influence and therefore interaction between these semi-confined groundwaters and the adjacent estuaries, another possible pathway for contaminants to take.

254 Appendix A: Conference Abstracts

Groundwater 2010 Abstract

TITLE: CLUSTER ANALYSIS TO SUPPORT GRAPHICAL METHODS IN

THE CHARACTERISATION OF GROUND AND SURFACE WATERS IN A

SUBTROPICAL COASTAL CATCHMENT, FRASER COAST,

QUEENSLAND

Author/s: Genevieve Larsen1 and Malcolm Cox

1

Affiliation/s: 1 Biogeosciences, Faculty of Science & Technology, Queensland University of

Technology

Introduction

Groundwater hydrochemistry and isotope hydrology are being investigated in the catchments of the

Fraser Coast region of Queensland. These catchments host plantation forests and are adjacent to the

Ramsar-listed Great Sandy Strait, a passage landscape between Fraser Island and the mainland. This

region is formed of a low-lying coastal plain with tidal creeks which drain elevated catchments within the bedrock ranges. Groundwater occurs within complex systems of semi-confined and confined

aquifers with variable connectivity to the shallow drainage system. Land-use in the region consists

mainly of Pinus plantations ranging from 16 to 30 years of age with native vegetation buffer zones

adjacent to natural waterways; on the coastal zone are small residential communities that typically use

groundwater locally.

Although natural waters in the area can have highly variable physico-chemical properties, based on

their major dissolved ions they tend to be of Na-Cl or Na-Mg-Cl type. Waters within these coastal

regions are typically Na and Cl dominated due to both the presence of cyclic salts in the local rainfall,

and to direct mixing of brackish-saline waters (McNeil et al., 2005). Further, mineralogical, and

physiographic variability is relatively limited in the study area. These features limit the ability to

group waters into hydrochemical facies, an important step in determining connectivity between different waters, and possible mechanisms/pathways for the transport of nutrients and/or metal loads

from the coastal zone to marine areas. After applying most of the conventional graphical methods,

such as scatterplots, Piper and Stiff diagrams, it was decided to compare the hierarchical cluster

analysis (HCA) approach to augment the interpretation.

Methods and Results

Hierarchical cluster analysis was used to partition the data into groups of similar hydrochemical

character. Cluster analysis datasets were identical to those typically used for the construction of Piper

diagrams, i.e. Na+, Mg2+, Ca2+, Cl-, SO42-, HCO3

- in % meq/L, to enable the direct comparison of

results from the two methods. All data were converted to z-scores to ensure equal weighting for all

variables and statistical analyses were carried out using Matlab 7.8.0 (R2009a). In order to examine

the grouping of fresh ground and surface waters in more detail, the data was separated into sets of fresh, brackish and saline samples.

Interpretation of the Piper and Stiff diagrams revealed six hydrochemical facies among the surface and

groundwaters in this region, three of which had two subfacies. Although there were many similarities

between the groupings using both the Piper diagram and cluster analysis, nine of the forty sites were

allocated to different groups. Differences are mainly due to the subjective nature of the graphical

method. Overall, HCA results revealed smaller-scale differences between samples, partitioning fresh

ground and surface waters that are difficult to differentiate using Piper diagrams. In addition, the

partitioning of samples within the fresh, brackish and saline datasets agrees well with what is known

about hydrological/hydrogeological processes and settings within the study area.

Conclusions The equal weighting of variables ensures that all ions, regardless of magnitude, contribute to the

partitioning of samples and reveals differences/similarities between samples that may not be detected

using graphical methods alone. HCA also has the advantage of being a more objective method than

graphical methods where the assignment of samples to hydrochemical facies can be influenced by


Appendix A: Conference abstracts 255

Unlike graphical methods, the results from HCA are not directly useful for identifying dominant

processes and factors contributing to the character of natural waters. However, HCA can be used to

enhance graphical interpretation and, in cases where waters have similar chemical character, makes

the partitioning of samples into hydrochemical facies a much more efficient and objective process.

References

McNeil, V.H., Cox, M.E. and Preda, M. 2005. Assessment of chemical water types and their spatial

variation using multi-stage cluster analysis, Queensland, Australia. Journal of Hydrology, 310, 181-

200.

256 Appendix A: Conference Abstracts

HydroEco 2011 Abstract

Controls over dissolved Fe within groundwater and surface water micro-environments in a subtropical coastal setting, Fraser Coast, Australia

