LIMNOLOGICAL STUDIES OF

DYSTROPHIC WATERS

by

Lee Clifford Bowling, B.Sc. ( Hons)

in the Department of Botany

Submitted in fulfilment of the

requirements for the degree of

Doctor of Philosophy

University of Tasmania

January, 1988

DECLARATION

This thesis contains no material which has been

accep ted for the award of any other h igher degree

or graduate d iploma in any tertiary institution

and that , to the best of the candidate ' s knowledge

and bel ief , this thesis contains no material

prev iously published or written by another person ,

except when due reference is made in the text of

the the s i s .

Lee C . Bowling

ABSTRACT

A number o f asp ects o f the l imnology o f dystrophic lent ic

freshwaters are covered in this thes is . Initially , studies covering

a wide range of heterogeneous lakes and reservoirs from several

different areas are reported , to give an overall perspective of many

o f the roles d i s solved humic substances play in v arious l imnological

processes . More detailed case s tudies of a number o f dystrophic lakes

and reservo irs are then outlined , to demonstrate how dissolved humic

substances actively influence the limnology of these individual waters .

Inves t igations o f the underwater l igh t cl imates of f ifty lakes

and reservoir s f r om Tasmania , thirty-seven from north-east New South

Wales , and o f twenty- s ix coastal dune lakes in south-east Queensland

showed that dissolved humic substances were the maj or attenuators o f

l ight i n all three areas . Increasing gilvin concentrat ions led to

the rap id ext inction o f l ight at shallow dep th s , and to changes in

its underwater spectral distribut ion from green-yellow in the

clearest water s , to red in the most humic . Turbidity and phytopl ankton

were important c ont r ibutors to attenuation in only a few of the waters

studied . Resul t s from Tasmania allowed the cons truction of a

predict ive model for use in estimating the underwater l ight climates

of the many remote l akes of the island where in s itu measurements are

impossible , from s imple laboratory measurement s o f small water samples .

The rap id attenuation o f l ight in humic waters also strongly affects

thermal strat i f ication , leading to strong thermal gradients , shallow

thermoclines , and l engthy periods of stratification .

Chemical aspects were also examined. S trong negative correlations

were found between the concentration of dis solved humic substances and

pH in coastal dune l ake waters from south-east Queensland , King and

Flinders Island s , and western and south-west Tasmania . In contrast ,

there was no correlation between these two parameters in north-east

New South Wales waters , probably due to lower humic concentrat ions

and buf fering by higher bicarbonate levels . Calcium and bicarbonate

l evel s were al s o sometimes low in acidic , dystrophic lakes .

A wide range o f photosynthetic organisms were present in the s ites

investigated from New South Wales , Queensland , and coastal l akes of

south-west Tasmania . Phytoplankton came both from the Chlorophyceae

and from o ther algal d ivisions , and desmids and d ino flagellates were

e specially common . Proportions of green algae decreased relative

t o those with acces sory pho tosynthetic pigments , as humic concentr at ion

increased , in the h ighly humic western and south-west Tasmanian lagoons ,

but this was no t app arent in the less dystrophic waters of the o th er

two areas . However , high humic concentrations reduced the number of

phytopl ankton g enera present from all group s . Chrysophytes dominated

the phytoplankton communities of polyhumic Lake Chisholm .

S tudies o f Lake Chisholm , the reservoirs o f the Pieman River

Power Development , and the meronictic lakes of the lower Gordon Riv er ,

all in Tasmania , showed humic materials played an important role in

their l imnology . The rapid attenuation of l ight , and sub sequent

s trong thermal s trat ification for much of the year lead to sluggish

c irculation , all owing near-mero�ict ic conditions in Lake Chisholm ,

and the protect ion and resultant slowing of the demise o f ectogenic

meromixis in the Gordon River l akes . The se features, along with

enhancing the sol��9ility of iron and manganese in the reduc ing ,

sulphide l aden bottom waters of the Pieman River reservoirs , enabled

their chemical s tratification . However , other factors , such as basin

morphometry and shel ter , are also of importance in the l imnology o f

these l akes and reservo irs .

ACKNOWLEDGEMENTS

I wish to thank my supervisor , Dr P A Tyler , for his valuable

as sistance and encouragement throughout the proj ect . I also thank

Dr M A Brock for her encouragement during the final stages of this

work , and for her construct ive c omments on the initial drafts of

this thesis .

I am grateful al so for the interest and assistance o f the staf f

and postgraduate studentsof the Dep artment o f Botany , Univer s ity o f

Tasmania during the earl ier stages o f this project . In the same v e in ,

I acknowledge the encouragement and assistance of the staff and

po stgraduate students o f the Department o f Botany , University of New

England , during the l ater period of the work , and for allowing me t o

continue with the proj ect after my move there .

I thank the Internal Resear ch Grants Committee , University of

New England , for research money whi ch allowed the collection of

data from nortfreast New South Wales and south-east Queensland , and

the Tasmanian National Parks and Wildlife Service for a research

grant and logist i cal support to enable sampling of remote coastal

lagoons in western and s outh-wes t Tasmania . The remainder o f the

work reported in this thesis was carried out using various research

grants made to my superv isor .

I am particularly indebted to the many people who freely made

time avail able to assist with f ield work . O f part icular note are

J M Ferris , who al so advised on use of the LIMNO computer program ,

0 Bourke for her assistance on Fraser Island , and R L Croome , with

whom data from the Gordon River has been j ointly collected and shared .

R. D. King also made his original field note-books avail able so I

could use data from 1 9 77 and 1 9 7 8 f or the computation o f stabilities ,

heat budgets , and other similar p arameters.

The cheerful help of Mrs Rosemaree Wickham throughout the proj ect

is al so acknowledged . Mrs J Hanlan is thanked for her t yp ing . I

thank R J Ban�ns for assistance with the nutrient analyses o f waters

from north-east New South Wales , south-east Queensland , and western

and south-west Tasmania .

Finally , I wish to thank my wife , Regie , and children for their

support and forbearance during the course of the proj ect , especially

during my many absences from home ; and my p arents for their

encouragement , and for funding the production costs o f this thesis .

I therefore dedicate this thesis to my family , without whose help

it would never have eventuated .

TABLE OF C ONTENTS

CHAPTER 1 : INTRODUCTION TO THE STUDY

1 . 1 Aims and Signif icance 1 . 2 The S cope of this Thesis

CHAPTER 2 : A REVIEW OF LITERATURE RELEVANT TO THI S STUDY

P ar t One : Descrip tion of S tudy Areas

2 . 1

2 . 2

2 . 3

A Limnological Background to Tasmania

2 . 1 . 1 2 . 1 . 2 2 . 1 . 3 2 . 1 . 4

The Western Limnological Province The Eastern Limnological Province The Coast al Limnological Province Additional Limnological Studies in Tasmania

A Limnological Background to North-east New South Wales

A Limnological Background to Studies on Coa s t al Lakes

2 . 3 . 1 2 . 3 . 2

The Nature of Australian Coast al Dune Lakes Studies of Coa s t al Lakes of the Australian

Mainland

Part Two : A Theoretical Background to the S tudies

2 . 4

2 . 5

2 . 6

The Nature of Humic Substances in Aquat ic Sys t ems

2 . 4 . 1

2 . 4 . 2 2 . 4 . 3 2 . 4 . 4 2 . 4 . 5

2 . 4 . 6

The Chemistry , Origin , and Distribution of Dis solved Humic Substances

Humic Sub s t ances and Colour Humic Sub s tances and pH Humic Sub s t ances and Metal Ions The Ecological Significance of Humic

Sub s t ances Limnological Features of Humic Lakes -

Examples from Finland

Factors Determining the Underwater Light Climates of Lakes

2 . 5 . 1 2 . 5 . 2

2 . 5 . 3 2 . 5 . 4 2 . 5 . 5

The Fate of Light in Water Components of the Aquatic Medium Caus ing

Ab sorption and Scattering The Op tical Properties of the Water Column The Attenuation of P . A . R . with Dep th Studies of Light At tenuat ion in Aus tralian

and New Zealand Inland Waters

A Background to Chemical Stratificat ion and Meromixis

2 . 6 . 1 2 . 6 . 2 2 . 6 . 3

The Nature of Chemical S tr atificat ion Meromixis in Impoundments Causes of Biogenic Meromixis in

Impoundments

1

1 2

5

5

5

5 8 9

10

10

1 1

1 1

13

18

18

18 19 20 20

2 1

23

27

27

27 29 3 1

3 1

34

34 35

36

CHAPTER 3 : STUDIES OF THE u�ERWATER LIGHT CLIMATES OF LENTIC FRESHWATERS FROM TASMANIA , NORTH-EAST NEW SOUTH WALES , AND SOUTH-EAST QUEENSLAND 3 7

3 . 1 Introduct ion 3 7

3 . 2

3 . 3

3 . 1 . 1 3 . 1 . 2

Methods

3 . 2 . 1 3 . 2 . 2

Resul t s

The Aims and S cope o f the Study The S tudy Sites

Sources of Data Collection and Analysis of Samples , and

Computation of the Data

P art A : Tasmania

3 . 3 . 1 3 . 3 . 2 3.3 . 3 3 . 3 . 4 3 . 3 . 5 3 . 3 . 6

Colour , Turbidity , and Chlorophyll a Attenuation of Total P . A . R . Reflectance and S cattering Coefficients Spectr al D is tr ibution of Underwater P . A . R . Secchi Disc Transparency Regres sion Analysis

P art B: North-east New South Wales

3 . 3 . 7 3 . 3 . 8 3 . 3 . 9 3 . 3 . 1 0 3 . 3 . 1 1

3. . 3 . 1 2

Surface Temperature , pH , and Conductivity Total Nitrogen and Total Phosphorus Turbidity , Colour , and Chlorophyll a The Attenuation of P.A . R . Reflectance and the Scattering

Coefficient The Sp ectral Dis tribution of Underwater

P . A . R . 3 . 3 . 1 3 Secchi Disc Tran sparency 3 . 3 . 1 4 Regres sion and Correlation Analyses 3 . 3 . 1 5 Phytopl ankton

Part C : South- east Queensl and

3 . 4

3 . 5

3 . 3 . 1 6 Temper ature , p H , and Conductivity at 1 8°C (K1 8 )

3 . 3 . 1 7 Total Nitrogen and Tot al Phosphorus 3 . 3.1 8 Turbidity , Colour , and Chlorophyll a 3 . 3 . 1 9 The At tenuation , Reflectance , and

S cattering of P .A . R . 3 . 3 . 20 Secchi Disc Transparency 3 . 3 . 2 1 Regression and Correlations 3 . 3 . 2 2 Phytoplankton

Discussion

3 . 4 . 1

3 . 4 . 2

3 . 4 . 3 3 . 4 . 4

3 . 4 . 5

Factor s Influencing the Underwater Light Climates of the Three S tudy Areas

Upwelling Irradiance , Reflectance , and Scattering

Humics , Turbidity , and Chlorophyll a Op tical Clas sifications of the Lakes

of the S tudy Areas Phytoplankton Diversity and Distribut ion

Conclusions

37 38

4 1

4 1

46

46

46 46 49 52 6 1 6 1

64

64 64 64 66

68

68 74 74 7 6

7 9

7 9 7 9 8 1

8 1 85 85 87

8 7

8 7

9 5 9 7

9 7 1 04

1 06

CHAPTER 4: PHYSICO-CHEMICAL STUDIES OF FRESHWATER COASTAL LAGOONS FROM WESTERN AND SOUTH-WEST TASMANIA , AND FROM KING AND FLINDERS ISLAND , BASS STRAIT 108

4 . 1 Introduction 108

4 . 2

4 . 3

4 . 4

4 . 1 . 1 The Aims and S cope of This S tudy

Methods

4 . 2 . 1 Collection and Analyses of Samples

Results

4 . 3 . 1 4 . 3 . 2 4 . 3 . 3 4 . 3.4 4 . 3 . 5 4 . 3 . 6 4 . 3 . 7 4 . 3 . 8 4 . 3 . 9

4 . 3 . 10

Thermal and Oxygen Profiles Turbidity and Colour Secchi Disc Dep th pH , Conduct ivity , and Salinity Maj or Ions Present Dis solved Iron and S ilica Nutrient Analyses Pearson Correlation Analysis Princip le Co-ordinates Analysis of the

Lagoons from the Bass S trait Islands Phytoplankton Present in the Coastal

Lagoons of Western and South-wes t Tasmania

Discussion

4 . 4 . 1 The Physicochemical Properties of the Coastal Lagoons

4 . 4 . 2 The Phytoplankton o f the Lakes of Western and South-wes t Tasmania

4 . 5 Conclusions

CHAPTER 5: DETAILED LIMNOLOGICAL STUDIES OF DYSTROPHIC LAKES AND RESERVOIRS FROM WESTERN TASMANIA

5 . 1 Introduct ion

5 . 2

5 . 3

5 . 1 . 1 5 . 1 . 2

Methods

The Aims and S cope of these S tudies The Study Areas

5 . 2 . 1 Dat a Collection and Analysis

Results

P ar t A : Lake Chisholm

5 . 3 . 1 5 . 3 . 2

5 . 3 . 3

Physicochemical Features of Lake Chisholm Thermal Stabilities and Birgean Wind Work

for Lake Chisholm Biological Features of Lake Chisho lm

Part B : The Reservoirs o f the Pieman River and Lake Barrington

5 . 3 . 4 5 . 3 . 5 5.3 . 6

Physico chemical Features of Lake Mackintosh Phys icochemical Features of Lake Nurchison Physicochemical Features of Lake Roseb ery

108

109

109

113

113 113 117 117 120 120 122 123

126

126

13 1

13 1

135

136

138

138

138 139

144

146

146

146

157 160

163

163 166 180

5 . 3 . 7 5 . 3 . 8 5 . 3 . 9

Physicochemical Features o f Lake Pieman 1 80 Physicochemical Features of Lake Barrington 1 83 Volume Weighed Average Temperature and

Oxygen ; Heat C ont ent s , Thermal Stabilities and Birgean Wind Work in the Five Reservoirs 1 85

P art C: The Lakes of the Lower Gordon River Area 1 9 0

5 . 3 . 1 0 Physicochemical Features o f Lake Fidler 1 90 5 . 3 . 1 1 Physicochemical Featur es o f Sulphide Pool 1 93 5 . 3 . 1 2 Physicochemical Featur es of Lake Norrison 1 99 5 . 3 . 1 3 Cal culations o f Meromictic S t ability 1 99

5 . 4

5 . 3 . 1 4 Thermal Stabilit ies , Birgean Wind Hark , Heat Content, and Volume Weighed Average Temperatures

D iscussion

5 . 4 . 1

5 . 4 . 2

5 . 4 . 3 5 . 4 . 4

5 . 4 . 5

The Role of Humics in the Limnology of these Lakes

The Inf luence o f Basin Morphometry , Alignment, and Shelter from Wind Action

Heating and Mixing Dynamics Meromictic Tendancies in the Lakes and

Reservoirs The Future of Meromixis in Lake Hurchison ,

Lake Barrington , and the Gordon River Lakes

5 . 4 . 6 Signif icance of the Gordon River Lakes to the World Heritage Area of South-west Tasmania

5 . 4 . 7 The Ecology of Phytoplankton in Lake Chisholm

5 . 5 Conclus ions

CHAPTER 6 : THE LIMNOLOGY OF DYSTROPHIC WATERS

6 . 1 Conclus ions from the Study

REFERENCES CITED

APP ENDIX 1: Papers Resul ting from this thesis

20 1

2 1 0

2 1 0

2 1 5 2 1 8

220

223

226

227

228

231

23 1

234

253

1

tlfEAPTER OINE

INTRODUCTION TO THE STUDY

1.1 AIMS AND SIGNIFICANCE

The genesis o f this thesis lies in the s trong influence dissolved

humic substances hav e on the limnological face of Tasmania . The island

can be divided into two distinct limnological provinces , an east ern one

of predominE.nt ly clear , oligotrophic water s , and a 1.;restern one dominated

by highly dystrophic wat ers . This results from a maj or geological ,

t opographical , vege t ational , and climatic discontinuity which occurs

on a north-west t o south-east axis , approximat ely midway acro ss the

island (Buckney and Tyler , 1973a , and references therein) . Additionally ,

a third province , taking in all coastlines , and containing all the

highly humic coa s tal lagoons , can also be recognized .

Dissolved h umic substances bestow special properties to water ,

and the se ar e t he topics of this thesis . Even at low concentration

they are a powerful determinant of the underwater light climate3 strongly attenuating and spectrally modifying penetrating irradiance .

Thi s has permit t ed a classif ication of lakes by their optical charac t ers

predicated in l arge measure on a gradient of humus concentration . Highly

humified lakes also d isplay special thermal characteristics , with sharp ,

strong thermal g radients existing at shallow depths . This creates a

predisposition t owards incipient meromixis , and aids the maintenance o f

meromixis i n sev eral small Tasmanian lakes , and in some dystrophic

reservoirs .

Additiona l ly , the limnological effects brought about by dissolved

humic substances on underwat er optics , thermal regimes , and hydrogen

ion concentration s trongly influence the ecology of dystrophic water s ,

determining the f lora and fauna found within them . A distinctive

f lora containing new genera and species occurs in the highly coloured

2

lakes in western Tasmania , and in the humic lagoons around the coast

( Croome and Tyler , 1 987a , b ; Croome et al , 1 987 and in press) . _ Dys troph ic

and polyhumic l akes have also been identified as rich sources of

phytoflagellates in Finland , and ecological and behavioural s tudies

of these organisms have centred on them ( Ilmavir t a , 1 980 , 1983 , 1984 ;

I lmavirta et al 1 98 4 ; Jones and Arvola , 1 984 ; Arvola 1 986 ) .

Thus , disso lved humic substances have a p ervading influence on

the physical , chemical , and biological character of many Tasmanian

inland waters . Because of this , this thesis concentrates on dystrophy

as a feature o f great interest and significance in the l imnology and

phytoplankton f loristics of the island . Additional to the investigation

of Tasmanian dystrophic lakes and reservoirs , it also enquires as t o

whe ther humus exer t s a s imilar dominant role i n the physico-chemical

l imnology and ecology of standing freshwaters from o ther parts of

Australia , notab ly t hose of north-eas tern New South Wales and of the

coast al dune ar eas o f south-east Queensland .

1.2 THE SCOPE OF THIS THESIS

This thesis has two obj ectives . Firstly , it aims to give an

overall perspect iv e o f the roles dissolved humic substances p lay in

determining the charact er of freshwater bodies , through its influence

on their physical and chemical properties , and on their b iology . The

second obj ective is t o demonstrate the effect dis solved humic substances

have on the l imnology of some individual lakes and reservoirs . These

more detailed indiv idua l studies , when considered together , also

represent a p r o gress ive series which illustrate many of the features

neces sary to bring about the es tablishment and maintenance of meromixis .

Chapt er Two present s reviews of the literature relevant to this

thesis . However , because several different aspects of the limnology

of dystrophic waters are addressed , this review takes a number of

parts . Fir stly , a detailed limnological introduction t o the main study

area , Tasmania , is prov ided , and the maj or featur es of lentic fresh­

waters from north-east Ne1.;r South Wales , where some comparative

investigations were undert aken , are also outlined . Additionally ,

various limnol ogical studies o f coastal lakes o f the Australian

mainland are rev iewed . The nature of humic sub s t ances in aqueous

sys t ems is then discussed and studies conducted on humic lakes in

Finland are used to examplify the effect s these have on the physio­

chemical l imnol o gy and ecology of small lakes . A theoretical

3

background on factor s affecting the spectral distribution and

attenuation of underwater irradiance is also presented , and the

literature dealing with the light climate s of Australian and New

Zealand inland waters discus sed . Finally , factors contribut ing to

the establishment o f meromixis in reservoirs are examined .

The third chap ter investigates factors bringing about the

attenuation of solar radiation and the resultant underwater l ight

climates of lentic inland waters . The inf luence of humus is examined

over a series of increasingly humic lakes and reservoirs from Tasmania ,

north-east New South Wales , and south-east Queensland , and relationships

between the light climates and attenuating factors sought . C omparisons

between the three areas can also be made , as nearly all s tudy sites in

New S outh Wales were impoundments , while those o f Queensland were

natural oligotrophic coastal dune lakes . The phytop lankton o f these

New S outh Wales and Queensland waters are also reported, and their

distr ibutional trends examined in relation to the underwat er light

climates and nutrient levels of their habitats . The resul ts o f the

survey o f Tasmanian waters have been used to develop a method for

predicting the light climates of remote lakes on the island where

in situ measurements can not be made .

Studies into various physio-chemical and ecological aspects of

humic coastal lakes and lagoons from western and south-wes tern

Tasmania , and from King and Flinders Island , in Bass Strai t , are

detailed in Chap ter Four . Such sites represent a rich limnological

resource . Optical parameters and the ionic and nutrient chemistry

o f these waterbodies wer e measured , and correlations sought b etween

them . Comparisons of the lagoons from the islands vlith those of

south-west Tasmania reveals similarities and differences , and the

waters from both areas p rovide opportunities to test the empirical

relat ionship s developed between op tical properties and attenuating

factors in Chap ter Three . The phytop lankton of some of the south­

wes t Tasmanian lagoons was also surveyed .

Chapter Five presents more detailed accounts of investigations

on individual lakes and reservoirs from western Tasmania . These

include studies of p olyhumic Lake Chisholm , the reservo4rs of the

Pieman River Power Development and Lake Barrington , and the small ,

dys trophic lakes along the lower Gordon River , in particular those

which were meromictic . The comp utation of the heating and mixing

4

dynamics o f these lakes has highlighted the dominant influence their

high humic concentrations have on their physico-chemical limnology , as

well as the various o ther factors pushing them t owards meromixis , or

o therwise . Some aspect s o f the phytop lankton e cology of Lake Chisholm

ar e also examined brief ly .

Thus , the d ifferent aspec t s of this study serve to illustrate the

important role p layed by dissolved humic substances in the limnology

o f dystrophic water s . Thes e are discussed in Chapter Six .

5

ICIHIAPTER nm

A REVIE W OF LITERATURE RE LEVANT TO THIS STUDY

Part One

Description of Study Areas

2. 1 A LIMNOLOGICAL BACKGROUND TO TASMANIA

2. 1 . 1 The Western Limnological Province

The wes t ern area o f Tasmania is a region of many l ow but rugged

mountain ranges , with a geolo gy composed predominantly of met amorphosed

pre-Cambrian rocks . The area receives high amounts of rainfall from

the prevailing wes t erly winds , and has cool temperate rainforest or

Cyperaceous sedgelands as its dominant vegetation . Th s produce a

thick mantle o f peat which overlies the nutrient poor b edrock. Many

of the lakes are o f glacial origin , occupying cirques . Although some

may vary in their chemical composition , the are for the mo s t part

dilute , with ionic proportions resembling seawater, acidic , and

humif ied (Buckney and Tyler , 1 9 7 3a , b ) . Most are either warm monomic tic

or polymi c t ic in thermal behaviour (Tyler, 1 974) , but some alp ine lakes

may be dimict i c (S t eane , 1 9 7 9 ) .

S tudies o f four small , humic lakes amongst the cool temperate

rainforest of the l ower Gordon River region typify the limnological

characteristics of wes t ern Tasmania . Three , Lake Fidler , Lake

Morrison , and Sulphide Pool , are of spec ial interest in that they

were meromic t i c when f irst investigated (King and Tyler , 1 98 1 a ,

1 982a , 1 98 3 ) , and are the subj ect o f fur ther investigat ions reported

in Chapter 5 . tf.;.;;.: llil

The���� tare backswamp lakes , at river level , but separat ed from f'illlti"' , I\ by silt levee banks. Their dilute surface waters over lie more saline

AT�.J?�pre � i\.\11�� jl

monimolimnions dominated by sodium and chloride ions, /,which originated

from an estuarine salt wedge (King and Tyler, 1 98 1 a ) p enetrated

up the Gordon R iver during periods of low f low (Kearsley, 1 978, 1 98 2 ) �

rais the salinity of the riverine wat ers, which then entered the

lakes via connecting creeks through the levee bank (Bowling, 1 98 1 ;

Tyler , 1 98 6 ) .

A notable feature of the meromixis�was shallow chemoclines,

positioned one metre or less below the surface (King and Tyler, 1 98 1a,

1 982a , 1 98 3 ) . The halocline spanned one metre or more of dep th, but

the abrup t change in redox potential between oxygenated mixolimnetic

wat er s and reducing, sulpheret ted monimolimnet ic waters provided the

best manif estat ion of chemoc line position . A marked peak in

bacteriochlorophyll and turbidity, due to micro-organisms was

associated with the waters were humic and acid, and :n•"

although concentrations ofAthe monimolimnion were considerably

high er, pH also increased below the chemocline (King and Tyler, 1 9 8 1a,

1 9 82a , 1 98 3 ) .

The micros tratification of chemical parameters and micro-organisms

have been inves t igated in Lake Fidler (Baker et al, 1 9 85a ; Croome, 1 984,

1 9 86 ; Croome and Tyler 1 984a,b, 1 9 85a) , employing thin layer samp lers

samp l ing at f iv e c entimetre depth intervals (Baker et al, 1 985b) . A

micro-aerophylic z one of about fifteen centimetres formed the bottom

o f the oxy cline"' . l)issolved sulphides appeared immediately below

this, concentra t ions of which increased rap idly with depth .

Microaerophylic and obligate anaerobic bacteria occupied distinct

layers, of ten less than ten centimetres thick, across thi s oxi c /

anoxic interface . These included Ach:x•ornatiu.m cf . oxa liferum

S chewiakoff, and cf. Beggiotoasp. in the microaerophyllic zone, and

Chlorobiu.m c f . Zimico la Nadson and cf . Pe lodictyon sp. immediately

below the redoxc line� responsible for the marked p eak in

bacteriochlorophyll (Baker � �' 1 985a) . Additionally, Croome ( 1 9 84,

1 98 6 ) and Croome and Tyler ( 1 9 84a,b ; 1 985a) found dense populations

of the euglenoid Trachlemonas vo lvocina Ehrenb . , and the t iny green

flagellate alga Scourfie ldia caeca (Korsh) Belcher & Swale o ccupying

discrete s trata above the redoxc line, while a mot ile bacter ial

consortium, " Chlorochromatiwn aggregatwn" Lauterborn was also a

promin�nt member o f the stratified microbial community, o ccurring

both above and below the redoxcline. The participation of large

accumulat ions of eukaryotic algae as permanent component s of microbial

stratifications is unusual (Croome, 1 98 6 ) . The calanoid c opepod

7

Calamoecia tasmanica ( Smith) also concentrated ���a;�« and

Chaoboruslarvae migrated diurnally across the chemocline ( Baker et al

1 985a , c ) .

The mix olimniorn: o f the /.. lakes have a considerable floristic

diver sity , but a generally low biomass (Groome and Tyler , 1 9 86 ) .

Twenty-four taxa have been recorded from Lake Fidler , and sixty from

Sulphide Pool , with only fifteen being common t o both . Chrysophyceae

were more frequent in Lake Fidler , al though desmids predominated in

Sulphide Pool , and together they constitute 5 7 % o f the t otal flora.

The mixolimnion s are particularly favoured hab itats for s ilica-s caled

chrysophytes , with s ixteen species , or hal f the recorded Austral ian

flora , being repo rted from them . Four occurred only in these lakes ,

and were frequent ly present in bloom proport ions (Groome and Tyler ,

1 985b ) . One species , MaUomonas tasmanica (Groome and Tyler) Asmund

& Kristiansen concentrates in a discrete zone midway in the mixolimnion

of Sulphide Pool by day , but becomes more evenly distributed throughout

the mixolimnion at night (Groome and Tyler , 1 98 3 ) .

A dam bui l t on the mid-reaches o f the Gordon River has markedly

al tered the f low regime !dl its lower sections (King and Tyler , 1 982b ) ,

considerably limiting the extent the estuarine salt wedge can intrude

upriver . As a c onsequence , the replenishment o f monimolimnetic salts

in the lakes is also reduced , resul ting in the elimination of meromixis

in Lake Morrison in e arly 1 978 . �� Lake Fidler and Sulphide Pool

is likewise thre atened (King and Tyler, 1 982b ) .

The stratif ied micro-organisms exis ted at irradiance levels

usually below 1 % of surface incident light , and compo sed almo st

entirely o f red wavelengths (Groome and Tyler , 1 9 85 a ; Bowling and

Tyler , 1 9 86) . L ight is a l imit ing factor for these organisms (Baker

� al , 1 985a) , and any reaching the depths occupied by them is rapidly

absorbed (Bowling and Tyler , 1 98 6) . Decay and sinking of the

chemocline has p laced the micro-organisms deeper the lakes , at

depths were insufficient light is available . This �had caused their

disappearance f r om Sulphide Pool by 1 986 , while only a few of the

organisms previously associated with the chemocline of Lake Fidler

remained (Groome and Tyler , in press ) .

The fourth lake o f the area , Perched Lake , is warm monomictic

(King and Tyler , 1 98 1 b ) . I t lies above river level , away from inf lows l•;;!{f

o f saline water. k is only moderately dystrophic , and although it

8

stratifies for almos t eight months of the year , hypolimnetic oxygen

is never depleted , indicating a .low productivity . Its water chemistry '·"····'!:>" ��.�"···

is similar t o t he o ther threek lakes , being acidic , o f low conductivity ,

and with the ionic proportions o f seawater . The phytoplankton of

Perched Lake i s dominated by chrysophytes and chlorophytes , especially

desmids , but no wel l defined seasonal changes in b iomas s or species

composition have been observed (King and Tyler , 1 98 l b ) .

2 .1.2 The Eastern Limnological Provinc e

I n contra s t with the wes t ern sector , the remainder o f the island,

comprising the C entral Plateau , Midlands Graben , and Eastern Tiers ,

is mo stly o f less rugged relief , and dryer . I t s geology is dominated

by Jurassic dolerite , and the vegetation by schlerophyll forests or

epa crid heathlands . The lakes here are much more diverse . The

maj ority lie on the Central P lateau and are o f glacial origin , or

have been subj ected to periglacial ac tivity (Buckney and Tyler , 1 973a) .

Many are large , shallow , and exposed to frequent wind actio� rendering

them polymi ct ic , and even in the deepest , such as Lake S t . Clair ,

thermal s tratifi cation never fully develop s , although a few may be

warm monomictic (Tyler , 1 97 4 ) . Mo st are uncoloured , IYith pH values litl,\<2'7

close t o neutral . The �in the highest rainfall areas are very dilute ,

wi th a seawater order o f ionic dominance prevailing , but those in

lower rainfall areas t o the east have increased ionic concentrations ,

and calcium and bicarbonate as the second dominant ions (Williams ,

1 96 4 ; Buckney and Tyler , 1 973a) . A number o f saline and hyposaline

endorheic lagoons , with alkaline waters dominated by sodium and

chloride , o ccur in the Midlands , where annual evaporation exceeds

preceip itation (Buckney and Tyler, 1 97 6 ; De Deckker and Williams , 1 982) .

Lak� Sorell and Crescent are two large subalp ine lakes , and Lake

Leake and Toorns Lake two low elevation reservoirs from the eastern

limnological p rovince , which have been the subj ects of comprehensive

studies (Cheng an� Tyler , 1 97 3a ,b , 1 97 6a , b ; Croome and Tyler , 1 9 72 , l·c"\V l•ib!\•J.>

1 973 , 1 97 5 ) . ThE$ekare all limnolo gically similar, b eing shallow ,

exposed , and thus polymi ctic , and although uncoloured are considerab ly

turbid , causing low water transparencies . Their dilute waters show

some enrichment with alkaline earth b icarbonates , but sodium and l\'"1ie chloride are s till the dominant ions , andApH 's near neutral.

Lake Leake and Tooms Lake are extremely oligotrophic with sparce

phytoplankton p opulations , and may rank amongst the world ' s mo st

9

unproduct ive lakes (Croome and Tyler , 1 97 3 , 1 97 5) . In comparison ,

Lake Sorell i s mesotrophic and

contrast exists between the.

restricted t o ei ther one lake

Lake Crescent eutrophic . A marked of L�>i(lf7 Sen:!! ( t p lanktonic f loras / , with many species U\ or the o ther . Lake Crescent has t en

times the bioma s s of Lake Sorell , composed mainly of d iatoms and

filamentous green algae , while desmids and chlorococcalean algae

dominate in Lake Sorell (Cheng and Tyler , 1 97 3a , b , 1 9 7 6 a , b ) .

2 . 1 . 3 The Coas t al Limnological Province

The coastal areas of Tasmania form a third distinct iv e l imno logical

province . The lakes within it are typically acidi�humic , and of low

conductivity , but cons iderable t emporal fluctuations may o ccur in

these p arameters . Their waters generally have ionic proportions !l!k6 s imilar t o seawater , although this varies locally . The l o f the

north-east and east coasts , while s till fresh , have salinit ie s of up

L- 1 , and less dilute than the of the wes tern t:.,.,.t

to 2400 mg

coastline . The � also display a greater inf luence of calc ium and

b icarbonate in t heir ionic compositions (Buckney and Tyler , 1 9 7 3 a ;

1 97 6 ; King and C ivil Investigation Division , Hydro-Electric C ommission ,

1 9 7 8b ; Croome and Tyler , l 987a ; Croome � al , 1 987 ) . The

dys trophic , acidic coastal lake waters have been shown to be perhap s

the riches t phy t oflagellate communities of all Tasmanian freshwaters

(Croome and Tyler , 1 987b ) ®�contain a considerable number of silica-

s caled chrysophytes (Croome and Tyler , l985b ) , as well as o ther

recently described genera of dinoflagellates and chrysophytes (Croome

and Tyler , 1 987a ; Croome � al_ , 1 9 87 and in press ; Ling e t �.

in pres s ) .

The coas tal limnological province also embraces the islands of

Bass S trait . The geomorphological origins of the lakes and lagoons lt.�;ii";

of King I sland have been described by Jennings ( 1 9 5 7 ) . These/... lie in

dunes ranging from highly siliceous to highly calcarious in composit ion>

and chemical analyses (Brand , 1 96 7 ; Buckney and Tyler , l 9 7 3a , 1 9 7 6 )

have shown that , whi le many have the ionic proportions o f seawater , �IJ(I''> someAare enriched with calcium , b icarbonate , and sulphate . Salinites

range from 200 to 1 700 mg L- 1 . S ome lagoons are only slightly

co loured , but o thers are highly dystrophic , and pH values vary from

less than 5 . 0 to more than 9 . 0 in the more calcarious waters (Brand ,

1 96 7 ; Buckney and Tyler , 1 97 3a , 1 9 76 ) . The chemical characteristics

reported for lagoon waters from the is lands of the Furneaux Group are

almost identical (Buckney and Tyler , 1 97 3a , 1 97 6) .

10

2 . 1 . 4 Additional Limnological S tudies in Tasmania

Desp ite i t s many natural lakes and t arns , art ificial wat erbo d ies

now make up the greater part of Tasmania ' s lentic waters (Kirkp a trick

and Tyler , 1 987 ) . Many of these are deep , narrow and s teep s ided ,

which has contr ibuted to the chemical stratification of some ( Ty ler ,

1 980) . Mos t no t able is Lake Barrington , where dissolved iron ,

manganese , a lkaline earth bicarbonates , and sulphides render it

meromi ctic (Tyler and Buckney , 1 97 4 ) . Morphometry related anomalous

s tratification b ehaviour may also o ccur , as in Lake Gordon , where co ld

dense underf lows displace existing hypolimnetic waters upwards ( S teane

and Tyler , 1 982 ) . However , construction of imp oundments t o create new

reservo irs or t o raise the levels o f existing wat erbodies have a t

t imes been t o the detriment of Tasmanian limnology , having caused the

loss of the original Lake Fedder with its unique flora and fauna

(Tyler , 1 986 ) , and also of the unusual f lo at ing island ecosyst em

of the Lagoon o f Is lands (Tyler , 1 9 7 6 , 1 980) .

Dystrophic Tasmanian lakes harbour rich collections o f phyto­

f lagellates , including new genera and species , and some o f great

rarity (Croome and Tyler , 1 9 87a) . Elsewhere , desmids may be impor tant ,

especially in numbers of species , while the large , shallow , t urb id

lakes of the eastern limnological province are d ominated by diatoms

(Tyler , 1 97 4 ) . Tasmanian lakes also contain fauna of considerable

interest , including Anasp ididae ( Sync arida) , Phreatoicidea ( I sopoda) ,

and the Eustheniidae (Plecoptera) (Williams , 1 964 ) . Additionally ,

Galaxcidae comp r ise 60% o f the twenty- five species of Tasmanian

freshwater fish (Fulton , 1 982 ) , a number o f which are endemic with

very limited d i s tributions .

2 . 2 A.LIMNOLOGICAL BACKGROUND TO NORTH-EAST NEW SOUTH WALES

North-east New South Wa les i s a region containing few natural

lakes , and some lagoons , but numerous reservoirs (Timms , 1 9 7 0 ) . A 0 'f 1..,�!>�� wo:drr:.

survey o f the optical properties and phytoplankt on�was undertaken

as p art o f this study , to provide comparisons with similar investigations

from Tasmania , and from south-east Queensland ( see Chap ter 3 ) . A

brief account o f the limnological features o f this region is given

to provide a b ackground for this survey .

The waters of the region are d ilute , with total dissolved solids

L- 1 usually b elow 300 mg . Sodium is the dominant cation , especially

in waters near t o the coast , whi le enrichment with calcium and

1 .. 1

magnesium occur s in many from further inland . Bicarbonate is the

dominant anion , exceeding chloride in all but a few locations c lo s e w«\o>

to the coast (Timms , 1 970 ) . . Th� �from the New England area are

strongly inf luenced by the igneous geology o f their catchment s .

from b asaltic catchments have the highes t conductivitie s , with

elevated p roport ions of alkaline earth b icarbonates , and pH values

above neutral; while those from granit ic catchments are sodium and

bicarbona t e dominated , with low c onduct ivites and pH (Banens , in

pres s ) . The limnological charac terist ics of coastal dune lakes from

north-eas t New S outh Wales are giv en in Section 2 . 3 , below .

The waters o f the region display a wide range of clarit ies .

Mean vert ical at tenuation coefficients for downwelling Photosynthetically

Availab le Radiat ion (P . A . R . ) ( see Section 2 . 5 . 3 (b ) , below) measured

in a number of r eservoirs from the upper Hunter Valley , Western

Slopes , New England Tablelands , and far North Coast by Scribner

(quoted in Kirk , 1 986) ranged from 0 . 36 m-1 to 2 . 24 m- 1 . However ,

corresponding <:,ofo�JI" , turbidity , and chlorophy ll a data were not

included . Secchi depth measurement s ( Scribner , in Kirk , 1 986 ;

Timms , 1 9 7 0 ) indicate wide seasonal f luctua tions occur in the optical

parameters o f the waters from this region of New South Wales .

Few local a lgal floras have b een described for Aus tralia (Ling

and Tyler , 1 986 ) , and north-east New South Wales is no except ion .

Some observat ions were made , on samples sent to them , by European

phycologi s t s las t cent ury (e . g . Borge , Nordstedt , Raciborski -

see Ling and Tyler , 1 986) , before Playf air ( 1 9 1 4 ; 1 9 1 5a , b ; 1 9 1 6a , b ;

1 9 1 7 , 1 9 1 9 , 1 92 1 , 1 923 ) compiled extensive lists and described many

new species o f phytoplankton from the Lismore district . These

studies also inc luded chytrids and other aquatic fungi , and some

zoop lankton . More recently , Skinner ( 1 9 7 5 ) studied the Zygnematales

(Chlorophyceae) of the New England Tab lelands , and some of the

diatoms have b e en described by Foged ( 1 9 78) . Ecological s tudies

of the algae of Chaffey Dam , near Tamworth , have also b een undertaken

(May and Powell , 1 986) .

2.3 A LIMNOLOGICAL BACKGROUND TO STUDIES ON COASTAL LAKES

2 . 3 . 1 The Nature of Australian Coastal Dune Lakes

Dunes , resulting largely from Quaternary geological events ,

cover extensive regions of the Aus tralian coastal lowlands (Coaldrake ,

1 96 1 ) . Many of these areas (Figure 2 . 1 ) contain lakes , which

W.A.

.) I

N.T.

12

r-- -·- - ---_I_ -- l I I

I I

QLD.

S.A. l- - - - -- - - - - ·- , .... "', I

N.S.W.

I S.E. Queensland

N.E. New South Wales

Myall Lakes Yorke Peninsular

S.W. Western Australia S.E. South Australia

Portland

'• . , . ........

East Gippsland . , Bass Strait Island1r

t�JN.E. Ta>mania

TAS.

Figure 2.1 The locat ion of coastal lowlands and other analogous regions

in Australia , where l akes ( both freshwater and saline ) occur . After

Coaldrake (1961).

13

���ko.lli arekdystrophic, acidic, of low salinity, and with ionic proportions

close to seawater (Timms 1 982, 1 9 86a) . Studies o f acid dune lakes

and swamp s along the entire east Australian coastal s trip have shown

an as semb lage o f o rganisms from very diver se t axonomic group s which

are virtually r e st r icted to these habitats (Arthington, 1 9 7 7 ; Timms,

1 9 86a) , while those o f Tasmania have b een identified (Kirkpatrick

and Tyler, 1 98 7) as being of considerable l imnological signif icance,

with specialized phytoflagellate communities (Croome and Tyler, 1 9 87b ) .

Timms ( 1 9 82, 1 986a) classified dune lakes from the eastern

Australian mainland into s ix types, depending on mode of origin .

These include: -

1 ) P erched dune lakes, in elevated siliceous leached dunes

where accumulated organic materials form an impervious I<J<!;;W?s,

basin f loor . These/,, appear to b e almos t exclusively

Aus tra lian ;

2) Lowland dune lakes, in swales and gut ters between

dunes close to sealevel ;

3) Watert able windows, where an interdune space dip s below

the l ocal watertable, and is consequent ly drowned ;

4 ) Dune-contact lakes, which overlie a solid sub strate,

but with dunes forming at least one shoreline ;

5 ) Marine-contact lakes, s imilar to lowland dune lakes in

formation, but with a present or recent connection to

the sea ; and

6 ) Frontal dune p onds, where wind created hollows i n frontal (J<>Wd"

dunes extend below the watertab le . The�:/�re often

ephemeral .

However, this classification is not all-inclus ive , and lakes of

different origin may occur in other coastal regions (Timms, 1 982,

1 986a) lt1k1t'li include dune b arrage lakes, where drainage is b locked

by a dune, and those occupying the axial hollows o f parabo lic dunes, Illites

such as on King I s land (Jennings, 195 7 ) . O ther k are of composite

formation, and d o no t fit easily into Timms ( 1 982, 1 986a)

classif ication .

2.3 . 2 Studies o f Coastal Lakes of the Australian Mainland

Although the dys trophic coastal lakes o f Tasmania are emerging

as a very signif icant third limnological province (Croome and Tyler,

1 987a,b ; Croome � al, in press ; Ling � al, in press ) , information

14

on them is still limited , and has been rev iewed in Section 2 . 1 . 3.

In comparison , t he coastal lakes of some par t s o f the Aus tralian

mainland , especially tho se of south-east Queensland and north-east

New South Wales , have b een more comprehensively studied , and

therefore best exemp lify the limnology of these waterbodies . Studies

of the optical p roper t ies , nutrient status , and phytop lankton of

freshwater coastal dune lakes from south-east Queens land and north­

east New South Wales are reported in Chap t er 3 , and s tudies of

Tasmanian dune lakes are the sub j ect of Chap t er 4 .

Whi le a few dune lakes occur on Cape York Peninsular , in far

north Queensland (Bayly and Williams , 1 97 2 ; T imms 1 986b ) , many more

are located in the siliceous coastal areas in the south-eas t of that

s t ate . North S tradbroke and Moreton Islands , and the Cooloola Sand

Mass , each have some , but the mos t numerous and best examp les are

located on Fraser Island , which has more sizeab le lakes per unit area

than anywhere else in Queensland (Bayly , 1 966) . This sandy coastal

country continues southwards along the New S outh Wales north coast ,

and several lakes are also present there .

Many of the Queens land lakes are of the perched dune lake type ,

but a few , however , represent watertable windows (Bayly , 1 964 ;

Bensink and Burton , 1 97 5 ; Lee-Manwar e t al , 1 980) . Lake Wabby , on

Fraser Is land , is a wat ertab le window type lake , but also shows some

characteristics of a dune barrage lake (Arthington et al , 1 986) .

The New South Wales lakes are o f more diverse formation , and include

lowland dune lakes , dune-contact lakes , marine-contact lake s , and IIi""'"'

frontal dune ponds (Timms , 1 982 ) . Many of these�are being degraded

by human activity (Timms , 1 9 7 7a ) .

Water colour varies from clear and highly transparent in some

lakes , esp ecially the frontal dune ponds , to humic and s tr ongly

attenuating in perched dune lakes (Timms , 1 982 ; Bayly, 1 964 ; Bayly

et al , 1 9 7 5 ) . Water transparencies , measured by Secchi disc , range

f rom 0 . 35 to 8 . 2 0 metres (Timms , 1 969 ; Bayly � al , 1 9 7 5 ; Bensink

and Burton 1 97 5 ; Miller et a l , 1 9 76 , 1 984 ; T orgersen and Longmore ,

1 984 ; Arthington � al , 1 986) , but considerab le temporal f luctuations

o ccur , attributable to changes in organic s taining , and to variab le

turbidities due to changing phytoplankton b iomass (Miller et al ,

1 984) . However , other than Secchi disc measurements , the optics

of these lakes have been lit t le studied , the excep tions being Blue

and Brown Lakes , on North S tradbroke Island . In transparent Blue

1 5

Lake , the eupho t ic depth was approximately 1 0 . 1 0 metres

light being the least attenuated wavelengths , while

with.green ,hf'lk

o f Brown

Lake was only 1 . 40 metres , and red light penetrated to the greatest

dep th (Bensink and Burton , 1 97 5 ) .

Mos t o f the lakes are p olymictic , without thermal , oxy gen , or

chemical strati f ication (Timms , 1 969 ; Bayly et al , 1 97 5 ; Miller� al ,

1 97 6 , 1 984) . Weak thermal gradients , coup led with hypolimnetic

oxygen depletio n , may develop in some lakes , but these are f leeting

episodes ( Bens ink and Burton , 1 97 5 ; Arthington � al , 1 986) .

Although some d e gree of thermal s tab ility may b e achieved due t o their

relative depths and surface area , exposure to wind and storms can cause

holomixis at any time of year (Arthington et al , 1 986) . However ,

deep , well she ltered , and dys trophic Hidden Lake , on Fraser Is land ,

is thermally and chemically s tratified for mos t of the year , with

anoxic hypolimnetic conditions (Longmore et al , 1 983 ; Torgerson and

Longmore , 1 984) , while Brown Lake , on North S tradbroke I sland , also

develop s pro longed strong thermal stratificat ion, and is probab ly \varm

monomi ctic (Bensink and Burton , 1 9 75) .

The freshwater coastal lakes of Queens land constitute a very

homogenous group with respect to water chemistry . All are dilut e ,

with an average salinity o f about 4 0 mg L-1 , with sodium and chloride

contributing almost 80% of the dissolved ions , although proximity to

the coast and altitude may cause variat ions (Bayly, 1 96 4 ; Bayly et al ,

1 975 ; Miller� al , 1 984 ; Little and Roberts , 1 983 ; Reeve � al , 1 985 ;

Bensink 1 9 7 6 ; Bensink and Burton 1 975 ; Arthington and Wat son , 1 982 ;

Timms 1 986b ; Bayly and Williams , 1 97 2 ) . The atmospheric supp ly of

ions from the sea is the maj or inf luence on lakewater chemistry ,

esp ecially as the lakes lie on deep , siliceous sands , so that the

supp ly of ions by weathering processes is negligab le (Bayly , 1 964 ;

Bayly et al , 1 97 5 ; Litt le and Roberts , 1 983 ; Reeve et al , 1 985) .

The silica content of Fraser Island lakewaters is low , suggesting \'ll!<��r'

that the1r �re d erived mainly from local rainfall rather than from

groundwater sources . Instead , the lakes probab ly drain s lowly but

continuously into the main underground water body , thus maintaining

their low salinities (Little and Roberts , 1 983) .

The coastal dune lakes of north-east New South Wales are more

variable in their physico-chemical characteristics , due to their

dif ferent types of formation . Some are humic , acidic , and of low

salinity , with ionic compositions strongly dominated by sodium and

16

chloride. Others have higher conductivities, are less coloured and

acidic, and have calcium and bicarbonate as their major ions (Bayly,

1964; Timms 1969, 1982).

The pH values of Queensland coastal lakes are generally below

6.0 (Bayly, 1964; Bayly et al, 1975; Bensink and Burton, 1975; Bensink,1967; Miller� al, 1976, 1984; Arthington and \\Iatson, 1982; Little and Roberts, 1983; Reeve et al, 1985; Timms 1986b; )3ayly and

Hilliams, 1972). Coloured organic acids are the principal determinants

of pH. Lakes with a pH greater than 5.0 are usually colourless, while those of less than 5.0 are humic, with pH decreasing as humus concentration increases (Bayly, 1964; Bayly� al, 1975). The pH values of New South Hales coastal lakes vary considerably, but the

larger ones tend mainly to be acidic (Timms, 1982).

The sparce nutrient data available indicates most of these

coastal lakes to be oligotrophic, with total phosphorus and total nitrogen levels of less than 10 pg L-1, and 1000 pg L-1, respectively (Miller et al, 1976; 1984; Reeve� al, 1985). Some eutrophication

may occur in affected by recreational useage (Miller et al, 1984).

A number of biological studies have been undertaken on Queensland 0 and New South Wales coastal lakes. ChlorJelAyll a contents reported

for a few locations are generally low, at less than 9 pg L-1

(Miller� al, 1976, 1984). Desmids are the most common phytoplankton present, and other green algae, dinoflagellates, diatoms, cyanobacteria, and chrysophytes have also been noted (Bayly, 1964; Bayly� al, 1975; Arthington � al, 1986). The most important component of

their zooplankton is usually the copepod Calomecia tasmanic� which has its highest population densities in the more humic lakes. Other planktonic animals are less common, but the lakes have a richer and

more diversified littoral invertebrate fauna, and fish are also

present. Emergent plants are also common around the shorelines (Timms, 1969, 1982; Bayly, 1964; Bayly� al, 1975, Bensink and

Burton, 1975; Bensink, 1976; Arthington, 1977; Arthington et al,

1986).

Freshwater coastal lakes located in the Gippsland and Portland regions of Victoria are also of diverse origins (Timms 1973; 1977b;

Brand, 1967). This hetrogeneity is clearly evident in their chemical features. Hhile many in Gippsland show some dystrophy,

are slightly acid, and dominated by sodium and chloride, a few are

17

alkaline and enriched with alkaline earth bicarbonates (Timms, 1973;

Brand, 1967). Those of the Portland region are also alkaline, due to enrichment with calcium and bicarbonate, and have clear, transparent

waters (Timms, 1977b).

Coastal lakes in South Australia differ from those of the eastern Australian coastline in that many are markedly saline. Although fresh water

lakes occur in the Beachport-Robe area (Brock, pers. comm.), others

have salinities ranging from about one and a half to ten times seawater. Sodium and chloride are the dominant ions, and pH values are above 7.0

(Bayly and Williams, 1966; Bayly, 1970). Similar saline coastal lakes are also located on the Yorke Peninsular (Williams and Buckney, 1976;

Tominaga et al, 1987).

A number of alkaline, saline lakes with similar ionic chemistry occur near Esperance, and along the Perth lowlands of Western Australia (Williams and Buckney, 1976). Several ephemeral and permanent lakes with seawater chemical characteristics are located on Rottnest Island (Edward, 1983), and although their salinities

range from less than 1 gm L-1 to greater than 100 gm L-1, only one

is consistantly fresh. Some display a seasonal meromixis, when fresh waters from winter rains overflow their otherwise hypersaline waters (Bunn and Edward, 1984). However, there are a number of freshwater

coastal lakes in south-west Western Australia. L�k�$ between Albany

and Cape Leeuwin are considerably humic (personal observation), with conductivities between 200 and 3000 pS cm-1 (Groome, pers. comm.), but other details of their chemistry are unknown. Lakes in the Perth area experience large seasonal changes in their salinities fluctuate considerably. sodium and chloride their dominant ions,

volume, and therefore J<il(<t�

The�Aare alkaline, with although some enrichment with

calcium and bicarbonate takes place, and many may be eutrophic (Williams and Buckney, 1976; Congdon and McComb, 1976; Gordon et al, 1981; Newman and Hart, 1984; Lane, pers. comm.). Although the data

is scant, it appears that freshwater coastal lakes in Western Australia may differ considerably from their eastern Australian

counterparts.

18

Part Two

A Theoretical Background to the Studies

2 .4 THE NATURE OF HUMIC SUBSTANCES IN AQUATIC SYSTEMS

2 .4. 1 The Chemistry, Origin, and Distribution of Dissolved Humic Substances

Humic substances in lake waters originate either from autochthonous sources (formed within the lake itself), or from allochthonous sources (leached into the water from terrestrial sources) (Jackson, 1975). A complex mixture of organic substances, they may be classified into three main fractions;:

1) Fulvic acids, which are water soluable at all pH values,

and have molecular weights of less than 10,000 Daltons;

2) Humic acids, which are soluable in alkaline media but

precipitate at low pH, and have molecular weights ranging from 10,000 to 300, 000 Daltons; and

3) Humins. These are insoluable at all pH values, have the highest molecular weights, and are present in colloidal rather than dissolved form. (HacCarthy et al, 1985; Giesy and Briese, 1978; Lawrence, 1980; Allen, 1976;

Pennanen, 1982).

Elemental analysis has shown humic substances to be about 50% carbon, along with, in descending order of percent composition, oxygen, hydrogen, nitrogen, and sulphur (Schnitzer, 1978). Fulvic acids

contain more oxygen and sulphur than humic acids, and less carbon. Structurally, humic substances are generally accepted to be predominantly aromatic and phenolic in character, being polymers of various carboxylic acids, benzenepolycarboxylic acids, and phenolic

acids (Schnitzer, 1978).

The physical and chemical properties of dissolved humic substances are dependant on the pH and ionic concentration of the

aquatic medium. Increasing ionic concentration will cause a decrease in the molecular size and weight of dissolved humic substances (Aho and Lehto, 1984; De Haan� al, 1987), while increasing pH has been shown to cause an increase in the molecular sizes and weights of

dissolved fulvic acids (Ghassemi and Christman, 1968; De Haan et al, M;],ll/:("''' it'"' <U<ti II I" 1983).

k may also be altered by freezing (Giesy and Briese,

197 8) .

19

Allochthonous humic materials are derived principally from

chemical and biological degredation of plant tissues, especially lignins, and from the synthetic activities of micro-organisms, with the end products often tending to be more stable than the starting materials (Schnitzer, 1 978) . Similar products have been isolated from both leaf litter and lake water, indicating a terrestrial origin of the dissolved aquatic humus (Hall and Lee, 1 97 4 ) . Th i s

4 .:; washed into waterbodies by lateral transport from the upper soil zone . The B soil horizon removes dissolved humus, so groundwater does not contribute to the humus content of lakewater (Cronan and Aiken,

1 985 ; Reeve and Fergus, 1 982) .

Autochthonous humic substances originate from the chemical degredation of the cellular constituents and exudates (principally carbohydrates, amino acids, and lipids) of indigenous planktonic organisms and aquatic plants. The maj ority are water soluable fulvic acids, which differ from allochthonous humic substances by having higher nitrogen contents (Kalle, 1 966 ; Jackson, 1 9 7 5 ; Ward and Wetzel,

1 984) . Autochthonous humic substances may constitute a large proportion of the dissolved yellow substances of eutrophic lakes with high phytoplankton productivity (Davies-Colley and Vant, 1 987) .

The structural chemistry of dissolved humic substances may vary considerably geographically, even within small localized areas (Szpakowska � al, 1 986) . Low molecular weight compounds predominate in most lakewaters (Lawrence, 1 980 ; Hama and Handa , 1 980 ; Pennanen, 1 982 ; Allen, 1 97 6 ; De Haan and De Boer, 1 986) , but the proportion of higher molecular weight compounds rises as the humus concentration increases, and these may comprise a large percentage of the humic substances present in polyhumic lakes (Pennanen, 1 97 5 ; Aha, 1 986 ;

De Haan et al, 1 987 ) . In some instances, colloids may account for over 50% of the humic substances present (Koenings and Hooper, 1 9 76 ;

Lock� al, 1 97 7 ) . The proportion of high molecular weight compounds also increases with depth (Pennanen, 1 9 75 , 1 982 ; Aha, 1 986) , and seasonal fluctuations, both in total humus content, and in the relative proportions of humic to fulvic acids, can be marked (De Haan,

1 97 2 ; De Haan and De Boer, 1 97 9 , 1 986 ; Pennanen, 1 982) .

2 . 4 . 2 Humic Substances and Colour

Humic substances dissolved in water have a yellow to brownish colour due to the oxidation of various phenolic constituents, principally hydroxyhydroquinones, to form deeply coloured intermolecular

20

quinhydrones (Flaig, 1 97 5 ) . Mixtures of substances thu s formed show

similar, nearly monotonic spectra with absorbance increasing with decreasing wavelengths of blue and ultra-violet radiation. These

spectra are approximately exponential in shape, and remarkably similar regardless of origin (Davies-Colley and Vant, 1 987 ) , and coloured humic s ubstances are in large measure quantitatively indistinguishable over a wide range of latitudes (Lewis and Canfield,

1 9 7 7 ) .

The larger molecular weight humic compounds are generally the

most highly coloured (Hall and Lee, 1 97 4 ; Ghassemi and Christman, 1 968;

Pennanen, 1 97 5 ; Aho, 1 986) . Humic acids have a greater intensity of colour than fulvic acids, and colloidal humus may also contribute greatly to water colour (Koenings and Hooper, 1 9 7 6 ; Lock et al, 1 9 7 7 ) ,

although low molecular weight fractions also significantly colour waters where they are the predominant humic substances (Hama and Handa , 1 980 ; Wheeler, 1 97 6 ) . However, the colour of humic substances in water varies with pH, increasing as pH increases, and decreasing with increased acidity (Bayly, 1 96 4 ; Ghassemi and Christman, 1 968; Hall

and Lee, 1 97 4) . Chelation with iron also increases the colour of dissolved humic substances (Hall and Lee, 1 974 ) .

2 .4. 3 Humic Substances and pH

The presence of dissolved humic and fulvic acids can make a significant contribution to the acidity of water, adding markedly to the hydrogen ion concentration down to a pH value of about 4 . 0

(Glover and Webb, 1 97 9) . The main functional groups of humic

substances which increase the acidity of natural waters are their carboxylic acids and phenolic hydroxyls. The extent to which these dis sociate varies with pH. Greater ionization occurs with decreased pH, due to the wide range of similar, but non-identical functional groups present in aquatic humic materials (Oliver� al, 1 983 ; Perdue

et al, 1 980) . - -

2.4 . 4 Humic Substances and Metal Ions

The solu bility of variou s metal carbonates and sulphides, -

especially those of iron and manganese, may be greatly enhanced by the presence of humic substances, and the solu . . bili ty of their

""JJ'i' hydroxides is also improved slightly (Rashid and Leonard, 1 9 73 ) .

The variou s acidic functional groups of humu s molecules are considered responsible for this . Low molecular weight molecules

21

have a greater metal-holding capacity than larger fractions, but this

also depends on pH , redox potential, and on the metal itself. Divalent metals are complexed considerably better than trivalent metals (Rashid, 197 1; Jackson, 1975; Szpakowska et al, 1986) . However, complexation may not always account for the greater solu, .bility of

�.,.·� the metal ions, which can be present in a dissolved state unassociated with humic substances (Koenings and Hooper, 1976; De Haan and De Boer, 1986) . Dissolved humic substances may reduce some metal ions, or prevent the oxidation of some reduced species (SziHigyi, 197 1;

Koenings and Hooper, 1976).

In comparison, alkaline earth metals, even at low concentrations,

and sodium, actively coagulate and precipitate dissolved humic substances (Sholkovit z and Copland, 1981) , and humus can be removed

from lakewaters by precipitation with calcium carbonate and ferric oxides (Otsuki and Wetzel, 1973; Tipping, 1985) .

2.4. 5 The Ecological Significance of Humic Substances

The presence of dissolved humic substances in lakewaters may have

considerable ecological significance. Specialized floras and faunas are found in humic lakes in North America (Patrick� al, 1981) , Australia (Timms, 1986a, Croome and Tyler, 1987b) and in polyhumic forest lakes in Finland (Ilmavirta, 1980, 1983, 1984; Ilmavirta � al, 1984; Jones and Arvola, 1984; Arvola, 1986) . A number of frequently conflicting hypotheses have been presented to explain the ecological

influences of dissolved humic substances.

Several adverse effects have been claimed, especially on primary

productivity, which typically is low in humic waters (Prakash et �.

1975; Salonen, 1984) . Dissolved humic substances strongly absorb blue light, decreasing that available to chloroplast pigments of phytosynthetic aquatic organisms which utilize these same wavelengths. The ability of some aquatic primary producers to photosynthesize and

grow may thus become progressively more impaired as the concentration of humic substances within the water increases (Kirk, l976b) . However, the remaining light climate, dominated by red wavelengths, may be

exploited by those with the necessary accessory photosynthetic pigments to do so, and it has been speculated (Eloranta, 1978; Kirk, 197 7b, 1979, 1981c; Jeffrey, 1980) that the characteristic pigment arrays of different classes of algae place each of them at an advantage somewhere in the range of light climates encountered in

natural waters.

22

Additional detrimental effects suggested include the immobilization of micronutrients by their formation of strong, stable complexes with humus (an exce s s of a chelator reduces the availability of trace elements to algae); excessive acidity of the water; or the presence of antibiotic substances such as phenols (Prakash et al, 1 97 5 ; Jackson,

1 97 5 ) . All these may inhibit primary productivity.

On the other hand , beneficial effects ascribed to the presence

of humic matter in aquatic systems are often contradictory to the adverse effects proposed . This includes the suggestion that humic substances may make metal trace element nutrients more available to

algae, by enhancing their solu bility (Jackson, 1 975 ; Prakash et al, 1 97 5 ) . Metal-humate complexes may also influence the availability of phosphorus, either through co-adsorption, or by allowing orthophosphate to remain free in solution (Prakash et al, 1 97 5 ; Koenings and Hooper, 1 97 6 ; De Haan and De Boer, 1 986) . Complex formation and removal of heavy metals such as cadmium and lead may also be ecological ly important (Szpakowska et al, 1 986) , and it has been shown (Gjessing, 1 981 ) that

algal and fish toxicity to cadmium is considerably reduced in the presence of dis solved humus.

While large concentrations of dissolved humic substances inhibit

algal productivity (Prakash� al, 1 97 5 ; Salonen, 1 984 - see above), small concentrations, especially of low molecular weight humic acids,

and to a les ser extent fulvic acids, produce positivegrowth responses . These include extended exponential growth phases and increased growth rates in planktonic marine diatoms and dinoflagellates, leading to greater cell yields, when grown in the presence of small amounts of

humic substances . The dissolved humic fractions may act as stimulants for algal cel l s and be involved in cellular metabolic processes, or could supply micronutrients which might otherwise be unavailable (Prakash and Rashid, 1 968; Prakash� al, 1 97 3 , 1 9 75) .

Humic compounds may provide an energy source for some aquatic

organisms, especially filter and detrital feeding forms, particularly if other organic molecules such as proteins and polysaccharides are

( <H" r�·�\.ih� ":r associated with them (Prakash� al, 1 97 5 ) . may form the basis of significant food webs, utilized by hetrotrophic bacteria, which

.e . are in turn fed upon by he�d:Jflagellates and zooplankton, with even phytoflagellates supplementing their autotrophy with phagotrophy (Bayly, 1 964 ; Arvola, 1 985) . The extent this occurs depends on the nature and content of the humic substances, which are usually considered

23

refractory and biologically non-utilizable . Generally only 20 to 30% lf(l�h·il1 of dissolved t\1 are/, biodegradable in natural, unpolluted waters, but may be much lower in some waters (Servais et al, 1 987 ) .

However, even i f only a small fraction of the vast store was biologically available, it would still comprise a significant contribution to the food webs of humic lakes (Salonen, 1 9 84) .

2 . 4 . 6 Limnological Features of Humic Lakes - Examples from Finland

Finland has many lakes, most of which are small and highly humic due to the input of water from surrounding forests and peatlands (Ilmavirta 1 9 7 9 , 1 982) . As such, they provide an appropriate introduction for studies of humic lakes from other areas such as Tasmania, and serve to highlight many of the limnological features

displayed by small polyhumic forest lakes .

The brown colouration of Finnish lake waters markedly influences the penetration of light within them, with the vertical attenuation

coefficient for Photosynthetically Available Radiation (P.A.R.) being closely linearly related to water colour (Eloranta, 1 9 7 8 ; Jones and Arvola, 1 984) . The proportion of longer wavelength light increases as colour increases, while the depth of the euphotic zone (the depth through which 9 9% of incident illumination is attenuated) decreases very rapidly at first with initial colour increases, until a certain point, when additional increases have little further effect.

The pattern of light penetration has important consequences for Hvl''�li:

the mixing regimes of�small, sheltered, polyhumic forest lakes (Jones

and Arvola, 1 98 4 ; Salonen, Arvola and Rask, 1 984 ) . In the absence of wind induced circulation, an inverse relationship occurs between water

colour and depth of mixing, so that the euphotic zone often equals the

epilimnion in v olume, due to the dependance of mixing depth on that of light penetration. The rapid attenuation of solar radiation close to the surface produces steep thermal gradients, which may form very early in spring, immediately after the break-up of winter ice. This

reduction of the vernal circulation period often leads to incomplete mixing and a tendency towards "spt:,ing meromixis" in what would otherwise be d imictic lakes (Salonen, Arvola, and Rask, 1 984 ;

Salonen, 1 984 ) .

Because of the strong thermal stratification, and possible "spring meromixis", the hypolimnetic waters, which can comprise much of the

volume lake}{ often become anoxic (Salonen, Arvola, and Rask , 1 984 ;

24

Arvola, 1985) . Consequent to this, a highly s tratified nutrient

chemistry occurs . Concentrations of phosphate, ammonia, and nitrate­nitrite are usually very low in the oxic, photosynthetically active surface waters , but abundant free nutrient s exist in the dark, anoxic hypolimnion ( Ilmavir ta, 1983, 1984; Salonen, 1984; Arvola, 1985) . Convective mixing within the epilimnion at night may bring some nutrients up from deeper waters to replenish the surface waters

(Arvola et al, 198 7 ) .

A further important feature of the water chemis try of Finnish

polyhumic forest lakes is their generally low pH, with the mos t highly coloured being the most acid ( Ilmavirta, 1980, 1983) . While the mean pH value i s around 6 . 0 (Ilmavirta, 1980, 1983; Ilmavirta

et al, 1984; A rvola, 1985, 1986) , that of individual polyhumic lakes can be as low a s 4 . 4 in some instances (Arvola, 1983, 1984a,b; Rask

et al, 1986) . However, pH tends to increase with depth in such lakes, often by as much as 1.0 unit.

Finnish polyhumic forest lakes are generally dilute, with conductivities of les s than 50 �S cm-1 (Ilmavirta, 1980; Ilmavirta

� al, 1984; A rvola, 1986 ) , although these may increase with depth, resulting either from biogenic meromixis, or from a buildup of solutes (e.g. Fe2+) during summer s tratification and hypolimnetic anoxia

(Arvola, 1983, 1984a; Rask � al, 1986). Calcium is the dominant cation, and sulphat e and bicarbonate the dominant anions (Ilmavirta

� g.l, 1984; Ras k e t al, 1986) .

Ecological s t udies of phytoplankton composition and productivity (Ilmavirta, 1980, 1983, 1984; Arvola � al, 198 7 ) show flagellates to

be the most import ant contributors to both biomas s and species numbers

in fl\4.\1'\� dark and oligotrophic Finnish lakes, with the percentage of these in the algal biomass increasing as water colour

increases .fj(l,,,e\lt'l�""us ually comprise more than 50% of algal biomass once water colour exceeds 50 mg L-1 Pt., and are very common in small lakes where low turbul€.nce enables them to exercise control over their

po sition in the wat er column ( Jones and Arvola, 1984 ; Arvola, 1986 ) . may also have an ecological advantage in acidic waters (Ilmavirta,

1984) . Only a few species dominate the whole community, the most important being from the Cryp tophyceae and Chrysophyceae (Ilmavirta

et al, 1984; Ilmavirta, 1984; Arvola � al, 198 7 ) , although flagellated chlorophytes also comprise a significant proportion of the algal

biomas s following ice-melt (Arvola, 1986) .

25

Rapid seasonal changes in the physico-chemical regimes of Finnish

polyhumic forest lakes make them unfavourable for any particular phytoplankton community, and therefore continuous changes in species composition take place , (Jones and Ilmavirta, l 978a; Ilmavirta, 1982) . This succession, described for a number of Finnish lakes (Arvola, 1983, 1984a; Arvola and Rask, 1984; Ilmavirta, 1982; Jones and Ilmavirta, 1978b; Rask � al, 1986) shows general trends . Initial blooms occur soon after ice-melt, utilizing the sudden increase in light h llU'I:'I';I>iil':) andf,temperatures; but are succeeded by other species better able to cope with the declining epilimnetic nutrient levels as summer

progresses. Further changes occur as solar radiation and temperatures decrease in autumn . Flagellates are always dominant during the most difficult and critical periods of the year, such as at ice-melt and during the last days of stagnation (Ilmavirta, 1984), but may be so at any other time, too (Arvola, 1986). The structure of the

phytoplankton community may also be affected by the rapid throughflow of epilimnetic waters (Arvola, 1985) .

Daily vertical migrations of phytoflagellates also occur in humic

Finnish lakes . Cryptomonads in particular move downwards in the afternoon and up again in the early morning, traversing a depth of two metres and a l 5 ° C temperature gradient, responding to changes in light intensity . In comparison, the diurnal vertical distributions of non-motile algae remain unchanged (Arvola, l 984b; Salonen, Jones and Arvola, 1984 ; Arvola et al, 1987). Ilmavirta (1983, 1984) suggested that vertical migration enables flagellates to find optimal light conditions, but also hypothesized the possibility of nutrient

retrieval from hypolimnetic waters . Cryptomonads have been shown to transport radio-active labelled phosphorus from depth to the surface (Salonen, Jones and Arvola, 1984).

The scarcity of epilimnetic nutrients, and the shallow euphotic zone, severely retard phytoplankton productivity in these lakes . Productivity is greatest close to the surface, and decreases rapidly

with depth (Arvola, 1983, 1984a,b; Ilmavirta, 1982). Diel variations occur due to changing light intensities during the day, and also because migrating phytoplankton shift their production to different

depths (Ilmavirta, 1982, Arvola, 1984b, Arvola � al, 1987) . Variations in climatic and biological parameters (e.g. species

composition) produce marked daily fluctuations in primary productivity

26

(Ilmavirta, 1978), while seasonally production follows changes in solar radiation and water temperature, increasing from a spring low to a strnrner maximum b efore declining again in autumn (Ilmavirta, 1982; Arvola, 1984a). However, several peaks and dips in production may occur throughout the spring and summer seasons (Arvola, 1983). While

radiant energy determines the seasonal pattern of productivity, the nutrient concentration roughly determines the level (Ilmavirta, 1979, 1982). One source of nutrients may come from the b acterial decomposition of organic allochthonous inputs (Ilmavirta, 1979, 1981, 1982; Salonen, 1981). Additionally, the r���� decomposition of autochthonously produced organic materials within the epilimnion of these lakes means

rapid recycling of nutrients takes place (Ilmavirta, 1981, 1983; Salonen, 1981; Arvola, 1984a).

The input of energy by allochthonous materials into polyhumic lake ecosystems is considerable, and may exceed that gained by net phytoplankton production by several times (Sarvala � al, 1981). Plankton respiration in such lakes is also considerably greater than phytoplankton productivity ( Salonen et al , 1983; Salonen, 1984), made

possible by the utilization of allochthonous sources of organic carbon

by bacterioplankton ( Salonen, 1981).

The low light levels and reduced turbulence of polyhumic lakes

may produce physiological effects on phytoplankton. Those in the h >t<l t' S't•,.,\1\ql'lt waters close to the bottom of the euphotic zone have intense

pigmentation, ensuring efficient utilization of the little available radiation (Jones and Ilmavirta, 1978b). Phytoplankton also have an increased photosynthetic efficiency and are more productive relative to the available light and their chlorophyll a content at depth than when closer to the surface (Arvola, 1984a,b; Arvola et al, 1987).

However, production efficiency varies considerably diurnally due to complex interactions between light intensity, nutrient concentration, and vertical migrations (Arvola, 1984b). In comparison, adaptations by phytoplankton for photosynthesis at particular irradiance levels do not occur in lakes with considerable circulation of the water

column (Jones and Ilmavirta, 1978b). The efficiency to utilize irradiance also varies annually, but due to changes in species composition rather than to changing irradiance (Jones and Ilmavirta, 1978b).

27

2 . 5 FACTORS DETERMINING THE UNDERWATER LIGHT CLIMATES OF LAKES

2 . 5 . 1 The Fate of Light in Water

"Light" refers to that portion of the solar spectrum to which the human eye is sensitive, comprising wavelengths between about 400 and

7 00 nm . These wavelengths also correspond approximately to those

utilized by plants for photosynthesis and termed ' 'Photosynthetically Available Radiatiorr ' (P. A. R. ) (Kirk, 1 983) .

Light penetrating water becomes diminished in intensity until

extinguished. Two factors, absorption and scattering, contribute to this attenuation . Absorption is the process whereby a photon is "captured" by a molecule of water or of some substance dissolved or suspended in it . The light energy exists briefly as electronic

excitation energy within the molecule before either being released as heat, or converted to chemical energy by photosynthesis. A tiny portion may be converted to light again by fluoresence, but this is usually re-absorbed (Kirk, 1 983) .

Scattering is when a photon interacts with some component of the medium so that it diverges from its original path without being absorbed . Rather than removing light, scattering impedes its vertical penetration, causing photons to proceed in a zig-zag path as they bounce from one scattering particle to the next. This increases the total pathlength a photon must travel to traverse a given depth, . p � "'t\:>11"' thereby increasing its chance of absorption en-route . SomeAmay also be scattered back, in an upwards direction and out into the air

(Kirk, 1 983) .

2 . 5 . 2

are : -

Components of the Aquatic Medium Causing Absorption and Scattering

Four components of the aquatic medium attenuate light. These

1) The water itself . Pure water is a weak attenuator of blue and green light, but its absorption increases at

wavelengths above 550 nm, and becomes quite significant in the red region of the vis$.ble spectrum (Kirk, 1 983) .

Molecules of pure water also scatter light very weakly, but this effect is not significant compared to its

absorption. Scattering decreases with increasing wavelength (Smith and Baker , 1 981 ) .

28

2) Dissolved yellow substances, termed "gilvin" by Kirk ( 1976b) , strongly absorb wavelengths below 500 nm, and longer wavelengths are also removed as concentration of gilvin

increases (Kirk, 1976b) .

3) In animate particulate matter (tripton) contributes both to absorption and scattering. Inanimate suspensoids have absorption spectra similar to gilvin, strongly attenuating the shorter wavelengths due to insoluable humus materials

adsorbed onto the surface of suspended mineral particks (Kirk, 1980a, 1 985; Davies-Colley, 1 983) . Tripton is responsible for the maj ority of light scattering in natural waters, increasing attenuation by 20-200% above that expected from absorption alone in inland waters (Kirk, 1 98 1 a, 1983; Davies-Colley, 1983) .

4) Photosynthetic biota (Phytoplankton , and macrophytes where present) both absorb and scatter light. The major photo­synthetic pigments, chlorophylls, absorb mainly blue

wavelengths, and also a narrow band of red light. Acces sory pigments include the carotenoids, which absorb wavelengths up to 500 nm, and the biliproteins, with absorption spectra centred about 600 nm (Kirk, 1 983) . Different taxonomic groups of the photosynthetic biota display considerable variations in the wavelengths they can utilize, resulting from differences in pigment

composition (Kirk, 1983; Davies-Colley et al, 1 986) .

The capability of phytoplankton to absorb light depends on several factors, including the "packaging" of their pigments within the chloroplasts of their cells; their size; and their shape (Kirk, 197 5a,b, 1976a ) . While the absorption spectra of species from within

the same taxonomic group are similar, the values of specific absorption coefficients differ considerably between species over most wavelengths (Davies-Colley � al, 1986 ) .

Phytoplankton cells also scatter light. Different scattering patterns occur between algal groups, but similar patterns occur within

groups. The scattering spectra of phytoplankton cells generally have an inverse relationship to their absorption spectra, resulting in part because absorption removes various wavelengths from the incident beam which would otherwise by available for scattering (Davies--Colley

et al, 1 986 ) . Phytoplankton may contribute more to underwater light

29

attenuation through scattering than through absorption, leading to the rapid extinction of light at only shallow depths in eutrophic lakes (Davies-Colley et al, 1986).

The effects of macrophytes on the underwater light field varies

greatly, depending on plant growth habit and morphology, although

attenuation is considered lower per milligram of chlorophyll in macrophytes than in phytoplankton (Kirk, 1983). However, dense stands of floating and emergent macrophytes can quickly attenuate underwater light.

2.5.3 The Optical Properties o f the Water Column

(a) Inherent Optical Properties

These optical properties belong to the water itself, being

determined entirely by it composition, and whose values are not affected by the prevailing distribution of light (Kirk, 1982, 1983,

1984; citing Preisendorfer, 1961). The most important of these are the absorption coefficient, �· and the scattering coefficient, �·

When a thin, parallel beam of monochromatic light illuminates an infinitesimally thin layer of water, some of it is absorbed by the layer, and some of it scattered. The fraction of the· incident light beam which is absorbed, divided by the thickness of the layer is the absorption coefficient, �; while the fraction which is scattered, divided by the thicknes s of the layer, is the scattering coefficient,

� (Kirk, 1 977a, 1982, 1983). The value of the absorption coefficient for a given aquatic medium may change considerably with wavelength, due to the presence of various absorbing components (e.g. gilvin or tripton (Kirk, 1976b, 1980a)), but the scattering coefficient is fairly uniform throughout the bandwidth of P.A.R. (Davies-Colley, 1983; Phillips and Kirk, 1984). The beam attenuation coefficient, �' is the sum of both the absorption and scattering coefficients (c = a + �) (Kirk, 1982, 1983).

A fourth inherent optical property, the volume scattering

function �6(8) , describes the angular distribution of scattering from that point in the thin layer on which the light beam in incident. It has a characteristic shape in any given medium, forming a radially symmetrical cone around the direction of the beam, specifying the probabilities of scattering at different angles (Kirk, 198la) . In all natural waters investigated, B (8) is such that most scattering

occurs in a forward direction, with about 50% at angles of less than

5 ° to the direction of the incident light (Kirk, 1 982, 1983).

30

(b) Apparent Optical Properties

These are the optical properties of natural waters most commonly measured . However they are not actual properties of the water itself, but of the light field established within it, but their values are determined predominantly by the inherent optical properties . They vary to some extent with both depth and changes in the incident radiation field, such as solar elevation (Kirk, 1 982 , 1 983 , 1 984) .

The vertical attenuation coefficient, K, (Kd for downwards irradiance, Ku for upwards irradiance) is an important apparent optical property expressing the rate light is diminished with depth. It provides a useful approximation of light attenuation attributable to a waterbody itself, and as such can be used to compare one water­body at a given time with another, or as a guide to temporal changes

in the optical character of a particular waterbody (Kirk, 1 986) .

With vertically incident light and an absence of scattering, K would

equal the absorption coefficient, a .

A further parameter at times regarded as an apparent optical

property is irradiance reflectance, R, a measure of the ratio of upward to downward irradiance, at any specified optical depth. Whether a waterbody looks clear or turbid is a function largely of irradiance reflectance, especially that occurring just below the

surface (Kirk, 1 986) .

The relationship between inherent and apparent optical properties

is significantly depend>��nt on the angle of the light flux incident on

the water surface (Kirk, 1 98l b , 1 984) . As the angle departs increasingly from vertical, both absorption and scattering intensifies

as photons travel more obliquely and less vertically. This increases their average p athlength per metre of depth, and thus their probability of being absorbed or deflected by a particle or molecule. If ab sorption remains constant, and solar elevation decreases, the

value of Kd increases, but becomes progressively les s responsive to

increased scattering . The rate of increase of Kd is dependant on the aquatic medium . In highly scattering inland waters, Kd is rather insensitive to changes in solar altitude, but in clear, oceanic waters, where scattering is low in comparison to absorption, Kd can

vary significantly with the angle of the sun . Likewise, irradiance reflectance also increases with decreasing solar altitude, because as the incident beam moves away from vertical, an increased proportion of the more intense forward scattering (due to the shape of the

31

volume scattering function) also moves away from the vertical, following the angle of the incident beam, and becomes upwards rather

than downwards scattering (Kirk, 1 984).

2 . 5 . 4 The Attenuation of P .A . R . with Depth

Monochromatic light penetrating a homogenous aquatic medium is attenuated exponentially with dep th, in accordance with Beer ' s Law,

E (z) = E (0)e-kz, where E (z) and E (o) are the values of irradiance at dep th z and j ust below the surface, respectively, and K the vertical attenuation coefficient for that wavelength of light. Thus a plot of the natural logarithim of E (z) against dep th should be linear.

In comparison, P. A. R. includes all wavelengths from 400 to 700 nm

and as it penetrates a waterbody, it becomes progressively spectrally impoverished as the most rapidly at tenuated wavelengths are removed close to the surface, leaving only those least attenuated remaining

at depth (Kirk, 1 983; Talling, 1 982, 1984; Howard-Williams and Vincent, 1 984). Concomitant with this, the attenuation rate of P. A . R. is greatest in the surface waters, and decreases with dep th. Thus a plot of ln E (z) against depth is curved rather than linear, with Kd decreasing with dep th. This is most readily apparent in non-turbid waters, either clear or coloured (Kirk, 1977a,b, 1983). However, it is less apparent in turbid waters where there is a countervailing tendancy for attenuatio� at all wavelengths, to increase with dep th as the downward flux becomes more diffuse through scattering (Kirk,

1 977a,b, 1983). Additionally, due to the rapid absorption of blue light by trip ton, the spectral modification of P. A. R. may occur so close to the surface that the change in at tenuation with depth is

not readily detected.

In most waters, even where attenuation of P. A. R. is noticeably

biphasic, it varies only slightly from the exponential model predicted by Beer ' s Law for monochromatic light (Kirk, 1 983). Attenuation of P. A. R. for a given waterbody can therefore generally be best characterized by a single, depth-averaged value of Kd (Kirk, 1977b,

1983, 1 986).

2 . 5 . 5 Studies of Light Attenuation in Australian and New Zealand Inland Waters

Extensive data on underwater quantum irradiance, and measurements of its spectral distribution are few in number (Roemer and Hoagland, 1979;

Jewson � al, 1 984�and although Kirk ( 1986) gave an extensive list of

32

optical properties for Australian inland waters, few of the studies he detailed gave information on actual underwater quantum irradiance.

This section reviews those which have been undertaken on Australian and New Zealand freshwaters to provide a background to the studies of the light climat es of lentic freshwaters from Tasmania, north-east New South Wales , and south-east Queensland, reported in Chapter 3 .

Initial studies by Kirk ( 1977b, 1979) examined the light climates of some inland and coastal waters from south-east New South Wales and

the Australian Capital Territory . Attenuation was weak in the clear, non-turbid coast al waters, with peak transmission being about 550 nm . In comparison, attenuation was much greater in the inland waters, but changed considerably with temporal fluctuations in turbidity and gilvin concentration. For example, the depth averaged Kd (Kd (av) ) varied by

eight times over a three year period in Lake Burley Griffin (Kirk, 1980b). Consequently the spectral distribution of the underwater light also changed, being centred at about 600 nm when turbidity was low, and at

700 nm when it was high (Kirk, 1979). Gilvin absorbs the greatest proportion of P. A. R. in most waters from this area (Kirk , l980a).

Large temporal variations in optical properties, including Kd (av) , turbidity, and Secchi disc depth, also occur in waters from other

areas of New South Wales (see Kirk, 1986).

A spatial concentration gradient of gilvin, chlorophylla, and

suspended solids results in changing light climates through t.l::re Gippsland Lakes , Victoria (Hickman et al, 1984). P . A . R. is most strongly attenuated in Lake Wellington, furtherest inland 1 and this

lake has a predominantly yellow spectral distribution with depth.

In comparison, attenuation is least in Lake Victoria, nearest the sea, and its underwater spectrum is centred on blue-green light. Despite seasonal variation, tripton is the main attenuating component in these lakes, although water itself is important in removing red light in the

clearer waters of Lake Victoria.

Light extinction is extremely rapid in many inland waters of south-east South Australia, especially in the turbid Murray River and Lake Alexandrina (Ganf, 1980; Geddes, 1984). Reservoirs of the

Adelaide area are clearer, although they still have euphotic depths of less than four metres, with light being extinguished by gilvin and suspended particulate matter, and blooms of phytoplankton also contribute significantly at times (Ganf, 1980) . Considerable seasonal variation occurs in the optical parameters of these waters too.

33

Turbidity is also the dominant parameter affecting the light

climates of Northern Territory billabongs , as g ilvin concentrations are always low , and phytoplankton blooms infrequent. Their tripton loadings increase greatly as they contract due to evaporation during the dry season , specifying an underwater spectrum of predominantly

red light and high Kd (av) values (Walker , 1984; Walker and Tyler , 1984). Absorption by particulates is usually greater than absorption by gilvin , and scattering by the particulate matter markedly increases Kd (av) for P. A. R. in most billabongs (Kirk and Tyler , 1986).

Studies from the Mt. Isa , Townsville , and Palm Island areas of Queensland (Finlayson et al , 1984; Finlayson and Gillies , 1982;

Hawkins and Griffiths , 1986) report considerably lower attenuation than in the turbid waters from other parts of Austral ia , with tripton being a minor attenuating component. However , seasonal changes are

still apparent , resulting especially from the effects of stratification of the water column , and from periodic epilimnetic blooms of phytoplankton. Absorption by phytoplankton at times contributes to over 40% of the attenuation in Solomon Dam , Palm Island , and gilvin was also present at moderate levels in this reservo ir (Hawkins and

Griffiths , 1986).

The underwater light climates of fifteen mainly montane Tasmanian

lakes were measured by Steane ( 1979). Their optics vary , depending on whether they l ie in either the eastern or western l imnological province of the island (see Section 2. 1). Those in the east are extremely clear , with very low attenuation , and with their spectral distribution of P. A. R. at depth centred between 550 and 600 nm. Attenuation was more rapid in the dystrophic lakes in the western limnological province , leaving a predominantly red underwater light field. The dystrophic lakes of the lower Gordon River area have similar underwater light climates (King , 1980; King and Tyler , 1981b , 1982a , 1983; Croome and Tyler , 1984a , 1985a) , although the characteristic stratification of photosynthetic m icro-organisms at the chemocline of the meromictic

lakes here markedly increases the attenuation of any light penetrating

to these depths (Bowling and Tyler , 1986).

Surveys of the underwater light climates of New Zealand lakes (Vant and Davies- Colley , 1984; Howard-Williams and Vincent , 1984)

reveal many to have high clarity waters , where attenuation of P. A.R.

is very low . Others however are turbid , due either to phytoplankton

dominated seston or to tripton , and including geothermal lakes with

34

varying amounts of suspended sulphur . Attenuation in these is similar to that in turbid Australian lakes, with light penetrating only to shallow depths. Humic-stained forest lakes from the South Island also rapidly attenuated l ight. Spectral changes in P . A. R. occur, with Lake Coleridge, the clearest lake, having a predominantly blue l ight field at depth. Green light is the most penetrating wavelength in other clearwater lakes and red light is transmitted best

in the more turbid, coloured, or eutrophic lakes (Howard-Williams and Vincent, 1 98 5 ) . Considerable temporal changes in attenuation, with Kd (av) varying by up to five times, have been demonstrated in some lakes (Vant et al, 1 986) . This variation was usually closely correlated to changes in the chlorophylla content of the water.

2 . 6 A BACKGROUND TO CHEMICAL STRATIFICATION AND MEROMIXIS

2 . 6 .1 The Nature of Chemical Stratification

Chemical stratification of lakes and reservoirs, usually known as meromixis, is the division of the water column into separate strata created by density differences arising from different concentrations of dissolved solutes in the water of each strat\lm, Waters with the greatest concentrations have the greatest density, and form the bottom strat�m, or monimolimnion,which is overlain by the more dilute and less

dense waters of the mixolimnion. The two strata are separated by a chemical gradient known as the chemocline. The density difference

between the mixolimnion and monimolimnion may be sufficient to prevent their mixing, even during winter when thermal stratification is absent and wind induced circulation is at its greatest. This results in a permanent layer of dense, stagnant, usually anoxic water at the bottom of the lake, which may be compared to an unstratified lake, where

circulation would normally reach even the deepest waters.

Meromixis may be classified into two distinct types : ectogenic and endogenic (Walker and Likens, 1 97 5 ) . Ectogenic meromixis is a condition created by external forces acting on a lake , such as a fresh water inflow over a pre-existing saline layer, or a saline underflow

into a fresh water body. This type of meromixis may also be created by subsurface inflows, either of fresh or saline water, from a spring in the lake bed (known as crenogenesis); while a third mechanism, triptogenesis, involves a density difference created by an inflow of turbid water settling at the bottom of a lake. In contrast, endogenic meromixis is produced by conditions within the lake itself , with

3.5

chemical stratification arising from the decomposition of organic materials in the deeper waters (biogenic meromixis) , or by the deepwater accumulation of salts precipitated by "freezing out" from a surface layer of ice (cryogenic meromixis) . Biogenic meromixis is

often aided by the size and shape of the lake basin, and by local catchment topography and forests, which reduce the amount of wind

induced circulation in a lake . This has been coined "morphogenic meromixis" by Northcote and Halsey ( 1 9 6 9 ) .

This thesis looks at the role dissolved humic substances play towards the establishment and maintenance of chemical stratification in a number of meromictic or near-meromictic Tasmanian lakes and reservoirs ( Chapter 5 ) . Of particular interest is the establishment of meromixis in impoundments .

2 . 6 . 2 Meromixis in Impoundments

Meromixis is an unusual phenomenon in water bodies, and as a

result, few meromictic impoundments have been documented . Tyler and Buckney ( 1 9 7 4 ) reported the rapid development of biogenic meromixis in Lake Barrington, Tasmania, soon after the formation of the reservoir in 1 96 9 . The monimolimnetic water, localized at the base

of the dam, was highly reducing, showed unusually large temperature rises, and considerable enrichment of such chemical species as iron,

manganese, hydrogen sulphide, calcium, and bicarbonate. The meromixis persisted for several years, but had become very weak by 1 978 (Tyler, 1 980) . A second reservoir, Lake Rowallan, also developed

anoxic b ottom waters with dissolved iron and manganese soon after filling, but this was removed by extensive drawdown from low-level

offtakes (Tyler and Buckney, 1 9 7 4 ) .