Genevieve Larsen1,2, Malcolm E. Cox1,2, James J. Smith1 1 Biogeosciences, Faculty of Science & Technology, Queensland University of Technology 2 National Centre for Groundwater Research & Training A multi-disciplinary study of surface and groundwaters and their hydrochemistry with particular emphasis on controls over Fe distribution has been conducted in forested coastal catchments and the adjoining coastal plains on the Fraser Coast in sub-tropical Queensland, Australia. The aim of the study is to determine the distribution of Fe, other metals and nutrients and whether there is potential transport of them to the marine environment. Also considered in the study is the complexity and variable scale of hydrological systems in this setting. In coastal settings, there are many forms of mixing between groundwaters and surface waters, including interaction between aquifers and rivers, estuaries, bays and ocean shorelines; all potential routes for solutes such as dissolved Fe. Within these systems, processes that affect Fe dissolution and speciation can often add to dissolved Fe loads ultimately transported to the marine environment. The aim of this paper is to describe some of these processes occurring at three sites within the study area. Regional characterisation of ground and surface waters within the study area established that waters are typically Na and Cl dominated due to the presence of cyclic salts in local rainfall, and direct mixing of brackish-saline waters. These waters showed consistent proportions of major ions (Na+, Mg2+, Ca2+, Cl-, SO4

2-, HCO3-) overall, but highly variable physico-chemical conditions (pH, Eh and DO),

organic input and microbiological activity which can all affect dissolution, speciation and consequently transport of Fe within these systems. Three sites or micro-environments were the focus of this study: a) a freshwater pond excavated for forestry purposes within the southern catchment drainage system; b) a shallow pool with intermittent interaction with the drainage system in the northern catchment; and c) a shallow monitoring well within a semi-confined alluvial aquifer close to the drainage system in the southern catchment. All three sites had unique physico-chemical and morphological characteristics and as such were considered as micro-environments within the context of broader-scale regional processes. The main sources and processes identified are water column stratification, organic complexation of Fe and microbial activity contributing to concentrations and speciation of dissolved Fe at these sites using organic (DOC), physico-chemical, ionic (Fetotal, Fe

2+), and isotopic (δ

15N, δ

34S and δ

13C) analyses. We also identify flow regimes,

morphology and lithology and relate them to various processes.

APPENDIX B:

Monitoring well graphic borelogs

Appendix B: Borelogs 259

P2 P3

P4 P5

P6 P8

260 Appendix B: Borelogs

P9 P10

P7


Only one borelog has been included for the Tertiary alluvium aquifer as all of the bores have very similar profiles – JL1, JL2, JL7, JL8, JL9,

JL10, JL13, JL20 and JL25. Elliot Formation varies from 2 to 12 m depth and the Tertiary Alluvium aquifer from 23 to 40 m depth in all cases

underlain by the Maryborough Formation

262 Appendix B: Borelogs

Transect of boreholes adjacent to Poona Creek estuary

P10 P9 P3 P6 P4 P8 P2 P5

Note that this transect has not been scaled horizontally. Borelogs are scaled vertically from the ground surface as metres below P10. P10 ground

surface is a 4.39 m AHD. Refer to earlier borelogs for description of sediment layers.


Schematic of the profiles from the Wang (2008) study showing regolith zone, geological profile, distribution of mineralogy (cumulative %), and

the depth of monitoring bores. C2d from this study is classified as a deep bore, C3 as an intermediate bore and C4 and C5 as shallow bores.

Source: Wang (2008)

Soil

Ferricrete

Mottled saprolite

Fine saprolite

Coarse saprolite

Bedrock

Clayey sand

Sandy clay

Clay

Fine to medium

sand Cemented iron oxide

Sandy clay Clayey sand

Clay

Mudstone

Quartz

Clay

Smectite

Kaolinite

Feldspart

Goethite +

Hematite

Regolith zones Profile Texture Bores

Intermediate bores

Shallow bores

Deep bores

Mineralogy

0 50% 100%

APPENDIX C

Photos of data collection sites

Appendix C: Data collection sites 267

B1, semi-confined groundwater (8.0m depth) 100m from Buttha Creek

P1, groundwater (4.5m depth) adjacent to mature forest compartment

Transect of boreholes was drilled parallel to this road oriented perpendicular to Poona Creek estuary (P10, P9, P3, P6, P4, P8, P5)

Forestry compartment 100m south of P10 (southern end of transect)

268 Appendix C: Data collection sites

P11, a shallow borehole (1.2m) in the muds and sands of the supratidal flats in between the transect road and Poona Creek estuary



View looking across the supratidal flats towards the estuary from the end of the transect. Poona village is located on the other side of the estuary


C2d, a confined fresh water borehole (13 m depth) in the Tuan catchment

C3, a brackish unsaturated groundwater borehole (7 m depth) in the Tuan catchment

C4, a brackish unsaturated groundwater borehole (3.8 m depth) in the Tuan catchment

C5, a brackish unsaturated groundwater borehole (4.0 m depth) in the Tuan catchment


LRB, a fresh water stream in the elevated Poona catchment

PB, an estuarine surface water sites in the Poona catchment coastal plain

PCM, a surface water site at the mouth of Poona Creek

PC9, an incised fresh water stream in the elevated Poona catchment


PC10, a fresh water stream in the elevated Poona catchment

WP11, an excavated water hole within the coastal plain

WP12, an excavated water hole within the coastal plain

WP31, an intermittent fresh water stream in the elevated Poona catchment


TCA, a fresh water stream in the Tuan catchment

TCB, an estuarine surface water site in the Tuan catchment

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