Biogenic meromixis also occurred soon after the filling of Kllcava and Flaje Reservoirs, Czechoslovakia. Biochemical decomposition of organic matter lead to anoxia and the concentration of dissolved solids, especially manganese, in their bottom waters, accompanied b y inverse thermal profiles. On another occasion, biogenic meromixis was again induced in these reservoirs by unusual meteorological conditions, when late winter ice cover and early s.ummer thermal

stratification prevented full vernal circulation. This allowed a building up of solutes in the bottom waters (Fiala, 1 9 7 9 ) .

Two cases of meromixis have been reported from reservoirs in the

United States. Inflows of dense, turbid water created triptogenic

36

meromixis in Hills Creek Reservoir, Oregon (Larson, 1979), while in Lake Powell, on the Colorado River , cold, saline winter waters enter

the reservoir as underflow currents to maintain ectogenic meromixis there (Johnston and Merritt, 1979).

2 . 6 . 3 Causes of Biogenic Meromixis in Reservoirs

The impoundment of heavily vegetated, steepsided river valleys

may predispose the resultant reservoir to biogenic meromixis (Tyler, 1980). The valley shape concentrates debris onto the reservoir floor, so that even meagre epilimnetic production would produce a heavy sediment load per unit volume of bottom water, and this, along with the newly flooded, decaying vegetation, creates a high oxygen demand, which under conditions of thermal stratification causes an anoxic hypolimnion occupying much of the volume of the reservoir. This allows a large contact area between the anoxic water and the reservoir basin, from which iron and manganese can be reduced and mobilized. Being denser than the surrounds, water containing these, and other solutes of biogenic origin such as calcium, magnesium, and bicarbonate, will accumulate by downslope and down-reservoir migration to form a monimolimnetic pool, and thu s establish a chemical gradient. The meromixis is localized in long, thin reservoirs, with the monimolimnion existing only as a small pool at the base of the dam (Tyler, 1980). A further factor aiding the maintenance of a chemical gradient is the shelter afforded by the steep valley sides and the dendritic nature of the reservoirs. This limits vertical turbu l�nce cau sed by wind induced autumnal overturn and winter circulation, which would other­wise erode the monimolimnetic pool, and allows it to persist unless disturbed by low level offtakes or artificial aeration (Tyler, 1980).

37

C HAPTER THREE

STUDIES OF T HE UNDE RWATER LIGHT CLIMATES

O F LENTIC FRESHWATERS FROM TASMANIA ,

NORTH-EAST NEW SOUTH WALES , AND

SO UTH- EAST Q UEENSLAND

3 . 1 INTRODUCTION

3.1 . 1 The Aims and Scope of the Study

The character of the underwater light climate is important not

only biologically, in affecting primary production (Prakash et al, 1 975; Salonen, 1984), the depth limitations of macrophytes (Vant et al, 1 986), and possibly influencing the comp osition of phytoplankton communities by enabling different algae with specific p igment arrays to each have an ecological advantage somewhere in the range of light climates encountered in natural waters (Eloranta, 1978; Kirk, 1 976b,

1 979, 1981c, 1983; Jeffrey, 1 980), but also in determining the optical quality of water and its suitability for domestic, industrial, and

recreational use (Kirk, 1982, 1983; Davies-Colley, 1983; Vant and Davies-Colley, 1 984). Thus, a knowledge of the optical properties of

the aquatic medium, and the effects of the various attenuating components involved, are essential for an understanding of the functioning of inland aquatic ecosystems, for both biological and

management p urposes.

A necessary first step towards determining the ecological role of light in freshwater ecosystems is the characterization of their

optical properties, and Kirk ( 1986) has stated that this task has scarcely begun for Australian inland waters. The major aim of this study was to characterize the optical properties of lentic freshwaters from several different areas of Australia, these being Tasmania, north-east New South Wales, and south-east Queensland . This was done by detailing the factors attenuating P.A.R. in these waters, and the

3.8

resultant light climates produced . Gilvin is an important light attenuating component of the aquatic medium, and emphasis has been made to determine its role in the optical limnology of the three study

areas. Comparisons can also be made between the three areas, particularily as the types of waterbodies studied differ considerably

from area to area.

A second aim of the studies undertaken in New South Wales and

Queensland was t o examine the distribution of phytoplankton in relation to the light climates of these study sites . Measurements of other

ecological parameters, especially of the nutrients present, were also made, as possibly these, rather than the light climates, were the dominant factors affecting phytoplankton distribution . In doing so, both the nutrient status and the phytoplankton present in many of the freshwater coastal dune lakes of south-east Queensland have been documented for the first time, and this is also true for many of the north-east New South Wales study sites.

Many of Tasmania ' s phycologically lakes lie in remote areas, such as in the alpine regions of the Central Plateau, or in the World Heritage Wilderness Area of the south-west , where access is limited by rugged terrain and dense vegetation . A further aim of this study was the development of an optical classification of Tasmania ' s lakes, which could be used predictively to estimate the underwater

light climates of the lakes from these areas, using only laboratory measurements of small water samples from them. Similar classifications were also done for north-east New South Wales and south-east

Queensland study sites .

3 . 1 . 2 The Study Sites

Tasmania has a considerable range of lake types, many with water of high purity; many with dark, dystrophic waters, and a few which are turbid ( Section 2 . 1 ) . This study covers all water types, from as wide a geographic distribution of the island as possible, including one site

on sub-Antarctic Macquarie Island. Basic limnological features of these lakes and reservoirs, with references to further data, are given in Table 3 . 1 and locations shown in Figure 3 . 1 . Fifty sites were

sampled, a number on more than one occasion .

Thirty-seven standing freshwaters were sampled in north-east New South Wales and adj acent south-east border regions of Queensland. A brief limnological background to the area is given in Section 2 . 2 ,

3.9

Table 3 . 1 : Tasmanian lakes o n which PAR measureme n t s have been carried o u t , g1v1ng b a s i c l imno logical d a t a . The l o c a t ion o f t h e l ak e s is g iv e n b y l ak e number i n Figure 3 . 1. O th e r numb e r s ind i c a t e t h e numbe r o f o c c a s ions when PAR measur e d . For a d d i t ional general l imnol o g i c a l d a t a s e e S e c t ion 2 . 1 .

Lake

No . Lake

O l i g o t r ophic c l ear w a t e r s

2 3 t, 5 6 7 8 9

1 0 1 1 1 2

1 3

1 4 1 5

1 6 1 7

1 8

1 9 2 0

P r ion

P e rry Esperance Har t z Ladies Tarn R i d g eway R e s ervoir Fenton S t Clair Lnura Hes ton J un c t ion Great

Echo

Lagoon of I s l an d s (nova) Risdon Brook Reserv o ir

(� r a n t s Lagoon S . D . Marshal l ' s Reservoir

Orml ey Leake

Trev a l l yn P e t R e s ervo i r

Dystrop h i c , non- turbid w a t e r s

2 1 2 2 2 3 2 1, 2 5

2 6

2 7 2 8 2 9 3 0 3 1 32 3 3 3 4 35

3 6 3 7 38 39 4 0 4 1 4 2 4 3 1, 4 4 5

4 6

Binney P ine Tier Dam Kj ng Will iam Mcad owbank B a r r in g t o n

Dove

Curly �.Jurr cnvina Diamond Rhona Fedder (nova) Gordon Murchison Rosebe r y B l ackmans Lagoon

Curries Riv e r Dam Frome D am C as c ad e s Dam ( f orme r l y B r i s e i s Dam) I s and ula M i kany Lle1;ellyn S t rahan Garcia P a r t ing Creek Dam B a s i n

Chisholm

Turbid w a t e r s ( s l ight to mo d e r a t e )

1,7 S o r e l l 4 8 C r e s c e n t

4 9 P r o s s er River Dam 5 0 To oms

T o t a l PAR

2 1 1 1

1 1 2

2 1 2

1 1 1 1

3 3 2

4

2

S p e c t r a l d i s t r i b u t io n

o f PAR

2

2

2

1 )

} J r

} } }

}

Limn o l o g i c a l char a c t e r s and c ommen t s

Macqu arie I s l and , sub-an t a r c t i c . Tyler , 1 9 7 2 ; Buckney & Tyler , 1 9 7 4

Glacia l , H a r t z Moun t a ins . D o l e r i t e , Kno t t e t 2.�· , 1 9 7 8

Ho b a r t w a t e r s u p p l y . C l ear moun t a in w a t e r . Glac ial , Mt F i e l d . Do l e r i t e

Gl a c io l . C r a d l e M t - Lake S t C l a ir Na t ional P ar k . P r e d ominant lv d o l er i t e . Tyl e r , 1 9 7 4 ; Huckney & T y l e r , l 9 7 3 a .

Cent r al P l a t eau , alp ine D o l e r i t e , Tyle r , 1 9 7 4 ; Huckney & Tyler , 1 9 7 3 a .

C e n t r al P l a t eau . D o l er i t e . H u c kney & Tyl e r , 1 9 7 3 a .

Sub- alpine . Cen t r al P l a t e au . Tyl e r , 1 9 7 6 . Hobart wa t e r supply . Treated w a t e r .

Ol igo t roph ic-me s o t ro p hic . Turbidity variabl e . Tyler , 1 9 7 4 , 1 9 80 ; Buckney & Tyler , 1 9 7 3 a .

Co a s t a]. J a go on , n o r t h-e a s t coas t . P r iv a t e r e s e rvo ir , Fingal V a ll e y .

O l i g r t ro p h i c r e s e rv o ir , Eastern Tiers . Dole r i t e . Gr oome & T y l e r , 1 9 7 2 , 1 9 7 5 ; Buckney and T y l e r , 1 9 7 3 a .

R e s e rv o i r , n e a r Laun c e s ton Town water supply , n o r t h-we s t coast , Basal t .

Al p ine r e s e rv o i r s . C e n t r a l P l a t e a u . D o l e r i t e .

R e s e rvo ir , Lower Derwent V a L l o y S l i g h t l y humic reserv o i r . Tyler & lluckney ,

1 9 7 4 ; T y l e r , 1 9 8 0 . Gl a c i al , C r a d l e M t - Lake S t Clair N a t ional P ar k .

Tyler , 1 9 7 4 ; Bucknev & Tyler , 1 9 7 3 a .

G l a c ial d y s t r ophic . Denison Range . Precambr i a n congl omer a te s .

D y s t rophic r e s ervo ir s , sou th-we s t . Buckney & Tyler , 1 9 7 3b ; S t eane & T y l er , 1 9 8 2 .

D y s t rophic r e s ervoir s , wes t coa s t .

Coas t al l a goon , nor th-eas t c o as t . Uuckney & Tyler , 1 9 7 3a .

R e s e rv o ir s , nor th-eas t . Buckney & Tyler , 1 9 7 3 a .

D y s t rophic r e s ervoir s , nor th-we s t coas t .

D y s t rophic d u n e l a ke s , wes t c o as t .

D y s t rophic r e s e rv o i r , w e s t c o as t . Glacial d y s t ro p hi c . Tyndall Range . P r e c amb r i an

c o n g l ome r a t e s . P o lyhumic f o r e s t l ake . Kar s t ic sink ho l e ,

Ar thur R iv e r

Meso-eu t r o p h i c , shallow . Central P la teau . D o l e r i t e . Cheng & Tyl er , 1 9 7 3 a , 1 9 7 6 a ; B u c kney & Ty ler , 1 9 7 3 a .

S l i g h t l y turbid r e s e rvoir , e a s t coast . Ol igo trophic , shallow r e s ervo ir . Eastern T i e r s ,

d o l e r i t e . C r o ome & Tyler , 1 9 7 2 , 1 9 7 5 ; Buc kney & T y l e r , 1 9 7 3 a .

Figure 3 . 1

40

4 0 4 1 ° 37

4 6 2 0 3 8 2 5

26 1 7

3 4 1 1 1 0 {S

4 2°� 3 3 1 2 4 4 9 &--' 1 8 43 8 2 2 1 4 �7 � 4 5 1 3

2 3 2 1 48

24 A.

7

4 3°

Location of sampling s ites in Tasmania . The numbers refer

to the lakes listed in Tables 3 . 1 and 3 . 2 . Note the location of Prion

Lake ( No . 1 ) on sub - antarctic Macquarie Is land . A , Perched Lake ,

Lake Fidler , and Sulphide Poo l , for which spectral distribution and

attenuation data have been reported elsewhere . ( King and Tyler , 1 9 8 1 b ,

1 98 2a , 1983 ; Croome and Tyler 1 984a , 1 985a ; Bowl ing and Tyler , 1 986 ) .

41

which is one of topographic, geological, climatic and vegetational

diversity . The eastern most section of the area includes the coastal plain and eastern foothills of the Great Dividing Range . Several coastal dune lakes, and a number of reservoirs, especially in the Richmond and Hunter River valleys, were investigated here (Nos . 1 - 1 0 ,

32-36 , Table 3 . 4 ) . The highland regions of the New England Tablelands comprise a second sector, containing many public water supply reservoirs

and some private irrigation storages (Nos . 1 1- 2 3 , Table 3 . 4) . Further west on the Western Slopes, are a number of large irrigation impoundments (Nos . 24-31 , Table 3 . 4 ) , while small, natural Yarrie Lake (No . 37 ,

Table 3 . 4 ) is located on the Western Plains. Figure 3 . 2 shows the location of each site , which were sampled only once .

Twenty-six freshwater coastal dune lakes were sampled in south­east Queensland, including twenty from Fraser Island, and two each from the Cooloola Sand Mas s, Moreton Island, and North Stradbroke Island (Figure 3 . 3 , Table 3 . 8) . The basic limnology of these lakes

was described in Section 2 . 3 . 2 . Because all have fairly similar thermal properties and ionic chemistry, but vary considerably in their humus content, they offer an excellent range of sites within a relatively small area on which to conduct investigations into the

limnological effects of humic substances.

3 . 2 METHODS

3 . 2 . 1 Sources o f Data

The maj ority of Tasmanian data for this study was collected

between 1 982 and 1 984 , inclusive . This was combined with additional data from other sources to obtain a sufficiently large data base to include all pos sible lake types from most geographical locations in Tasmania. This was important to allow comparisons both between individual lakes, and between those from different parts of the island .

Data prior to 1 97 8 was collected by P.A . Tyler (unpublished ) , while much of that for 1 97 8 came from Steane (1 97 9 ) ; the remainder being

measurements by R. D. King and P . A. Tyler (unpublished) . Data for 1 97 9 was that of M . S . Steane (unpublished ) , while the results from Lake Strahan came from Bowling ( 1 981 ) . With the exception of that

of Steane ( 1 9 7 9) and Bowling ( 1 9 8 1 ) , all additional data was in the form of raw field measurements requiring computation to obtain the final results for each lake . As Steane ( 1 9 7 9 ) had not applied a correction to account for the difference in refractive index of light

, '

.. .. � . /

.. , · � . .. � ..

� .. . .

.

Moree ..

, . ... .. . ._?oondiwindi ' .. . .. . .. .. . . .. ..

Narrabri 37 •

25

27

42

... � .. �

.. .. ··

1\l

.. .. 12) 24:

/.. \ . ·ij-· Tenterfield • 14

15

Glen Innes • 16

17 18

19 • Annidale 20

1

Grafton •

Lismore •

6 7

2

3

5

22 21

Figure 3 . 2

• Gunnedah

28

29

Tamworth •

30 31

32

• Muswellbrook33 34 35

23 .

36

North 1 i I �----1_0_0 __ k __ m ____ �1 1

--�-------- �

The location of sampling s ites in north-east New South

Wales . The numbers refer to the lakes and reservo irs l isted in Tables

3 . 4 and 3 . 5 .

• B.undiaberrg

• Mary borough

, Gym pie

• Nambour

Brisbane

43

North I

45 6 1 0 7 89 1 1 Fraser Island

1 2

Cooloola Sand Ma�

"bie Island

orth Stradbroke Island

Figure 3 . 3 The location of sampling s ites in s outh - east Queensland .

The numbers refer to the lakes listed in Table 3 . 8 .

in air compared to that in water, much of his data had to be

recalculated before its inclusion in this study.

Data from north-east New South Wales was collected between July 1986 and September 1987; while that from south-east Queensland was obtained over a three week period from late April to early May, 1987.

3 . 2 . 2 Collection and Analysis of Samples , and Computation of ilie D�a

Upwelling and downwelling measurements of P. A. R. (400-700 nm) were made with a Lambda Licor LI-185 quantameter and LI-192 S underwater quanta sensor, always referenced to incident radiation measured

simultaneously with a Licor LI-190S quanta sensor (deck cell) held horizontal above the lake surface. Measurements were usually made

within three hours either side of solar noon, and, weather permitting, under clear skies. The depth of the first underwater measurement was

always 0. 10 metre, and the deepest measurements taken either at the euphotic depth or the bottom of the lake, whichever was the shallower.

From these measurements, mean upwelling and downwelling vertical attenuation coefficients for P. A. R. (Ku (av); Kd (av)) were calculated

by linear regression (Kirk, 197 7b). The regression coefficients (r2) for these were usually better than 0. 98. These single, depth averaged values of Kd best typify the attenuation of P. A. R. within a given waterbody (Kirk, 1986), despite decreases in the rate of attenuation

occurring due to the narrowing of the spectral distribution of P. A . R. with depth (Talling, 1982, 1984) . Reflectance, R, was also calculate� as the ratio of upwelling to downwelling irradiance at any depth (Kirk, 197 7b). Euphotic depth, Zea, the depth of 1% of incident

radiation, was determined directly from the measured downwelling

P. A. R . profile. The scattering coefficient, � . was calculated from upwelling and downwelling values of P.A. R. at the midpoint of the euphotic zone (Zm � 10% of surface irradiance), following Kirk (1981a).

The spectral distribution of upwelling and downwelling P. A. R. from 400 to 700 nm, was measured with a Techtum Q . S. M . 2500 submersible quantaspectrometer (half-power bandwith = 15- 18 nm). These were always made under a cloudless sky close to solar noon, under calm

conditions. A slight rippling of the water surface was tolerable and under these conditions the output of the equipment was smoothed electronically with a device similar to the one described by Kirk (1979). Two scans were taken at each depth, one forward from 400 to 700 nm, and the second the reverse, thes·e being recorded on a

45

constant speed chart recorder (TOA). There was always a slight discrepancy between scans in opposite directions . The start would be recorded correctly but the end of the scan would be indicated by the wavelength trace before the quantum trace had reached equilibrium. This error was overcome using the method of Steane

( 1 97 9 ) , where both mirror image scans, recorded in opposite directions, were superimposed in coincidence . The start of each scan was then marked as the finish of its partner . Remaining errors were minimized by scaling each scan and calculating means, at 1 0 nm

intervals .

Approximate estimates of in situ total absorption coefficients were calculated at 1 0 nm intervals from the underwater spectral data

for selected Tasmanian lakes, following Kirk ( 1 9 7 9 ) . This involves correcting the measured vertical attenuation coefficients for

monochromatic downwards irradiance for solar altitude and refraction at the water surface. Absorption coefficients for pure water between 400 and 5 8 0 nm were taken from Hulbert ( 1 945 ) , and those from 580 to 740 from Sullivan ( 1 9 6 3 ) , while those attributable to gilvin were

o btained from spectrophotometric scans of filtered water (0 . 45 prn '

membranes), measured relative to distilled water (Kirk, 1 9 7 6b ) , in a Pye Unicam SP 8- 1 0 0 UV/VIS scanning spectrophometer . The apparent contribution of tripton was then calculated as the difference between

each total absorption coefficient and the sum of the coefficients for gilvin and water at that wavelength . However, because of the unavoidable contribution of scattering to attenuation of P.A.R., the values of both the total absorption coefficients and those for tripton, calculated by these methods, must exceed their true values to

an extent dependant on the turbidity of the water ( Kirk, 1 97 9 ) .

Transparency was measured with a standard 20 em black and white quartered Secchi disc, surface water temperature with a mercury

thermometer; and pH and conductivity (at 1 8 ° C ) with a Jenco 6 7 3 pH meter and a P T 1- 1 0 conductivity meter respectively, the electrodes of each being suspended over the side of the boat into the water.

Samples of phytoplankton were collected by towing a 20 pm plankton net. These were preserved i��J�rmalin, pending microscope

identification, using Prescott ( 1 9 7 0) , McLeod ( 1 9 7 5 ) , Skinner ( 1 9 7 5 ) ,

Ling and Tyler ( 1 9 8 6 ) , Foged ( 1 9 7 8) and Thomas ( 1 983 ) as reference

texts .

45a

S amp l e s f o r l ab o r n t o ry ana l y s i s wer e c o l l e c t ed in o p a q u e

p o lye thy l e n e b o t t l cc: s f r om b e lo w the s u r f a c e . Turb id i ty (Tn) wa s

m e a s ur e d in a Hac h 2 1 0 0 turb i d ime t e r against forma;>, an s t anda rch; .

S amp l e iJ w e r e thc�n LLL t e r ed through O . Li 5 p. m membr ane f i l te n> a nd

co l o u r ( = g i lv i n ) was m e a s u r e d in lla zen '( mg J�t L -- 1 ) u n it: s \>l i t h a

Lov i b o nd 1 0 0 c o l o ur comp ar a t o r (A . P : H . A . , 1 9 7 1 ) , or as an �J s o r p t ion

c o e f f i c ient at 4 4 0 nm ( g 4 4 0 • ln uni t s - Kirk , 1 9 7 6b ) with a Ce c i l

CE 2 9 2 sp c c l: r o p h omc t e r (Ta smani a ) o r a J'ye Un:i cam SP 3 0 s p c c t rophomc L: er .

(N e'iv S o u t h W a l e s a n d Q u e e n s l a n d samp le s ) aga irHi l: a cU s t i l lc d \va t e r

b l an.k in L1 e m q ua r t z g l a s s c uve t t e s . The s e m e ;:w ur emen t s \v0c :c e mad e

a s s o on a s p o s s i b l e a f t e r s amp l ing . Ad d i t iona l water sarrv l c s w e r e

f i l t e r e d t h r o u g h Wha tman G F / C g l a s s f ib r e f i lters bnmediatcly afte r s amp ]j ng . The :[' i l t er s vvcr e t. hen s t o r e d f r o � en in d a r kn e s s p end

s p e c t ropho t ome t r ic an a ly s i s of phy t op l a nkton chl o r ophy l l a by the

t r i chroma t i c m e t h o d of Strickland a nd Par son s ( 1 9 68 ) f o l l owing

ex t r a c t ion in a c e tone (T asmanian samp le s ) , o r in m rc� th ano l f o l lowing

t he r e c ommend a t: :L ons of Mar ker -���- ���. ( 1 9BO) (N . S . W . and Queen s l aJJd

s amp l e s ) .

Further s amp l e s w e r e c o l l e c t ed f o r nut r i ent ana l y s e s :Ln a c i d

\va shed p o ly e thy lene h o t t l e s . Ana ly f; e s were p e r f o rmed on a T e chnicon

A u t o ana i y s e r II u s in g t h e a s c o r b i c a c id

f o l l owing a c :L d p er s ulpha t e cl:i. ge s t ion (A . P . H . A . , 1 97 t o t a l

a. lkaline p m: s u l p h a t e d i gc t> t Lon (D 1 E l ia �:�- _'.l:L , 1 9 7 7 ) '/ Line a r and mu l t i� J . e r e gr e s s i.on analy s e s o f v a r i o u s o p t i c a l

charac t e r l s t l c s o f Ta smanian lakes w e r e c a r r i e d o u t u s ing t h e T e d d y b ear

c o mp u ter p r o gr am , d e v i s e d b y J . B . Wi l son , O t a go Un :Lvend t y , w i th

n a t ur a l l o g ar :L tl 1m ic t r ans f o rmat ions to corr e c t f o r f; ke\ved and

kur t o s ed d i s t r i b u t ions o f the d a t a . S :Lm:Uar analy s e s on da t a f r om

Ne\v S o u th Wa l e r, an.d Q u e en s l and w e r e done u s ing the Nin:L t ab p r o gr am

(M:l n :L t ab In c . , 1 9 135 ) f or r e g r e s s io m: , a nd S P S S ( N i e _E:_t:. _<<): , J 9 7 5 ) f o r

P e ar son corr e lc:J t Jo n s . C l u s t e r ana ly E; e s emp loying t h e Ave r a z e L inka ge

Me thod with the p a r a me t e r s g 4 4 0 , t urb id i ty , and t l1e 8 4 4 0 t o t u r b i d :L t. y

r a t i o were don e u s ing t he p r o g r am C lu s tan 3 (Wishar t , 1 9 7 8) .

3 . 3 RESULTS

46

PART A TASMANIA

3 . 3 . 1 Colour , T urbidity and Chlorophylla

Data for co lour , turbidity and chlorophylla for the f i f ty lakes

studied are given in Tab le 3 . 2 . The least coloured water recorded was

that of Lake Per ry with a g4 LfO of 0 . 058 m-1 , while the mos t dystrophic

was Lake Chisho lm , at 2 7 . 22 8 m- 1 . The median value for Tasmania was

2 . 30 3 m- 1 . The absorpt ion coefficient at 440 nm (g440) was taken as

the precise meas ure o f colour in this study . The relationship between

this and the o lder , sub j ective method emp loying p latinum units (Hazen

scale) is shown in Figure 3 . 4 . Hazen values were approximated to the

nearest match in the incremental series of dyed discs , hence the

vert ical series of points at higher values of colour . Data from this

s tudy , and from studies of coastal lagoons (Table 4 . 1 ) were supp lemented

with additional data of King ( 1 9 80 ) . A linear relationship was found

between the two colour measurements , expressed by the equation

g440 = 0 . 0 8 1 Hazen + 0 . 40 (r2 = 0 . 9 84 , n � 320 ) . King ( 1 9 8 0 ) had

demonstrated this relationship up to a Hazen value of 400 mg P t L- 1 ,

and inclusion o f the extra data now extends it to at least 600 mg Pt L-1 .

S imilar relationship s exis t between the Hazen scale and spectrophotometric

measures o f colo ur a t 420 nm for Finnish lakes (Eloranta , 1 97 8 ; Jones

and Arvola , 1 984 ) .

The lowest turbidity (0 . 1 8 N . T . U . ) was recorded from Lake St . C lair ,

while the mo st turbid lake was Tooms Lake ( 1 7 . 0 N . T . U . ) . The median

turbidity , 0 . 7 2 N . T . U . , shows Tasmanian inland waters are generally

less turbid than many o f their mainland Aus tralian counterparts (see

Section 2 . 5 . 5 . ) . Only e ight values were recorded for chlorophyll ,

and six o f these were below 1 0 #g L- 1 . Lakes Sorell and �rescent

are amongs t the more eutrophic o f Tasmania ' s lakes .

3 . 3 . 2 Attenuation of Total P .A . R .

( a ) Downwelling P . A . R .

The attenuat ion o f downwelling P . A . R . ( 400-700 nm) i s shown for

selected lakes in Figure 3 . 5 . These cover the extremes of water

c larity , turb idity , and dystrophy found in Tasmania . An increase in

slope is apparent with depth in e ach prof ile , consequent upon the

e arly eclip se of the spectral r egions with high attenuation coeff icients ,

in the surface water s . The mean values o f the vertical attenuation

47

Tnh.le J . 2 : t r �� :l n downwell ing v e r t i c a l n t tenu n t 1 o n c oe f f i c i en t s for PAR (Kd ( nv Y • mc.an upwe l l ing v c r t l C'al a t t e n u n tinn coe f f i c i e n t f o r t'AR (Ku (nv )) t>ll p h o t i c d e p t h s {Zeu , 17. downwellin g ) , s c a t t e ri ng C'o c f f i c i c n t s ( b ) , and rcL1 ted data for Tasrnani nn J akes . Figures i n parentheses are ranges prev io u s l y p u b l isht'd (n� f e rences in 'fable 3 . 1 )

[ ,;lke !lo .

01 I !',o1 rnph i I' c 1 1 !' 1· i n n

P e r r y

E s p r. r n n c c ! l n r t z L n d I p <; T;�rn

: 1 l t• r co

I{ i d gc1..rn y R L' s c r v o i r Fen ton S t . CJ air

9 l .n u r a 1 0 l·lf' s t nn I I . J un e t ion 1 2 C n - · n l

1 J Echo

1 4 Lagoon o f l �> l <1nds

1 5 R.lsdon Brook Re s e r v o i r

1 6 G r a n t � Logoon 1 7 S . l l . /·l n r sh,, l .l ' �>

J{ c s ervoi r , 01-n1 l ey 1 8 Lcak0

19 ' ) 'r('vn l l y n 2 0 P e t Reservoir

JJy s t r np h 1 c non- t u r b i d w n l c r 2 1 !\ i rmey 2 2 l ' i tw T lc r f);1 111 2 3 Lnke K i n g \Hl J J am

t1.1 in Arm C.ue l p l l B a s in

2 1� M e n d oto�b n n k 2 5 Barrington

26 Dove

2 7 2 8 2 9 30 3 1

3 2

3 3

]/� 3 5

C u r l y \.Jurrawina D.l.mnond Rhona Pedder (Nova)

Gordon

H u r c h i. s o n

Rosclwry Blnckmans L;1goon

]6 Cu r r ie s River Dam 37 Frome Dam

38 Cascade s Dam

19 I �_; nwlul a

M) r!.iknnv lt l L1 ewc1 l yn 1� 2 S t r nh:111 !1] C a r c l <l 4 4 P a r t i n g C r e e k Dam

1,�) B a s i n

4 6 Chisholm

Co ] nur_ 1 (rng l't L )

2/+- 1 0- 7 9 � ') (< 5-5)

1 0 - 0 1• - 7 8 < 5 8-0/l-83 '( 5 7 -" 1 1 - 7 8 < 5 7 - 1 1 -" 78 < 5 7 - 1 1 - 7 8 < 5 9-(}(>"- 8 3 < 5

1 4 - 1 1 - 82 < 5 2 8 - 0 2 - 7 9 < 5

( < 5 ) 8 - 1 0 - 7 8 "" 5

23-02- 7 8 < 5 2 5 - 0 2 - 7 8 < 5 (,- I 0-8?. < 'l u,- o :. - u J < s

(< 5 ) tl- 0 2-Btl < 5

(< 5 ) 1 5- 0 7 - 82 1 0

( 1 0) 2 5- 0 h - 7 6

2- l l - 7 8 1 5 2 f>-0 3 - 7 9

/-1- 0 5- 8 1 30-01,-82

1 -" 0 5- 8 2 < 5 1 5-or,-81,

(< 5 ) 26-011 - 8/t 1 0

1 -0 7 -81, I O I 6- 0 7 - 8 2 5

(< 5 ) 2<',-f)ll - 8 3 5

1 5-03-84 < 5

5 � 0 7 -- 8 !! 5 - 0 7 - 811

2H-OrJ-f\/l 2 8 - 0 0 - 81,

5 - 0 7 - 81, 1 3- 0 3 - 7 8 2 2 - 0 9 - 7 8

2 - I 0-82

3- 1 0- 8 2

2 2 -0 1 - 7 8 20-0 I - 7 8 1 7 -11 I - 7 8 1 7-0 1 - l fl 2 6 - ll H - 7 5 2 1 - 0 7 - B 2 2 7 - 0 G -81•

t•-0 1 - 7 8 l- 1 1 - 7 8

2 3 - 0 J- 81,

B - 1 1 - 82 1 7- 0 J - [ll, 1 8- 0 J-fll, 2 5 - 0 i·-811

I J I O

20 25 20 30 35

( I U- 4 0 ) 3 5

( 20 ) 6 5 7 5 90 6 5

7 0 90 80 85 5 5

( PO- I OO) 80 55

( 7 0 )

1< --0(, - 8 ) 6 0 25-04-81, 811

( /• 0 ) 26-0'• - 8 4 r.o

( 2 11 ) 1 .1 - 0 J-81, 2 5 I (,- O J - HI, 30 1 5-- 0 J- 8 1, 1 1 0

1 1>- 0 1 - 8 1 1 2 0 1 2-08-81, 1, 0 1 2-08-84 I 80 I 11-0B-81, 1 2 5 1 8-02-81, 3 2 0 I 6-04-81, 3 0 0 1 11-IJ(,-81, 300 I 3-08-81, 320

Turbid H a t e r s ( s l i g h t to mod e r a t e )

4 7 S o r e l l

4 8 C r e s c P. n t

/1 9 P r o s s e r River D<111i 50 Tooms

�lED I AN m:AN S'J'AN ilARll llEV 1 AT! ON

I '•- 0 7 - 8 2 5 (<5)

1 5- 0 7 - 8 2 I 5 (< 5 ) 2 5 - 0 2 - 8 11 60 2 2--0 (J-- 7 8 1, 5 3 1 - 0 G - 8 2 1, 5

< < o )

2 5 5 ] 7 7

g'�'-� 0

- 1 ( m )

0 . 1 1 5

() ' 0 5 8 0 . 0 5 8 0 . I 1 3 0 . ! 1 5 0 . h 0 3 n . 2 30 0 . 2 30 0 . 5 7 (,

0 . 7 ldi O . l dJ l 0 . 80() I ) . 2 )(] () . 0 5 8

0 . 2 JO

I . 0 36

0 . 9 7 9

0 . 2 30

0 . 9 7 9

() . E:\(,1, 1 - 2 0 9

o . 7 4 8 0 - 3 4 5

l . 6 1 2

! . 669 2. 1 8 8 2 . 8 7 8 2 . 1 88 3 . 0 5 1 3 . 3 3 9

3 . 3 3 9

Tu r h i d i t }' (NTll)

0. 39

0 . 37 0. 20 0 . 2 7 0 . 2 8 0 . 26 0 . 80 0 . 35 0 . 1 8

0 . 22 0. 37

0 . )8 0 . ')0 0 . /0

1 . oo

0 . 7 5

1 . 5

4 . 4

2 . o 0 . 7

l . l

1 . 2 1 , /J

( 3 , 1, - 9 . 0 ) l . J I . 0

7 . 0 I . 2

() ' ().') 1 . 0 1 . 5 1 . 5 5 l , 0!1 0 . 50

(> . 0 5 6 0 . 80 _) . 9 8 7 0. 50 7 . 0 9 3 0 . 30 4 . 90 5 0 . 1, 0

r) . so s 0 . 7 3 8 . 1 7 4 0 . ) 8 8 . 2 8 9 0 , 61, 7 . 02 3 0 . ) 2 1, . 9 5 1 0 . 7 1

('J . 2- 8 . ] ) ( 0 . 30-0 . (> 5 ) r,. r, 7 8 o . r, 5 !, • 7 211 (] . 5 (, , so s o . 5 J t • • 1, 90 0 . 9

t. , ll ) J G . 7 9 3

r, . 5 4 8

I . 900 2 , 1. ! 8 7 . 886

1 I . (J 28 ) . 799

1 6 . 4 6 l, 1 0 . 7 0 7 2 7 _ 2 2 8 2 1, . 6 9 5 2 !, . 2 3 5 2 6 . I 9 2

1 . 2 0 9

1 . 7 2 7

5 . 69 9 1, , 0 30 I, . 6 6 3

2 . 3 0 3 /1 . () 2 9 6 . 2 9 2

I . 60 1 . 5

1 . 0

1 . 4 1 . 3 2 . �� 0 , /j 0 . 5

0 . 85 0 . 5 1 0 , /1 ] 0 . 1, ] 0 . 7 5 0 . 55

4 . 3

9 . 4

7 . l 1 7 . 0 1 2 . o

( 1 0 . 0- 1 1, . 0 )

o . 7 2 I . 55 2 . 7 9

Scc c h i ( m )

C l 1 l o ro-Kd ]'hyJ 1 f :.,v)

()•li L-" 1 ) (,- I )

Z e u

(m)

I 1 . 5 0 . 1 4 > 1 0 . 0 0 . 09

I \ . 0 1 5 . 0 I 6 . 8

9 . I /' 5 . 8

I 0 . 5 I I . 2 5

II . 8 I 5 . 0

> 7 . 2 '> 7 . 0

h , l,

6 . 2

> I . 0

I . 9 5 5 . J 1. , 8 1 . 4 1 . 7 ! . G S 5 . 7

1 . 5

0 . 2 1 o _ 2 I 0 . 2 5 0 . 2 5 O . Ld 0 . 2 3 0 . 3 3 0 - 4 I

(I . ': 3 0 . 2 7 r) . t� 8 f) . J/. 0 - 39

0 - 3 7

0 . i 6 0 . 6

I . ; J 0 . 6 (! . 5

{L 6 !.. l . 2 1 -'35

o_ 5 3

2 . 9 O . P S ;:;. 2 . 5 7 . 1 9 0 . 9 ( I . '• - 3 . 3 )

'J . 2 () . 7/, 2 . 8 0 . S I

J . 2 J . 0 2 . 8 3 . I 3 . 2 3 . 3

:! . 2 5 J . 8/1

3 , I 0 2 . 90 2 , 1, 2 . 1 1 . 7 3 2 . 2 2 , l; 2 . 55 2 . 9

( 2 . 0 5 - 2 . 9 5 ) 2 . 7 0

2 . 2 :7 1 . 7 5

2 . 1 5

1 . 5 I . 7 5 I . 1 5 0 . 'I 3 . ] 1 . 2 1 . (, 0 . 8 0 ' 9 5 I . I 0 I . 0 5

l . 9

! . 0 2 r1 . G l (0 . 1 - 1 . 2 )

0 . 6 2 8 - 06 ( 0 . 1 -0 . (,)

1 . 1 I . 2 1 . 1

( I . 'S--2 . 1 )

!1 . r,!1

(_j . li l I I . 2 6

1 . 1 9 i . 2 7

I . q /, l . 2 9 ' . 7 5 l - i 7 2 . 3 2 . 4 8 : . J,S L . 2 5 i - 9!, I _ 4

I - 7 6 l . 7 5 L 7 7 � . i 7

1 . i J 2 . 0 3

j ' i 3

l - 2 8 l . ! I

,, . 5

3 . 2 ) /, . 88 4 . 5 1 5 - 17 3 . 82

i . 8

J . 9 6

, / '} , ] () _ 1 5

• 21J . 5 5 . 2 4

> 1 6 . 0 20 . 0 I 8 . 0 1 8 . 0

> 5 . 5 1 8 . 5 I J , 3 1 1 . 4

1 0 . 7

1 (> . 5 :.> () , () > () , ') > 7 . 5

1 2 . 0

0 . 1 8 (] . 30 0 . 2 3 0 . 1 8

0 . 39 0 . 4 1

O . ld

0 . 1"1 0. 35

> 0 . 9 0 . 4 1

2 . 6 7 . 5 0 . 6 2 9 . 0 J . 5

" . 2 5 ... . u ] _ 2 2

> 5 . 0

2 . 7 S

'j . 0 > 2 . 0 0 . 9

() ' 0 0 . 6 4 > J . 0

() , () /! . 0 3 . 1 5

3 . 9 3 . 5

2 . 3 :J . 6

> 2 . 0 2 . 6 2 . 0 1 . 6 1 . 7 2 . o 2 . 2 J . O

2 . 5 2 . 5 2 . 5

> I . 7

1 . 1 5 I . 6 3

I . 0 4

3 . 8 7 3 . 8 2

2 - 58

3. 8 1 . 24 2 . 0

> I . O

3 . 5 1; . 0 I . 7 5

> () , 7 2 . 0 1 . 0 l . 2 5 0 . 8 0 . 9 (] . 7 1 . 0

) I . 8

1 . 1

2 ' 5 2 . 0 2 . I

I . 8 2

3 . 7 6

2 . 1 2

J. 5 0 0 . () ll 5 . 1 1 1 . r,o 5 . I 4 l . 99

h. - 1 ( m )

0 . 60

0 . 2 7 0 . 4 7 O . ld

0 . 3 0 0 . 3 7

0 . 38

l . 78

2 . 6 6

2 . 8 7

I . 1, 5 l . 1 3

0 . 7 5

0 . 6 1 . 3 2

0 . 9 8

2 . 4 4

7 . 9 6

I S . 1 7

() . ')11 2 . H I 3 . 88

I E

0 "' <j-Cj,

48

50

4 0 •

• 30 •

' � . • '

20 • ! a a I

• • 1 0 •

..

1 0 0 2 00 300 4 00 5 00 600 H oz e n ( mg P t 1 - l )

Figure 3 . 4 The relationship between colour measured by the platinum

( Hazen ) scale , and a s g i lvin C g440 ) for Tasmanian inland waters .

49

coefficient , Kd (av) , obtained from a line force-fitted by regress ion

analysis , are g iven in Tab le 3 . 2 , and are used to typify the underwater

l ight climates o f T asmanian lakes . Euphotic depth (Zeu) is also given

in Table 3 . 2 . The med ian values for Kd (av) and Z eu were 1 . 20 m- 1 , and

3 . 5 metres , resp ect ively .

Table 3 . 2 and Figure 3 . 5 reveal that both t urbidity and colour

markedly increase the vertical attenuation coefficient , Kd (av ) . The

highest values (gr eatest attenuation and shallowest euphotic depths )

were measured in the turbid , eutrophic , but low coloured Lake Crescent ,

and from Lake Chisholm , a non-turbid , polyhumic forest l ake . The

least attenuation was in the very oligotrophic glacial lakes on dolerite

bedrock , such as Lakes Perry , Laura , and Meston , and in Prion Lake on

Macquarie Island . Midway were the moderately dys trophic Lake

Barrington and the slightly turbid Lake Leake and Risdon Brook Dam .

At tenuation in Lake Crescent was slightly higher than expected for

its turbidity , e sp ecially when compared with the more turbid Tooms

Lake , possibly due to additional absorption by chlorophyll a .

(b) Upwelling P . A . R .

In most lakes , the mean attenuation coefficient for upwelling

P . A . R . (Ku (av ) ) was approximately equal to that for downwelling P . A . R .

(Table 3 . 2 ) . Notable excep tions were Lad ies Tarn and Lagoon of

Islands , where Ku (av) was considerably less than Kd (av) . Both are

shallow , with almos t 1 0% of surface irrad iance reaching the sediments .

S teane ( 1 9 7 9) attributed the differences in the Ku (av) and Kd (av)

values from Ladies Tarn to a contribution to upwelling light by

reflection from the bottom . This may also be true for Lagoon of

Island s . In contrast , attenuation of upwelling irradiance in humic ,

non- turbid Lakes Gordon and Fedder (nova) exceeded that for downwelling

irradiance . This �s most likely the resul t o f poor ins trumental

accuracy at the very low level s of upwelling irradiance present in

these lakes .

3 . 3 . 3 Reflectance and S cattering Coeff icients

Reflectance profiles from eight of the lakes are presented in

Figure 3 . 6 . The p redicted pattern of reflectance becoming constant

with dep th af ter an initial increase (Kirk, 1 97 7b , 1 98l a) does no t

appear to hold f or Tasmanian l akes . In most , reflectance first

increased with d ep th but then l evelled off before decreasing . The

5.0

% I n c 1 d e n t r o d i o t 1on

1 · 0 2· 5 5 · 0 1 0 2 5 50 : oo

E .c. 6 0. Q)

0 c 7 0

o - I I

I 8 10 ,/ I I

F igure 3 . 5 Attenuat ion profiles of downwelling P . A . R . (400- 7 0 0 nm . ) for s e lected Tasmani an waters . ( A ) Lake Perry , 0 8 - 0 4 - 1 983 ; ( b ) Lake

Laura , 0 8 - 1 0 - 1 9 7 8 ; ( C ) Risdon Brook Dam, 02- 1 1 - 1 9 7 8 ; ( D ) "S . D . Marshalls '

Reservoir " , 0 1 - 07 - 1 98 4 ; ( E ) Lake Barrington , 2 2 - 0 9 - 1 97 8 ; ( F ) Lake Rhona ,

1 7 - 0 1 - 1 97 8 ; (G) Tooms Lake, 3 1 - 0 8 - 1 98 2 ; (H ) Lake Fedder (nova ) , 2 2 - 0 7 - 1982 ;

( I ) Lake Crescent , 1 5 - 0 7 - 1982 ; ( J ) Lake Chisho lm, 1 8 - 0 2 - 1984 . See

Table 3 . 2 for further data on the opt ical character istics of thes e

lake s .

5 1

0 · 1 0

0 ·08 A

D 0·02

- F

H 2 3

D e p : h ( m )

Figure 3 . 6 Ref lectance/depth profiles for selected Tasmanian lakes .

( A ) Tooms Lake , 3 1 - 0 8 - 1 9 8 2 ; ( B ) Lake Sorel l , 1 4 - 0 7 - 1 9 8 2 ; ( C ) Lake Crescent ,

1 5 - 0 7 - 1982 ; ( D ) Risdon Brook Dam , 0 1 - 05 - 1 982 ; ( E ) Lake Leake , 1 6 - 07 - 1 9 8 2 ;

( F ) Curr ies River Dam , 0 4 - 0 6 - 1983 ; ( G ) Lake Barrington , 02 - 10 - 1 982 ;

( H ) Lake Fedder ( nova ) , 2 1 - 0 7 - 1 9 8 2 .

52

reasons for the highly variable reflectance profiles of Lake Crescent

and Tooms Lake c anno t be explained . The measurements were made under

almost ideal condit ions of cloudlessness and c alm water , and

instrumental malfunctions are unlikely . However , possibility o f

small errors i n pos itioning the sensors at v ar ious depths during

measurement , and vertical heterogeneity of phytoplankton and trip ton

during calm periods of measurement , may account for some variation .

The low quantities of trip ton caused both the clear and the humic

lakes to have l ow ref lectance values , with upwelling P . A . R . usually

being less than 1 . 5% of downwelling values . Excep tions were the more

turbid lakes (Tooms , Sorell , Crescent ) , where upwe lling P . A . R . ranged

from 5% to 10% o f the downwelling measurements . As a result , the

scattering coe f f icients �) for most Tasmanian lakes (Table 3 . 2 ) were

also low , being usually less than 3 . 0 m-1 , excep t for Lakes Sorell and

Crescent and in Tooms Lake , where , due to the greater turbidity , they

were up to five times higher .

3 . 3 . 4 Spectral Distribution o f Underwater P .A . R .

(a) Underwater sp ectra

The underwater spectral distributions o f P . A . R . ( 400- 7 40 nm) for

various Tasmanian lakes are given in Figure 3 . 7 (a-e ) . Figure 3 . 7 (a )

shows the resul t s f o r the four lakes where attenuation o f P .A . R . was

least . In Lake Perry , the cleares t , red light was at tenuated slightly

more rapidly than b lue light , leaving a spectral distribution centred

on the green wavelengths , around 560 nm . In the other three lakes ,

attenuation of both b lue and red wavelengths was almost equal , leaving

orange light , c entred around 580 nm , penetrating to the greatest

dep ths . This spect ral shift towards the red end of the spectrum

indicates that very small quantities of gilvin or tripton cause

perceptible changes in the underwater light climates . As turbidity ,

gilvin , or both increase , so does attenuation of blue light relative

to red , so that the centre of the spectral distribution moves towards

the longer wavel engths . This tendancy is further illustrated by

Lagoon o f I sland s , with slightly increased colour ; Lake Leake , and

slightly turbid but almost colourless Risdon Brook Dam (Figure 3 . 7b ) .

These waterbodies d isplay a rather broad plateau in their underwater

spectra , but with maximum transmission centred around 600 nm .

The effec t s o f increased turbidity are seen in Lakes Sorell ,

Crescent and Tooms (Figure 3 . 7 c ) , where the spectral bandpass has been

2500 La k e P e rr y , 2 1 . 0 Ci . 3 3

... � -Q 2000

><

I 1 500 V1 � E

0 c 0 1000 :J o·

<lJ u c 0 D 500 2 �

400 500 600 Wa v e l e ngth \ ;l m )

2 4 0 0 L a k e S i C l a i r , 2 8 . 02 . 7 9

""� Q X

' E 1 8 00 c

' v> N

' E 0

·- 1 20 0 c 0 :J 0'

0! u c 0 u

600 2 �

W a v e l e n g t h ( nm )

700

53

1600

'!2� 0 : 1 200

I E c

I (}) N

' E .::: c 0 :J CY

0 400 u 0 � �

400

24 00

0 X

I

E _c 1600 l {fl N I

E 0

-t­c 0 :J 0'

(\) u c 0

u 0 �

8 0 0

400

G reat Lu k e , 2 6 .05 .8 3

500 6 00 700 Wa v e leng t h ( n m )

�o K e L a u r o , 8 . : 0 .7 8

500 600 70 0 W o ve l e n g l :> ( n m )

F igure 3 . 7 ( a ) Spectral distr ibutions of downwelling P . A . R . from Tasmanian

lakes - clear water lakes .

"' . -0

><

'E c

' V> N

I E .2 c 0 :J tJ"

Q) u c 0

u 0 '-'-

1 500

1 000

5 00 ·

If) Q

>< T E

c ' "'

N ' E 0

� c 0 :J o-

(l) u c 0

"Q 0 � '-......

54

4 0 0 La g oon o f I s l a nds , 1 5 .07. 8 2

300

2 0 0

1 00

·j-�,.-.---,.1--,,---...--..,.--...,.--..., 4 0 0 500 600

W a v e l e n g � h ( nm ) 700

Lake Le a k e , 1 6 . 0 7. 8 2 1 500 R t s d o n B roo k D a m , 1 .05 .8 2

"" Q

>< ' E 1 000 c I "' N ' E .2 c 0 :J o-

� O m >��

OJ 500 u c 0

'0 0 '-'-

\. ...j.;olll!l:;..'"f"'""--r-, �-r, ·---,-......,.-_,..1 -w..,.r

4 0 0 5 0 0 GOO 700

Wa v e l e n g t h ( n m )

4 0 0 500 600 700

W o v e l e n g t h ( n rn )

Figure 3 . 7 ( b ) Spectral d istributions of downwelling P . A . R . from Tasmanian

lakes - sl ightly coloured or turbid lakes .

,., 0 X

I E c

' Vl N ' E .2 c 0 ::J o-

(\) (.) c 0

D 0 � �

"' 0

X ' E

c T Vl N I

E .2 c 0 ::J 0"

(\) u c: 0 v 0 �

1 500

1 000

500

4 0 0

2500

2000

1 5 00

500

4 0 0

L a k e S o re l l , 1 4 . 07. 8 2

I 600

Wa v e l e n g t h ( n m )

Too m s Lo l \l: , 3 1 .08. 8 2

5 0 0

Wa v e l en g t h ( n m )

I 700

I 700

55

1500 La ke Cr escent , 1 5.07. 8 2

on� 0 ><

I E 1000 c

I "' N ' E

0 c 0 ::J o-

500 <1> u c g

� ......

4 00 500 600 700

Wove l e n g t h ( n m ) 1 500

Too m s La ke, 2 2 .06.78

""' 0 X

' E

1000 c ' Vl ';' E

0 -0 ::J o-

<1> 500 u '-:::!

D 2

400 500 600 700

W a v e l e n g t h \ n m )

Figure 3 . 7 ( c ) Spectral distributions of downwelling P . A . R . from Tasmanian

lakes - turbid lakes .

... -0 ><

I E c

I If) N I

E 0 ..... c: 0 ::> o·

OJ u c: 0

"0 0 ,_ '-

I{) 0 X

I E c:

I If) N

I E .2 c: 0 ::> CT

Q) u c: 0

"0 0 L '-

.._.

3 500 L o l\ c B a r r i n g t o n 1 1 3 .03 .7 8

3000

2500

2000

1 500

1000

500

400 500 600 700

Wa v e l e n g th ( n m )

4000 L a l\ e W u r r a w i n a 1 20 .0 1 , 7 8

3000

2000

1 000

56

3200

"' Q X 2400

I E c

I If) N I

E 1600

2

8 00

:::

400

4000 "' Q X

I E c: 3000

I (/) N I

E 0 c 2000 0 ::J CT

Q) u c 0

"0 1000 0 L '-

4 00

La k e B a rr i n gt o n , 22 .09 .78

La 'Ke

500 600 700

Wa v el e n g t h ( n m )

C u r l y 1 2 2 .0 1 . 7 8

500 600 700

Wa v e l e n gt h ( n m )

Figure 3 . 7 ( d ) Spectral distributions of downwelling P . A . R . from Tasmanian

lakes - moderately dystrophic lakes .

.n 0 X

I E c I Vl "' I E

0 � c 0 :J a

QJ u c 0

"0 0 '-

"' 0 ><

I E c:

I "' N I E .2 c 0 ::J o-

Q) u c �

u 0 '-'-

57

1 500 La k e P ed d e r , 2 1 . 07 . 82 800 La k e P e d d e r , 27 . 06 . 8 4

Vl

-0 X 600

1000 I

E c I <f) N I

E 400

.:: c 0 ::J

500 v

(l) u 200 c "0 "0 0 '-

,.'::;

400 500 500 700 W a v e l en g t h ( nm ) W a v e l e n g th ( n m )

3500 L a k e S t r o h a n , 1 6 . 0 1 . 8 1 3600 L a k e C h i s h ol m , 1 8 . 02 .8 4

3000- !\� 2 500 0 · 1 m x I I E

c 2400 I Vl

2000 N I

E 0 -c

1 500 0 ::J

1 200 1000 \j I O m �: 9

0 · 5 m x I

...j...-.,.,........c;;;.,..__,.___,,.._�r·�� 400 500 600 700

W a v e l e n g t h ( n m )

0 � '-

400 500 600 W a v e l e n g t h (nm)

700

F igure 3 . 7 ( e ) Spectral distributions of downwel l ing P . A . R . from Tasmanian

lakes - highly dystrophic lakes .

58

further narrowed and moved to the right . Lake Sorell had low

concentrations o f gilvin , but is eutrophic , with its moderate

turbidity cause d in part by phytop lankton , predominantly

Bacillariophyceae and Chlorophyceae (Cheng and Tyler , 1 97 3a ) . Blue

light is quickly a ttenuated , leaving a transmis s ion plateau between

about 5 8 0 to 7 0 0 nm . This is interupted by a trough centred between

6 7 0 and 680 nm , caused by the absorption of these wavelengths by

chlorophylla contained in the phytoplankton in the water . In more

turbid Tooms Lake and Lake Crescent the plateau is ab sent , and the

transmission p eak is close to 700 nm. A slight shoulder , possibly

due to chlorophyll a , is present at about 660 nm in the scans from

Lake Crescent . In these turbid lakes , all wavelengths less than about

500 nm are rapidly extinguished , in the case of Lake Crescent in the

first 1 . 5 metres .

The presence o f dissolved humic materials in non-turbid , dystrophic

lakes produces an underwater light climate very similar to that of

colourless , turbid lake s . The spectral distrib ut ions o f light at

various depths are shown in Figure 3 . 7d for mesohumic Lakes Barrington ,

Wurrawina and Curly ; and in Figure 3 . 7e for the more dystrophic Lakes

F edder (nova) and S t rahan , and for polyhumic Lake Chisholm , which had

the highest gilv in content of all Tasmanian lakes studied . Wavelengths

below about 5 0 0 nm are quickly removed from the downwelling P . A . R . ,

with the wavelength of maximum transmission lying at the red end of

the sp ectrum , between 650 and 700 nm . The more humic the water , the

f urther the transmis sion p eak lies towards the longer wavelengths .

The spectral distribut ions o f upwelling P . A . R . were measured in

one of each of the three principal types of lake - c lear , humic or

turbid . These are shown in Figure 3 . 8 . They were lit tle different

from the downwelling patterns at depth for the same lake s , apart

from the greatly reduced amplitude . The paucity o f upwelling

irradiance in Lake F edder , compared with the o ther two lakes is notable .

(b ) Derived Spectral Coefficients

Kirk ' s ( 1 9 7 9) method for comparing the extent to which each

component of the aquatic medium contributes to the extinction o f

underwater light w a s app lied t o s ix Tasmanian lakes , inc luding examp les

with clear , humic , or turbid waters (Figure 3 . 9 ) . P ar ticulate matter

p lays very lit tl e p art in attenuation , especially of shorter wavelengths ,

in the state ' s oligo trophic and dystrophic lakes (e . g . P erry , Curly) ,

"'

0

I E c

I Vl

CJ I E 0 c 0 ::J G Q) u c D

D 0

59

60 G r e a t L a k e , 2 6 . 0 5 . 8 3 1 50 TGo m s Lo i< e , 3i .08 . 8 2 I S G L o k e P e d d e r , 2 7 . 0 6 . 8 4

"' "' 0 Q

I 40 I 100 E E 1 00 c

c I 7 on Vl

� �· E E 0 .2 c c 0 '-' :J ::J u CT

50-1 I I

'Q I 2

Ql u c 0 D 0

400 500 600 700 4 00 5 0 0 6 0 0 700 400 500 600 W a v e l en g t h (nm) Wav e l e n g t h (nm) W a v e l e n g t h (nm)

'

Figure 3 . 8 The spectral distribution of upwelling P . A . R . in c lear ,

turbid , and dystrophic Tasmanian lakes respect ively . Note that the

irradiance scale for Lake Pedder (nova ) is l o - 2 that of the other two

lakes .

700

� c <lJ ·u ::: <1) 0 u c .2 0. 0 "' �

' E c

.'.! �

<1) 0 l)

c 0 2-0 "' .0 <(

1·0

4 ·0

3 ·0

2·0

1 · 0

I

L a k e P e r r y , 21 .04 . 8 3

Wa v e l en g th ( n m )

, L a ke B a rr i n g t o n , 1 3, 0 3 .7 8

\

\ \ \ \ \

• •

\ \

"• \ '\ .. \ " \

\ . ·, ' · · . · , -' .. . - · - ·

' ......... ' , ..... . ......

400 500 600 700

4 · 0 \

W a v e l e n g t h ( n m )

L a k e S ore l l , 1 4 .07. 82

\ \

\ \

Wa v e l en g t h (nm)

60

3·0

c "' 0 2·0

" 0 u c 0

La k e Le a k e , 1 6 .07 . 8 2

\ \

\ . \ '. \ \ \ '

\ " .; ..., , . · , ...... . - · ,,.., · - · � .........

4 00 500 6 00

W a v e l e n g t h (nm)

l La k e Cur l y , 22 .0 1 . 7 8

· - : o o l \ -::- . I

L 8 ·0-i \ 3 I I . :i: 6 · 0 I ' . 5 \ \ u \ ·, \ . c 0 4 ·0 \ '

\ '

700

\ '· , ;: 2 ·0 .... --�� · .... . _ _ _ , /

. .......... .. ...... ...... ... . . -�_,..-.,..-__,..--;;;:::::::;:::::::� ........ 4 0 0 500 600

Wa v e l en g th ( nm)

j T o o rn s La k e , 22.06 .7 8 �-

8·0-j \ . \

c 6 · 0 � .. \

. \ " 0 u 4 ·0 c 0

·. \ .. '. .. \

700

� 2 ·01 ' , , ..... � .. �> . - . / -.':1 ' •• - · - ·

..... • ...... e-o. • ..... .... - -

500 600

W a v e l e n g t h ( n m )

F igure 3 . 9 Compari son of calculated absorption coefficients at 1 0 nm .

intervals over the P . A . R . spectrum for selected Tasmanian lakes. ----

Absorption coeffic ient due to water. - - - - - - , Absorption coefficient

due to g i lvin . - · - · - · - · - j The apparent total absorpt ion coefficient obtained

by quantaspectrophotometry within the lakes, . . . . . . , The difference 1

between the apparent total absorption coefficient and the sum of those

for gi lvin and water , giving an est imation of the contribution of tripton

to total absorpt ion . Some of this contribution mus t also be due to

the scattering effect of tr ipton .

61

where either g ilvin or water are the dominant extinguishers of light ;

but in the sligh tly more turbid lakes ( e . g . Barrington , Leake ) , there

is , naturally , a greater contribution , which may exceed that of the

o ther component s . P articulate matter is the dominant inf luence ,

however , in the turbid Tooms Lake and Lake S orell , with a contribution

from chlorophy l l in the latter , shown by the increased absorption

coefficients cal culated for trip ton from 660 to 680 nm .

However , i t mus t be s tressed that this method is approximate ,

providing a guide only . lhis is especially so where irradiance values

are too l ow to measure accurately , such as below about 450 nm , causing

spurious apparent t otal absorp tion coefficients for these wavelengths

in the turbid or more dystrophic l akes . Kirk ( 1 9 7 9 ) discussed

shortcomings of the technique for regions of rapid change in attenuance ,

such as at the r ed end o f the spectrum .

3 . 3 . 5 Secchi Disc Transparency

Secchi disc depths (Z sD) for each lake are also presented in

Table 3 . 2 . Secchi disc dep ths were greatest in the clearest lakes ,

but decreased markedly with increased gilvin or turbidity . The

maximum depth measured , 1 6 . 8 metres , was in Lake Esperance , and the

minimum , 0 . 60 , in Lake Crescent . The median Secchi disc dep th for

Tasmanian freshwaters was 2 . 65 metres .

3 . 3 . 6 Regression Analyses

Regres sion analyses (Table 3. 3 ) shows the mean vertical attenuation

coefficient for downwelling irradiance , Kd (av ) , is greatly influenced

by gilvin concentration , with a statistically satisfactory regression

l inking the two . In comparison , turbidity measurements are poor

predictors of attenuation in Tasmanian lakes with the regression Kd ( av)

against Tn being non-s ignificant at the 5% level , al though natural

l ogarithmic transformat ion improved this considerably . The multiple

regress ions of Tn and g440 against Kd (av ) do little to improve on

tho se between g440 and Kd (av) alone . There was no correlat ion between

g440 and turbidity in Tasmanian lakes (r = -0 . 0 7 2 ) .

Altho ugh a highly s ignificant linear r elationship exists between

Secchi disc dep th and euphotic depthJ Secchi disc measurements generally

underestimate Z eu for many cl ear-water Tasmanian lakes and over-

estimate it for dys trophic waters . In many instances the Secchi disc

depth actually exceeded the euphotic dep th measured by the

quantaradiometer in dys trophic waters (Table 3 . 2 ) .

62

Table 3 . 3 : S impl e and mul tiple regression analysis showing the relat ionships between various op tical characteristics o f Tasmanian l akes

Equation No . r z n

1 Kd (av ) = 0 . 7 4 6 + 0 . 1 7 3 g440 0 . 747 65

2 lnKd (av) = 0 . 508 ln g 440 - 0 . 2 1 5 0 . 806 65

3 Kd (av ) = 1 . 44 0 + 0 . 0 7 4 Tn 0 . 0 27 65

4 lnKd ( av ) = 0 . 1 49 + 0 . 3 1 3 lnTn 0 . 1 1 0 65

5 Kd (av ) = 0 . 5 7 1 + 0 . 1 7 7 g440 + 0 . 1 02 Tn 0 . 7 9 8 6 5

6 lnKd (av ) = 0 . 49 1 lng440 + 0 . 20 3 lnTn - 0 . 1 6 7 0 . 852 65

7 Zeu = 0 . 2 2 4 + 1 . 2 65 ZsD 0 . 88 1 5 1

8 b 0 . 37 6 + 1 . 1 8 6 Tn 0 . 88 7 2 3

p

0 . 00 1

«' 0 . 00 1

0 . 1 95

0 . 00 7

"'< 0 . 00 1

<<' 0 . 00 1

<'< 0 . 00 1

<< 0 . 00 1

r�o .

1 2 3 4

5

6 7 8 9

l O

1 l � 2 1 3

i !, 1 5

1 6 1 7 1 8 1 9 20 2 1 22 2 3 2 4 2 5 2 6 2 7 28 2 9 30 3 1 3 2

3 3

3 4

3 5

36 3 7

63

Table 3 . 4 : Lo c a t ion and d e s c r i p t ion o f t h e s i t e s s u rveyed in N . S . 11 . * d en o t e s t h a t t h e s p e c t ra l d i s t r ib u t ion o f P . A . R . was a l s o m e a s u r e d f o r these w a t er s . For add i t io n a l limno l o g i c a l i n f o rma t ion, s e e T imms ( 1 9 7 0 , 1 98 2 ) a n d S e c t ion 2 . 2 . T h e s i t e s c an b e l o c a t e d by n umb er in Figure 3 . 2 .

L ake

Toonumbar D am C l ar r ie H a l l D am R o c ky C r e e k D a m ;,Lake Ainswor t h

C o o ks Lagoon

,·,Lake Minnie lva te r

'''Lake H i aw a t h a

Karangi D am

R o s e n d a h l R e s e r v o i r

( P o r t: �1a c q u a r i e Dam) B o o t mva Dam

''' S torm Ki n g D am Beehive D am (Wal l an g a r r a Dam) :; l He] en a Dam

Ten l: e r f le ] d E e s ervoir Ranger V a l l ey Dam

Beardy Wa t ers R e serv o i r '''t!a l p as D am P udd l e d o c k Dam ''D umar e s q Dam

G a r a Darn ''' Cl a ky Dam

Ken t uc ky C r e e k Dam Y a l g o o R e s erv o i r

G h m Lyon D am '''l' ind a r i D am Lake Inve r e l l

'' C o p e ton D am

i<La ke Keep i t

Q u i p o l l y D am ;\ C ha f f ey D am

D ungowan D am

Glenb a1m D am

Lake Lid d e l l

L a ke S t C l a i r ( Gl e n n i e s Creek

L o s t o c k D am

C h i ch e s t e r Dam

7<Y a r r i e L a k e

D am)

D e s c r ip t ion and U s e ( p l u s add i t i o n a l r e f e rences whe r e a p p r o p r i a te)

I r r i g a t ion Wa t er S u p p l y , near Kyo g l e Town W a t e r S u p p ly , Murwi l l umbah Town W a t er S up p ly , L i smor e C o a s t a l D une Lake , Lennox H e ad

( Ba y ly , 1 96 4 ; T imms , 1 982 ) C o as t al Dune Lake , Ev ans Head

(Tinuns , 1 9 8 2 ) Coas t al Dune Lake , Hoo l i ( T imms ,

1 96 9 , 1 9 82) Coas t a l D une Lake , Woo l i ( T imms ,

1 96 9 , 1 982 ) O f f - c r e e k s torage r e s e r v o ir .

Town w a t e r s up p ly , C o f f s Harbour O f f - c r e e k s to r age r e s ervo i r . To1m

w a t er s u p p l y , P o r t M a c q u ar i e O f f - c r e e k s torage r e s e rv o i r . Town

wa t e r s up p ly , Taree ToHn lva ter Supply , S t an t h or p e , Q l d Town Wa t er Sup p ly , Ha l l anga r r a , Q ld D i s u s ed W a t er Sup p ly f o r Mea tHo rks ,

\�a l langarr a Tmvn \•! a t e r S u p p ly , T e n t e r f ie ld

P r iv a t e I r r i ga t ion Dam , near G l e n Innes

ToHn Hater S u p p ly , Glen Innes Town Ha t e r S up p l y , Armid a l e Town W a t e r S u p p ly , Armid a l e D i s used ToHn W a t e r S up p ly . Now

r e c r e a t ional u s e , Arm i d a l e ToHn H a t e r S u p p ly , Armid a l e Hydr o e l e c t r ic imp oundment , e a s t

o f Armid a le Town Water Supp ly , Ur a l l a P r i v a t e I r r i g a t ion S u p p l y ,

near W a l e l1a Large I r r i g a t ion S t o r age, l'!o l e River , Q ld Large I r r i g a t ion S to r a ge , near Ashford Disused ToiV!1 \·later S up p ly , nov.' a

\·!i l d l ife Sanct uarv , In·;el· e .Ll Large I r r i g a t ion S to r a g e , near Invere l l

Large I r r i gat ion S t o r a g e , near Gunnedah

Tmm \Va ter Supp ly , Her r i s Creek I r r i g a t ion S t orage and Town H a t er

S up p ly , Tamwo r t h (May & P owe l l , 1 9 86 ) To1m W a t e r Sup p ly , T amwo r t h Town W a t er Sup p ly and I r r ig a t ion

S t o r a g e , Scone , H un t e r V a l ley . S u p p l y o f c o o l i n g w a t e r f o r Thermal

P ower S t a t ions , near M u swe l lb ro o k , Hunt e r V a lley

Town W a t e r S up p l y and I r r i g a t ion S t o r a g e , Hunter V a l l ey

I r r i g a t ion \Va t er S t o r a g e , H u n t e r V a l l ey

ToHn W a t er S u p p l y , H u n t e r V a l l ey

Tur b i d , s h a l l oH n a t u r a l l a ke , n e a r Narrabri

64

PART B NORTH-EAST NEW SOUTH WALES

3 . 3 . 7 Surface Temperature , pH , and Conductivity

Data for surface temperature , pH , and conductivity (at l 8 ° C ) are

g iven in Table 3 . 5 . Surface tempera ture varied depending on the time

o f year , location , and meteorological factors . The thermal s tratification

patterns o f the s e waterbodies were not determined .

pH values ranged from 5 . 60 in Cooks Lagoon to 9 . 1 0 in Toonumb ar

Dam , with a med ian value of 8 . 05 . These are g enerally h igher than

recorded previously for the region ( e . g . T imms , 1 96 9 , 1 98 2 ) , but with

the considerabl e enrichment with bicarbonates in many of the se waters

(Timms , 1 970 ; Banens , in pres s ) , alkaline pH values are to be expected .

Conductivity (K1 8) varied markedly between waterbodies , even

between those in close proximity , so that no particular locational

patterns were evident . The lowest measurement , 30 . 9 M S cm- 1 , was for

Oaky Dam , while the highest , 2 1 40 )1.1 s cm- 1 , was recorded in Lake

Liddell . The median value was 1 50 p.s cm-1 .

3 . 3 . 8 Total Nitrog en and Total Phosphorus

Data for these two parameters are also g iven in Table 3 . 5 . Total

nitrogen values ranged from 1 00 pg L- 1 in Rosendahl Reservoir to

1 460 pg L- 1 in Yarrie Lake (median value 420 pg L- 1 ) , while to tal

phosphorus varied from 6 pg L- 1 in Lake Minnie Water to 5 6 8 pg L- 1 in

Yarrie Lake . The median total phosphr�S value for the area was 28

pg L- 1 . Most o f the dune l akes and o f f-creek storage reservoirs from

along the coast , and the Hunter Valley reservoirs , had the l owest

nutrient level s . The remaining waterbodies ar e eutrophic , and some

are markedl y so .

3 . 3 . 9 Turbidity , Colour and ChlorophylJ;a

The result s for these parameters are listed in Table 3 . 5 . Apart

from Lake Ainsworth , the natural coastal l akes and off-creek storage

r eservoirs (Karangi , Rosendahl , Bootawa) were the least turb id waters

o f the area , along with the reservoirs o f the Hunter Vall ey and some

of the l arge impoundments o f the Western Slopes . The se , and two other

reservoir s , Malpas and Gara Dams , all had turbidities of less than

1 . 5 N . T . U . The maj ority o f the o ther waterbodies fall within the

range 2 . 0 to 4 . 5 N . T . U . However a number exceeded thi s , including

Quip olly and S t . Hel ena Dams , where turbidity was due to blooms of

No . Name

1 Toonumb ar D am 2 Clarrie H a l l Dam 3 Rocky Creek Dam 4 5

6

7 8 9

Lake Ainswo r t h Cooks Lagoon Lake Minnie Ha ter Lake Hiawatha Karangi Dam R o s endahl Reservoir

10 B o o t awa Dam 1 1 S t orm King Dam 1 2 B eehive Dam 1 3 S t . Helena Dam 1 4 Ten t e r f i e l d Res . 1 5 Ranger Valley Dam 1 6 Beardy Wa ters Res . 1 7 Halp a s D am 1 8 Puddledock Dam 1 9 Dumaresq Dam 20 Gara Dam 21 Oaky Dam 2 2 Kentucky Creek Dam 2 3 Y a l goo R e s ervoir 2 4 G l en Lyon D am 25 Pind ari Dam 26 Lakeinvere l l 2 7 Cop e t on Dam 28 Le1kc Kccp i t

Q u i p o l l y Dilm Cha f f ey Dam

2 9 3 0 3 1 Dungm<an Dam 32 Glenbawn Dam 33 Lake Liddell 3 4 Lake S t . C l a i r 3 5 L o s t o ck Dam 3 6 Chiche s t e r Dam 37 Yarrie Lake

NED IAN clEAN ( E )

Tab l e 3 . 5 : Temp eratur e , chemical , and o p t ical d ata from f r e s hwater lakes and reservoirs o f nor th-ea s t New South Hale s

D a t e S amp led

2 6- 1 1 - 86

1 5- 7 - 8 7 26- 1 1 - 8 6 2 7 - 1 1 - 8 6 2 7- 1 1 - 86

25-8-86

25-8-86 1 0- 9- 8 7 1 1 - 9 - 8 7 l l - 9- 87 1 1 - 1 2- 8 6 1 4- 7 - 8 7 1 1 - 1 2- 8 6 1 2- 1 2- 8 6 1 2- 1 2- 8 6 2 6 - 7 - 8 7 4- 1 1 - 8 6 1 3- 8 - 8 6 3 1 - 7- 8 6 1 3- 8 - 8 6 4 - 9 - 8 6 7 - J - 8 7 7 - 1 - 8 7 1 4- 7- 8 7 2 6 - 7 - 8 7

2 5 - 7 - 8 7 25- 7 - 8 7 .1 9- l 2 - fl (J 1 9- 7 - 8 7 2 1 - 1 0- 8 6 2 1 - 1 0- 8 6 1 9- 7- 8 7 1 8- 7 - 8 7 1 8- 7 - 8 7 1 7- 7 - 8 7 1 7- 7 - 8 7 1 8- 1 2- 8 6

Temp erature and Chemical D a t a

T o t a l Temp .

o c

2 7 . 0

1 5 . 4 2 6 . 0

25 . 0 26 . 0

1 8 . 0

1 7 . 0 1 8 . 1 1 7 . 0 1 7 . 2 23 . 4

9 . 8 2 5 . 0 2 2 . 2 2 1 . 8

7 . 5 1 8 . 2 1 0 . 0 1 0 . 0

1 1 . 0 1 2 . 9 2 7 . 0 2 3 . 0 1 4 . 0 1 1 . 9 1 0 . 7 1 2 . 7 2 1, . 1 1 1 . l 20 . 6 1 6 . 3 1 2 . 8 1 5 . 2 1 3 . 0 1 2 . 2 1 2 . 8 2 6 . 1

pH

9 . 1 0

7 . 4 0 7 . 20 7 . 1 0 5 . 60

8 . 3 0

8 . 30 7 . 80 7 . 6 0 7 . 60 8 . 35 8 . 2 0 8 . 85 8 . 2 0 8 . 7 5 8 . 2 0 8 . 60 8 . 2 0 8 . 3 5 7 . 95 8 . 1 5 7 . 9 5 8 . 00

7 . 4 5 7 . 85

7 . 9 5 7 . 80 8 . J 0 8 . 6 5 8 . 1 0 8 . l 0 7 . 90 8 . 0 5 7 . 5 5 7 . 85 7 . 5 0 8 . 0 5

K1 8

foi S cm - 1

1 4 7

8 3 . 4 4 0 . 0

1 6 6 7 5 . 0

1 0 4

1 0 4 5 7 . 9

1 3 2

1 36 9 9 . 6 3 1 . 4 5 7 . 9

2 0 5 4 4 7 3 7 7 2 3 3 5 0 9 1 50 4 8 2

3 0 . 9 8 5 . 7

1 2 5 2 3 9 2 5 0 6 8 5 1 80 2 2 8 5 2 1 :3 2 9

5 2 . 2 3 32

2 1 40 2 3 4 1 9 9

6 5 . 5 1 4 6

N p

p. g L- 1

8 2 0

6 0 0 7 2 0

1 2 40 3 3 0

1 60

2 8 0 1 20 1 0 0 1 1 0 6 0 0 3 5 0

1 0 60 7 1 0 8 90

5 6 0 4 1 0

1 0 9 0 8 3 0 3 0 0 4 2 0 5 7 0

1 0 7 0 5 5 0 2 7 0

3 30

3 5 0

1, 0 0 1 2 0 0

4 60 4 7 0 3 1 0 3 5 0 2 8 0 1 1 0 1 90

1 4 6 0

2 5

2 2

7 8

8 6

1 1 9 7

1 6 3 4 2 0 8 6 2 6

1 4 6 8 8 3 0 6 2 5 4 3 1 4 2

1 5 9 1 3 3

1 9 2 2

1 2 3 3 1

v. 1 7 4

:38 20 1 5 2 3 1 1 1 1 1 4

5 6 8

Tn

N . T. U .

3 . 5 6 . 2 3 . 3

2 . 1 0 . 4 5

0 . 9 2

0 . 50 0 . 9 7 1 . 2 1 . 8 2 . 4 2 . 5

2 0 . 0 3 . 5 2 . 2 5 . 7 1 . 3 4 . 4 3 . 6 1 . 4 4 . 4

4 7 . 0

3 . 6 1 . 2 1 . 3

7 . 4 1 . 7 ! . . O 6 . 8 2 . 7 2 . 5 0 . 8 1 1 . 0 0 . 7 3 1 . 2 1 . 1

425

Optical Data

Chlorophyll S e c c h i

Kd ( av ) Zeu g 4 4 0

a D i s c

- 1 - 1 m p..:g L

0 . 4 6 1

2 . 6 4 8 0 . 7 4 8

1 6 . 35 1 7 . 1 9 7 0 . 9 2 1

0 . 0 5 8 0 . 1 7 3 0 . 1 1 5 0 . 7 4 8 2 . 7 0 6 2 . 0 1 5

1 1 . 2 2 7 1 . 5 5 5 0 . 9 2 1 2 . 82 1 1 . 2 6 7 l . 6 1 2 6 . 50 6 0 . 4 6 1 4 . 60 6

1 2 . 4 94 5 . 4 7 0 0 . 0 5 8 1 . 0 3 6 1 . 4 9 7 l . 0 3 6 0 . 7 1; 8 0 . 3 4 5 J . 0 3 6 0 . 9 7 9 0 . 1 7 3 0 . 0 5 8 0 . 5 7 6 0 . 80 6 0 . 6 3 3

1 1 . 5 1 5

m

1 4 . 3 1 1 . 3 5

5 . 7 3 1 . 40

3 9 . 4 3 1 . 5 0

4 1 . 8 9 0 . 9 0 1 . 92 "' l . 80

4 . 2 4

2 . 0 1 3 . 1 2 3 . 50 2 . 5 4

1 0 . 1 8 5 . 8 4

5 8 . 3 6 l . 5 1

1 5 . 6 3 2 0 . 8 8

8 . 3 7 4 4 . 2 6 2 2 . 2 3

7 . 8 6 1 7 . 0 6 1 3 . 8 2 1 5 . J 5

8 . 2 1 1 . 9 3

2 3 . 1 0 7 . 2 2 9 . 2 2

2 86 . 6 6 6 . 1 5 5 . 1J 2 8 . 7 2

1 2 . 6 1 6 . 3 6 2 . 6 5

1 5 . 0 5 2 . 4 2

3 . 4 5

:>- 5 . 5 0 3 . 9 5 2 . 4 5 3 . 7 5 1 . 80 1 . 9 0 0 . 5 0 2 . 40 2 . 65 1 . 1 5 3 . 0 5 0 . 9 5 l . 2 0 2 . 45 l . 7 5 0 . 5 0 1 . 4 0 2 . 4 0 4 . :) 0

0 . 7 5 3 . 5 0 1 . 5 0

ll . SO 2 . c,o 2 . 1 5 3 . 3 5 3 . 1 0 3 . 1 0 3 . 60 3 . 60 0 . 0 1 5

- 1 m

l . 2 3

l . 6 6 l . 3 5 3 . 8 9 1 . 9 1

0 . 84

0 . 33 0 . 4 6 0 . 55 0 . 65 l . 4 9 l . 4 3 3 . 9 2 1 . 1 9 0 . 95 1 . 5 8 0 . 8 1 1 . 7 2 l . 6 8 0 . 9 1

1 . 5 9 3 . 94 l . 72 l . 2 3 0 . 6 2

l . 9 7 0 . 7 4 0 . 94 2 . 4 8 0 . 9 5 0 . 84 0 . 6 8 0 . 6 3 0 . 8 5 0 . 5 8 0 . 70

4 8 . 20

m

3 . 6 5

2 . 6 6 3 . 2 3 0 . 92

> 1 . 7 0

5 . 1 2

:>5 . 00

9 . 50 8 . 5 2 6 . 7 1 3 . 40 2 . 8 9 0 . 9 5 3 . 7 6

4 . 3 9 2 . 65 5 . 70 2 . 6 8 2 . 4 1 4 . 6 9 2 . 5 3 1 . 05 2 . 4 6 3 . 7 0 6 . 9 7 2 . 35

5 . 96 4 . 7 4 l . 7 0 4 . 6 4 5 . 4 3 6 . 30 6 . 80 4 . 9 7 7 . 3 8 6 . 2 7 0 . 0 8

Ku (av) R

( o )

- 1 m

1 . 0 6

l . 5 6 1 . 2 8 4 . 22

- (A) 0 . 8 1

- (B) 0 . 4 7 0 . 5 1 0 . 6 3 1 . 4 6 l . 3 9 4 . 1 2 l . OS 0 . 8 7 l . 50 0 . 6 8 1 . 6 6 l . 5 8 0 . 7 2 l . 5 4 3 . 5 6 l . 5 2 - (C ) 0 . 5 7

l . 7 6 0 . 7 2 0 . 8 1 2 . 2 9 0 . 8 7 0 . 70 0 . 6 5 0 . 7 7 0 . 84 0 . 5 7 0 . 7 0

3 6 . 5

%

3 . 6 5

5 . 0 4 2 . 82 0 . 3 8 0 . 1 4 0 . 9 4

- (B ) 2 . 3 7 3 . 0 2 3 . 7 7 2 . 00 l . 6 8 5 . 60 3 . 9 8 l . 7 5 5 . 9 2 l . 3 2 3 . 40 2 . 3 4 2 . 20 2 . 2 1

1 3 . 9 8 l . 7 0 2 . 7 5 2 . 00

6 . 75 3 . 2 9 4 . 3 8 4 . 1 5 2 . 7 1

3 . 3 5 2 . 9 3 3 . 35 l . 6 5 2 . 6 5 1 . 9 9

l l . 40 (D)

.Q

- 1 m

5 . 3 7 6 . 3 1 3 . 6 9 2 . 6 1 - ( A) 0 . 8 6

- (B) l . 30 1 . 5 3 2 . 06 2 . 3 7 2 . 7 6

2 1 . 9 4 3 . 2 6 2 . 0 3 5 . 9 6 1 . 4 8 5 . 9 3 4 . 5 1 2 . 4 7 3 . 3 9

3 8 . 5 9 3 . 9 3 - ( C ) 1 . 5 2 9 . 3 3 2 . 2 1

3 . 1 4 1 0 . 9 2

2 . 6 9 2 . 4 0 1 . 6 9 1 . 6 8 1 . 4 6 1 . 9 1 1 . 6 3

2 8 3 . 3

STANDARD DEVIATION ( E )

1 7 . 0 8 . 0 5 1 7 . 1 7 . 9 6

± 5 . 8 0 . 60

1 5 0

2 5 6 3 6 1

4 2 0

5 1 7

3 2 5

2 8

4 7

4 7

2 . 4

4 . 3

8 . 1

1 . 0 3 6 8 . 3 7

2 . 4 95 2 0 . 9 3 3 . 6 4 3 4 7 . 47

2 . 1 5

2 . 20 l . 0 8

1 . 1 9 4 . 6 4

1 . 3 6 4 . 3 3

0 . 9 3 2 . 1 7

1 . 0 5

l . 3 2 0 . 9 6

2 . 7 9

3 . 20

2 . 3 8

2 . 6 5

4 . 90 7 . 2 4

(A) Too shal lm,• f o r calculat ion (B) Upve l l i n g irradiance no t measured

( C ) Ins trument f a i l ur e during p r o f ile ( E ) Excluding Y a r r i e Lake (D) R

( o ) is f o r 0 . 05 metre d ep th

0\ CJ1

66

photosynthetic o rganisms , and Clarrie Hall and Kentucky Creek Darrts ,

which had high tripton load ing s . The greate s t turbidity recorded ,

425 N . T . U . , was for the natural , shallow Yarrie Lake . The median

turbid ity for the l akes stud ied was 2 . 40 N . T . U .

Most o f the waterbodies investigated had low to moderate l evels

of dissolved org anic colour , and only twelve h ad gilvin values

ex ceeding 2 . 0 m- 1 . The more turbid waters al so tended to be the more

dystrophic . S t . He lena and Kentucky Creek Dams, and Yarrie Lake , all

had high level s of g ilvin . The coastal dune l akes were extremely

variable in humic content , with Lake Ainsworth being the most

dystrophic of al l s i tes studied , and Lake Hiawatha one of the least .

The median g440 value , 1 . 036 m- 1 , reveal s how uncoloured most o f the

study sites were .

The chlorophyll a content o f the waters was highly variable , being

as l ow as 1 . 5 1 pg L- 1 in Tenterfield Reservoir , and reaching a maximum

o f 28 7 pg L- 1 in Quip olly Dam , with the median value being 8 . 37 pg L-1 .

Chlorophyl1 a concentrations exceeded 1 0 fg L- 1 in sixteen of the

locations . ,

3 . 3 . 1 0 The Attenuation o f P . A . R .

Values for the mean downwelling vertical attenuat ion coefficient

(Kd (av) ) , and the measured euphotic depth (Zeu) , are given in Table 3 . 5 .

measurements only , and do no t take account of

seasonal variat i ons , which may be considerabl e ( Scribner , in Kirk ,

1 986) . Profil es of l ight penetration with dep th are given for

selected lakes with dif ferent optical properties in Figure 3 . 1 0. Lake

Hiawatha (Kd (av) = 0 . 3 3 m- 1 ) was the cleares t , but as gilvin ,

turbidity , and chlorophylla concentrations increased , so did

attenuation with a consequent decrease in euphotic depth . However ,

mo st lakes and r eservoirs had Kd ( av) values of less than 2 . 0 m- 1 , and

eighteen had values below 1 . 0 m- 1 . Attenuation \<las more rap id in a

few of the turbid , h ighly coloured , and eutrophic waters , such as

St . Helena Dam (Kd ( av) = 3 . 9 2 m- 1 ) , and the greatest attenuation

occurred in highly turbid Yarrie Lake , where Kd (av) was an extremely

high 48 . 2 m- 1 , and 9 9% of incident light ha d b een attenuated eight

centimetres below the surface . The typical biphasic curve , with

67

% Incident radiation

1

2

6

7

Figure 3 . 1 0 Attenuat ion profiles of downwelling P . A . R . ( 40 0 - 7 0 0 nm . ) for selected north-east New South Wales lentic freshwaters . A . Lake

Hiawatha , 2 5 - 08 - 1 986 ; B . Karangi Dam, 1 0 - 09- 1987 ; C . Malpas Dam ,

0 4 - 1 1 - 1 9 8 6 ; D . Lake Keep i t , 1 9 - 1 2- 1 9 8 6 ; E . Tenterf ield Reservo ir ,

1 2 - 1 2 - 1986 ; F . Storm King Dam, 1 1 - 1 2 - 1 9 86 ; G . Oaky Dam, 0 4 - 0 9 - 1 9 8 6 ;

H . St . Helena Dam, 1 1 - 1 2 - 1 9 8 6 ; I . Yarr ie Lake, 1 8 - 1 2 - 1986 . See Table

3 . 5 for further data on the opt ical properties of these waters .

attenuat ion grea test close t o the surface , was apparent in many of

the lakes (Figure 3 . 10) . A marked increase in attenuat ion also occurred

below about 2 . 50 metres in S to rm King Dam , probably due to z onation of

the phyto flagellate Ceratium :hirundeneUa (MUller ) Schrank , which was

present at those depths , but absent from the surface water s . A

simil ar , small er change was app arent in Tenterfield Reservoir . The

median vertical attenuation coefficient , Kd (av) , for the area was

1 . 1 9 m- 1 , while that for euphotic dep th was 4 . 64 metres .

Mean upwell ing vertical attenuation coefficients (Ku (av ) ) were

generally not greatly different from the corresponding Kd ( av) for

each l ake , al though they were usually sl ightly lower . Any differences

were probably due to decreased accuracy in measuring the much lower

intensities of upwell ing irradiance , especially at depth . Mo st

locations were suf f iciently deep to avoid any contribut ion from light

reflected off the bottom to upwelling irradiance .

3 . 3 . 1 1 Reflectance and the S cat tering Coeffic ient

Reflectance close to the surface , at 0 . 1 0 metres (Ro ) , is given

in Table 3 . 5 . This usually exceeded 1 . 5% and was highest in the more

turbid locations , but varied considerably when turbidity was l ower .

Changes in reflectance with depth are shown for a number o f waters of

dif fering turbidity in Figure 3 . 1 1 . Reflectance initially increased

with depth , and in mc\.st ins tances continued to do so . This was

especially marked in Kentucky Creek Dam and in Lake Inverell . In

some , notably Malpas and Puddl edock Dams , Lake Minnie Water , and

Ro sendahl Reservoir , reflectance tended to appro ach an asymp totic

value after the init ial increase , but in St . Helena and S torm King

Barns decreased af ter peaking at shallower depths .

Values for the scat ter ing coefficient , �' ranged from 2 8 3 m- 1 in

Yarrie Lake , to 0 . 86 m- 1 in Lake Minnie Water . The median value was

2 . 65 m-1 .

3 . 3 . 1 2 The Spectral Distribution of Underwater P .A . R .

The spectral distr ibut ion o f P . A . R . (400- 740 nm) was measured in

twelve o f the lakes and reservoirs . These are shmm in Figure 3 . 12 (a- c) .

The distribution o f underwater light in the clearest l ake , (Lake

Hiawatha) , was centred at 5 8 0 nm , with almost equal extinct ion of the

wavelengths either s ide of this , specifying a predominantly green to

yell ow underwater l ight climate . Attenuation of blue l ight increased

69

0.26

0.24 A

0.22

0.20

0.1 8

'2 � 0.1 6 0 '1:l w ......_ 0.. 0.14 :=

� (I) 0.12 u � 1':) B ..... u .S!

... 0.10 Cl) ex:

0.08 [Yx o .,. ... - - .. , ' "'

- � ·

0.06 -,_,..

I '

0.04 H

0.02 --------------- I --- J.

1 2 3 4 5 6 7 Depth (metres)

Figure 3 . 1 1 Reflectance/depth profiles for selected north-east New

South Wales lentic freshwaters . A . Kentucky Creek Dam . 0 7 - 0 1 - 1 9 8 7 ;

B . Lake Inverel l , 25 - 0 7 - 1 98 7 ; C . St . Helena Dam, 1 1 - 1 2 - 1986 ; D . C larrie

Hall Dam ( dashed line ) , 1 5 - 0 7 - 1 98 7 ; E . Puddledock Dam , 1 3 - 0 8 - 1 98 6 ;

F . Rosendahl Reservo ir , 1 1 - 0 9 - 1 98 7 ; G . Yalgoo Reservoir , 0 7 - 0 1 - 1 9 8 7 ;

H . Malpas Dam , 04- 1 1 - 1986 ; I . Lake Minnie Water , 26 - 0 8 - 1 986 ; J . Lake

Ainsworth , 2 7 - 1 1 - 1 9 8 6 .

-' VJ

0 0 0 �

0 0 a l t� I I

Lake Hiawatha, 25.08.86

Wavelennth (nm) '

Copeton Dam, 25.07.()7 _//� /

O ! m d \ /

2.0 m x 2 I .i 0 ,(/ I �g (� { �� If) .•

.::: : I

�-··� 6.0 m " l 0

400 500 600 700 Wavelength (nm)

70

0

� 1

Pindan Dam, 26.07.87

0. 1 m x 1

660 Wavelength (nrn)

j Malpas Dam, 04, 1 1.86

0.1 m x 1

Figure 3 . 1 2 ( a ) Spectral distribut ions of P . A . R . from north - east New

South Wales lentic freshwaters - the clearer water lakes and reservoirs .

71

0 0 0 M Lake Minnie Water, 26.08.86

0. 1 m x 1

·�-----...---,---·-··

N ' E .8 c: "' :::l $

0 0 0 M

CJ O u o c: o "' ..... � r� J:;

Lake Keepit, .1 9.12.86

p /_ \ I I I I ( /

2.0 m x 4

400 500 600 700 4 0 6oo �oo--' Wavelength (nm)

0 0 0 ,....

Wavelength (nm)

Chaffey Dam, 2 1 . 1 0.86

0 . 1 m x 1

;::::, I

5 . 0 m x 1 0

400 --,--56-o -- ' 6llo 7 Wavelennht (nm)

0 0 lt)' o '0 � '""

X ,.... ' c: c o .... 0 . 'Vl 0 M N · -t:

� ;:a Z. o � 0 o-CJ N u c 10 � 10 l:

0 0 0 .....

Storm King Dam, 1 1. 1 2.86

0.1 m x 1

I I '

I I -� -r-• 4bO ' 5u0. GoO --7tr� Wavelennth (nm)

F igure 3 . 1 2 ( b ) Spectral distributions of P . A . R . from north-east New

S outh Wales lent ic f reshwaters - s lightly coloured or turbid lakes

and reservoirs .

0 0 0 (")

..... ' E o c:: o 0 M C>J

'II) c-J 'S

/ / /

I I 1/ I

72

L//� � --r----r-- --,-� , - -- ----,. 400 GOO GOO 'iOO

..... ' V> 0 . 0 N l() ' E ,.... . � iS ;:l ..::!

0

\Vavelenf]lh (nm)

Lake Ainsworth, 27. 1 1 .86

0.1 rn x 1

0.5 m x 2

0) 0 u o C:: M 1\\ I I � \ � I I /JO "' ' '' \ I / '

-· --= / !-.-------.-----1 400 5�- 700 Wavelength (nm)

Dumaresq Dam, 3 1.07.86

660 Wavelength (nm)

Yarrie Lake, 18 .12.86

0. 1 m xl

7�'

f t' l r I 0.25 In X GOO

J�-To-�-7(J'o ___ , Wavelength (nm)

F igure 3 . 1 2 ( c ) Spectral distributions of P . A . R . from north-east New

S outh Wales lentic freshwaters - the more dystrophic or turbid lakes

and reservoirs .

73

in compariaon t o red light as concentrations o f g ilvin and trip ton

increase . Thi s is shown in the series P indari , Copeton , and Malpas

�ams , and Lake Minnie Water , where wavel eng ths shorter than 500 nm

are ext inguished progressively more rap idly within the fir st few

metres below the surface . Despite this , these waters are s t ill clear

enough so that the wavelength of peak transmission changed only

sl ightly , to 5 9 0- 600 nm . The sl ightly turbid but low coloured waters

of Chaffey Dam and Lake Keep it also quickly extinguish blue l ight ,

but even here the wavelength of maximum transmission remained near

600 nm . However , the spectral distributions of these reservoirs

display a broad plateau of wavelengths between 590 and 660 nm , rather

than a s ingle p e ak wavelength . This is interup ted by a shallow

absorption trough centred on 620 nm . This was al so present in the

underwater spe c trt£�1\of Lake Minnie Water , and as a shoulder on s cans

from P indar i , Copeton , Malpas , and Storm King Dams . The cause o f

this absorp tion trough cannot be explained ( see Section 3 . 4 . 1 , below) .

The spectr al distribution o f P . A . R . in Storm King Dmn showed

changes due to this reservoir ' s h igher gilvin content , with a broad

tr ansmission p e ak now centred at 660 nm . The probable stratificat ion

of Ceratium hirundineZZa caused a marked absorpt ion trough centred at

6 8 0 nm in the spectral distribution of l ight b elow two metres ,

corresponding t o absorpt ion by chlorophyll a . A bloom o f the diatom

Asterione Ua formosa Hass. also inf luenced the spectral dis tribution o f

underwater P . A . R . i n Dumaresq D am , caus ing a s imilar absorption

trough at 680 nm . Consider able g ilv in concentrations , as well as

phytoplankton and tripton , all contribute to the rapid attenuation

of the shorter wavelengths in this reservoir .

The spectral scans from Oaky Dam and Lake Ainsworth are typical

o f humic waters . Maximum transmission in moderably humic Oaky Dam

was at 680 to 6 9 0 nm , and at 700 nm in highly humic Lake Ainsworth ,

where the transmiss ion window had also been further narrowed . Any

contribution from the hi3h chlorophyl�a contents of these waters is

no t obvious .

The underwater spectrum in extremely turbid Yarrie Lake was very

s imilar to tho se from humic l akes , but the transmission peak was

even further to the right , being centred on 7 1 0 nm . Most wavelengths

below 650 nm wer e extinguished within the surface twenty- f ive

centimetres of water .

7 4

3 . 3 . 1 3 Secch i D i s c Tran s p ar ency

Measurements o f Se cchi d i s c transparency are given in Tab le 3 . 5 .

Secchi dis c dep th exceeded 3 . 0 metres in twelve o f the s tudy si tes , b eing

greatest in Lake Hiawatha , b u t were shallower than 1 . 0 metre in seven ,

including polyh umic Lake Ainswo r th , the turb id Lake Inverell , S t . Helena

and Kentucky Creek Dams , and in Quipolly and Puddledo ck Dams , where blooms

of phytoplankton w ere presen t . The minimum value , 0 . 0 15 metres , was in

Yarrie Lake . The medium value was 2 . 15 me tres .

3 . 3 . 1 4 Regres s ion and Correlat ion Analyses

Pearson correlation analysis was conducted b e tween mos t of the par­

ameters lis ted in Tab le 3 . 5 , and linear and mul tipl e regression analyses

undertaken us ing either Kd ( av ) or b as the dependen t variab l e , and turbidity ,

g , and chlorophyll a as the ind ependent variab les . D ata from Yarrie Lake 4 4 0

were excluded , as these were considered atypical o f the s tudy area , and

may have placed considerab le b ias on the resul ts o f these analyses .

Highly sign i f ican t correlations wer e found b etween mos t optical

p roper t ies . Thes e included positive correlations b e tween Kd ( av) and

turb idity , g , and chlo roph yl l a ( see Table 3 . 6 ) , and negative correlations 4 4 0

b e tween Secchi d i s c depth and a l l o ther optical parameters . Additionally ,

g and turb idity were pos i t ively correlated ( r = 0 . 49 9 , P = 0 . 00 2 ) , but 4 4 0

chlorophylla was no t significan tl y correlated with either . Thus , mos t o f

the suspended particulate mat ter may have been mineral particle , detritus ,

o r o ther tripton , rather than phytoplankton .

Several o ther s i gnifican t correlations are of not e . Water colour and

temp erature were weakly posit ively correlated ( r = 0 . 4 1 5 4 , P = 0 . 0 12 ) ,

pos s ible b ecaus e coloured waters rapidly ab sorb mo st so lar radiation at

shallow dep th , therefore caus ing warmer s urface temperatures . This hypo­

thesis is suppor t ed b y a further but weak significan t pos itive correlation

b etween temperature and Kd ( av ) ( r = 0 . 3545 , P = 0 . 0 32 ) . The rapid atten­

uat i on of ligh t in the surface waters o f humic lakes , resul t in g in their

warming , may pos s ib l e con tribute to such a relationship . However , these

correlations may also b e artifacts of seasonal sampling , as the mos t

h i ghly coloured l akes ( g > 10 . 0 m- 1 ) were al l sampl ed during sunnner . 4 4 0

S easonal data are unavailab l e to tes t these relationships f o r o ther times

o f the year . Bo th nutrients were significantly co rrelated with chlo rophylla

( To tal nitrogen : chlorophyll a , r = 0 . 5365 , P < < 0 . 00 1 ; Total phosphorus :

chlo rophylla , r = 0 . 5 6 35 , P < < 0 . 00 1 ) , reve aling algal res ponses to

inc reas ed nutrient lo adings . To tal nitro gen was also s ignifican tly

75

Table 3 . 6 : Regres sion analysis showing the relationship s b etween various op tical characteristics o f north­east New South Wales standing freshwaters .

Equation No . r z n

1 Kd (av ) 0 . 8 1 2 + 0 . 220 g 440 . 7 5 0 36

2 Kd ( av ) 1 . 02 + 0 . 0 7 9 5 Tn . 48 1 3 6

3 Kd ( av ) 1 . 20 + 0 . 00 7 5 Chla . 1 4 8 36

4 Kd (av ) 0 . 75 + 0 . 0 4 Tn + 0 . 1 7 6 g440 . 8 4 1 36

5 Kd (av ) 0 . 6 8 9 + 0 . 2 1 5 g 440 + 0 . 00 7 Chla . 86 1 36

6 Kd (av ) 0 . 9 1 6 + 0 . 07 5 T n + 0 . 006 Chla . 56 1 36

7 Kd ( av ) 0 . 646 + 0 . 0 35Tn + 0 . 1 7 6g440 + 0 . 006Chla . 9 3 1 3 6

8 Zeu 0 . 386 + 1 . 7 8 Zsn . 7 9 6 3 5

9 b 0 . 9 4 8 + 0 . 85 Tn . 96 5 3 3

p

.!.(.', 0 . 001

0 . 00 1

0 . 20<Pdl';:O . OS

� 0 . 00 1

<.<. 0 . 001

..::;.:: 0 . 00 1

«0 . 001

0 . 00 1

4t'D . 001

7 6

co rrelated 'ivi th co lour ( r == 0 . 5 1 7 4 , P = 0 . 00 2 ) , p rob ab l y resul ting from

nitro gen forming p ar t of the elemental comp o s ition of dis s o lved humus ,

as was total pho s phorus with turb idity ( r = 0 . 56 8 3 , P << 0 . 00 1 ) . This

coul d be due mainly to phos phorus bein g ab s o rb ed ont o the outer surface

of tripton par t ic l e s .

Despite wide variation in temperature due t o s easonal and locational

differences , no s i gnif icant correlation exi s t ed b e tween temperature and

chlorophyll a , s ugges t ing tha t water temperature h ad l it tle influence on

the quantity o f phytoplankton pres en t . Also , no s ignifican t correlation

was found , b etween pH and the humic conten t o f the waters , p os s ib ly b ec ause

of b uffering by the dominant anion , b icarb onate ( T imms , 19 70 ; B anens , in

pres s ) .

The resul t s o f regress ion ana lyses are shown in T ab le 3 . 6 . Natural

logarithmic tran s f o rmations did little to improve the relationships b e tween

the p arameters o f these regre�ons , and are therefore omitted . Dissolved

organic co lour is the maj o r attenuator of l i gh t in these waters , al though

turbidity is also a s igni ficant contributor , and chlorophyll a a minor one .

All three components accoun t for almo s t all the var i ability ob s erved in

Kd ( av) ' and turb i di ty is the maj o r factor influen c in g the s ca ttering

coefficient , b .

The relationship b e tween Secchi dis c depth and eupho tic depth was

also examined , and a highly s ignific ant p o s i t ive correlation foun d between

thes e .

Phytoplankton

The dominant phytopl ankton found in the s in gl e s amples from each

s tudy site are g iven in Tab l e 3 . 7 . The s e dat a g ive an indica t ion o f the

cons iderab le r an g e o f phytoplankton presen t in north-eas t New South Wales

freshwa ters , des p ite their lack of s easonal i ty and that some taxa have

b een identified o nly to genus level . Add i tionally s ome of the smaller

species may well have b een missed by the s ampling me thod , pass in g through

the 20 �m mesh o f the plankt on net .

Al gae from the Divis ion Chl o rophyceae were particuarly common , especially desmid s and colonial species su ch as Botryococcus braunii

Ktltzin g , Dictyosphaerium spp . , Oocystis spp . and a cocco i d alga of the

Sphaerocys-ris schroe tervr: Chodat type . S!:aurastrwn was the main desmid

genus present , and f requently encountered s pecies included So freemanii

Hes t & Wes t , S" sonthalianwn Turner , S. paradorwn Meyen , S. sexangulare

(Bulnheim) Rab enhors t , and S. tohopeka ligenese Wo lle , while a t riradiate

W W W W W W W W N N N N N N N N N N _ _ _ _ _ _ _ _ _ _ ,J G\ v1 J:"· w r'"' ..... o <..0 co ---.j 0'1 VI .�> w N ,_ o 1.0 co '-...) (J\ v, � w N ,...... o 1..0 co "'-..J 0'> VI .t.. .... w N - Lake No�

t'l'l r: (0 ro-

f � ill

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Eu.doPina e legans Ehrenb e r g Goniwn f'or.•moswn Paschet· Pwzdol'ina mor•wn (HUller) 3ory Vo l vox s p . A s tel'ococcus supePbus ( C ienk) Scherf G loeoey stis gigas (KII t z i n g ) Lagerhelm Te tr•aeclr•on gr'au-i le l l<lnsgr ig c f . SphaerocyB t -/ s C h o d a t Ank i:;tJ•odesmus c f . lO�ID1-r;.TLma Lemm . KirchncPic Nephr·ocy tizun lwwtwn H . Hest Oocystin spp . Quach•igu/.a sp . Botryoaoccus braunl-i. KUtzing D·iccyosphaer•iwn spp . c f . D-z:morphoPoucw; hmat:nJ B raun Actinas trum han t;-;suld-i. Lagerhei.m Coe lao tr•wn .sp .

({UUdi•a ta �!orren spp .

H!Jdl'od·iutyon r•c c i .ozz iacwn (L . ) Lagerhe:lm PecUastr'W71 dup Zt:::t: �!eyen U l o tJn• i.;c

l>r-eld,;nonii i'Ir:!neg].ni

Ca.:Jrnar>iwn Des:rri(li�jm sp . ��1-ic -eos tePia:J s p p . Plew�otaerdwn sp ,

e:1;c::uu G ! t1il Ra l. f s s p p .

Sta tu�odewmw spp . 'l'riptoeer-as gPaeUe B a l l e y Xanthld·iwn sp . Euglena s p p . 'Pr'ache lomonas sp p . Pr10Y'ocentl�wn p layfa-iri Croome & Ty l e r Per•1:diniwn sp p . Cemhz.un h il•undirze l la (l·IUller) Schr ank '/Meroh•iehia baei l la ta flereschk01;sky Ur•og lena s p •

Dyrzobr•yo11 spp . Ma l lomonas s p p •

Synuru sp . Me losh•a gPamz lata (Ehr . ) R a l f s Cyc lote l la sp . c f . S tephanodisaus sp . A ttheya zauhal'iasi Brun . RJdzoso len-ia eriens{s H . L . Sml t h As ter'ione l la j'ol'mosa !lass . FPagilaria sp . Synedra sp . Tabe l laria sp .

� .,.

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> :2 II '< " � 0 CT 'Cl c � � 5 w ?> � � ,., � . � n ..-. " 3

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Large Pennate dia toms (mo stly benthic species) Mer•'imnopedia sp . Mial'ocys t·is aePuginosa KU tzing emend . E l enkin Lyngbya sp . Osai Z la toPia l imrzosa (Ro t h ) C . A . Agar d h . Arzo.baena j'los -aquae ? (Lyngbye) Brebisson

1 S

s pecies wi th aff init ies to S. pingue Teiling was presen t in mos t

reservoirs o f the New England Tab lelands . F l agella ted green algae

such as Vo lvox s p . and Eudorina e legans Ehrenb erg were also prominent

components o f the phytoplankton at s everal locations .

D inoflagel l a t es , in particular Peridinum s pp . ( es pecially P. vo lzii

Lemmerman) , and Ceratium hirundine lla (MUl ler) S chrank wer e also abundan t

in many location s . C. hirundine l la formed an almo s t mono specific b loom

in Quipol ly Dam . Frorocentrum pa lyfairi Croome & Tyler was recorded from

three coastal l o c at ions , Toonumb ar Dam, Cooks Lagoon , and Lake Hiawa tha .

Euglenoids were also pres ent in mos t samples , with Trache lomonas vo lvacina

Ehrenberg , T. hispida (Perty) S te in , and T. armarta ( Ehrenb erg) S t e in

b e in g th e mos t c ommon , while Euglena oxyuris S chmarda was the dominant

alga in Cooks Lagoon . Chrysophy t e s were much l e s s common , and when presen t

wer e usually Dinobryon cy Zindricum Imhoff o r D . sertularia Ehrenb er g .

A long-spined species o f Ma Uomonas formed an almo s t monos pecific bloom

in Puddledock Dam and M. sp lendens (G . S . Wes t ) Playfair was recorded

from Lake Hiawa th a , and Glenbawn , Beehive , Cl arrie Hal l , Chi ches ter

and S to rm King D ams .

Diatoms were locally abundant . Me losira granulata ( Ehrenb erg)

Ralf s and Rhizoso lenia eriensis H . L . Smith were present in a nt�b er

o f the sites , while Asterione l la formosa Has s . formed a dens e b loom

in Dumaresq Dam . Anabaena flos-aquae ( ? ) ( Lyngb ye) Breb is s on and

Microcystis aeruginosa Kiltz ing emend . Elenkin were the main b lue-green

algae pres ent .

79

PART C SOUTH-EAST QUEENSLAND

3 . 3 . 1 6 'I'emmperature , pH , and Conductivity at 1 8 ° C (Kl s) Surface temperatures , pH , and K1 8 for each lake are presented in

Table 3 . 8 . Temperatures ranged from 2 1 . 0 ° C to 25 . 2 ° C , probably

resulting from day by day variations in weather , during the three week

sampl ing p eriod , rather than underlying differences between the lakes

themselves . Mo s t of the lakes are isothermal and polymictic (Bayly

eJ:_ al , 1 97 5 ; Arthington � al , 1 9 86) .

Red Lagoon had the l owest pH , 4 . 25 , whilst the highest , 7 . 5 5 , was

from Lake Minke r . pH values were higher than previously reported in

all but Brown Lake , and four were above neutral . The median value

was 5 . 60 . Secchi disc depths indicate that the humic content o f many

lakes was lower during this survey than in previous studies , and with

a s trong positive correlation exis ting between water transp arency and

pH (Bayly � al , 1 975}_, with greater water clarity , higher pH values

are al s o l ikely .

The K1 8 measurements ranged from 5 2 . 1 � S cm-1 to 5 7 6 � S cm- 1 with �

the median value being 96 . 7 ;AS cm- 1 . These are close to tho se

previously reported for the lakes (Bayly , 1 96 4 ; Bayly et al , 1 9 7 5 ;

Miller et al , 1 9 84 ; Little and Roberts , 1 98 3 ; Reeve et al , 1 9 85 ;

Bensink , 1 9 7 6 ; Bens ink and Burton , 1 9 75 ; Arthington and Wat son , 1 98 2 ) ,

excep t for Lakes Wabby , Woonj eel , Minker , and Ocean Lake , which were

considerably higher . This may result from evaporative concentration

of ions in these lakes , where cons iderable amount s of exposed beach

indicated lower than normal water level s . These four lakes al so had

pH values above 7 . 0 , possibly due to their greater ionic concentrations

allowing greater buffering capacities (see also Chap ter Four ) .

3 . 3 . 1 7 Total Nitrogen and Total Phosphorus

Nutrient levels were generally low , and mo st lakes were oligotrophic .

Values are given in Table 3 . 8 . Total nitrogen values ranged from , I I Cl 1 0 60 �ig L- 1 in the southernmo st o f the Boomerang Lakes , to l in

several , including Lakes Freshwater , McKenz ie and Birrabeen , and in

Honeyeater Lake (Median value = 1 50 �g L-1 ) . Twenty-one of the l akes

had total phosphorus levels of 1 0 }4 g L- 1 or l ess , with a minimum value

of 3 j.\g L- 1 in L ake Birrabeen on Fraser Island , Blue Lagoon on Moreton

Island , and Blue Lake on North Stradbroke Island . The maximum amount

of total phosphorus recorded in these lakes was 20 g L- 1 , in Ocean

Lake .

No .

1 2 3 4 5 6 7 8 9

1 0 1 1 1 2 1 3 1 4 1 5 1 6 1 7 1 8 1 9 2 0

2 1 2 2

2 3 2 4

2 5 2 6

Table 3 . 8 : Temperature , chemic a l , and o p t i c a l d a t a f o r the f r e s hwa t e r coastal dune lakes of s o u t h - e a s t Que enslan d .

Name

FRASER I S LAl'm

Lake Minker Lake Hoonj e e l O c e a n Lake Hhi t e Lake Lake Bowarrady Lake Allom D eepwa t e r Lake Lake Coomboo Hidden Lake B o omerang Lake ( n o r t h ) Boomerang Lake ( s o u t h ) Lake Garawongera Lake Habby Lake NcKen z ie B a s i n Lake Jennings Lake Lake B i rrabeen Lake Benaroon Lake Bo omanj in Red Lagoon

COOLOOLA SAI\TD HAS S

Lake F r e s lwa t e r Lake Cooloomera

HORETON I SLAND

B lue Lagoon Honeye a t e r Lake

NORTH STRADBROKE I SL&�D

Brown Lake B l ue Lake

�1ED IAN NEAN STANDARD DEVIATION

Lo c a t i o n s of the lakes are shown in Fi gure 3 . 3 . p "' cf- �d �''"'

Temp e r a t ur e and Chem i c a l D a t a

Temp . pH K1 8

o c �s em - 1

2 4 . 2 7 . 5 5 5 7 6 2 4 . 7 7 . 30 5 0 7 2 3 . 8 7 . 40 2 4 3 2 3 . 6 5 . 20 7 5 . 4 24 . 0 6 . 45 8 2 . 6 2 3 . 9 5 . 40 5 8 . 4 2 3 . 5 6 . 2 5 9 9 . 3 2 4 . 2 5 . 1 5 6 3 . 2 2 3 . 6 5 . 1 0 5 7 . 0 2 4 . 5 5 . 20 9 8 . 1 2 5 . 2 5 . 1 0 1 1 6 2 1 . 7 5 . 1 0 o 7 . 7 2 4 . 1 7 . 40 2 1 3 2 3 . 3 5 . 80 9 5 . 3 24 . 8 6 . 40 5 2 . 1 2 4 . 0 5 . 05 8 7 . 0 2 3 . 0 5 . 60 7 2 . 9 2 2 . 0 5 . 4 5 8 8 . 2 2 1 . 2 5 . 90 1 1 0 2 1 . 2 4 . 25 1 1 5

2 1 . 0 6 . 4 0 J 3 5 2 2 . 0 5 . 1 5 1 6 2

2 2 . 0 5 . 6 0 1 1 0 2 2 . 4 5 . 90 1 1 2

2 3 . 0 5 . 05 6 1 . 3 2 3 . 4 6 . 40 6 7 . 0

2 3 . 5 5 . 60 9 6 . 7 2 3 . 2 5 . 8 3 J 3 6

1 . 2 0 . 8 7 1 2 8

T o t a l N p

- 1 - 1 jAg L JA'g L

400 9 4 0 0 8 1 80 20 2 60 1 7 3 2 0 7 1 7 0 1 0

2 0 4 3 2 0 1 0 1 30 1 0 1 20 9

1 0 60 6 1 60 (, 1 1 0 9 i.iO 5

400 6 90 6

tJD 3 1 2 0 4

40 9 480 1 2

WI) 5 4 4 0 1 7

4 3 f<IP 9

2 2 0 1 9 ND 3

] 50 9 2 1 1 9 2 3 2 4 . 6

Tn g 440

- 1 N . T . U . m

0 . 7 2 1 . 0 9 4 0 . 44 1 . 0 3 6 0 . 9 1 l . 4 9 7 1 . 6 0 1 . 2 6 7 0 . 6 3 0 . 2 88 0 . 88 0 . 6 9 1 0 . 5 3 0 . 000 l . 20 7 . 7 1 5 0 . 5 8 3 . 2 2 4 l . 3 0 0 . 864 J . 00 9 . 3 8 5 0 . 5 9 1 . 2 0 9 1 . 00 0 . 0 5 8 0 . 2 7 0 . 0 5 8 1 . 00 0 . 4 6 1 0 . 5 5 4 . 1 45 0 . 40 0 . 4 0 3 0 . 8 1 0 . 9 7 9 0 . 5 3 2 . 5 9 1 1 . 00 2 7 . 86 6

J . 00 0 . 000 0 . 5 5 1 4 . 2 2 1

0 . 5 1 0 . 000 0 . 81 0 . 000

3 . 00 l . 9 5 8 0 . 6 2 0 . 08 6

0 . 7 7 1 . 00 8 0 . 8 6 3 . 1 1 9 0 . 5 3 6 . 0 7 2

A - indicates that no measureme n t s were mad e .

Optical D a t a

Chlorophy l l Sec chi a D i s c Kd ( av ) Zeu Ku ( av ) R ( o )

- 1 - 1 - 1 % ,!A. g L m m m m

1 . 90 :;;> 2 . 80 0 . 7 1 2 . 6 4 > 2 . 30 0 . 84

1 2 . 8 2 . 2 . 45 1 . 0 9 :> 3 . 2 5 0 . 9 8 1 . 0 6 7 . 9 9 ' 1 . 8 0 0 . 92 > 2 . 7 5 0 . 90 2 . 4 1 6 . 1 8 > 2 . 50 0 . 5 8 5 . 4 7 . 3 . 45 0 . 7 1 > 3 . 50 2 . 4 3 ' :> 4 . 55 0 . 32

l l . 7 7 1 . 40 l . 96 2 . 00 1 . 72 0 . 3 9 l . 80 2 . 90 1 . 2 3 3 . 38 1 . 2 4 0 . 2 9 2 . 5 7 7 1 . 65 1 . 3 3 l. 3 7 > 0 . 7 5 3 . 4 7 3 . 0 7 . 7 4 . 25 0 . 8 1 - - -4 . 5 9 2 . 85 0 . 4 8 > 7 . 00 0 . 3 7 3 . 0 8 0 . 2 1 ::> 7 . 75 0 . 1 9 1 . 6 9 5 . 65 0 . 4 9 > 6 . 50 0 . 4 2 1 . 1 8

- > 2 . 90 1 . 3 0 0 . 5 3 > 5 . 60 0 . 2 6 3 . 2 8 . -;- 2 . 60 0 . 9 1 3 . 1 7 2 . 90 1 . 1 3 3 . 7 1 l . 2 3 0 . 5 1 1 . 0 6 0 . 65 4 . 9 1 0 . 7 3

l l . 0 2 > 1 . 00 0 . 6 6 6 . 0 4 l . 30 3 . 1 5 1 . 2 1

4 . 5 6 > 4 . 20 0 . 39 > 3 . 7 5 6 . 6 3 3 . 60 0 . 40 > 4 . 2 5

1 5 . 8 9 0 . 85 2 . 88 1 . 42 2 . 5 3 2 . 07 3 . 4 9 6 . 35 0 . 42 "7 6 . 5 0 0 . 3 2 1 . 04

3 . 28 - 0 . 8 3 - - 1 . 1 8 4 . 8 9 - l . 2 1 - - 1 . 34 4 . 1 2 - 1 . 1 6 - - 0 . 97

b

- 1 m

l . 3 7 2 . 30

2 . 0 8 0 . 5 8

- 00 1 . 5 3

0

0 . 63

1 . 1 4

6 . 32 0 . 5 7

l . 3 7 l . 8 4 1 . 80

8 1

3 . 3 . 1 8 Turbidity , Colour and Chlorophylla

Turbidity , colour (as g440) , and chlorophyll a measurements are

also listed in Table 3 . 8 . Turbidity was low in all lakes , and only

f our exceed ed 1 . 0 N . T . U . Brown Lake , North Stradbroke Isl and , was

the mo st turbid , at 3 . 0 N . T . U . , f ollowed by White Lake on Fraser

I sland , at 1 . 60 N . T . U . Median turbidity for all twenty- s ix lakes

was 0 . 77 N . T . U .

Dissolved humic substances were below the level o f detection in

several o f the l akes , and mos t were only sligh tly to moderately

coloured . Only seven had g 440 values greater than 2 . 0 m- 1 , the two

highes t being 2 7 . 86 6 m- 1 in polyhumic Red Lagoon , and 1 4 . 2 2 1 m-1 in

Lake Cooloomera . The median g440 value was 1 . 008 �-1 .

The highes t chlorophyll a concentration , 1 5 . 9 ,.U g L- 1 , was in

Brown Lake , and planktonic algae may have considerably enhanced the

turbidity of the water there . Chlorophyll a also exceeded 1 0 ,�.A.g L - 1

in t.akes Coombo o and Freshwater , and in Ocean Lake , whilst the lowest

values were recorded for clear-water Lakes McKenz ie and Birrabeen .

The lakes had a median chlorophyll a value o fi 3 . 24"1 ,Ug L - 1 . The

sample for Jennings Lake was misplaced between fil tration and

analysis .

3 . 3 . 1 9 The Attenuation, Reflectance and Scattering of P . A . R .

Attenuation was measured from an inflatable rubber dinghy

anchored near the centre of each lake . This may not necessarily

correspond with the deepest p oint in each l ake .

Values of both the mean downwel ling and upwelling vertical

attenuation coefficients , Kd (av ) and Ku (av) , and the scattering

coefficient � are presented in Table 3 . 8 . Kd (av) Yalues range from

0 . 1 9 m- 1 in Lake McKenz ie , the clearest lake , to 4 . 9 1 m- 1 in highly

dys trophic Red Lagoon , the median value being 0 . 83 m-1 . Gilv in was

the main component causing increased attenuation coef f icient s ,

al though phytoplankton may have contributed in Bro�� and Ocean takes ,

and turbidity in White and Brown lakes . The influence o f these

attenuating component s are illus trated for some la�es in Figure 3 . 1 3 .

Biphasic curves are apparent in most , the change in slope o ccurring

below about 2 . 0 metres in the clearer water lakes . In dystrophic

waters , such as Lake Cooloomera and Red Lagoon , the change in slope

i s much shallower , at less than 0 . 5 metres , resulting from the

rap id ext inction of blue light in these waters by gilvin . Weather

1.0

I I

1 K ----t-

J� I -

2 H_.....___..---

� · .1:1 3 OJ s -£i I 0. G�· � 8 4- I

5-

6

7

82

2.5 % Incident radiation 5.0 10

/

25

I B I l �II

Figure 3 . 1 3 Attenuation profiles of downwelling P . A . R . ( 400- 700 nm . )

for selected south-east Queens land coastal lakes , April/May , 1 9 8 7 .

A . Lake McKenz i e ; B . Lake Birrabeen ; C . Honeyeater Lake ; D . Lake Wabby ;

E . Lake Allom ; F . Lake Garawongera ; G . Lake Boomanj in ; H . Lake Coomboo ;

I . Brown Lake ; J . Lake Cooloomera ; K . Red Lagoon . See Table 3 . 8 for

further data on the opt ical characteristics of these lakes .

50

83

conditions wer e poor for the measurement of underwater l ight , with

considerable wind r ipple on the lake surface , and broken cloud cover

c,:ausing incident radiation to fluctuate markedly and continuously . 'IN''<\\ 11�:

ThisAcaused s om e error in recording irradiance , evidenced by the

kinks in some o f the profile s , and prevented the measurement of the

spectral distr ibution of P . A . R . in the lake s .

Euphotic d ep th s could only b e directly measured in s ix lakes

( see Table 3 . 8 ) . In the o ther s , euphotic depths were greater than

the actual dep th at the samp ling point . The shallowest of those

measured were f r om Red Lagoon (0 . 73 metre s ) and Lake Cooloomera

( 1 . 2 1 metres ) , the two mo st dystrophic lake s , and from Brown Lake

( 1 . 42 metres ) , which had the highest turbidity and chlorophyll a

content .

Kd (av) and Ku (av) were mos t ly similar in thos e lakes where

upwelling irradi ance was measured , although Ku (av) was usually less .

The greates t d i f f erences between the two were in Lake Wabby and Blue

Lake , where Ku (av) was only 7 7 . 1 % and 76 . 2% of Kd (av) , respectively .

Some enhancement o f upwelling irradiance by reflection o f light from

off the bot tom may have o ccurred in these l akes , as euphotic depth

exceeded actual dep th . Ku (av) was more than Kd (av) in humic Lake

Boomanj in , due p o s s ibly to inaccuracies in measuring the low levels

of upwelling irradiance J was so weak in highly dys trophic

Lake Cooloomera and Red Lagoun that measurement was impos s ible , even

close to the surface .

Reflectance profiles varied considerably between l akes (Figure

3 . 1 4 ) . Thes e t o o could be influenced by reflection from the bottom

or low irradianc e measurements . Reflectance was greate s t in Lake

Wabby , despite i t s l ow turbidity , and least in humic lakes such as

Coomboo , Boomanj in , and Hidden Lakes . Three type s of p rofiles were

apparent . Fir s tly , reflectance increased continuously with depth ,

as in Lake Wabby , although s ometimes in a rather haphazard manner

(e . g . Brown Lake) . The second type , examplified by White Lake (and

to a much less extent by Basin Lake) , was where reflectance peaked

after an initial increase , and then declined . The third type was

where very low reflectance values stayed virtually constant with

depth , as in Lake Boomanj in and Hidden Lake . Some fluctuations

within the profiles may be due to rapid changes in the intensity of

the incident l ight f ield during measurement .

0.07

0. 06

0.05

cv g 0.03 B $ u � .... Q) 0::

0.02 \/

0.01 , G

-�------H � I

1 2

84

A

E ----. ., ---··F

3 4 5 6 Depth (metres)

Figure 3 . 14 Reflectance/ depth profi les for selected south-east Queensland

coastal lakes , April/May , 1 98 7 . A. Lake Wabby ; B . White Lake ; C . Brown

Lake ( dashed line ) ; D . Ocean Lake ( dotted line ) ; E . Blue Lake , North

Stradbroke I s land ; F . Bas in Lake ( dashed line ) ; G . Lake Coomboo ; H .

Lake Boomanj in ( dashed line ) ; I . Hidden Lake .

85

Measurements of the scattering coefficient , l• could only be made

on nine of the lakes . Values r anged from 6 . 32 m- 1 in Brown Lake to

0 . 5 8 m- 1 in Hidden Lake , and mo st were higher than anticipated for

non-t urbid waters .

3 . 3 . 20 Secchi Disc Transparency

Water transparency , as n1easured by the Secchi disc , is also

indicated in Table 3 . 8 . In half the lakes , this exceeded the depth

of the bottom at the sampling p oint . The minimum value was 0 . 65

metres in polyhumic Red Lagoon , and the deepest was in Lake McKenz ie ,

where the Secchi disc was still visable lying on the bottom , 7 . 7 5

metres deep .

3 . 3 . 21 Regression and Correlations

The resul t s of linear and multip le regression analyses of t urbidity ,

gilv in , and chlo rophylla agains t Kd (av) are shown in Table 3 . 9 . Gilvin

was the main factor affecting light attenuation and determining Kd (av) in the waters of these lakes , while turbidity and particularily

chlorophyll a were of much less importance . Both turbidity and

gilvin together as the independ«!.nt variables (Equation 4) improve the

prediction of Kd (av) slightly , but further inclusion of chlorophyll a

in the mul tiple regression does not . Log normal transformation o f the

data made no improvement of fit for these regressions , and so are not

shown .

Use of Pearson correlat ion analysis shows several of the parameters

to be s trongly correlated . Wat er colour was negatively correlated

to pH (r = -0 . 52 3 3 , P = 0 . 0 0 6 ) , with pH d ecreasing as the humic content

of the water rises , as shown previously by Bayly ( 1 964) . Due to this ,

and the strong influence of colour on the vertical at tenuation

coeff icient for downwelling irradiance , a significant positiv e

correlation was also recorded between p H and Kd (av) . pH also

correlated s ignificantly with Kl S (r = 0 . 667 9 , 0 . 00 1 ) , s upporting

the suggest ion ( S ection 3 . 3 . 1 6 ) that b uff ering capacity was increased

in those lakes with higher ionic concentrations .

There were no significant correlations between Kd (av) and either

turbidity or chlorophyll a ( see Table 3 . 9 ) . However , turbidity was

significantly p o sitively correlated with chlorophyll a (r = 0 . 6652 ,

P 0 . 00 1 ) , indi cating that much of the particulate mat ter in these «:i!>•llti

lakes A phytoplankton , rather than trip ton . Addit ionally , t otal

Table 3 . 9 :

Equation No .

1 Kd (av )

2 Kd (av )

3 Kd (av)

4 Kd (av)

5 Kd (av)

6 Kd (av )

7 Kd ( av )

8 b = 2 . 26

86

Regression analysis showing the rel ationsh ip s between various op tical parameters in the freshwater coastal dune l akes of south-eas t Queensland

r2

0 . 68 1 + 0 . 1 7 1 g 440 . 805

0 . 49 1 + 0 . 83 7 Tn . 1 4 9

1 . 0 4 + 0 . 035 Chla . 0 1 5

0 . 06 2 + 0 . 7 3 Tn + 0 . 1 67 g440 . 9 1 8

0 . 37 2 + 0 . 1 7 5 g 440 + 0 . 06 1 Chla . 85 1

0 . !+ 9 3 + 1 . 2 1 Tn = - 0 . 0 7 1 Chl a . 1 8 9

0 . 05 6 + 0 . 7 7 6Tn + O . l 6 6g440 -0 . 008Chla . 9 1 9

Tn - 0 . 7 88 . 93 5

n p

2 6 0 . 00 1

2 6 0 . 052

2 5 0 . 562

26 << · 0 . 00 1

2 5 0 . 00 1

2 5 0 . 2Q�,;,p..: Q . O S

2 5 0 . 00 1

9 0 . 001

8 7

phos phorus was s i gnifican t ly po sitively co rrel ated with both turb i d i ty

( r = 0 . 5 5 12 , P = 0 . 00 4 ) and chlorophyl l a ( r = O a 59 9 6 , P = 0 . 00 1 ) , b ut

to tal nitro gen was cor rel ated s i gnifican tly only with g ( r = 0 . 52 5 9 , 4 4 0

P = O o 006) .

Phy topl ankt on

Phytoplankters which were abundant o r common in at leas t one

locat ion are given in Tab le 3 . 10 . Becau s e their taxonomy was , for the

mos t part , t aken only to g enus level , only thirty groups are given , b ut

many more wou l d h ave resul ted had it b een pos s ib le to identify everything

to species l evel . O ther s pecies may have b een mis s ed by the 20 �m mesh

plankton net emp loyed for s ampling,

The two main comp onent s were the desmids and the dinoflagellates .

Peridinium was ab s ent only from Red Lagoon , and no desmids were pres en t

in B lue Lake , Nor th S tradb roke Is l and . A t leas t four differen t s pe c ie s

o f Peridinium were identifiab l e , with P . granuZosum Play fair b e in g the

mos t common , and presen t in almos t every lake . There were als o a n umb e r

o f s pecies o f Staurastrum and Staurodesmus . Dynobryon cy Zindricum Imhof

was pre sent in many of the lakes , b ut D. sertuZaria Ehrenberg was a l s o

present in l ar ge numb ers i n Ocean Lake . A small , green coccoic co lonial

alga of the Sphaerocystis type was al s o common or ab undant in a numb er of

lakes , bt;.t th e r emaining taxa were usually present in small numb ers onl y .

At the taxonomic level given , there appears t o b e little difference

b e tween the s pecies diver s i ty of those lakes with the highes t nut rient

and chl orophyl l a concentrations , and tha t o f the more ol igotroph i c lakes ,

o r between the l e as t attenuating and the more highly attenuating waters .

3 . 4 D ISCUS S ION

3 . 4 o 1 F a c tors Influencing the Underwater Ligh t Climates o f the Three S tudy Areas

Al though wate r itsel f may be a s ignificant attenuator in the cleares t

lakes , dis s o lved humic s ub s tances cons titute the mos t important comp onent

of the aquatic med ium inf luencing the underwater ligh t climates o f all

three s tudy areas . Many Tasmanian lakes , especially tho se from the

wes tern half o f the i s l an d , are considerab ly dys trophic , more so than

thos e from e l s ewh ere in Aus tralia (Tab le 1 in Kirk , 1 9 86 ) ,

l 2 3 4 5 6 7 8 9

1 0

ALGA

LAKE La ke �l inker L a ke Wo onj e e l O c e a n Lake \-lh i t e Lake Lake B ow n r r ad y L a ke /\1 1om Jle epwnter Lake l, g ke Coomboo H i d d e n Lake Boomerang Lake

(n o r th ) 1 1 Boomerang Lake

( s o u t h ) 1 2 L a ke Garawongera 1 3 La ke \va b b y 1 4 L n ke McKe n z i e 1 5 B a s in Lake 1 6 J ennings Lake 1 7 L\J ke llirrabeen 1 8 L ake ll enaroon 1 9 Lake lloomanj in 2 0 Red Lagoon 2 1 L a ke F r eshwa t e r 2 2 L a ke Coo loome r a 2 3 Blue Lagoon 24 Hone y e a t e r Lake 25 B r own Lake 2 6 B l ue Lake

88

1'able 3. 10: Phytoplankton from the freshwater coa s t a l lakes o f south - ea s t Qu eens land . A = abundan t , C = common , x = p r e s e n t i n

c X X

X X X A

A

c c

c A

X A A X

X A c X X

A X

sma l l numbe r s .

X X

X C C

c

X

X c X X

c C C A X c

c

X X C C A C

X C X X X X X

X C X X X X A X

X

X

X

X A

X X

X

X

c

X

A

X X

X X

X X A

X X

Chlorophyceae

A X

X X X

X X X

X X X

A C X X X A A C A X C X A c X C

c X C X

X X

X X X

X

A A C C A c c c A C A .A C .A A A A X X

X X C X X X X X X C C C A t; C X X A C. X

A A X. X C A. X

X X

X X X

X X X

X c

X

X

X X X A X X X C A C X X x c C X X X

X X

X

A A C X X X c c C A c X X X X X A C A c

X c X X C X

c

X c

X X c

X

c A X. A X A C X C

X A X A X. A X A X X X A X A

X c X X C X X X X

X

X X C

A

X X X X X

X X

X

X

X

X

X

cLy1op1yceae clanophycele Euglenaphyceae Bacillariophyceae

Dlnophyceae

89

or from New Zealand (Vant and Davies-Colley , 1 984 ) . Gilvin

concentrations in the l entic freshwaters of north-east New South

Wales and the coastal dune l akes of south-east Queensland were at only

sl igh t to moderate l evel s , but this was s t il l the mo st s ignificant

att enuator of P . A . R . in the maj ority of these waters al so . Gilvin

too i s responsible for the greater part of l ight at tenuat ion in

inland waters f rom s outh-east New South Wale s and the Austral ian

Cap ital Territo ry (Kirk , 1 9 7 6b , 1 9 7 7b , 1 98 1 c ) , and north Queens land

(Finlayson , et .§J-1 , 1 9 84 ) .

The Queensland coastal dune l ake water s , and mos t of the Tasmanian

l akes and reservoirs s tudied were of low turbidit y , and even the more

turbid o f them generally had lower concentrations of suspended

particulate mat ter than many inland waters from elsewhere in Aus tral ia

(Table 1 in Kirk , 1 9 86 ) , and some from New Zealand (Vant and Davies-

Col l e y , 1 9 84) . The s tudy s ites of north-east New South Wales were �"''"'

for th e mo st p art�low generally more turbid , but even these

Therefore , while being of local importance such as in Kentucky Creek

Dam and Yarrie Lake in New South Wales , and in Tooms Lake , Tasmania ,

overal l tripton plays only a small role in the ext inction of underwater

l ight in these areas , its effect s being surpassed by gilvin . Elsewhere

however , such as in Gipp sland , South Austral ia , and the Northern

Territory , turbidity can be the maj or attenuator , at l east seasonal ly

(Hickman et al , 1 984 ; Ganf , 1 980 ; Geddes , 1 9 8 4 ; Walker , 1 98 4 ; Kirk

and Tyler , 1 98 6 ) .

Phytoplankton are considered significant attenuators of P . A . R .

onl: · at chlorophyl l a concen trat ions exceeding 1 0 1�JJ,'g L- 1 (Tall ing ,

1 9 60 ; Kirk , l 97 7b ) . Siuce the maj ority of Tasmanian l akes are

oligotrophic (Tyler , 1 9 7 4 ) , phytoplankton is therefore unlikely to

contribute much to l ight attenuat ion within them , and the same is

true for mo st coas tal dune l akes o f south-east Queensland . However ,

phytoplankton would probably s ignificantly at tenuate light in some

o f the eutrophi c north-east New South Wale s reservoirs , especial ly

Quipolly , S t . Helena , Dumaresq , and Puddledo ck Dams , in a manner

comp arable to that in Solomon Dam , Palm Island , Queensland (Hawkins

and Griff ith s , 1 98 6 ) .

The lakes and reservoirs covered in thi s s tudy represent a range

o f clarities . However , values o f the mean vert ical attenuation

coeff icients , e sp ec ially tho se for Tasmania and south-east Queensland ,

fell mostly towards the lower hal f of the range reported for other

90

Australian waters ( Kirk , 1 9 7 7 b , and Table 1 , 1 98 6 ) . The clearwater

coastal dune lakes of Queensland are usual ly considered to be of the

water-table window typ e (Timms , 1 982 ) , and have Kd (av) values similar

to many of the non- dystrophic montane l akes of Tasmania , and New

Zealand (Vant and Davies-Colley , 1 9 84 ; Howard-Will iams and Vincent ,

1 984) . In comp arison , the Kd ( av) values of the lentic waters of

north-east New S ou th Wales correspond to the upper h alves of the ranges

reported for dystroph ic Tasmanian lakes , and tho se from New Zealand

(Vant and Davies-Colley , 1 9 84 ; Howard-Williams and Vincient , 1 984) ,

being ins tead s imilar to some Northern Territory b illabongs (Kirk and

Tyler , 1 9 86 ) and Mt Isa , Queensland , reservoirs ( Finlayson � al ,

1 984 ) . The resu l t s o f this study of north-east New South Wales waters

are in close agreement with the measurements of attenuation made

previously on s ome reservoirs from the region by Scribner ( quoted in

Kirk , 1 986) , and the attenuation of broadband P . A . R . in Blue and

Brown Lakes , Nor th S tradbroke Island , Queensland , fell within the

ranges estimated for these two lakes from the resul ts of Bens ink and

Burton ( 1 9 75 ) , and Lee-Manwar (unpublished) ( 0 . 30 to 0 . 59 m- 1 for Blue

Lake ; 1 . 28 to 7 . 09 m- 1 for Brown Lake) .

The strong influence of gilvin in determining the underwater l ight

fields of inland waters can be seen even in the clearest lakes , such

as Lakes Perry , Laur a , S t . Clair , and Great Lake , in Tasmania , and

Lake Hiawatha in New South Wales . Al though gilvin levels in these

lakes are at the thr eshold of detection by the laboratory methods

employed in th is s tudy , there is still sufficient present to cause the

percept �ble attenuat ion of blue light in these waters at dep th ,

resulting in spe ctral distributions centred on the green to yellow

wavelengths . The non-turbid , non-humic oligotrophic Queensland lakes

would have simil ar l ight climates , as shown by measurement s from Blue

Lake , North S tradbroke Island , obtained by use of coloured filters on

a broadband sensor ( Bensink and Burton , 1 9 75 ; Lee-Manwar , unpublished) .

The spectral dis tributions and irradiance pro f iles from the clear­

water lakes of thi s study are more akin to those o f coastal waters off

south-east Australia (Kirk , 1 97 7 a , 1 9 7 9 ) . Clearer inland waters

however , with considerably l ower values of Kd (av) (as low as 0 . 1 0 to

0 . 1 2 m- 1 for Lake Coleridge) exist in New Zealand (Vant and Davies­

Colley , 1 984 ; Howard-Williams and Vincient , 1 984 ) , and there was no

equivalent o f ext remely pure Crater Lake , Oregon , where blue light

d8minates the P . A . R . spectrum at depth ( Smith and Tyler , 1 96 7 ;

Smith et al , 1 97 3 ) .

91

The rate o f increase of attenuation , and concomitant decrease in

euphotic dep th , is greatest at initially low gilvin levels , but

decreases as g ilvin concentrat ion increases (Canfield and Hodgson ,

1 9 8 3 ; Elo r ant a , 1 9 7 8 ; Kirk , 1 9 7 6b ) . The spectral distribut ion o f

underwater P . A . R . also change s as humic content increases , with the

wavelength of maximum tranmiss ion moving from the green reg ion o f the

sp ectrum towards the r ed , along with an as sociated narrowing of the

transmission window . In highly coloured dystroph ic l akes the influence

of gilvin is ext reme , with rap id and almost complete ext inction of blue

l igh t within the first metre o f water . Gilvin at high concentrat ions

also absorbs g reen , yellow , and even some orange light ( see for examples

the ab sorp tion spectra of g ilvin in Figure 3 . 9 , and in Figure 4 . 4) ,

leaving narrow underwater spectral distribut ions centred on red l igh t ,

at 650 to 700 nm . Th1s is shown clearly by the P . A . R . spectra for

Lake Ainsworth , New South Wales , and Lakes P edder (nova) and Chisholm ,

Tasmania , as well as for o th er h ighly dystrophic lakes from the

Gordon River area o f south-wes t Tasmania (King and Tyl er , 1 98 1 b ,

1 982a , 1 98 3 ; Croome and Tyler , 1 98 4a , 1 9 85a ; Bowling and Tyler , 1 98 6 ) .

Dystroph ic Queensland l akes such as Lakes Coomboo and Cooloomera , and

Red Lagoon , would h ave s imilar underwater l ight climates . The effect

o f gilvin on th e spectral bandpass of downwell ing P . A . R . is summarised

in Figure 3 . 1 5a , where data from the measured euphotic dep th are shown

for a series o f selected Tasmanian lakes of increasing gilvin

concentrat ion .

While trip ton undoubtedly contributes something to light attenuation

in all but the clearest water s , it was a maj or contributor in only a

few l ocat ions , even in north-east New South Wales . The effect of

increas ing turbidit y , summarised for a series of increas ingly turbid

Tasmanian lakes in Figure 11 5b is identical to that of increas ing

g ilvin concentration , caus ing increased attenuat ion , decreased euphotic

dep th s , and a shift in the spectral distribution of P . A . R . with dep th ,

from being centred on g reen l ight at low tripton concentrat ions , to

being centred o n red l igh t when they are high . The almos t identical

underwater spectra shown by turb id lakes such as Lake Crescent and

Tooms Lake , Tasmania , and Yarrie Lake , New South Wales , to those o f

non- turbid , humic l akes , suggests that the attenuat ion pat tern produced

by suspended matter , espec ially tripton , resul ts less from its

scattering effect than from absorption by humic materials either bound

to the out s ide of the mineral particles , or exist ing as free particles

1 00 ( /\ )

80 QJ u c 0

"0 6 0 2 L

E ::J E " 4 0 0 2

� 0

20

400

Q) u c 0

1 00

80

"0 6 0 0 L L

E :J E 4 0 X }:J 2 � 0

( 8 )

92

[: 0 /2 ' Q] "' "

(\; \!' 0

nj .:..< " 2 Q.QJ ::; 0 ..J .....J

_j

�1'-"����-4 so 5 0 0 5 5 0 600 650 ruu -rso

[: 0

cj (\;

fYJ' co v: 0

r:v· -< , .... QJ Q.

v:o v e \ e n g\ 11 ( n m )

/'/\_ , I /)�. � 0 )( �J z '¢\11 �' ......-.. �· ...... ::J ,-,

if, \ 1 i -; ' -c;,

6 0 0 650 W o v e i e n g t h (n m )

v i . :-"" i 0 • CP \ m \ � I

7 0 0 750

Figure 3 . 15 Effect of g i lv in and turbidity on the spectral bandpass

of downwel ling P . A . R . at the measured euphot ic depth for selected Tasmanian

lakes . ( A ) A series of increas ing g i lvin concentrations . ( B ) A

series of increas ing turbid ity . For ease of comparison , in each case

values are plotted a s percentage of the irradiance at the most penetrat ing

wavelength . Values for g i lvin and turbidity can be obtained from Table

3 . 2 .

(Kirk , 1 980a ; 1 983) . The absorption spectra o f particulate matter

have much the s ame shape as tho se o f dissolved humic substances (Kirk ,

1 980a; Davies-Colley , 1 983 ) .

The spectral distribut ion and attenuance of irrad iance in turbid

Tasmanian l akes is comparable t o that measured on occasions in Lake s

Burley Griffin and Ginninderra , from the Austral ian Capital Territory

(Kirk , 1 97 9 ) , s ome Northern Territory b illabongs (Walker , 1 984 ,

Walker and Tyler , 1 984 ; Kirk and Tyler , 1 986 ) , and in Rust der Winter

Dam , South Africa (Walmsley � al , 1 9 80 ) , where turbidity was al so the

maj or attenuating factor . The extreme turb id ity of Yarrie Lake , New

South Wales cau sed a s imilar underwater spectrum , composed almost

entirely o f red light , but , unlike the others , its wavelength o f

maximum tranmis s ion exceeded 700 nm , resul ting from its much greater

tripton loading . Its downwelling vertical attenuation coefficient

al so exceeded any others measured in highly turbid Austral asian waters ,

including Lake George , New South Wales (Kirk, 1 9 77b) ; Lake Alexandri na ,

South Aus tralia (Geddes , 1 984 ) ; Georgetown Billabong , Northern

Territory (Kirk and Tyler , 1 98 6 ) , and Lake Wairarapa , New Zealand

(Howard-Williams and Vincent , 1 98 4 ) .

Phytoplankton may influence the underwater l ight climates o f

eutrophic l akes , no t only removing blue light (along with gilvin and

trip ton) , but al so caus ing not icable absorp tion troughs in the vicinity

of 6 7 0-6 80 nrn , as shown by the spectral distribut ions o f P . A . R . from

Lake Sorell in Tasmania and Dumaresq Dam in New South Wales . Similar

absorpt ion troughs due to phytoplankton chlorophyll a have been

reported f rom Lake Burley Grif f in , Austral ian Capital Territory (Kirk ,

1 9 7 9 ) ; Island Billabong , Northern Territory (Kirk and Tyler , 1 986 ) ;

Lake Kinneret , Israel (Dubinsky and Berman , 1 9 7 9 ) , and Lough Neagh ,

Northern Ireland (Jewson , 1 9 7 7 ) . Phytoplankton were present in

sufficient quantity in Brown Lake , Queensland , to al so modify its

underwater l ight climate , � it toe:JJ 'WCJ1.tll1 , have

a spectral distribut ion of P . A . R . s imilar to Dumaresq Darn .

Stratif ication o f phytoplankton in Storm King Dam noticably increased

P . A . R . attenuat ion below 2 . 0 metres in this reservoir , and had

modified its spectral distribut ion at 3 . 0 metres to include a marked

chlorophyll a absorp tion trough at 680 nrn . S tratified phytoplankton

and photosynthetic bacteria cause s imilar heterogeneous l ight climates

in meromictic Tasmanian lakes (Bowl ing and Tyler , 1 98 6 ) .

93

The spectral distributions of a number of lakes with only slight

level s of g ilvin and turbid ity (e . g . around 1 . 000 m- 1 and 2 . 0 N . T . U . )

showed a broad transmis s ion plateau of wavelengths b e tween about 590

to 6 6 0 nm , rather than a sharp peak of maximum transmission . A slight

absorpt ion trough , centred at 620 nm , bisected this plateau in some ,

includ ing Lake Leake and Risdon Brook Dam from Tasmania , and Lake

Minnie Water , Lake Keep it , and Chaf fey Dam from New South Wales , and

was present as a shoulder on spectral scans from o thers . Similar

troughs and sho ulders were al so present in spectral scans from Lakes

Burley Griff in and Ginninderra from the Australian Capital Territory ,

and Burrinj uck D am in south-east New South Wales (Kirk , 1 97 9 ) . No

expl anat ion can be offered to account for the sl ightly higher

absorption of l ight at these waveleng ths . Phycocyanin contained in

blue-green algae created .:hn absorption trough close to 620 nm in

spectral distributions from Lough Neagh , Northern Ireland (Jewson ,

1 984 ) . However the l ow chlorophyll a contents o f the s tudy sites ,

plus the absence o f chlorophyll a attenuation troughs at 680 nm in

the spectral scans , indicates that phytoplankton were present in

insufficient quantities to appreciably attenuate l ight . Additionally ,

cyanobacteria const ituted only a small part of the phytoplankton flora

of these l akes , or were entirely absent .

Although s t atistically meaningful relationship s were obtained

between Secchi d i s c dep th and euphotic depth for Tasmanian (Table 3 . 3 )

and New South Wales (Table 3 . 6 ) waters ( insufficient data were

available for Queensland lakes ) , care should be exercised in the use

of such emp irical relationship s . The results from these two studies

suggest that d i f fer ent attenuating component-s of the aquatic medium

had dif fering e f fects on Secchi disc depth . This is especially true

for non-turbid dystrophic waters , where the Secchi disc is often

vis i ble below the measured euphotic dep th .

Variations in the predict ion of euphotic dep th , and vert ical

attenuat ion coefficients (Kd (av) ) from Secchi disc measurements resul t

from these being dependant not only on Kd (av) • but al so on the beam

attenuat ion coe f f icient (�) , and these may vary independantly of each

other to some extent (Tyler , 1 96 8 ) .

This study was restricted to one sampl ing per waterbody in north­

east New South Wales . The l imited data of S cribner (quoted by Kirk ,

1 9 8 6 ) indicate that considerable seasonal and temporal fluctuations

o ccur in the a t t enuating components and underwater l ight climates of

94

these water s , a s they do in many o ther Austral ian inland fresh waters

(Kirk , 1 97 7 b , 1 97 9 , 1 986 ; Hickman e� al , 1 9 84 ; Ganf , 1 9 80 ; Geddes ,

1 98 4 ; Walker , 1 9 84 ; Walker and Tyler , 1 98 4 ; Finlayson and Gillies ,

1 982 ; Finlayson et al , 1 984 ; Hawkins and Griffith s , 1 98 6 ) . Therefore ,

any extent of s easonal change , and the variability this may have

caused between s ites s ampled at different times during the s tudy ,

cannot be asses sed . However , Scribner ' s data (quo ted by Kirk , 1 986 )

indicate temporal changes of much smaller magnitude for the waters of

this area comp ared t o those which occur in Northern Territory b illabongs

(Walker , 1 984 ; Walker and Tyler , 1 984) , or reported for Nebraska

reservoirs , one of which varies over a thirty-four fold range (Roemer

and Hoagland , 1 97 9 ) .

Measurement s o f various optical parameters from Blue and Brown

Lakes , North Stradbroke Island (Bensink and Burton , 1 9 7 5 ; Lee-Manwar ,

unpublished) , indicate s imilar temporal variation is l ikely in the

fre shwater coas tal dune l akes of s outh-east Queensland , and is

probably why Secchi disc depths for many lakes of this s tudy exceeded

tho s e reported previously (Bayly !:.!:_ al , 1 9 7 5 ; Bensink and Burton ,

1 975 ; Miller et al , 1 97 6 , 1 9 84 ; Arthington !:.!:_ al , 1 98 6 ) . With g reater

Secchi disc dep th s , the lakes were probably considerably l e s s humic

than during earlier s tudies , but there are no published values of

colour as either g440 or as Hazen (mg Pt L- 1 ) with which to compare

those of this survey . Previously only op tical densities at 385 nm

have been reported (Bayly , 1 9 6 4 ; Bensink and Burton , 1 9 7 5 ) , and

al though giving an indication of which lakes were more humic than

o thers , make comparisons impos s ible .

Although data on seasonal variation in Tasmanian l akes i s limited ,

dystrophic lakes have been shown to be humic all year (King and Tyler ,

1 98 1 a , b , 1 982a , 1 98 3 ; S teane and Tyler , 1 982 ) ; the few turbid lakes

always turbid (Cheng and Tyler , 1 9 7 3a ; Croome and Tyler , 1 9 72 ) , and

the clearwater l akes are always s o (Tyler , 1 96 7 ) . ( See al s o Table 3 . 2

f or previously publ i shed ranges o f colour and turbidity in s ome

Tasmanian lake s ) . Such seasonal variation as does occur in Tasmanian

inland waters , such a s change s in gilvin concentration in the dune

lakes of the wes t and south-wes t coasts ( see Chap ter Four ) , are

l ikely to produce variations of degree , rather than kind , in the

underwater l igh t climate . The greates t variat ion in Tasmanian waters

occurred in Risdon Brook Dam , an urban water s torage , where water is

added sporadically f rom a number of sources by the management authority .

95

3 . 4 . 2 Upwelling Irradiance , Reflectance , and Scattering

Upwelling irradiances were attenuated in much the same way with

depth as downwelling irradiance in the waters from all three s tudy

areas , as found al so by Kirk ( 1 9 7 7b ) for south-east New South Wales

waters . However , the attenuation coefficient for upwell ing irradiance ,

Ku (av) • was in mos t cases slightly less than the corresponding

coefficient for downwelling P . A . R . This is b ecause measurements o f

upwelling irradiance are made o n light that has been spectrally

modified by removal of the more readily absorbed waveleng ths ( see

Figure 3 . 8) , with the upwell ing l ight stream therefore containing a

proportional ly greater amount o f less readily attenuated wavelengths

than does downwelling P . A . R . at the same depth . The greatest

variations between Ku (av) and Kd (av) occurred in some of the shallower

clear-water l akes , such as Ladies Tarn in Tasmania and Lake Wabby in

Queensland , p o s sibly through the enrichment of upwelling irradiance by

reflection from off the bottom , and in highly humic lakes l ike Lake

Fedder (nova) (Tasmania) and Lake Boornanj in (Queensland ) , where low

levels o f upwelling irradiance make accurate measurement difficult .

The maj ority o f surface reflectance values , R (o ) , calculated for

the inland waters o f north-east New South Wales fell toward s the lower

end o f the range listed for o ther Australian waters by Kirk ( 1 9 8 6 ) ,

and from New Zealand (Howard-Williams and Vincent , 1 984 ) . Surface

reflectance values measured in Tasmanian and south-east Queensland

lakes were generally even l ower than those from north-east New South

Wales . Reflectance near the surface was highest in the turbid l akes ,

but the non-turbid , humic lakes o f all three study areas had extremely

low R (o ) values .

Changes in reflection with dep th followed one of three forms .

In many north-east New South Wales waters , and some Queensland coas tal

lakes , it increased continuously with depth . This type of prof ile has

also been recor ded in transparent New Zealand lakes (Howard-Williams

and Vincent , 1 984) , where reflection from the bottom increased the

ratio of upwelling irradiance to that of downwelling with increas ing

dep th . However , this is unl ikely for many of the deeper , turbid

lakes , where these profiles occurred in this study . In o thers , such

as White Lake , Queensland ; S t . Helena Darn , New South Wales , and Lake

Sorel l and Tooms Lake , Tasmania , reflectance decreased following an

initial increase with dep th . Jewson ( 1 984) also found s imilar curved

reflection p ro f iles in two Aust rian lakes with suspended calcite

%

particles . Only in a few lakes in New South Wales and Queensland d id

reflection values l evel off to approach a constant value with dep th ,

producing prof iles similar to those for reservoirs in south-east New

South Wal es and the Austral ian Cap ital Territory (Kirk , 1 97 7b ) , s ome

New Zealand l akes (Howard-Williams and Vincent , 1 984) , and Lough Neagh ,

Northern Irelan d (Jewson , 1 984 ) . No explanations can be made for the

variat ions from this theoretical (Kirk 1 97 7b , 1 983 ) asymptotic depth­

reflectance curve in most of the waters of this study .

The s cattering coef ficients , �' calculated for the three s tudy

areas were cons istant with the ranges reported elsewhere for Australia

and New Z ealand (Kirk , 1 98 1 a , 1 986 ; Kirk and Tyler , 1 986 ; Phill ip s and

Kirk , 1 98 4 ; Vant and Davies-Colley , 1 984) , although tho se from Tasmania

and Queensland were for the mos t p art lower than tho se from north- eas t

New South Wales , being instead s imilar to those calculated for the

coas tal waters o f Jervis Bay (Phillip s and Kirk, 1 984) and for non­

turbid New Zealand lakes (Vant and Davies-Colley , 1 9 84) . That f o r

Yarrie Lake is h igher than any p reviously recorded . An approximate

1 : 1 ratio between � and nephalometric turbidity has been f ound in a

number o f d iverse l ocations (Di Toro , 1 9 7 8 ; Kirk , 1 98 1 a ; Kirk and

Tyler , 1 98 6 ; D avies-Colley , 1 98 3 ) , and many of the waters o f north­

east New South Wales also fit this pattern . The range in the Tn/b

ratio for t hi s area was 0 . 50 to 1 . 50 , with a mean of 0 . 89±0 . 23 .

This does not hold for the Tasmanian lakes however , where the range

of Tn/� was 0 . 2 9 t o 1 . 2 2 , with a mean of 0 . 68±0 . 2 3 . The ratios

between turbidity and the _scat tering coef f icients for the nine

coas tal f reshwat er lakes of south-east Queensland where £ was measured

were highly var iable , ranging between 0 . 46 to 1 . 5 9 (x = 0 . 80±0 . 3 7 ) .

The wat ers with the lowest Tn/�. ratio s f rom all three study areas

were tho se with the lowest turbidity values ; and these were

considerably l ower than the turbidity values given for the waters

studied by Di Toro ( 1 9 7 8 ) , Kirk ( 1 9 8 1 a) , Kirk and Tyler ( 1 9 8 6 ) , and

Davies-Colley ( 1 98 3 ) . Thus , it is suggested that the accuracy of

measurement o f � by Kirk ' s ( 1 98 l a) method may become more precise at

higher levels o f turbidity , and therefore scattering . Regression

analyses f rom each of the three study areas (Tables 3 . 3 , 3 . 6 , 3 . 9 )

indicate that turbidity is the maj or factor contributing to the

scatter ing coeff icient . The turbidity to scattering coefficient

ratio for twenty-f ive New Zealand lakes , many of them turbid ,

calculated from data given in Vant and Davies-Colley ( 1 984 ) , also

reveal d is crepencies from 1 . 0 (range 0 . 33 to 1 . 88 , x = 0 . 85 ±0 . 37 ) .

3 . 4 . 3 Humics , Turbidity , and Chlorophylla

Kirk ( 1 9 80a) proposed that the origin of both the suspended

particulate fraction and dissolved humic substances in turbid , yellow

Aus tralian inland waters was from the soils o f the catchment . If so ,

both gilvin and tripton would be washed into a lake or reservoir

together , and c oncentrat ions of both should rise and fall concurrently .

Such interactions would explain the s ignificant positive correl ation

between g ilv in and turbidity found in the north-east New South Wale s

waters of this s tudy , although this was somewhat weaker than the one

(r = 0 . 80 ) reported by Kirk ( 1 9 79 ) for south-eastern New South Wale s

and Austral ian Cap ital Territory waters . Here level s o f both increase

after heavy rainfall and consequent soil erosion , although not exactly

in parallel . However , the h igh levels o f dissolved organic colour in

the non- turbid , dystrophic lakes of Tasmania and sou th-east Queensland

must originate from o ther sources , being derived especially from

decaying vegetation in the cat chment , and then dissolved and washed

into the l akes by surface runoff after rainfall . Such a mechanism has

been proposed for the presence of dissolved humic substances in New

York lakes (Cronan and Aiken , 1 98 5 ) .

Coloured organic materials may also be derived from photos ynthetic

microorganisms with in the water column , through their excretion and

decomposition . Al though no signif icant correlation was found between

g 4 40 and chlorophyll a , it is possible that some of the dissolved

humics in the eutrophic freshwaters of north-east New South Wales with

high chlorophyll a concentrat ions , such as S t . Helena Dam , are

produced aut o ch thonously by their phyt opl ankton in this manner . A

similar source of colour has been suggested for some highly eutrophic

and productive New Zealand lakes (Vant and D avies-Colley , 1 98 7 ) , and

in highly stratif ied meromictic Tasmanian l akes , where both g440 and

pho to synthetic microorganisms increase markedly together with dep th

(Baker et al , 1 985a ; Bowling and Tyler , 1 9 8 6 ) . However , this would

be an unl ikely source o f gilvin in Tasmanian and Queensland lakes of

this study , as mos t are considered oligotrophic and unproductive (see

Sections 2 . 1 and 2 . 3 . 2 ) .

3 . 4 . 4 Optical Classifications of the Lakes of the Study Areas

Cluster analyses were undertaken to classify the lakes of the

study areas in terms of their optical characteristics and l igh t

climates , based on the measured gilvin and turbidity values for the

lakes .

98

Tasmania ' s lakes fal l readily into a series of categories

(Figure 3 . 1 6 ) . Group I contains lakes o f l ow colour (x = 0 . 626 - 1 m '

r:J" = 0 . 4 1 ) and t urbidity (x = 0 . 6 9 N . T . U . , cr == 0 . 4 4) . From regression

Equation 5 for Tasmanian waters (Table 3 . 3) , these waters could be

expected to hav e averag e downwelling attenuation coefficients o f - 1 around 0 . 7 5 m , and underwater spectral distribut ions o f P . A . R .

similar t o thos e o f Lake Laura (Figure 3 . 7a) o r Lake Leake (Figure

3 . 7b) . Group I I contains lakes with slightly higher colour (x = 2 . 3 1 6

m-1 , � = 1 . 1 3) or turbidity (x = 1 . 49 N . T . U . , r:1' = 0 . 3 6 ) ; would hav e

Kd (av) values o f approximately 1 . 1 3 m- 1 , and spectral distributions

close to those of Risdon Brook Dam (Figure 3 . 7b ) , or Lake Barrington

on 1 3- 3- 7 8 (Figure 3 . 7d ) . There was little distance between these

two groups in the clus ter analysis .

Lakes with moderate colour (x = 5 . 70 m- 1 , r:1' = 1 . 45 ) but low

turbidity (x = 0 . 8 2 N . T . U . , r:1' = 0 . 52 ) account for Group III . These

would have average downwelling attenuation coeff icients of about

1 . 66 m- 1 , and h ave spectral distributions of P . A . R . at depth centred

around 6 7 0-680 nm , as in Lakes Curly and Wurrawina (Figure 3 . 7d) .

Conversely , Group IV contains those lakes o f moderate turbidity

(x = 4 . 35 N . T . U . , r:1' = 0 . 0 7 ) but low colour (x = 0 . 72 m-1 , r:1' = 0 . 6 9 ) .

The expec ted Kd ( av ) for this type of lake would approximate 1 . 1 4 m- 1 ,

and it would have spectral distributions s imilar to those typified by

Lake Sorell (Figure 3 . 7 c ) , where blue l ight is rapidly attenuated ,

but a broad tran smis sion plateau between 5 7 5 and 7 00 nm remains .

The highly coloured lakes (x = 1 0 . 1 8 m- 1 , r:J" = 3 . 62 ) with low

turbidity (x = 0 . 46 N . T . U . , 0" = 0 . 2 1 ) make up Group V , while the few

lakes o f lower colour (x = 4 . 0 3 m-1 , a = 1 . 6 8 ) but consid erable

turbidity (x = 1 1 . 38 N . T . U . , d = 4 . 25) fall into Group VI .

anticipated Kd (av ) values Hould be around 2 . 42 m-1 and 2 . 45

Their - 1 m '

respectively . The typ ical spectral distribution o f underwater P . A . R .

for Group V would b e l ike those o f Lake Fedder on 2 7- 6-84 , and Lake

Strahan (Figure 3 . 7 e ) , while that for Group V I would be very similar ,

resembl ing thos e from Lake Crescent and Tooms Lake (Figure 3 . 7c ) .

Lake Chisholm , a polyhumic lake (x = 25 . 59 m- 1 , d = 1 . 38 ) of low

turbidity (x = 0 . 54 N . T . U . , a = 0 . 1 5 ) on all o ccasions s tood apart

as the sole rep r esentat ive of Group VII .

The classif ica t ion of lake types so obtained agrees favourably

with one based on edaphic and chemical data by Buckney and Tyler

( 1 9 7 3a) . Thus , the maj ority of alpine and l owland l akes o f Tasmania ' s

!-'· >.:j ;J !-'· H-0 .:::

rj (/l (D (D <: w (D ;J }--'

0\ OQ rj 0 .::: t::J

'd (D (/l ;J

p. rj

0"' 0 Pl OQ (/l rj (D Pl p. s

0 (/l ;J 0"'

0 H- � 0"' !-'• (D ;J t:"l !-'• OQ rj

H-OQ 0"' !-'· (D f-' <: Pl !-'· rj ;J rj

Pl Pl ;J ;J OQ p. (D

s u

H- (D .::: ::i rj H-0"' !-'· 0 p. 1-h !-'• H- t-3

'-< Pl !::.1

(/l <: s Pl Pl r1 f-' ;J .::: !-'· (D Pl (/l -

(/l 8 f-' Pl !:';"' (D ';1 (/l

P" on 2 -l . !0 . 79 '====1 - -�--'-���-'--���-'--���--'-���----'���-'���-'����'--���L..��--' 0 7 N (n N UJ .!:-. l.'J '-'" (," 0 ""'-1

0 (J1 -:-J b l0 VJ

l0 .b. CD .b. CD ())

L a k e ! 0 .0"! . 7 3 _____j L a k e 03.0L�. 8 3 __j

L"';'£;:;""' Sl : Ul -q Lake Fe:� t o n ! 4 . J 1 . C 2

l�;Ji�� t;�; 8� . \ ? : �§ ---Loke f,,.i e s t c: <"J 2� . ',)2 . 7;.3

J u n c t i o n L'Jk.e '.�5 . 0. ·2 . 78.

Lo Ke LCJ•JrG c:s . I 0 . 78 -p ,d q e "

10�a�����;�: �� };l ·8�li =t--

P e t Rese· ·· " " 1 5 - Cr3 . SL;. � Lo c oon of I s : :::; r ; ci s I ::: .. 07 . 8 2 -

R1 sdon Bro o �. J /1:-;1 ! 5 . 06 - 24 L a k e Ki:�a W i l ! i a m - r.1 o in o � 1n 22.0G . 8�1

• R : s d c n B roo k Ooc1 02 . I I . 7 8 � L a ke Tre v o l l v n 24.0 4 . 8 3

L o k e l.e o k e 1 G .0 7 . 8 2 � - -� G r a n t s L o r; o o n 2 6 .04 . 84 =.=-:J J!Morsh o i l 's R e s e r v o 1 r11 0 1 .07 . 84

-----��-- P 1 n e T:er Darn 05.0 7 . 84 - I R 1 sdon Br ook Dom 0 1 . 05 . 82 --._ _ Lake B 1 nney 05.0 7 . 84 ---' l

L a k e K i ng W i l l , o rn - G u e i p h Bo s 1 n 28

.

0 6 .8" � l L a f: e B o r r 1 n g :on 2 2 . 09 . 78 -�-

l.o k e t.l e od o w b 'l n k 05.07 . 84 -Lake B or r 1 nq ton ! 3 . 03 . 78 --

L o k e I S 1 n ci , l fJ 1 5 -03 . 8 4 -L a k e �.·t ! k o n y ! G .0 � - 8 '1

�-- -�- - C u r n e s R,ve r Dam 04 -06 . 83 �� � - j L a k e Barr i n g ton 02 . 1 0 . 8 2

Dove L a k e 03 . 1 0 . 8 2 L a k e G a r c i a 1 2 .08 . 84 -

Lake C u r l y 2 2 -02 . 78 -­L a k � G o r d o n 2 3 - 03 - 84 �

Blo c k m e n s L a o o o n 2 5 .04 . E4 -Cascade Dam 26 .0 4 . 84

L. o k e W u r r o w i n a 28 . 0 1 . 78 3 L a k e R o s e t

.� c r y ! 8 .03 . 8 4 -� i

L a ke Pe d d e r 2 1 - 0 1 . 22 � Lake M u rch iSOn 0 3 . 1 I . 5 2

L o ke R h ona 1 7. 0 1 . 7 8 :==1 , _ _ L o �.e �·!1 u rc h i s o n ! 7. 03 - Sd

L a k e G o rdon 06 - 0 ! - 7 8 Frome D a rn 25 -04 . 8 ·"\

L a k e L l ew e l l y n 1 5 . 03 . 84

'-'" "'"" (.-1

l R i s d on Brook Darn 04 -05 . 8 I -..__

�---- ---- Lake S o r e l l 1 4 .07 . 22 --' - - -Lake Pedd e r 27. 06 - 8 4 ----"1 Lake Go r d o n 03 . 1 I . 78 3

D 1 a rnond L a k e 1 7 . 0 1 . 7 8 Ba s 1n L o ke 1 0 . 08 . 8·'1 - - -

(J1 VJ ()) (;1 N N

(J1 .!:-.

Lake Strahan 1 6 . 0 1 . 6 1 -------� P a r t i n g C r eek La ke 1 2 . 08 . 84 ---- - ­

L a ke Cre scent I 5-0"i' . 82 � Prosser River Ooro1 25.02 . 8·-+ - - 1 Toorns Lak e 3 1 . 08 . 82

�����--��"""7--.--' oorns L a k e 22 -0 6 . 78 ���­L a ke C h i s h o l rn 1 8 . 02 .84 � La k e C h i s h ol m 1 6 .04 . 84 _ _ La k e C h 1 s h ol rn I 3 -08 .84

---��----- L ake C h i sholro1 1 0 . 06 . 84

0 0 ""'-1 U)

�

100

wes tern areas (Province I o f Buckney and Tyler) are moderately to

highly dystrophic (Group s III and V, above ) , lying on anc ient

quartzitic rocks supporting highly humic vegetation , such as

Gymnoschoenus sphaerocephaZus (R . Br . ) Hook . sedgelands , cool temperate

rainforests , or wet heath s , and with an ionic character close to

seawater . In comparison , lakes on Jurassic dolerite , such as those

in the Central Plateau , Mt . Field , and the Hartz Range (mainly lying

within Province II of Buckney and Tyl er) , whose ionic character lies

between seawater and World Average Freshwater , ar e the clear , non-turbid

typ es of Group I . The few turbid lakes , forming two discrete group s

( IV , V I ) , l ie in the dryer , rainshadow areas o f central and eastern

Tasmania (mainly Province IV of Buckney and Tyler) , where evaporation

may exceed precipitation . Here the climate is closest to that of

sou th-eas tern Australia , where many similar turbid lakes o c cur (see

Section 2 . 5 . 5 ) . Group II includes lakes which are located either in

areas between the two maj or rock types , or between the dryer and

wetter regions o f the south-east , and some come from the north coas t

(Province III o f Buckney and Tyler ) . f, may therefore represent a

transitional g roup between clear lakes and either the humic or turbid

ones f ound in these areas .

The groups of the cluster analyses int ergrade to a certain extent ,

and the several categories o f dystrophic groupings would , by more

subj ective means , be s imply grouped all together as "dystrophic " .

The presence o f some lakes , sampled on several occas ions , in more

than one category of the dendrogram ( e . g . Lake Barrington , Lake

Gordon) , is an indication o f the extent of temporal change . The mo st

variable of the study sites , Risdon Brook Dam , thus fell into three

g ro up s of the classification , due to its differing colour and turbidity

at different sampling dates . By the same token , the edaphic

differences of the catchments of the Main Arm (clear water s ) and the

Guelph Arm (dys trophic) of Lake King William were recognized by the

clus ter analysis . Polyhumic Lake Chisholm was also separated from

the o ther humic lakes as Group VII , on account o f its much h igher

humic content .

The cl assification reveal s that Tasmanian lakes have distinctive

underwater l ight climates , which are dependant on their gilvin and

turbidity content . Thus , for many lakes , the general opti cal

characteristics can be predic t ed , with a considerable measure of

confidence , from laboratory measurements of gilvin , and p erhaps

101

turb id ity , alone . Es timates o f mean downwel ling attenuation

coefficients can be calculated from such measurements by use of the

emp ir ical rel a t ionship s devised by the regress ion analyses . Likewise ,

laboratory measurements can be used to estimate the spectral P f�f{

distribution o f�lakes by allowing them to be placed into one of the

categories of the class ificat ion , for which comparable spectra­

radiometric data is available from lakes which typify that group .

Al though it is not suggested that such methods permit the accurate

prediction of quantum irradiance at any dep th (Bowling and Tyler ,

1 9 8 6 ; Howard-Williams and Vincent , 1 984 ; Jewson � al , 1 984) , for

ecological or management purposes , prediction o f optical water qual ity ,

such as attenua t ion coefficients and the spectral distribution of

underwat er light , is important (Kirk , 1 982) , especially when species

comp o s i tion and primary product ion are cons idered . The results o f f'1 l!IJiH. h15i!;)> fi" tl

this survey p e rmit k �or Tasmanian lake s , where _i_n _s_i_t_u measurement

would be imp o s s ible , ' using only a small sample of wat er .

A s imilar optical classification was made on the standing fresh­

waters of north-east New South Wales (Figure 3 . 1 7 ) . The maj ority o f

the l akes ( 2 5 ) all fell int o one group (Group I I I ) , this representing

thos e of low col our (x = 0 . 836 m- 1 , � = 0 . 645) and of slight turbidity

(x = 1 . 93 N . T . U . , � = 1 . 1 1 ) . The typ ical Kd (av) value for these - 1 waters would b e around 0 . 97 m , and their spectral distribut ions are

represented by measurements from Lakes Hiawatha , Minnie Water , and

Keep i t , and from Chaffey , Storm King , Copeton , Halpas and P indari Dams .

The o ther groups o f the optical classification were all small .

The moderately turbid and coloured Dumaresq and Oaky Dams , along with

Yalgoo Reservoi r made up Group I (Mean turbidity = 3. 8 7 ±0 . 46 N . T . U . ;

mean g440 = 5 . 5 2 7±0 . 95 1 m- 1 ) , while the more turbid (x = 6 . 53 N . T . U . ,

a' = 0 . 7 4 ) but less coloured (x = 1 . 828 m- 1 , rf = 1 . 1 50 ) Clarrie Hall

and Quip olly Dams , Lake Inverell , and Beardy Water s Reservo ir

constitute Group I I . Two dystrophic coastal lakes , Cooks Lagoon and

Lake Ainsworth , made up a group of their own (Group IV) , while highly

coloured and increasing turbid S t . Helena Dam , Kentucky Creek Dam ,

and Yarrie Lake , were each separated into group s o f their own .

Overall , the resul ts of thi s optical classification show that the

maj ority of the lentic freshwaters of north-east New South Wales are

opt ically homogeneous , and only slight differences exist between their

underwater ligh t climates . However , some excep tions to this general

tendancy do exi s t , and differences of some individual study sites were

0 >-:tj 0 1-'· OJ Ul (::! rt ti OJ (1) 1--'

w 1--' . OJ I-' ?;"' 00 (1) Ul

1-'• CJ ::::! (1) rt ::::! 0 p..

ti Ul 0 f-'· (JQ X ti

OJ (JQ 3 ti 0 Ul (::! ::;'

'0 0 Ul �

1-'· 0" ::::! OJ (JQ Ul (1) rt p.. ::;'

(1) 0 ::::! OJ

ti rt ti ::r � (1) ::::! 1-'· (JQ l"i (1)

3 (JQ (1) 1-'• ::::! 1--' rt < 1-'• 0 ::::! H1

=:

OJ Ul ::::! 0 p.. (::! <

rt rt ::;' � I ti (1) 0" OJ < 1-'· Ul p.. rt 1-'• rt .0

'-< (::! $

(1) < (1) � ::::! 1--' Ul � 1--' (1) � Ul ::::!

p..

_ Blue Lake N.S.l.

. Blue Lagoon l\i.l. Deepwater Lake

L"lke McKenzie -

Horieyeater Lake

L!ke Wabby

Lake Freshwater j-­Lake Birrabeen

Basin Lake -

Lake Bowarrady � North Boomerang Lake --��

Lake Allom .. J I Lake Benaroon - ..,:

·· Lake .Minker --��

Ocean Lake . ..JI Lake Woonjeel _j

Lake Garawongera J White Lake

Brown Lake -

� ,....... t-V N � W e;;: N U1 \.0 W "-J l-" '-'' \0 W C\ I- '-0 00 .....J "'' � l;,).j tv 0 \0 ;..... ec · (..., N z.o � � ;..... oo � � W � � � 00 0 � W A -1 ,........ C'\ 0 "' \0 C;.:l co � c-.

Jennings Lake .11 Hidden Lake -�

lake. Boomanjin - _;

South Boomerang Lake � I Lake Coomboo _J-J

· Red Lagoon ------

Lake- Cooloomera -----------'

� (/J ::::! 0 p.. �

rt rt ::;' � ti ::E:: 0" OJ 1-'· 1--' p.. (1) f-'· Ul rt

'-< 1--' (1)

< ::::! � rt 1--' 1-'· � () (1) Ul H1

ti . (1) Ul � Ill rt-(1) l"i [ll .

1-'· ::; rt 0

Ul (1) < (1) ::;

(JQ l"i 0 �

'0 Ul

0" PJ (Jl (1) p..

,) :j:

rt ::Y (D 1-'·

. r:

ao · _ ..., . . 1--' < 1-'· :j

"'d 1-'·

(::! ti (1)

w . I-' "-..!

CJ (1) ::::! p.. ti 0

(JQ l"i Ill 3

Ul ::;' 0 � 1-'· ::::!

(JQ

rt ::;' (1)

OJ l"i ti Ill ::::!

(JQ (1) 3 (1) ::::! rt

0 H1

::::! 0 ti rt ::;' I (1) OJ (Jl rt

z (1) �

� "' "' � A "' � .._, "" � "' � ., � "' ..., "" "' .... 0, "' 00 A � "' .... 0\ "' ;.., ;., c, ·<., 0 0, "' 0 :.., :., 00 0\ ... "' .... "' ...., "' "' "' t - _f____ _____L___ j

Dumaresq Dam Yalgoo Reservoir 3

--------:::c:- · · Oak':'_ Dam _j Ciarrie HaH Dam �

:::: Beardy \.Vaters Reservoir ----{ Quipolly Dam _ __j

Lake lnverell _I ----P"'"u-J,!!e-;!o�k Dam � ·Tenterfield Reservoir -1

Toonumbar Dam ------< 1 Rocky Creek Damj l

Lake Keepit rl Du��:%:� �=: g I

Ranger Valley Dam . I Storm King Dam - ! Beehive Dnm- I

Gara Dam Chichester Dam

Lostock Dam -: Copeton Dam�·

Bootawa Dam Lake Minnie

-Witter

Lake St. Clair -Mal pas Dam · Pin�ari ba;n --j

Lake Hiawatha I Gfenlyon Dam ---{

I n I

Rosendahl Rese

.

rvoir� -------- -

Lake Liddell -- I Glenbawn Dilm _______ 7

K��ngi D3m � _ Cooks Lagoon ---< . . i �

- Lake A�wort 1 ---' --<-,-------;. St. Helena Dam -----

'""' �

? :I<�'C�� Dam-----------------------------'

·"!

=: Yarrie Lake W

103

extreme . Unlike the opt ical classification of Tasmanian lakes , no

geographical d i s tributions of the lakes in the groups are obvious ,

and tho se that d if f er markedly f rom the typical optical properties

of the area p robably do so due to local effects .

Apart from p o ssibly helping spl it Brown Lake off into a group

of its own (Group I I I ) , turbidity differences between the lakes were

too slight to contribute much to the optical classification o f

Queensland lakes (Figure 3 . 1 8) . The remaining lakes can b e grouped

according to their gilvin concentrations alone . Group I includes all

those with the clearest waters , with very low level s of g440 (� = 0 . 242 m- 1 , � = 0 . 300) , while Group II includes those with only

slight levels o f colour (� = 1 . 1 80 m- 1 , cr" = 0 . 1 88 ) . Three mesohumic

lakes , Jennings , Hidden , and Boomanj in , form another distinct group

(Group IV) , while Lake Coomboo and the southernmost of the Boomerang

Lakes comb ine to form Group V . These two groups have mean g440 values

of 3 . 320±0 . 7 80 m- 1 , and 8 . 550± 1 . 1 8 1 m-1 , respectively . Finally ,

highly dystrophic Red Lagoon and Lake Cooloomera constitute Group VI .

This optical classificat ion o f Queensland freshwater coastal dune

lakes , based on the ir humi f ication , may result partly from their ..___,�

mode of origin . It has been suggested ( Bayl y , 1 9 64 ; Bayly � al ,

1 9 75 ; Bensink and Burton , 1 9 75 ; T imms , 1 982 , 1 9 86a) that op ti cally

clear lakes are of the water-table window type , comp ared to perched

lakes , which are humic . However , exceptions do o ccur , revealed by

the presence o f the two Boomerang Lakes , both perched l akes , in

separate group ing s of the classificat ion , the northernmos t being

placed the clear-water lake type Group I , and the southernmos t one

in dystrophic Group V . S imil arily , both Jennings Lake and Lake

Birrabeen , two lakes in such close proximity and el evat ion to be

almost l inked, al so fall within different group s of the classification .

Unfortunately the g eomorphic orig ins of many o f these l akes are

poorly documented , and so canno t be stated for many in each grouping

of this classif ication .

As well as cluster analyses , regression analyses were al so

undertaken to derive s tatistical relationsh ip s between the vertical

attenuation coefficient , Kd (av ) • and the various attenuating components

of the aquatic medium . These were done for each area , sep arately .

However , some o f the resul ting relationship s appear very s imilar ,

and comp arisons us ing the t-test showed no s ignificant differences

(at the 5% level ) between the slopes of the Kd (av) verses g 440

1 0 4

regress ions (b efo re log normal transformation) , indicating that

increas in g gilvin concentration increas es the attenuat ion of ligh t

in a s imilar manner in the waters of all three s tudy areas . Further

t- tes ts on the intercepts of the three regre s s ions found only one

pair , tho s e for New South Wales and Tasmania , to b e s i gnifican t ly

different ( t( 2 ) , ( g s )

= 3 . 6 2 , P = O . O O l ) c B e caus e o f this , the

Tasmanian and New South Wales equations canno t b e u s e d interch angeab ly

to estimat e Kd ( av) from a g4 4 0

measurement , b ut the o th e r equations may

b e sub s tituted for e ach o ther , wi th only sli gh t differences in the

result ob tained .

The s lopes o f the regres s ions b e tween Kd ( av) and turb idity , prio r

t o l o g normal trans f o rmation , were als o t-te s t e d o There wer e n o s ignif­

icant dif ferences ( a t the 5% level) between thos e o f Queens l and and

Tasmania , and b e tween New South Wales and Tasmania , b ut one was shown

b e tween Queens lan d and New South Hales regr e s s ions ( t( 2 ) , ( s g )

= 2 . 32 ,

0 . 05 < P < 0 . 0 2 ) . However , t- te s t s b e tween the intercept s o f the o ther

e quations wer e s i gnifican t ( t( 2 ) , ( g s )

= 2 . 7 1 , P = 0 . 0 1 b e tween New South

Wales and Tasmani a ; and t( 2) , ( s s )

= 3 . 15 , 0 . 0 1 < P < O o 00 1 b e tween

Queensland and Tasmania) . Th es e regre s s ion e quations are therefore not

interchangeab l e , wi th the s i gnificant differences b e tween them p rob ably

res ul t in g from turb idity b eing a poor predictor of Kd ( av) ' esp ecially

in Tasma�ian waters and the s outh-eas t Queens land coas tal l ake s .

S imil arly , varia tions in the contribution of turb idi ty to attenuation

in each of the three areas does not allow interch angeab l e us e of the

mul t ip le regres s ion equa tions of turb idity and gilvin a gains t Kd ( av) '

Phytoplankton Diversity and Distrib u t ion

Few local a l gal floras have b e en des crib ed from Aus tralia (Ling

and Tyle r , 19 86 ) . Although taxonomically incomple te , and s ub j e c t to

the l imitations o f s ingle samples (which take no account o f temp oral

changes in communi ty composition) and the mesh s ize of the s ampling net ,

the s u rv ey o f t h e n o r th - e a s t :Je\v S o u t h �·Jal e s f r e s h\va t e r s r eve a l s a diverse

planktonic flo r a o Many s ites had a considerab l e ran ge o f taxa , while

in contras t , almo s t monos pecific b looms o f Mal lomonas s p . and Cer>atiwn

hir>undine lla were presen t in Puddledo ck and Quipo lly Dams , respectively .

Cyanob acteria and diatoms also formed b looms in a numb e r o f the lakes

and res e rvoirs , but green algae and dinoflagell ates were particularly

widespread . One unusua l and uncommon dino f l agellat e , Pror>ocentr>um

1 0 5

p layfairi , firs t recorded in New South Wale s freshwaters b y Pl ayfair

( 19 19 ) ( as Exuvie Ua Uma ( Eh r) S chutt . ) , and only recently reported

again from Tasmanian coas tal lakes ( Croome and Tyler , 1 9 8 7a) , was also

collected from two l akes and a reservoir in coas t al parts of north-eas t

New South \vales , in this s tudy ,

B et\veen lake comparis ons are however not o ften pos sib le , as. the

s amples were col l ected a t different times o f yea r , and s ome variation

may therefo re be due to seas onal differences o Factors. s.uch as the

water temperature ( dependent on location and s amp l ing t ime ) , and more

particularly the extent o f eutrophication of each waterb o dy , would

probably als o contrib ute to differences in phytoplankton . The underwater

l igh t climates may also h ave an effec t , For example , the low l i gh t

levels in extremely turb i d Yarrie Lake would almo s t certainly cause its

depauperate phytoplankton , despite its very high nutrien t concentrat ions .

May and Powell ( 19 86 ) found the pres.ence o f individual taxa in Chaffey

D am was related t o changes in waterflow , depth , temp erature , the

avail ab ility o f nutrients. , and successional changes .

Chlorophyll a values indicate low trophic l evels and s parse phyto­

p lankton popul ations in mos t of the freshwater coas.tal dune lakes o f

south-eas t Queens lan d . B ayly e t a l . ( 1 9 75 ) foun d tha t desmids , Chl o ro­

co ccales , Peridinium , and Dynobryon were the predominan t algae in

Fraser Islan d l ak es , as was the cas e in this s t udy , al though they l is ted

a less diverse f lora . Al tho ugh l imited to spot s amples taken with a

20 �m pl ankton net over a three week period , no dis t rib u tion patterns

based on the o p t i cal properties o f the lakes were apparent from this

s urvey . It has b een propo s e d ( Kirk , 1 9 7 6b , 1 9 79 , 1 9 8 1 a ; Eloron t a , 19 7 8 ;

Jeffery , 1 9 80 ) that taxa with acces sory photosynthetic pigments may b e

a t an eco lo gical advan ta ge i n s ome underwater l igh t clima tes . In contras t ,

Arthington e t a l . ( 19 86 ) h ave a ttributed faunal differences b etween

lakes of Fras e r Islan d , particularly in the compos it ion of lit toral

inverteb rates and fish , to differences in their geomo rphic o rigin and

resultan t water co lour .

It is acknowl edged that p il o t s urveys such as thes e are unl ikely to

s how any dis tin c t differences b e tween phytopl ankton communities .

Quantitative s amplin g and coun ting at a s pecies level woul d b e required

to determine if variations do exis t in phytop lankton compos i tion be tween

l ake s of differing o p ti c al properties .

3 . 5 CONCLUSIONS

1 0 6

The result s o f these s tudies have shown that , with a few exceptions ,

dissolved humic s ub s t anc es play the maj or part in the ext inction o f

light in the standing inland freshwaters o f the three areas o This i s

espec ially s o in Tasmanian lakes , and tho s e o f the coas tal dune areas

of south-ea s t Que ens land , which cover a wide range o f concen trations

of dissolved humic sub stances . Al though mos t lakes and reservoirs o f

north-eas t New South Wal es have only sligh t to moderat e concentra t ions

o f gilvin , and only a few are h ighly dys trophic , it never-the-les s s till

plays the dominant role in attenuating P . A . R . in the s e water s too . Mo s t

New South Wales water s are also slightly t o moderately turb id , and a few

are highly turbid , so suspended particulat e mat t er al so contrib utes to

att enuation in these lakes and res ervoirs , al though usually to a much

les s er ext ent tha n gilvin . In c omparison , and unl ike o th er inland waters

from other par t s o f Aus tralia , lakes from Tasmania and south-eas t

Que ens land are usually non-turb id , and tripton i s an important att enuator

in only a very f ew of them . However , even in turb id waters , humic

mat erial s al s o contribute greatly to light extinct ion , due to their

sorption onto the outs id e o f suspended mineral particles ( Kirk , 19 80a) o

Chlorophyll a is rarely a consideration , except in some o f the mor e

eutrophic lakes , such a s tho s e o f north-eas t New South Wales , and water

i t s el f would b e a significant attenuator of P . A . R . only in some o f the

cleares t lakes of the three area s , in par t icular tho s e from Tasmania

and Queens land .

A predict ive optical class ifica t ion was devis ed for Tasmanian lakes

which clos ely follows one bas ed on chemical and edaphic features ( Buckney

and Tyler , 19 73a) . A similar clas s ification o f north-eas t New South

Wales waters was less succes s ful , due to the maj ority of thes e waters

b eing optically f a irly homogeneous , but one f or the coas tal dune lakes

of south-eas t Que ensland showed dis t inct groups differing mainly in

gilvin concentrat ion o S tatistical relationships were derived b e tween

Kd( av)

and the various attenuating component s of the aquatic med ium for

each o f the thr ee areas , with those for gilvin b eing very s imilar ,

indicating that gilvin attenuates ligh t in a nearly identical manner

in the waters o f all study areas .

Some temporal var iation in humic content was evident in the

Queensland lakes , as the ir tran s parency was b etter than in earlier

s tudies ( e . g . Bayly et a l . , 1 9 7 5 ; Ar thing ton et a l o , 1 9 86 ) , implying

lower gilvin conc entrations and higher pH values " The humic nature o f

1 0 7

o f these lakes was the cause o f their acidity , with a s trong negative

correlation apparent b etween pH and gilvin conc entratio n , confirming

similar ob servations by Bayly ( 19 6 4) and Bayly et a l a , ( 19 75 ) o In

�ontras t , levels o f humics were ins ufficient to affect pH in the New

South Wales waters , and their pres ence was o f f s et b y b uffering b y the

dominant anion , b icarb onate , and salinities of up to 300 mg L- 1

(Timms , 19 70 ; Banens , in pres s ) o

Divers e phytoplankton floras were found in b oth the New South Wales

and Queensland freshwaters o Species from the D ivis i on Chloro phyceae ,

in particular desmids and Chloro co ccal es , were abundan t , al though

flagellates and diatoms were also presen t in cons iderab l e numb ers , and

cyanobacteria were common in s ome New South Wales waters o However the

data are insufficient to show whe ther various ecological factors , and

especially the op tical proper t ies of the various waters , are inf luencing

the dis tributional patterns of the s e algae o Inve s tigations using

quantitative techniques would b e required to determine if correlations

exi s t between species comp o s it ion of phytoplankt on communities , and

the humic content of lakes o However , the surveys do provide additional

information to the depauperate knowledge o f the phytoplankton of these

two regions , providing a b as is for future res earch on thi s topic o

108

C HAPTER FOUR

PHYSICO-C HEMICAL STUDIES OF FRESHWATER COASTAL

LAGOONS FR0�1 WESTERN AND SOUTH-WEST

TASMANIA , AND FROM KING AND FLINDERS ISLAND ,

BASS STRAIT

4 . 1 INTRODUCTION

4 . 1 . 1 The Aims and Scope o f this Study

Freshwater coastal dune l akes occur in numerous locat ions along

the Aus tral ian and Tasmanian coast lines , and s tudies of these have

been reviewed in Section 2 . 3 . Al though originating from a number o f

geomorphic pro cesses , they are typ ically acidic and of low sal inity ,

with an ionic chemistry dominant ed by sodium and chloride ions . Water

clarity varies cons iderably , with some being cleanvater lakes , while

o thers are highly dystrophic (Timms , 1 982 , 1 9 86a - see also Chapters

Two and Three ) .

The Bass S trait islands h ave many l entic Haterbodies , and others

are located along the west and south-west coasts of Tasmania . Despite

the mainland Aus tral ian coastal l akes having been considerably s tudied ,

those o f Tasmania have attracted l ittle l imnological attention . The

maj or ity are h ighly dystrophic , and thus are ideal sites for s tudies

of humic waters . Additionally , humic coastal lagoons of Tasmania have

very rich planktonic floras (Croome and Tyler , 1 9 8 7a , b ; Croome � al ,

1 9 8 7 and in press ) , and those o f the Bass S trait islands are l ikely

to , too . Because o f the emerging phycological importance o f these

waters , th is s tudy aimed at invest igating their physico-chemical

propert ies . The extent of any l imnol ogical s imil arities or dif ferences

between King I�land lagoons , due to local variations in dune

geochemistry , formed a suit able subj ect for mul tivariate analysis ,

and the l agoons of both Bass S trait islands Here compared in the

same manner . The remoteness of many prevented the direct measurement

of the spectral distribution and attenuation of l ight within them ,

109

but it is p o s s ible to speculate on their underwater l ight climates ,

using the proce qures developed in Chap ter Three o f this thesis . '"""'&� '

The species d i stribution and d iversity of the phytoplankton of some

of the l agoons of western and south-western Tasmania , and the

influence of humics on th is , were also examined .

4 . 2 METHODS

4 . 2 . 1 Collection and Analysis of Samples

Surface samples from s ix Flinders Island and seventeen King Island

l agoons were collected in May , 1 982 , after an extremely dry summer . A

sample o f groundwater from a freshwater spring near Surprise Bay , King

Island , .was als o collected . Thes e sites , shov.7Il in Figure 4 . 1 and

identified in Table 4 . 1 , represent only a small proportion o f the

standing waters on the two island s . The samples , in one l itre black

p olyethylene bottles , were airfreighted to Hobart and stored at 4 ° C

pending l aboratory analyses .

Most samples from wes tern and south-western Tasmania were

collected in January and Februar y , 1 9 87 , and include some obtained by

P . A . Tyler , R . L . Croome , and B . V . Timms from the South-east Cape and

New River Lagoon areas , and from Hibbs Lagoon . Rebecca Lagoon was

sampled in February , 1 9 8 4 , and additional data from November , 1 984 ,

i s included for Lakes Garc ia , Strahan , and Ashwood . The sampl ing

l o cations are shown in Figure 4 . 2 , and identified in Table 4 . 2 .

Access to many of the remoter s it e s was by helicop ter , which l imited

collections to one litre water samples , taken in black polyethylene

bottles , and to phytoplankton , o b tained by tows with a 20 pm plankton

net . All water samples were s tored at 4 ° C , and the ionic analyses

were done by the Tasmanian Government Analyst . Plankton samples were h;,¢{,

fixed with�formalin for micro s co p ic identification using the texts

referenced in Section 3 . 2 . 2 .

Water colour was determined as g 440 (Kirk , 1 9 7 6b) , and (for King

Isl and) on the Hazen (mg P t L- 1 ) s cale (see Section 3 . 2 . 2 for detail s

o f these methods ) . Complete absorption scans (400-750 nm ) were under­

taken on selected filtered (0 . 45 p m) King I sl and samples against

distilled water blanks , using a Pye Unicam SP 8 / 1 00 U . V . /V I S . double

beam spectrophometer . The turbidity of the samples was measured using

a Hach 2 1 0 0 turbidimeter , agains t formazan standards .

K I N G I S L A N D

Figure 4 . 1

Bo 0 9 ' 1 2

11 •

K I HG 1. 9

0 10

110

!ISS S T R i l l

km

f L I HDlRS �I. "i2

F L I N D E R S I S L A N D

Locat ion o f sampling s ites of coastal lagoons o n King

and Fl inders Is lands , Bass Strait . The numbers refer to the lagoons

listed in Table 4 . 1 .

1 1 1

'!---------------------------.�� ---.

WESTERN TASMANIA 5'-l2�� 1 OA ;::::--_7 1 1---, .. 12�

0

North

50 km

Figure 4 . 2 Locat ion of sampling s ites of coastal lagoons from western

and south-west Tasmania . The numbers refer to the lagoons listed in

Table 4 . 2 .

1 12

pH and ele ctrical conduct ivity at l 8 ° C (K1 8 ) were measured

electrometrical l y in the laboratory using Radiometer equipment .

Chemical analyse s were perfonned on filtered ( 0 . 45 }! �n) s amples , with

suitabl e d ilutions when necess ary . Sodium , potassium , and magnesium

ion concentrat ions were determined by atomic absorp t ion spectroscopy ,

and calcium by the colourimetric method of Kerr ( 1 9 6 0 ) . Bicarbonate

was determined by p o t entiometric titration against 0 . 0 1N HCl to pH

4 . 5 (Gol terman e t al , 1 9 7 8) , chloride by conductimetric t it r ation

against AgN03 (Gol terman et al , 1 9 78 ) , and sulphate turbidimetrically

using barium chloride (A . P . H . A . , 1 9 7 1 ) . Sal inity , in mg L- 1 , was

cal culated as the sum of these s even maj or ions . Total d is solved

iron was analysed b y atomic absorption spectrophometry , while silica

was measured by the molybdate yellow method (A . P . H . A . , 1 9 7 1 ) . Total

phosphorus was d etermined following prediges tion with potassium

persulphate by the s tannous chloride method for the Bass Strait

island samples , but the ascorbic acid method was used for samples

from wes tern and south-western Tasmania . Total nitrogen was analysed

following D ' Elia � al ( 1 9 77 ) . A Technicon Autoanalyser I I was used

for the nutrient analyses of the samples from south-west Tasmania ,

which were coll ected in acid washed plastic bottles .

The lakes near S trahan are more easily accessable , and were

sampled from an inflatable rubber boat . Thermal and conductivity

profiles were measured with a W . T . W . LF 1 9 1 conductivity meter , and

dissolved oxygen with a W . T . \\T . OXI 91 oxymeter . pH was al so measured

in situ with a Methrom E558 pH meter , and water transp arency with a

20 em quartered black and white S ecchi disc .

A princip l e co-ordinates analysis (Gower , 1 9 66 ) , using fourteen

variables - turbidit y , g440 • pH , K1 8 • dissolved iron , SiOz , total P ,

the four cations (expressed as a percentage o f total cations ) , and

the three anions (expressed as a percentage o f total anions ) - was

employed to show variability between the twenty-f our s amples from

the Bass S trai t islands . Pearson product-moment correlati ons ( r ) were

calculated between p arameters using the SPS S computer p rogram (Nie

et al , 1 97 5 ) .

4 . 3 RESULTS

113

4 . 3 . 1 Thermal and Oxygen Profiles

Thermal and oxygen profiles from eight lakes near Strahan , and

from Hibbs Lagoon , are shown in Figure 4 . 3 . Ap art from clearwater Lake

Bantic , and ex�remely shallow South Strahan L agoon , all showed a marked

thermal gradient with dep th . Lit t le Bellinger Lake showed a temperature

drop of 5 . 5 ° C over j us t three metres , while there were s imilar changes

over 1 . 3 metres dep th in Lake S trahan , and 4 . 0 metres in Hibbs Lagoon .

Only Lake Garcia disp l ayed a thermal profile typical o f a thermally

stratified l ake , with a distinct epil imnion , a thermocl ine between

five and s ix metres deep , and a colder hypol imnion .

The oxygen profile confirmed the existance of thermal stratification

in Lake Garci a . Dissolved oxygen decreased markedly at the s ame dep th

as the thermoc line , t o hypolimnetic levels o f less than 1 0% saturation .

A marked oxycline was also present in Little Bell inger Lake , changing

from almos t complete s aturation at the surface to nearly anoxic

conditions clo s e t o the sediment s , despi.te the shallowness o f this

lake . Oxygen also decreased sl ightly with dep th in Lake Koonya ,

especially over the bottom metre , bu t oxygen profiles in this and

o ther l akes indicate frequent mixing and ventilation throughou t .

4 . 3 . 2 Turbidity and Colour

Resul ts from the Bass S trait islands are listed in Table 4 . 1 .

Tur bidity values were generally below 1 N . T . U . , al though three King

Island l agoons , Shearing Shed , Ridge , and Dead Sea , were markedly

turbid , with D ead Sea much more so than previously recorded (Buckney

and Tyler , 1 9 7 6) . Turbidity was measured for only four o f the

lagoons from western and south-wes t Tasmania , and was below 1 . 0 N . T . U .

in all cases . Qualitative observations indicate that mos t of these

coastal l agoons would hav e low turb idity .

The most notable feature o f many o f these waters is their

extremely high gilvin concentrations . The King Island lagoons all

contained some dissolved organic colour . was least in Penny

Lagoon (g4 40 = 3 . 4j� m- 1 ) , but mo s t l agoons were considerably more

dystrophic , and fou� had extreme amounts of organic colour . In

contrast , the s ix Flinders Island lagoons were all vir tually uncoloured ,

with g440 level s below 2 . 0 m- 1 (Table 4 . 1 ) . Median wat er colour for

the two islands was 6 . 7 m- 1 .

Ul � .:: OJ _§ ..c � 0. OJ Q

Ul C) 1::: �

_§ :S 0. OJ Q

0 2 0 4 0 6 0 8 0 1 0 0 1------L...__ _L.----'

1 0 1 1 1 2 1 3 1 4 1 5 {� :1 I ) I 4 1 I

I I

I 5 1 I : . . /

6 1 � ; � .

i 7 � Lake Garcia

31/1/87 8

9

1 14 80 1 0 0

�

1 6 1 6 1 7

{ 2

3

4

: j . J'ffi7777. 7(7l7>TTlT'.,;!TTI 7 Lake Bantic

31/1/87

6 0 8 0 1 00 % Sat o2

1 4 1 5 1 6 1 7 1 8 T °C I

I ) 1

2 , I

3 1 :� .. Hibbs L a g o o n

711187

60 80 1 00 0 20 40 60 80 1 0 0 4 0 60 80 1 00 % S a t o2

1 3 1 4 1 5 I �-

i ! 1 1 :

2

3 I '

4 1 Lake Mallanna l!V87

80 1 00 L--.....-l

2-I

' I

. . .

3 .;-�??'77r??V777 ;;;�

Utile Bellinger Lake

l/V87

80 1 00 '-----'

1 t I I

2 ) I I I

3LI ./ I . :

4 ... ·•

Lake Koonya

VV87

1 6 1 7 1 8 1 9 2 0 1 5 1 6 1 7 1 8 1 9 20 2 1 22 ��,�---�_LI ��---+� --�� --.·;LI--�1 --�� --�� --:;�· I

11Ll ..--/

1 J ,......;-----:' .7?77??0?'/.,. ...... ;o�

2 7Tff77777LTT.r""""""'''T1117771 2 j Lake S tra h a n Lake Ashwood 1 /2/87 1 12/87

(-�) I( -

Sout11 Strahan Lagoon

31/1/87

Figure 4 . 3 Summer thermal" and oxygenl profiles from lagoons from the west coast of Tasmania .

Table 4 . 1 :

S amp le S i t e a n d g r i d r e f er enc e

Flinders Island S o u t h Chain Lagoon L o g an s Lagoon S andy Lagoon North Chain Lagoon N o D u c k Lagoon S t icks Lagoon K.:ing Isl<md Big L n ke Wood l an d s Lagoon La ke F l an igan Seal Roc ks Lagoon Dembys Lagoon Pioneer Lagoon S he ar ing S h e d

L a g o o n At t r i 1 l s L a g o o n ? e ar s h a p e Lagoon Grani te Lagoon P enny Lagoon S u l l ivan s Lagoon G r o undw a t e r near

S u rp r ise Bay L a ke Mar t h a Lav inia Lagoon n o r t h o f

B i g Lake 5 4 GYA 3 8 8 5 7 3

Un-n&-ned L a g o o n 5 5 G B S 4 7 2 0 7 8

D e a d S e a R i d g e Lagoon

HED IAN HEA.t'j STA.t�DARD DEVIATION

P hy s i c o ch emical char a c t e r i s t i c s of lagoon waters ( in order of d e c r e a s ing s a l in i t y ) f r om King and F l inders I s l ands Blank s p a c e indi c a t e s no anal y s i s was c o nducted . 0 ind i c a t e s the charac t e r i s t ic was und e t e c t abl e . Grid references are g iven for lagoons that are un-named .

Nc.+

K+

Sample Turb i d i t y Gilvin pH K 1 8 No . (NTU) ( g440 , (P t uni t s, - 1 - 1 - 1 ()lS e m )

ID ) mg L )

5 0 . 5 0 l . 5 1 6 8 . 00 5 0 3 8 0 6 7 2 1 7 . 1 6 0 . 50 1 . 7 2 7 7 . 20 3 6 6 6 0 4 3 5 1 3 . 3 2 0 . 50 1 . 6 7 0 7 . 00 3 0 1 5 0 3 3 3 l l . O 4 0 . 5 0 l . 6 1 2 7 . 80 2 3 80 0 2 2 8 7 . 6 2 3 0 . 50 0 . 345 7 . 30 1 7 1 0 0 1 30 5 . 1 3 1 0 . 50 0 . 6 3 3 4 . 90 6 8 1 4 . 9 6 0 . 2 1 7

1 8 0 . 7 0 7 . 0 8 2 90 8 . 1 5 1 2 7 8 2 1 1 1 3 . 9 9 2 3 0 . 65 6 . 50 6 8 0 7 . 80 2 3 7 4 1 5 . 1 0 . 5 3 7

7 0 . so 7 . 3 7 0 1 00 8 . 30 2 0 2 4 1 4 . 2 0 . 58 8 1 9 0 . 80 1 3 . 8 7 6 1 7 5 7 . 0 0 2 2 9 2 1 6 . 6 0 . 7 7 5 2 0 2 . 1 0 2 3 . 8 3 6 300 7 . 30 20 7 1 1 4 . 4 0 . 43 0 2 2 0 . 90 9 . 7 8 8 1 2 5 7 . 9 0 1 9 6 5 1 7 . 4 0 . 5 1 2 2 1 1 9 . 00 1 8 . 5 3 9 2 0 0 6 . 5 0 1 8 7 0 1 2 . 8 0 . 4 7 6

1 6 1 . 30 5 . 9 3 0 7 0 7 . 9 5 1 3 30 7 . 8 7 0 . 1 9 2 1 5 1 . 9 0 6 . 85 1 80 7 . 40 1 3 1 0 7 . 5 7 0 . 3 3 8

8 0 . 5 0 8 . 348 1 1 0 7 . 3 0 1 2 5 4 1 0 . 3 0 . 3 8 4 1 2 0 . 2 5 3 . 45 5 20 7 . 4 0 9 0 9 7 . 8 3 0 . 3 8 4 1 4 0 . 80 6 . 3 3 3 8 0 7 . 80 7 7 6 3 . 9 1 0 . 0 9 0 2 4 1 . 0 0 1 . 7 2 7 2 0 7 . 5 5 6 9 7 2 . 1 7 0 . 2 0 5

1 1 1 . 0 0 35 . 2 3 6 450 5 .. 5 5 6 9 3 4 . 1 3 0 . 3 8 4 1 7 1 . 0 0 5 2 . 7 9 6 600 4 . 90 6 2 6 4 . 3 9 0 . 0 3 8

9 0 . 5 5 3 8 . 1 1 5 500 4 . 2 5 5 9 6 4 . 1 7 0 . 2 30

1 3 2 9 . 0 0 6 . 6 2 1 3 0 5 . "0 5 4 5 3 . 9 4 0 . 0 9 0 1 0 1 5 . 00 4 7 . 7 8 7 600 4 . 40 3 5 3 2 I � · " ' 0 . 1 6 0

0 . 7 5 6 . 7 3 6 l O S 7 . 30 1 6 0 0 1 1 . 6 0 . 40 7 3 . 3 3 1 2 . 82 1 2 0 2 6 . 3 8 805 1 86 . 0 2 . 6 7 7 . 1 9 1 5 . 3 6 4 1 9 9 l . 2 6 1 3 6 6 3 1 6 9 4 . 7 6

C a2+ Mg2+ - so_2

_ C l 4

meq L - 1

6 8 . 8 1 7 3 7 4 0 5 6 . 3 5 1 . 6 1 4 2 485 1 00 5 7 . 5 8 2 . 2 400 6 1 . 5 5 7 . 5 6 9 . 9 2 9 5 4 3 . 8 7 4 . 6 3 4 . 5 1 9 4 5 0 . 0

0 . 4 3 8 l . 2 3 5 . 7 0 0 . 0 52

6 . 00 6 0 . 2 1 4 8 1 5 . 8 4 . 1 3 7 . 40 1 7 . 1 5 . 7 3 2 . 35 6 . 85 1 5 . 6 0 . 9 6 9 l . 0 5 6 . 9 5 2 0 . 2 0 . 9 90 2 . 1 0 5 . 6 5 1 7 . 2 2 . 6 6 2 . 85 4 . 6 1 1 5 . 8 l . 6 6 0 . 90 0 4 . 34 1 5 . 1 1 . 0 2

5 . 1 7 3 . 9 1 7 . 60 3 . 7 5 2 . 7 8 3 . 55 9 . 7 0 0 . 1 9 8 l . 3 3 3 . 1 7 1 0 . 7 5 0 . 9 1 7 0 . 5 7 5 2 . 1 4 7 . 9 5 0 . 3 1 3 2 . 0 8 2 . 30 4 . 7 5 1 . 0 0 2 . 3 1 l . 8 9 1 . 1 0 2 . 1 6

0 . 5 7 5 l . 8 9 5 . 8 5 0 . 2 6 3 0 . 4 0 0 l . 6 5 5 . 3 0 0 . 1 8 3

0 . 4 2 5 1 . 3 2 4 . 9 5 0 . 25 2

0 . 2 7 5 l . 3 0 4 . 2 4 0 . 2 2 9 0 . 3 2 5 0 . 84 7 3 . 0 8 0 . 0 60

2 . 2 1 4 . 1 3 1 2 . 9 1 . 0 1 1 4 . 4 2 5 . 9 1 0 1 1 4 . 6 2 5 . 3 4 7 . 0 1 9 2 2 6 . 9

Hco; S alinity Fe S io2 To t a l �: - 1 p

.,.___(mg L ) --""(pg L- 1 ) (%)

3 . 9 .5 4 8 8 0 4 0 . 50 0 . 0 4 0 8 6 3 . 6 -" 3 5 6 7 2 0 . 40 1 . 2 9 0 9 2 2 . 7 1 2 7 5 4 6 0 . 30 8 . 0 40 9 6 3 . 0 8 2 0 3 0 9 0 . 30 2 . 1 50 9 4 1 . 0 6 1 44 6 4 0 . 2 5 0 . 3 40 1 0 0 0 . 0 3 4 3 5 3 0 . 90 4 . 0 1 1 5 8 5

3 . 3 3 9 7 7 5 0 . 00 0 . 3 9 0 9 2 3 . 7 9 1 6 5 5 0 . 00 0 . 7 6 5 9 8 4 . 4 3 1 3 5 2 0 . 1 0 0 . l 2 0 8 8 l . 2 8 1 3 4 7 0 . 2 0 0 . 1 1 60 9 2 1 . 1 5 1 2 7 4 0 . 40 0 . 2 6 0 9 3 3 . 50 1 1 9 6 0 . 0 0 0 . 1 so 82 2 . 3 1 1 1 0 9 0 . 2 0 0 . 1 350 9 9

2 . 9 1 9 6 7 0 . 20 1 . 1 1 50 8 3 3 . 7 0 8 6 5 0 . 2 5 0 . 1 5 7 0 9 6 0 . 5 5 7 7 7 3 0 . 00 0 . 0 0 8 1 0 . 7 7 1 5 7 7 0 . 00 0 . 0 30 83 2 . 5 2 5 3 4 0 . 1 0 1 . 2 2 0 88 3 . 05 4 5 6 0 . 1 0 0 . 4 6 0 9 6

0 . 1 1 5 3 7 2 0 . 30 0 . 5 2 30 8 9 0 . 0 8 2 3 3 2 0 . 70 0 . 1 2 9 0 8 6

0 . 00 0 3 1 7 0 . 20 1 . 8 3 0 8 5

0 . 0 8 2 2 8 3 0 . 8 5 1 . 0 4 0 0 8 1 0 . 00 0 1 9 2 0 . 2 0 3 . 1 l l O 8 3

2 . " 2 1 0 3 8 0 . 2 0 0 . 3 5 6 3 8 9 2 . 00 7 1 0 5 0 . 2 7 1 . 1 0 1 2 8 8 9 l . 55 1 3 0 7 7 0 . 25 1 . 80 1 4 3 6

1-' 1-' en

1-< <!) § z <!) � "'

1 2 3 4a 4b S a S b 6 7 8 9a 9 b

1 0 1 1 1 2 1 3 1 4 1 5 1 6 1 7 1 8 1 9 20 21 22 23 24 25

Table 4 . 2 : Op t i ca l , chemical , and nutrien t p a r arne t e r s from the co as t a l lakes and lagoons o f 1ves tern and south-we s t Tasmania

D a t e S e cchi Field Lab Na+ +

Name g 440 K1 8 K S amp l ed Dep th p H p H

- 1 - 1 m m p.Scm

Rebecca Lagoon 1 1 - 2- 84 3 . 39 7 - - 8 . 1 5 1 1 9 2 1 0 . 8 65 0 . 1 75 Lake Mallan a 1 - 2- 8 7 2 7 . 2 3 3 0 . 70 4 . 25 4 . 20 1 2 8 0 . 7 5 7 0 . 0 3 1 Lake Bantic 3 1- 1 - 8 7 0 . 1 7 3 .,. 6 . s o 5 . 60 5 . 7 0 1 0 3 0 . 7 1 3 0 . 0 2 3 Lake Gar c i a 9- 1 1- 8 4 9 . 326 - - 4 . 90 l OS 0 . 9 3 4 0 . 0 1 5

3 1 - 1 - 8 7 6 . 44 8 2 . 00 5 . 1 0 5 . 00 1 0 5 0 . 6 9 6 0 . 0 1 5 Lake Ashwood 9- 1 1 - 8 4 1 1 . 05 2 - - 4 . 60 1 5 2 0 . 80 8 0 . 0 3 0

1 - 2- 8 7 4 . 8 9 4 ?' 1 . 80 4 . 70 4 . 60 1 40 0 . 84 3 0 . 0 2 1 L i t t l e Bel linger Lake 1 - 2- 8 7 1 2 . 6 6 7 1 . 00 4 . 60 4 . 60 1 1 0 0 . 6 9 6 0 . 0 1 5 Lake Koonya 2- 2 - 8 7 3 1 . 8 3 9 0 . 70 - 4 . 20 1 1 5 0 . 6 7 8 0 . 02 6 Ocean Beach Lagoon 1 9- 2- 8 7 1 3 . 9 3 3 - - 4 . 70 5 5 0 4 . 1 30 0 . 0 7 2 Lake S t rahan 9- l l - 8 4 2 8 . 5 5 2 - - 4 . 7 5 2 2 5 1 . 6 60 0 . 0 42

1 - 2- 8 7 2 7 . 406 0 . 60 4 . 65 4 . 60 2 3 3 1 . 6 5 2 0 . 0 38 S o u t h S t rahan Lagoon 3 1 - 1 - 8 7 5 1 . 1 2 7 0 . 40 4 . 00 4 . 00 2 5 6 l . 7 3 9 0 . 0 3 1 Heron Pond 1 8- 2- 8 7 45 . 3 6 9 - - 4 . 00 2 9 5 2 . 00 0 0 . 04 1 T e a l Pond 1 8- 2- 8 7 3 1 . 6 66 - - 4 . 1 0 450 3 . 2 1 7 0 . 0 5 9 Hib bs Lagoon 7- 1 - 8 7 8 . 5 7 9 - 6 . 80 6 . 30 1 45 0 . 8 7 0 0 . 0 3 6 N y e B a y Lagoon 1 6- 2 - 8 7 3 . 2 8 2 - - 7 . 20 480 2 . 95 7 0 . 0 7 9 Mu l c ahy Bay Lagoon 1 2- 2 - 8 7 2 0 . 1 5 1 - - 4 . 40 1 5Lf 0 . 9 3 9 0 . 0 7 7 P a rad i s e Lagoon 1 2- 2- 8 7 1 9 . 057 - - 7 . 1 0 350 3 . 4 3 5 0 . 0 6 2 Freney I.:agoon 1 3- 2 - 8 7 8 . 7 5 1 - - 4 . 00 9 2 0 . 5 9 1 0 . 0 2 6 Pl i l lar Lagoon 1 3- 2 - 8 7 1 0 . 0 1 8 - - 4 . 30 308 0 . 6 3 5 0 . 0 2 3 Pond 1 New River 1 5- 1 - 8 7 5 . 9 8 8 - - 4 . 80 1 20 0 . 7 7 4 0 . 0 38 Pond 2 Ne1v River 1 5- l - 8 7 8 . 6 36 - - 4 . 80 1 30 0 . 82 6 0 . 0 4 6 S . E . C a p e Lagoon l 8- 9- 8 5 - - - 5 . 2 0 3 6 6 2 . 6 5 2 0 . 0 4 9 S . E . C a p e Lagoon 2 8 - 9 - 8 5 - - - 4 . 30 2 8 0 1 . 95 7 0 . 0 4 1 S . E . C a p e Lagoon 3 8- 9- 8 5 - - 4 . 30 2 9 4 2 . 1 30 0 . 0 4 4 G i b b s Lagoon 2 3- 1 - 8 7 2 5 3 . 33 - - 4 . 60 1 5 1 0 1 3 . 1 7 4 0 . 3 3 6 B i g Lagoon 2 3- 1 - 8 7 1 4 . 85 4 1 . 25 7 . 1 0 6 . 5 0 7 70 5 . 5 6 5 0 . 1 6 2

MEDIAL'{ 1 2 . 6 6 7 1 . 0 0 4 . 70 4 . 60 2 2 9 1 . 30 0 0 . 04 0 MEAN 1 6 . 8 5 0 * - 5 . 20 5 . 00 3 2 7 2 . 4 2 5 0 . 05 9 S TAND�ZD DEVIATION 1 3 . 48 9 * - 1 . 1 0 1 . 0 8 3 3 4 2 . 9 9 5 0 . 06 6

* Exc ludes g4 4 0 d a t a f rom G i b b s Lagoon

ca2+ Mg 2+

so2--Hco; C l

4

meq L - 1

0 . 8 6 5 3 . 5 7 0 8 . 45 0 1 . 0 50 3 . 7 3 6 0 . 0 60 0 . 20 7 0 . 89 3 0 . 04 4 0 . 000 0 . 060 0 . 1 65 0 . 8 1 1 0 . 00 1 0 . 025 0 . 0 2 8 0 . 1 9 6 0 . 83 0 0 . 0 6 0 0 . 0 33 0 . 0 60 0 . 1 65 0 . 8 3 1 0 . 0 1 3 0 . 00 8 0 . 0 5 7 0 . 3 4 3 1 . 0 8 0 0 . 30 3 0 . 0 1 4 0 . 0 9 0 0 . 2 40 1 . 000 0 . 1 1 5 0 . 00 2 0 . 0 7 5 0 . 1 7 4 0 . 84 5 0 . 00 1 0 . 00 2 0 . 0 5 5 0 . 1 7 4 0 . 8 1 1 0 . 0 0 1 0 . 00 0 0 . 1 90 1 . 0 9 9 4 . 9 3 0 0 . 50 8 0 . 00 4 0 . 0 1 3 0 . 1+ 6 9 1 . 8 60 0 . 2 7 4 0 . 0 30 0 . 0 80 0 . 42 1 l . 8 8 7 0 . 0 9 0 0 . 00 2 0 . 1 20 0 . 4 1 3 2 . 05 6 0 . 04 6 0 . 000 0 . 1 40 0 . 4 4 6 2 . 4 2 3 0 . 0 6 3 0 . 00 0 0 . 1 5 5 0 . 6 8 6 3 . 80 3 0 . 1 8 8 0 . 000 0 . 1 40 0 . 32 2 0 . 9 30 0 . 1 0 0 0 . 1 84 1 . 65 0 0 . 7 9 3 3 . 4 9 3 0 . 3 4 6 0 . 5 7 4 0 . 1 20 0 . 2 5 6 1 . 1 2 1 0 . 0 9 6 0 . 000 1 . 65 0 0 . 4 8 8 2 . 2 99 0 . 200 0 . 4 9 2 0 . 05 5 0 . 1 1 6 0 . 6 4 8 0 . 0 0 1 0 . 00 0 0 . 05 5 0 . 1 49 0 . 7 9 7 0 . 00 4 0 . 000 0 . 0 6 0 0 . 1 82 0 . 9 3 0 0 . 1 5 6 0 . 0 0 4 0 . 0 7 0 0 . 1 92 1 . 000 0 . 1 5 6 0 . 00 5 0 . 1 35 0 . 6 1 2 2 . 90 1 0 . 2 9 2 0 . 0 26 0 . 0 7 5 0 . L+ 05 2 . 1 4 1 0 . 2 2 9 0 . 00 0 0 . 0 7 5 0 . 42 1 2 . 2 5 6 0 . 25 0 0 . 000 0 . 7 4 0 2 . 6 4 5 1 5 . 04 2 1 . 4 1 7 0 . 030 0 . 400 1 . 38 8 6 . 50 7 0 . 56 3 0 . 1 33

0 . 0 7 8 0 . 3 7 4 1 . 4 9 1 0 . 1 36 0 . 00 4 0 . 2 60 0 . 5 9 8 2 . 5 9 2 0 . 2 3 5 0 . 1 89 0 . 44 0 0 . 7 7 8 3 . 0 7 2 0 . 32 3 0 . 70 9

c r

%

8 5 . 5 8 8 . 8 8 7 . 1 7 8 . 7 9 1 . 0

1 1 2 . 8 9 3 . 5 8 8 . 3 8 7 . 0 9 9 . l 9 9 . ] 90 . 3 9 1 . 2 9 4 . 6 9 6 . 9 8 8 . 7 80 . 5 8 7 . 4 5 3 . 1 8 2 . 4 92 . 9

1 0 3 . 4 1 0 2 . 6

9 3 . 4 9 5 . 6 9 3 . 9 9 7 . 6 95 . 9

9 2 . 1 9 l . l 1 0 . 4

To t al T o t al Sal ini t y S i0

2 N p

- 1 - 1 � m g L ·=-------- �g L ---7

8 9 5 . 6 5 6 . 1 4 . 1 8 4 7 0 1 0 5 0 . 9 0 . 1 4 320 4 6 1 . 1 50 . 9 0 . 57 1 6 0 8 7 8 . 8 6 6 . 9 l . 9 0 2 8 0 6 5 1 . 3 3 . 4 2 2 7 0 l l 4 8 . 7 2 . 2 3 3 6 0 1 3

3 1 5 . 3 ..-:::. 0 . 1 0 4 5 0 2 5 1 2 6 . 8 - - -1 1 8 . 5 1 . 2 6 5 2 0 5 8 1 23 . 8 1 . 7 5 7 7 0 1 6 1 44 . 8 1 . 2 8 5 5 0 1 0 2 3 1 . 7 < 0 . 1 0 5 2 0 1 9

7 7 . l 2 89 . 3 0 . 1 1 3 30 2 8

7 4 . 5 1 . 1 8 2 6 0 5 2 4 1 . 5 0 . 5 9 2 9 0 2 5

40 . 2 0 . 48 1 0 0 8 4 6 . 9 0 . 6 5 2 0 0 9 6 4 . 2 < 0 . 1 0 6 8 . 5 < 0 . 1 0

1 9 1 . 6 1 1+0 . 0 1 44 . 3 9 6 6 . 7 1 9 . 8 4 25 . 2 0 . 1 2

9 8 . 7 0 . 6 2 3 2 5 1 1 1 85 . 4 l . 9 9 3 6 6 1 6 . 4 2 3 1 . 4 4 . 35 1 7 1 1 3 . 4

..... ..... 0'\

1 1 7

Lake Bantic was the only non-dystrophic coastal l ake from western

and south-west Tasmania, while Gibb s Lagoon was the most highly coloured

o f all , with its shallow waters being almo st black due to its g440 o f

2 5 3 m- 1 . The median v alue for this area was 1 2 . 6 {,'7 m- 1 . Some

temporal variat ion is app arent in Lake Garcia and especially Lake

Ashwood (Tab l e 4 . 2 ) .

Absorption sp ectra o f filtered water from a number o f King Island

l agoons , rang ing from the most dystrophic to the l east dystrophic , are

shown in Figure 4 . 4 . These v ividly reveal how l ight attenuation

increases , especially in the shorter waveleng ths , as g ilvin levels

rise , al though absorp tion of l onger wavelength l ight is also increased .

The scan for Dembys Lagoon (number 20) is comparable to that of

Sulphide Pool , the mos t dystrophic o f the Gordon River lakes (King

and Tyler , 1 9 82 a , Figure 2 6 ) .

4 . 3 . 3 Secchi Disc Depth

The few Secchi d i s c measurements for the l akes near Strahan

(Table 4 . 2 ) indicate how rapidly l ight is ext inguished with dep th in

the highly dys trophic waters o f some coastal l akes . Water transparency

was moderate in mesohumic Lakes Ashwood and Garcia , while the greatest

clarity was observed in Lake Bantic , where the Secchi disc was still

visable on the bottom , at 6 . 50 metres .

4 . 3 . 4 pH , Conductivity and Salinity

The l agoons o f the Bass S trait islands showed a considerable range

of pH values , al though most were close to or above neutral (Table 4 . 1 ) .

Sticks Lagoon was the only excep t ion on Fl inders I sland , while there

were six acidic lagoons on King Island , five o f which had salinities

of less than 3 7 5 mg L- 1 . The higher pH values o f o ther lagoons are

probably maintained by their higher sal inities , with concomitantly

higher concentrations of bicarbonate providing buffer ing even in the

presence o f considerable amounts o f yellow organic sub s t ances . Median

pH for the two island s was 7 . 30 .

In contrast , almo st all the lakes from western and south-west

Tasmania were acidic (Table 4 . 2 ) , with the lowest pH , 4 . 0 , being

recorded for Heron Pond , and in South S trahan and Freney Lagoons .

Only five had pH values greater than 6 . 0 , and three were above neutral .

The highest pH , 8 . 1 5 , was measured in Rebecca Lagoon . Median pH for the area was 4 . 60 .

F igure 4 . 4

V) ."!::! c:: :::1 c:: --

,.q--:.s ..... ·C:: ()) ..... u ..... -...... ()) 0 (,) c:: 0 ..... ..... 0. ).., 0 (J) ..0 <r:

1

118

5 0 0 5 5 0 600

Wave l e n gth ( nm) 7 5 0

Absorpt ion spectra of f iltered water from selected lagoons

on King Is land , relative to distilled water . Numbers refer to the

lagoons listed in Table 4 . 1 .

1 19

Comparisons of measurements o f p H made in situ in s ome

wes tern Tasmanian lagoons , and tho se made later on water samples in

the laborato ry , show only minor d if f erences , never more than 0 . 1 0 o f

a unit . The laboratory measurements are therefore considered an

accep table determination o f hydrogen ion concentration .

With the excep t ion of St icks Lagoon , the Flinders Island l ag o ons

were considerably more sal ine than those o f King I sland (Table 4 . 1 ) .

South Chain Lagoon was hypersaline while Logans Lagoon had a sal inity

close to that o f seawater . Using 3 g '· L- 1 as the division b etween

fresh and s al ine waters (Bayly and Williams , 1 966 ) , all the King

Island l agoons apart from Big Lake can be classified as fresh , whereas

Sticks Lagoon was the only fresh exampl e from Flinders I sland . Big

Lake i s subj ect to o ccasional incursions of seawater (Jennings , 1 95 7 ) ,

and the s al ine lagoons of Flinde r s Island are probably al so receiv ing

marine inflows . The median conductivity value for the Bass S trait

islands was 1 600 JA,S cm- 1 .

The conduct ivi1t ies of mos t o f the we'stern and south-west Tasmanian

coastal l agoons were low (Table 4 . 2 ) . This is notable considering that

most are within a kilometre f rom the sea , and all were fresh . Gibbs

Lagoon and Rebec c a Lagoon had the highes t conductivities , with K1 8 values o f 1 5 1 0 .M S cm-1 and 1 1 92 P, S cm- 1 respectively , while the mos t

dilute was Frensy Lagoon , where K1 3 was 92 p. S cm-1 .

Regression analysis showed that the salinities o f the l agoon water s

were closely rel ated to their c onductivities . The relationship

cal culated for the King and Flinders Island lagoons was : -

l og l O Salinity = 1 . 1 2 log1 oK1 3 - 0 . 5 7 5 (r2 = . 998 , n=2 4 , P <� 0 . 00 1 ) ,

while the regre s s ion equation f o r the western and south-west Tasmanian

coastal l agoons was : -

log 1 0 Salinity = 1 . 1 0 log1 0K1 3 - 0 . 52 9 (r2 = 0 . 9 1 4 , n=28 , P��J . 00 1 )

Logarithmic tran s formations were u sed t o correct for skewed data

distribut ions . These two equations appear to be very similar , and a

t-test o f their slopes showed no significant differences between them ,

at the 5 % l evel o f significance . However , a t-test o f their intercep t s

showed these to b e highly s ignif i c antly different (t ( 2 ) ( 4 9 ) = 34 . 00 ,

P..:::< O . OO l ) . A s imilar equation b etween salinity (in g L- 1 ) and

conduct ivity (at 25 °C) has been described for Australian salt lakes by

Williams ( 1 9 8 6 ) , while Buckney and Tyler ( 1 9 7 3a) found an approximately

linear relationship between conductivity and ionic concentration in

Tasmanian waters up to 300 mg L- 1 .

120

4 . 3 . 5 Maj or Ions Present

The concentrations of the seven maj or ions are given in Tables

4 . 1 (for the B a s s S trait islands ) and 4 . 2 (for western and south-wes t

Tasmania) . An e s t imate o f ionic imb alance , where total anions are

expressed as a per centage o f total cations , is also given . These

imbalances may be attributed to interference by gilvin in determinations

of calcium , and in p articular of sulphate , causing an underestimation

of this anion by the BaClz method used . Some changes may also have

occurred in b i c arbonate concentrat ions during transport . However , the

imbalances are usually not of sufficient magnitude to af fect inter­

pretations of these data .

Sodium was the dominant cation in all case s , with the cationic

order of dominance in almost all l agoons being Na+ > Mg2+ > Ca2+ > K+ .

Excep tions were No Duck Lagoon on Fl inders I s l and , Attrills Lagoon on

King Island , and Nye Bay and Paradise Lagoons from western Tasmania ,

all of which had elevated l evel s o f c al cium , their cationic orders

being Na+ > ca2+ > Mg2+ > K+ . Additionally , Lake Strahan on 9 November ,

1 984 had the c ationic order Na+ > Mg2+ > K+> c a2+ . Chloride was the

dominant anion in all lagoons . Twenty-two samples from western and

south-west Tasmania , and sixteen from the Bass S trait islands had the

anionic dominance o rder Cl- > SO�- > HCO; , while Cl- > HC03 > soz- was

the anionic order in all the remaining lagoons . Groundwater from near

Surprise Bay , King I sland , was d ominated by calcium and bicarbonate ,

but sodium s t i l l comprised one third of the total cations , and relative

proportions of chloride indicate a considerable marine influence still

present in its chemical composition .

The ionic compo s it ions of the Bass Strait island lagoons are shown

in the ternary d iagrams of Figure 4 . 5 , while tho se of wes tern and south­

west Tasmania are shown in Figure 4 . 6 .

4 . 3 . 6 Dissolved Iron and Silica

Iron was measured only in the samples from the Bass Strait islands

(Table 4 . 1 ) , and values were all low , as expect ed from oxygenated -1 waters . The g r eatest amount , 0 . 90 mg L , was found in S t icks Lagoon

on Flinders I s l and . The values are mos tly equal to or lower than those

reported by Buckney and Tyler ( 1 9 7 3a) for waters from King and Cape

Barren I slands . The three highest values in this study were all from

lagoons with l ow p H , but not all acidic lagoons had similar levels .

121

s o 2 -'\·---------------------H�C oJ-

. f 2<1

16 . ,., .

;•J . IE 2 � •'

�·

Figure 4 . 5 Ternary diagrams showing the ionic proportions of the

lagoon waters from K ing and Flinders Is lands , Bass S trait . Numbers

refer to lagoons l i sted in Table 4 . 1 . F = World Average Freshwater ,

s = seawater .

Ca"'l.""

Figure 4 . 6

16 14

s

sar Hco� �----------------------------�· 3

M :l+ g .

s

y cf

Ternary diagrams showing the ionic proportions of the

lagoon waters from western and south-west Tasmania . The ionic proportions

of most lagoons fall within the shaded areas . Others are indicated

by number , as listed in Table 4 . 2 . F = World Average Freshwater ,

s = s eawater .

122

Silica concentrat ions of the Bass S trait island ' s lagoons (Table

4 . 1 ) were likewise low , with princip>'l.l excep t ions being Sticks and

Sandy Lagoons o n Flinders I sl and , while Ridge Lagoon had the highest

levels o f the King Island waters . Even silica levels in the ground­

water were low . These data support those o f Buckney and Tyler ( 1 9 7 3a )

for King Island lagoons , but g ive n o indication o f the extent of

siliceous dunes in the lagoon ' s catchments .

Silica values from the western and south-west Tasmanian coastal

lagoons were mor e v ariable (Table 4 . 2 ) , ranging from less than 0 . 1 0

mg L-1 in Ocean Beach Lagoon ) Teal Pond , and the dune ponds near

New River Lago o n , to 4 . 1 8 mg L- 1 in Lake Mallana . However , Gibbs - 1 Lagoon fell well outside this rang e , with a value o f 1 9 . 8 mg L .

The median value for these waters was 0 . 62 mg L- 1 .

4 . 3 . 7 Nutrient Analyses

Total phosph�r�� l evel s of the Bass Strait Island lagoons were

mostly very high (Table 4 . 1 ) , and they can be describ ed as highly

eutrophic (OECD , 1 9 8 2 ) . The highest level s occurred in the King

Island l agoons , especially tho se from the southern end o f the island ,

where considerable amounts of phosp�lr�s were present , even in the

groundwater . The variation amongst the l agoons possibly reflects

different input s o f locally applied agricultural fer t ilizers i n

their catchment s , or from the decay of surrounding vegetation , rather

than direct geochemical influence . However even l agoons close together ,

such as the f iv e at the north-eastern end of King I sland , and which

are in a nature reserve , show wide variation in total pho sphOII"ll�>

levels . The s e l ocal v ariations cannot be expl ained .

The total phosphor'OAS. levels of the lagoons from western and south­

western Tasmania were much lower (Table 4 . 2 ) , due to the undisturbed

nature of the c atchments of mo st . However several are still

mesotrophic t o eutrophic (O . E . C . D . , 1 9 8 2 ) , with the highest value

58 p.,g L- 1 , being measured in Lake Strahan .

To t al nitrogen levels varied from 1 00 �g L- 1 in Freney Lagoon - 1 to 7 7 0 pg L in South Strahan Lagoon (Table 4 . 2 ) , with a median

of 325 p g L- l Based on Voll enweider ' s ( 1 9 7 1 ) criteria , these total

nitrogen data also indicate the l agoons to be mesotrophic to

eutrophic .

123

4 . 3 . 8 Pearson Correlation Analysis

P earson correl ation analys es were undertaken on the physico­

chemical paramet er s of the lagoons from the two study areas . Gibbs

Lagoon , in south-wes t Tasmania , was considered very atyp ical compared

to the remainder of lagoons from that area , and the resul t s from it

were therefore excluded from these analyses .

Several marked features are evident f�om these analyses . Firstly ,

strong p ositive correlations ( s ignificant at the 5% level ) were found

between conduct iv ity and all seven maj or ions , in the waters of both

study areas (Table 4 . 3 ) , resul t ing from increased concentrations of

solutes causing h igher conductivities . Concentrations of all seven

maj or ions increase in parallel , causing significant positive

correlat ions between mo st of them .

The second maj o r feature can be seen when the cations and anions

are cons idered as r elative proportions of total cat ions and anions ,

respectivel y . P o s i t ive correlations , s ignificant at the 5 % level or

greater , usuall y o c cur between ions indicat ive o f either marine (e . g .

sodium and chloride) or geochemical (e . g . cal cium , magnes ium ,

b icarbonate , and sulphate) origins (Gibbs , 1 9 7 0 ) (Table 4 . 3) . Likewise ,

strong negativ e correl ations exist between many of the marine and

geochemical ion s . Thes e correlations show that geochemical enrichment

took place in s ome o f the lagoons , decreasing the relative proport ions

of ions of marine origin in their waters . They al so show some

differences occurred in this enrichment between the lagoons of the two

study areas . C al cium and bicarbonate were the main ions responsible

for the geochemical enrichment o f lagoons from western and south-west

Tasmania , but magnesium and sulphate also contributed s ignificantly

in those from the Bass S trait islands .

The pH values of the coas tal lagoon waters of western and south­

west Tasmania were als o s ignificantly positively correlated with

conductiv ity , and with the concentrations of each of the maj or ions .

In comparison , correlations between pH and these p arameters (apart

from bicarbonate ) were not s ignificant in the Bass Strait island lagoon

waters . These dif f erences probably result from the ionic concentrations

of the lagoon waters of King and Flinders Islands being moderately

high , and are therefore already buffered , so that fur th er increases in

salinity have no further ef fect on pH, whereas the more dilute waters

of the western and s ou th-west Tasmanian lagoons are less well buffered

Table 4 . 3 : P ea r s o n c o r r e l a t i o n coe f f i c i e n t s ( r ) b e tween various p ar&�e t e r s me asured f r om the coas t al l ag o on wa t e r s o f King and Flind e r s I s l ands , and from we s t e r n and south-we s t Tasman ia . N S = Not s ignif i cant . * S i gn i f i c ant a t t h e 5 % l evel . ** Signif i cant a t the 1 % l ev e l . *** S i gnif i c ant at the 0 . 1 % l evel o r g r e a t e r .

PARAMETERS

+ K1 8 : Na K1 3 : K+ Kl s : ca 2+ K M 2+ 1 8 : , g K1 3 : C l

2-Kl 8 : S0 4 Ku �: : HCO] Na+ : K+ Na+ : ca2+ Na+ : Mg2+ N a+ : c l -

+ 2 -N a : S0 4 + -

Na : HC 0 3 K+ : c a 2+ K+ · �r 2+ • L g K+ : c l-T.-+- 2 -1\. ' : so 4 K+ : HCOJ ca2+ : Jvlg 2+ C a2+ : C l­C a2+ : SO�­Ca 2+ : HCOJ

BAS S STRAIT I S. S . W . TASHANIA PARAMETER BAS S STRAIT I S. S . W . TASMlu�IA PARAMETERS BAS S STRAIT I S. S . W . TASMANIA

. 9 8 9 * * *

. 9 9 8 >'<* *

. 8 9 0 ***

. 9 8 4 ***

. 9 9 7 ***

. 9 1 0 * * *

. 4 3 3 *

. 9 9 0 * * '''

. 8 3 3 * * *

. 9 84* * *

. 9 9 7 **'"

. 8 6 4 * * * . 4 2 4 * . 8 7 6 "'** . 9 8 5 >'<>'d:

. 9 9 6 * * *

. 9 1 7 """ *

. 42 4*

. 8 0 8* *'"

. 8 6 6 * '"*

. 8 9 2 '"* '"

. 3 1 1 N S

. 9 76 ***

. 9 1 0 ***

. 486 **

. 9 4 7 ***

. 9 7 8** *

. 9 1 4 ***

. 7 7 6 ** *

. 8 9 9 '''* *

. 4 9 8**

. 9 7 6 ***

. 9 6 J >'< >H

. 9 2 7 ***

. 8 45 ***

. 4 7 9 *

. 8 7\.l "'**

. 9 1 5 ***

. 8 7 7 ***

. 6 9 2 ***

. 4 1 1 *

. 4 3 7 *

. 4 2 0 *

. 4 6 3 *

F e : % C l Hg 2+ : Cl-

Hg 2+ : so l ­Mg 2+ : HCO] C l- : SO�-

- -C l : HC0 3 2- -so 4 : HC0 3 %Na+ : % C a 2+ %Na+ : %Mg 2+

. 4 0 9 *

. 9 84 **'"

. 8 8 9 *'""'

. 4 6 1 *

. 8 8 3 "'* *

. 4 2 0 *

. 3 7 0 N S - . 8 8 7 ''"''* - . 4 3 1 *

%Na+ : % C l- . 8 8 3 >'«'<>'< 2 -%Na+ : % S04 - . 7 2 6 *>'d<

+ -%Na : %HC0 3 - . 7 9 1 *** % C a 2+ : %Mg 2+ - . 0 2 2 NS % C a 2+ : %C l- - . 8 1 9 *** %Ca 2+ : % S O�- . 7 7 6 *** %Ca 2+ : %Hco; . 6 6 3 ***

? + 2-%Mg- : % S 0 4 . 0 9 1 N S %Mg2+ : %HCO; . 4 3 5 *

- 2-% C l : % S0 4 - . 7 9 9 *** % C l - : %Hco; - . 9 1 1 *** % SO �- : %HCO� . 4 8 1 * p H : K1 3 . 3 1 1 NS p H : Na+ . 2 8 2 N S

No t measured . 9 2 1 * * * . 8 3 2 *** . 9 0 8 * ** . 9 1 4 * * *

. 6 9 3* * *

. 7 7 7 '"'**

- . 8 4 4 * * * - . 0 0 8 NS

. 5 5 1 *'" - . 1 9 6 N S - . 5 6 7 '" '" - . 5 0 7 '""' - . 3 6 3 NS - . 0 5 9 N S

. 5 L 7 '" '''

. 4 20 "'

. 0 34 N S - . 6 4 1 * * * - . 8 1 2 * * *

. 0 7 3 N S

. 6 3 8 >'" '' *

. 6 7 6 ''""'"'

Fe : %HCO'J + p H : K

p H : Ca2+ p H : Mg2+ p H : C l

2-pH: s o 4 p H : HCOJ p H : %Na + p H : %K+

- . 4 0 4*

. 2 9 0 N S

. 2 8 8 N S . 3 1 3 NS . 2 9 1 N S . 25 7 N S . 8 1 1 * * *

- . 3 7 0 N S - . 4 1 0 *

N o t measured . 6 7 0 ***

. 7 6 9 * * *

. 662 >'<**

. 5 8 9 **

. 6 5 2 * * *

. 7 0 0* * * - . 5 9 7 ** - . 2 7 3 NS

p H : %Ca 2+ . 3 7 8 N S . 5 7 8 ** p H : % C l- - . 5 2 0* * - . 7 6 4***

2-p H : % S 0 4 . 4 6 9 * . 1 34 NS p H : %Hco; . 4 3 7 * . 8 9 1 ***

K1 8 : %K+ - . 2 1 4 N S - . 3 9 9 *

K 1 8 : % C l- . 1 7 3 N S - . 5 2 2 ** K1 3 : % HC0 3 - . 3 6 0 NS . 60 7 *** p H : g4 4 0 - . 7 0 8* * * - . 4 8 1 *

2+ g4 4 0 : Ca - . 4 1 2 * - . 1 7 6 N S g4 4 0 : Hco; - . 5 6 9 * * - . 2 50 N s p H : Fe - . 5 4 0 * * No t measured

2-S i0 2 : S0 4 . 3 1 5 N S - . 4 6 1 *

g4 4 0 : To t al N N o t measured . 8 1 1 * ** Tn : To t al P . 5 2 0 * * No t me asured

.... "" ol:o

125

and therefore pH may rise as concentrations o f solutes , in particular

alkaline earth b icarbonates , increase .

Other s ignificant correlations o f note l i sted in Table 4 . 3

include tho s e between total pho sphorus and turb idity , g440 and t o t al

nitrogen , p H and iron , and pH and g 440 · Phosphorus may be absorbed

onto the sur f ace o f tripton particles , and in some cases turbidity

may result from organic matt er in the water , so that phosphorus and

turbidity both increase together . A s imilar s ignificant positive

correl ation was found between total phosphate and turbidity in New

South Wales inland freshwaters (Chapter Three) , as was one be·tween

g4 40 and total nitrogen . This was considered due to nitrogen comp r is ing

up to 5% of the elemental composit ion of dissolved humic sub s t ances

(Schnitzer , 1 9 7 8 ) . The s ignificant negative correlation between p H

and iron may b e due t o iron being more solu ble in acidic water s .

Signif ican t negative correlations were found between water colour

(= g 440) and pH in the waters of both study areas , as acidic dis solved

organic substances depress pH . S imilar negative correlations were

found for the dune l akes of south-eas t Queensland ( Chapter Three) , and

have been documented for coastal dune lakes elsewhere (Bayly , 1 9 6 4 ;

Bayly � al , 1 9 7 5 ; Timms , 1 982 ) . Regres sion analysis showed the

following r elat ionship s between pH and g440 in the three areas o f

this s tudy : -

Equation 1 ) . Wes tern and south-west Tasmanian coastal l agoons .

g4 40 = 45 . 5 - 5 . 65 pH (r2 = 0 . 232 , n = 24)

Equation 2 ) . King and Flinders I sland co astal l agoons .

g 440 = 7 2 . 4 - 8 . 66 pH (r2 = 0 . 5 0 1 , n = 24)

Equat ion 3 ) . S outh-east Queensland freshwater coas tal dune l ake s .

g440 = 2 3 . 4 - 3 . 64 pH (r2 = 0 . 27 4 , n = 26)

t-tests shows no significant dif ferences between the slopes of

Equation 1 ) and 2 ) ; or between Equation 1 ) and 3) , but the slopes of

the regres sion equations for the Bass S trait island lagoons (Equation

2) and the south-east Queensland l akes (Equation 3) were s ignificantly

different ( t ( 2 ) ( 46 ) = 2 . 0 7 ; 0 . 05 < P < 0 . 02 ) . However , additional

t-tests of the intercepts of Equations 1 ) and 2 ) , ( t ( 2 ) (45) 3 . 1 0 ;

0 . 0 1 P 0 . 00 1 ) , and Equation 1 ) and 3 ) ( t ( 2 ) ( 4 7 ) = 8 . 96 ; P 0 . 00 1 )

were highly significant . Thus , although significantly correlated , the

responses of pH to changes in g440 are suff ic iently different in all

three areas , due probably to differences in ionic concentrations

causing different buffering effec t s .

1 2 6

Principal Co-ordinates Analyses of the Lagoons from the Bas s S trait I s l ands

Many King Isl and l agoons are in clo s e proximity to each o ther , b u t

despite this show cons iderab le dif ferenc es in their phys iochemical

properties . A principal co-ordinates analysis ( Gowe r , 1 9 6 6 ) was used to

display this variab il i ty , and also diff erenc es b etween lagoons from b o th

King and Flinders Islands .

An ordination showin g the dis tribut ion o f l agoons in the spac e

defined by the f i r s t two coordinate axes is shown in F igure 4 . 7 , and the

pr incipal component loadings f or the paramet ers used are g iven in Tab l e

4 . 4 . Al though mo s t parameters contributed , the f ir s t coordinate axis

reflects increas ing g eochemical influences and changing pH, iron con c en­

tration , turbidit y , and water co louration, while the second coordinate

axi s mainly descr ibes variability due to conductivity , silica , total

phosphorus , and the two opt ical parameters .

Although the ordination revealed a continuous variation spread over

both axes , some groupings of the lagoons are apparen t . It effectively

s eparates the F l i nders Is land from the King Island lag oons , on the s econd

coordinate axis , although Sticks Lagoon ( No . 1) is also separated from

the o ther f ive F linders Is land lagoons , due to its low pH and condu c t ivity ,

and higher iron , total phosphorous , percent sodium, and percent chloride .

For the King Isl and s amp l es , the highly coloured or turb id lagoons with

high levels o f t otal phos phorus form one dis t in c t group ing , whil e the

less coloured and turbid waters with some g eo chemical enrichment formed

a s econd group . A third group , also with lower colour and turb idity , but

with higher prop ortions of ions of marine origin , lies between them.

Pearshape Lagoon (No . 15) was s eparated from all groups due to its h igh

total phosphorous l evel s , and the groundwater sampl e (No . 24) was also

divided from the King Island lagoons by the dominance of alkaline ear th

b icarbonat es in i t . However , this ordination reveal s only 56% of the

total variab il i t y among s t the samples ( Tab le 4 . 4) .

Phytoplankton Pre s en t in the Coas tal Lagoons of Wes tern and South-wes t Tasmania

Net phytoplankton were collected from eighteen of these lagoons

during January and F eb ruary , 19 8 7 (Tab le 4 o 5 ) . Mo s t of the algae have

b een identifi ed only to the genus level v

Botryococcus braunii Ktltzing was the mos t widely dis trib uted taxon ,

Table 4 . 4 :

Parameter

Turbidity

g440 p H

K1 8 Fe

Si02 Total p

%Na +

% K+

% c}+

% Mg2+

% Cl 2-% so4

% Reo;

Cumulative % variation

127

P r incipal component loadings for coordinate axes one and two

F ir s t coordinate axis Second coordinate

0 . 1 6 0 . 25

0 . 22 0 . 35

-0 . 3 1 -0 . 24

0 . 02 -0 . 50

0 . 2 3 -0 . 03

0 . 1 0 -0 . 26

0 . 1 0 0 . 36

0 . 38 -0 . 20

0 . 1 7 0 . 20

-0 . 36 0 . 00

-0 . 1 4 0 . 38

0 . 4 1 -0 . 1 1

-0 . 35 -0 . 1 1

-0 . 36 0 . 24

o f

exp lained 3 7 . 5 2 55 . 82

axis

(!)

-\_) 1-0 0 0

0 ll IJ,)

2

0

(/) -2

K i n g I s l a n d

F l i n d e rs I s l a n d

128

H, g e o c h e m i c a l i n f l u e n c e i n c re a s i n g

O p t i c a l p a ra m e t e rs , F e i n c r e a s i

- 4

- - - - - �- - - - - - -

0 F i rst c o o r d i n at e a x i s

/ ./

./

I J

4

!

(') 0 ::J CL r.: 0 ���

:S . ... -:·

:< w '

(/) 0

1--.l

::J 0 ..., <t> QJ Vl ::J (Q

Figure 4 . 7 Ordinati on , by principal coordinates analys is , showing

0 u ,...,. 0 OJ

u ru -... OJ 3 m r+ (1) ""'i (.;) .-;. (.) r> t·l

-a

c� 7': +

?ft. :;:

(Q N +

?ft. I () 0

w I

:J 0 ..., (!) OJ Vl :::1 (Q

pos itions of the lagoons from King and Flinders Islands , Bass Strait ,

in the space defined by the f ir s t two coordinate axes . Numbers refer

to the lagoons listed in Table 4 . 1 . Dotted l ine emphas izes the separation

of the two is lands , while the so lid l ines emphas ize divis ions within

the is lands .

l l '1

occurring in fourt een of the lagoons o Desmids were also very common and

widespread , especially a b iradiate spec ies o f Staurastrum , which is

probably an undescrib ed species ( P a A o Tyler , pers o c ommo ) o Several o ther

species of Staurastrum wer e also present , while Closterium spp o ,

Cosmarium spp a , Staurodesmus s pp o , and Xanthidium sp a were o ther

commonly occurrin g desmids o O ther green algae which o ccurred frequently

included a colonial , cocco id green alga of the sphaerocystis typ e , and

Asterococcus superhus ( Cienk) S cherf o

Taxa from o th er phycological divisions wer e also common, in particular

various spec ies o f Ma l lomonas ( Ghrys ophyceae) , which were present in

elev en of the lakes . The thr ee mo s t frequen tly encountered s pecies were

M. sp lendens ( G . S . Wes t ) Play f air , M. tasmanica ( Groome & Tyl er) Asmund

& Kri s t iansen , and M. morrisonensis Croome & Tyler. Species o f Peridinium

( D in ophyceae) wer e pr esen t in eleven lagoons , while various pennat e and

centr ic diatoms (Bacillariophyceae) occurred in fifteen . These included

Me losira granulata ( Ehrenb erg) Ralf s . , Pinularia s p . , Cymbe l la s p . , Navicula

spp . , F.rus tu Ua rhomboides ( Ehrenberg) Di Ton i , while Asterione Ua formosa

Has s . was present in Gibb s Lago on . Euglenoids were also present in some

o f the lagoons , b ut cyanobac teria were rarely encoun tered .

A numb er o f s pecies o f freshwater flagella tes appear to be conf ined

almo s t ent irely t o these coas t al lake environments ( Groome and Tyler ,

19 8 7 a ; Groome et a l . , 19 87 ; Groome et a l . , in press ; Ling et a l o , in

pres s ) o The s e include the d inoflagellates Thecadiniopsis tasmanica

Groome , Hallegraef f , and Tyler , present in eight o f the lagoons ( see

Tab l e 4 a 5 ) , and Prorocentrum p layfairi Groome and Tyler , found in s ix of

the s tudy s ites ; and a newly des crib ed chryso phyte , Dynobryon unguentari­

forme Groome , Ling , and Tyler , wh ich o ccurred in Freney and Miller Lagoons o

The greates t range o f phy toplankton o ccurred in Mul cahy Bay Lagoon ,

while Lake Ban t i c and Freney , Mi ller , and B ig Lagoons also had

cons iderab le numb ers of dif f eren t taxa o In comparison , Lake Mallana ,

Gibbs Lagoon , and Heron and Teal Ponds were depauperate in phy toplankton ,

and a virtually monos pecific b loom o f Ma l lomonas tasmanica was present

in Lake Koonya o However , s ome species , especially nanoplankton and

picoplankton , may have been mis s ed by the sampling method used. The

contrib ution of these algae to community diver sity and abundance is

unknown a

(") ::r 0 a '0 f . (I)

(11 c:: (0 � -::l "' "£. «: () o--ro -· Ql ::l (I) 0

'0 ::r '<! () (I) (") Ql ::r ro -

� (f) 0 '0 ::r '<! () (I) "' -ro

� . s-:::!. 0 '0 ::r '<! () � (j <ll

-.:: -llJ ::l 0 '0 ::r

� ro

� � :;; :: ; � ; ;:: � S 'D m --._j 0'\ ln .P.. w N Lake No.

� � � � � � z � � � � o � � � � � r l-'• !-'· t-l· 1'1 c.- ;::: �< G r;. o w n ;:J ,....... >ll Ai t� w / � � � ro " � o � � = � ro � n � � � �

� � c � n � c n ro � n n ro ro ro ro t""i w OJ ro o... � o:: ;:; ;r ::J r Ill " '< r'· :::" � "U U) ?' CJ > G� "' :.<:

/ � � m � � c � "' n "' c m ill � � O PJ r-' L' ffi ;:J O rt ri iJ O ::;,;::; ;::r' H ::l f--' f""'1 0 0Q \ll W t.:d r' C... :: t"i P.) P.l ;::l G :E! n rt r-- :I> � g og o;j � � ; � s. g ; � � g �· h· 5 c :_:j 0 0 OQ 0 Cl ::l r"• 0.. � l ' l

;:I '?0 L"' (JQ ro 0 CJ. 0 , 0 G� 0 ;: 0 ;:l c-<

c c g ; g c E;' � / s � > � ro S >

X Eudor·ina e legans Ehrenber� X PancloPina morwn (HUller) Bury

X " >< >< " Asterococcus 81-tperbus ( C lenk . ) Sche r f . X X X " X )( X X c f . SphaeY'Ocys t·iB X X Ankis trodesmus f'a lea t wJ ( C o r d a ) R a lf s .

)( " X OocysHs sp .

X >< X >< X X >'= X X >< X X X X Botr•yococcus brauni1: Kll t z i.ng

X Dictyosp haer1:um sp .

" Actinastrwn lumtzschi·i Lagerhelm

X Coe lastrum sp .

" )( " Pec/·iac ·trum dup lex Heyen

X )( "' X X Unknown F i l amen t o u s g reen a l g a

>< Unid e n t i f i ed S a c c o d e rm d e smid

X " Spir•ogyra sp .

X >< >< >< X )( " "' Clos terium spp .

)( X X X X X .x . Cosmariwn spp .

X X " Euastrwn spp .

X X X X Microsterias s p p .

)( X )( >< P l e urotaenium s p .

)( F i l amentous d e smid (Sphaer•ozosma ? )

)( X X X X X X X X X Staur·astrum s p p .

)( )( X X X X Stauroc/esmus s p p .

X X Triploceros graci le B a i l e y

X X " " X X " Xan thic/iwn sp .

X X " X " )( )( Euglena sp .

" Tr•ach lemonas vo lvacina Ehrenb e r g

>< X >< " X >< Pror>oaentrum p layj'a·iri Croome & Tyler

X >< X X " )( >< >< >< >< X Peric/iniwn spp .

Thecadiniopsis tr•asmanica Croome , " )( ,. X >< >< " " H a l l e grae f f & T y l e r

X " X >< >< Dynobr·yon spp .

" " >< " " " " >< >< >< >< Ma l lomonas spp .

X Synura sp .

" X " " " " X Me los·ira granulata ( Ehrenb e r g ) Ralf s .

>< X ,. >< " " >< C e n t r ic d i a toms ( u n i d e n t i f i e d )

>< Asterione l la formosa Has s .

>< Frustu lia rhomboides (Ehrenb e r g ) D i Toni

x · x X >< X X X >< X X Pennate d i a toms ( un i d en t i f ied)

>< >< Merismopec/ia sp . " X X Osci l la to1•ia sp .

X >< X Anabaena sp .

OCl

� .,. I= Ill :-. ' 1,9 ..

Ill "" ::; ::r' r:L � ri" m o 0 '0 c ,... rt Ill ::r ::: I �

� rt ro o (f) ::l ri" '0 ;-3 " {ll " m "' 3 ro Ill ::l ::; rt >'· Ill ..,. • ::l

CT >u ::r' 1--t ro ro m n ro o ::; Ill (') 'Jl ro n-'" 0 c � "'" � rJ uo

>'· 0 (/J 0 ::l >'· Ul ::; r:L O >'· H1 n Ill .: n- ro ro U'J r:L ri" ro

" ::;

4 o 4 D ISCUSSION

I ?I I

4 o 4 o 1 The Phys io chemical Properties of the Coastal Lagoons

The coas tal l akes and lagoons of the Bass S trait islands and

wes tern and south-west Tasmania are typically non-turb id and dys trophic .

Al though turb id waters are commonplace on the Aus tralian mainland

(Kirk , 19 85 ) , they are unus ual in Tasmania (Chapter Three) , and suspended

par ticulate mat ter would be of importance limnologically in only three

King Island lagoons o In contras t , al though highly coloured coastal

dune lakes have b een r eported from elsewhere in Aus tral i a , (Bayly ,

19 6 4 ; T imms , 19 7 3 , 19 82 , 1 9 8 6b ) , the results of this s tudy ( and o f

Brand , 196 7 ; and Buckney and Tyler , 19 7 3a ) indicate that some lagoons

from the two s tudy areas rank amongst the mos t highly coloured natural

wat ers yet recorded o Their gilvin concen trations are considerab l y

greater than thos e o f coas tal dune lakes from south-ea s t Queensland and

nor th-eas t New S outh Wales ( Ch ap ter Three) , and also exceed tho s e o f

the polyhumic fores t lakes common t o F inland ( Arvo l a , 19 8 3 ; Jones and

Arvo la , 1984 ; Salonen , 19 84) o

The h igh h umic content o f many of these lagoon waters caus es

the rapid attenuation o f solar radiation o Al though it was not pos s ib le

to measure their underwat er ligh.t climates , the s e can be estimated

us ing the procedur es developed in Chapter Three" With turb idity so

low, meas urements o f gilvin alone may b e us ed to calculate the expected

mean downwellin g v ertical attenuation coefficients , Kd( av)

' for thes e

waters o The leas t coloured o f the lagoons , Lake B an tic , would have a

Kd ( av) value o f approximately O o 33 m- 1 , and an underwater spectral

dis tribution of the ligh t s imilar to that of Great Lake ( s ee Chap ter

Three) , wi th the 'ivavelengths of maximum transmi s s ion centred around

5 7 0 to 580 nmu Mes ohumic Rebecca and Penny Lagoons would have Kd( av)

- 1 values o f about l u 50 m , whil e the higher g o f Hibb s and Granite 4 4 0 Lagoons woul d give them Kd

( av) values of about 2 . 40 m

- 1 , and under�ater

spectral dis t r ib utions like tha t of Lake Pedder (nova) ( see Chapter

Three) , where only predominant ly red ligh t ,

132

centred around 6 80 nm , remains . The polyhumic waters o f this study

would have underwater spectral distribut ions akin to that of Lake

Chisholm , with l i ght of 7 00 to 7 1 0 nm being transmit ted best . Examp les

of Kd (av ) values for some would b e 4 . 04 m- 1 for Dembys Lagoon , 4 . 6 7 m- 1

for Teal Pond , 5 . 60 m- 1 for Heron Pond , and 5 . 95 m- 1 for South S trahan

Lagoon . Should t he relationship between ln Kd (av ) and ln g440

(Equation 4 , Tabl e 3 . 3 o f Chapter Three) remain l inear up to the g440

value o f 2 5 3 . 33 m- 1 r ecorded for Gibbs Lagoon , this would give it a

Kd (av) o f 1 3 . 42 m- 1 . The attenuation of light in the maj ority of these

coastal lakes and lagoons is considerably greater than that measured

in s imilar lakes from south-east Queensland (Chap ter Three) . However ,

the attenuation c alculated for extremely dys trophic Gibbs Lagoon is

still much less t han that measured in extremely turbid Yarrie Lake in

New South Wales ( Chapter Three) , sugges t ing that high levels of

turbidity may have a greater effect on light attenuation than high

concentrations o f humic sub stances .

Summer thermal measurements made on a few lagoons from western

Tasmania showed only one , Lake Garcia , develop ed definite thermal

strat ification . Although the remainder d isp layed steep thermal

gradients , high levels of oxygen in their bottom water s show this

would be trans i t o ry , and polymixis would be normal , due to their

shallowness and exposure to considerab le amounts of wind . Coastal

lakes from northern New South Wales (Timms , 1 9 69) , Fraser Island ,

Queens land (Miller � al , 1 9 7 6 ; Bayly et al , 1 975 ; Arthington � �.

1 9 86) , and from Georgia , U . S . A . ( Stoneburner and Smock, 1 97 9 ) have

al so been shown to b e predominantly polymic t ic .

The s teep t hermal gradients would result from the high humic

contents o f the s e lagoons . Light is absorbed by gilvin and converted

to heat energy c lose to the surface , warming these waters considerably , ()(Ji, Vi f >

while the bot tom waters remain cold . 7his h especially hot ,

sunny day s , but the stratification would probably diminish as the

lagoons cool at night , and they would circulate comp letely during

intervening p eriods o f dull , windy , and p o s s ibly wet weather . Such

thermal patterns would be similar to the daily regime of s tratificat ion

and circulation shown by Northern Territory billabongs (Walker , 1 9 84) .

In c omparison t o the highly dystrophic lakes , Lake Bantic showed no

signs o f a thermal gradient , as its transparent wat ers allow light

to penetrate right to its bottom , thus creating an even distribution

of heat energy throughout its entire dep th .

133

However , t hermal s tratification may o ccur if lakes are sufficient ly

well sheltered f rom wind action , and this would probab ly account for

the warm monomictic nature o f Lake Garcia , and the almos t comp lete

dep letion of o xy gen in the bottom waters of Little Bellinger Lake .

Both are surrounded by forests and hills . Similar stratif ication

o ccurs in Brown Lake , North Stradbroke Island (Bensink and Burton ,

1 9 75) , and Hidden Lake , Fraser I sland (Longmore et al , 1 98 3 ;

Torgerson and L ongmore , 1 984 ) . The importance o f shelter allowing

stable thermal s tratification is further illustrated by the studies

reported in Chap ter Five .

Dissolved humic substances may also contribute considerab ly to

the acidif ication o f ��i�If��'�h,:aters (Glover and Webb , 1 9 7 9 ; Henricksen

and Seip , 1 9 80) . This �was p articularily so in the lagoon wat er s of

s outh-west and western Tasmania , where salinitie s were low enough to

prevent buffering . pH values here were typ ical of tho se from the

d ilute coas tal l akes of north-east New South Wales and of Queens land

(Chap ter Three ; and Bayly , 1 964 ; Bayly � al , 1 9 7 5 ; Bayly and Williams ,

1 97 2 ; Bensink and Burton , 1 97 5 ; Timms , 1 96 9 , 1 982 , 1 98 6b ; Bensink ,

1 9 7 6 ; Arthington and Wat son , 1 982) . However , tho se o f King and

Flinders I s land s were higher , and more s imilar t o the pH ' s reported

for some of the more saline Australian coastal lakes (Bayly and

Williams , 1 96 6 ; Timms , 1 97 3 , 1 9 7 7b ; Williams and Buckney , 1 9 7 6 ;

Congdon and McComb , 1 9 7 5 ; Gordon e t a l , 1 9 8 1 ) .

The water chemistry of the lagoons from western and south-west

Tasmania fo llows the same pattern found ( Buckney and Tyler , 1 9 7 3a ,b )

for mos t other inland waters of the area . Although dilute , they are

generally less so than many coastal lakes from eastern Aus tralia ,

such as tho se f rom Fraser I sland (Bayly , 1 96 4 - see also Chap ter Three) ,

or northern New South Wales (Timms , 1 969 , 1 982 , 1 9 86a) . In

comparison , the lagoons from the Bass Strait islands had considerably

higher sal inities . These too were more saline than nearby coastal

lagoons in east ern and western Victoria (Timms , 1 9 7 3 , 1 9 7 7b ) , but

had salinities s imilar to some from the eastern and north-east coasts

of Tasmania (Buckney and Tyler , 1 97 3a , 1 9 7 6 ; Groome and Tyler , 1 987a)

and south-wes t Wes tern Australia (Gordon et al , 1 9 8 1 ; Newman and Hart ,

1 984 ; Congdon and McComb , 1 97 6 ) . These higher salinit ies may be

explained by the high westerly wind regime exper ienced by the west

and south-west coast s of Tasmania , and the Bass Strait islands

depositing greater amounts of cyclic salts within their lagoon

134

catchments . This would be coup led with annual evap oration exceeding

p recip itation on the Bas s S trait islands (Buckney and Tyler , 1 9 7 6 ) ,

which would increase the salinities o f their lagoons still f ur ther .

However , even in the mos t saline lagoons of Flinders Island ,

evaporative concentration is still insuf ficient to produce the

salinities typical of many coastal lakes of South Australia (Bayly ,

1 9 70 ; Bayly and Williams , 1 966 ; Williams and Buckney , 1 97 6) , or o f

Rottnest I sland (Edward , 1 98 3 , Bunn and Edward , 1 9 84) .

The Na+ > Mg2+

> Ca2+ > K+p attern of cationic dominance typ ical

o f the lagoons from the two areas of this s tudy , is also common in

many Australian coastal lakes (Bayly , 1 964 ; Bayly and Williams , 1 966 ,

1 97 2 ; Timms , 1 96 9 , 1 97 3 , 1 982 , 1 986b ; � Hilliams and Buckney , 1 9 7 6 ;

Congdon and McComb , 1 97 6 ) , excep t ions being in s ome from western

Victoria (Timms , 1 97 7 ) and Cape York (Timms , 1 98 6b ) , and in some

calcium dominated lagoons in northern New South Wales (Timms , 1 982) .

Buckney and Tyler ( 1 97 3a , 1 97 6 ) reported several lagoons from King

and Cap e Barren islands where Na+ > Ca2+

> Mg2+ > K; and one ,

Pear shape Lagoon , where calcium was the dominant cation . This

contras t s with the results from this lagoon from this study , where

calcium was third in order of cations . The differences may be temporal ,

dep ending on sampling t ime , or resulting from the dry summer prior to

samp ling for this s tudy . The chemistry o f the lagoons near S trahan

was s imilar to that reported previously (King and Civil Investigat ion

D ivision , Hydro-Electric Commission , 1 97 8b) for three of them .

The Cl 2-

> so4 > HCO; order of anionic dominance is also

predominant in coastal lake waters elsewhere in Australia , although 2-the Cl > Hco3 > so4 order occurs frequently too (Bayly , 1 964 ;

Bayly and Williams , 1 96 6 , 1 972 ; Timms 1 9 7 3 , 1 97 7 , 1 982 , 1 98 6b ;

Williams and Buckney , 1 97 6 ) , and both anionic orders have been

r eported previously from lagoon waters from the Bass S trait is lands

and other coas t al areas of Tasmania (Buckney and Tyler , 1 97 3a , 1 97 6 ;

King and C ivil Investigation Division , Hydro-Electric Commission ,

1 977b) . However , b icarbonate dominated coastal lake waters occur

in western Victoria , east G ippsland , and northern New South Wales

(Timms , 1 97 3 , 1 97 7b , 1 9 82 ) .

Although the chemistry of the lagoons was dominated by ions of

o ceanic origin (Gibb s , 1 97 0 ) , most showed at least slight enrichment

with calcium , magnesium , and bicarbonate , in p articular No Duck

Lagoon on Flinders Island ; Woodlands , P ioneer , Attrills and Sullivans

1 3 5

Lagoons and Lake F lanigan on King Island , and Reb ecca , Hib b s , Nye

Bay , and Paradis e Lagoons from wes tern Tasmaniao The groundwater s ample

f rom King Island showed th e closest aff inity to a World Average Fresh­

water type ioni c dis tribution o Such enr ichment was due to lo caliz e d

variations resul t in g f rom the nature o f the surrounding dune mat erial .

Brand ( 19 6 7 ) f ound elevated l evels o f calcium in King Island lakes

surrounded by calc areous dunes o

Silica values were mos tly too low to reveal any connect ion b e tween

siliceous dunes and water chemis try . Concentrations o f the s ou th-we s t

and wes tern Tasmanian lagoons were mos tly higher than thos e o f the

Bass S trait islands , and also exceeded tho s e of the. F ras er Is land lakes

(Little and Rob e r ts , 19 83 ) , although s ilica concentrations of lak e waters

from the Co oloo l a Sand Mas s were greater (Reeve et a Z o , 19 85 ) o Low silica

concentrations are c onsidered indicat ive o f short res idence times for

the waters of co as tal dune l akes , while high s ilica contents indicate

equilib rium with the surrounding s il iceous dunes (Little and Rob erts ,

19 83 ) 0

Ordination p rocedures appear to b e rarely used in phys io ch emical

l imnology , Es t rada ( 19 7 5) success fully characterized differences between

Spanish res ervo irs using principal components analys is , while Ilmavirta

et a l o , ( 19 84 ) w ere ab le to div ide Finnish lakes into eigh t groups b ased

on their physio chemical properties , using the s ame methodo Diff erences

b etween lake waters and thos e of various creek catchment b as ins on

Fraser Island h ave also b een h ighligh ted (Little and Rob erts , 19 83 ) using

canonical variates and dis criminant analysis o In thi s s tudy , a principal

coordinates analysis revealed limnologi cal diff erences b e twen wat ers of

the Bas s S tra i t Islands o w�e ther this is mat ched by a b io ti c dissimilarity

is unknowno

4 . 4 . 2

1 3 6

The Phytoplankton o f the Lakes of Wes tern and South-wes t Tasmani a

Al though only a b rief examination o f the phytoplankton o f these

coas tal lagoons , the resul ts indicate that desmids cons titute th e maj o ri ty

o f the green algal taxa pres en t , and apart from the diatoms and the f ew

cyanob acteria , al l the non-ch lorophyte algae pr es en t were flagella t es o

However , the results o f this s tudy are those for s ingle samp les only ,

ob tained about mid-summer , and different algal t axa may wel l b e pr e s en t

at o ther times o f the year . No additional data are availab le to de termine

if the composition of the phytoplankton communities o f the s e waters

changes s easonally o

Flagellates are cons idered to b e at an ecolo gical advantage in

humic acid waters ( Ilmavirta , 19 84) , and tho se o f the D ivis ions Chryso­

phyceae and Cry p tophyceae have b een found to dominate the phyt op lankton

communities of Finnish polyhumic lakes ( Ilmavirta , 19 84 ; Ilmavirta e t

a Z o , 1984) . Many dys trophic Tasmanian lakes , especially f rom coas tal

areas , al so contain r ich collections of phytoflagellates , especially

chromophytes (Croome and Tyle r , 19 8 7b ) . Likewis e , dilute acidic waters

with low calcium and magnes ium concentrations are also cons idered a

typical hab itat for desmids (Lee , 19 80 ) , However , the data f rom this

survey are insufficient to conclude whether these ecological factors

have any influence on the phytoplankton pres ent in these wes tern and

s ou th-wes t Tasmanian coas tal lakes .

Freshwater acidic coas tal dune lakes along the entire eas t Aus tralian

seaboard have a homogeneity in their fauna, with many species virtually

res tricted to such hab itats (Arthington , 19 7 7 ; Timms , 19 86b ) o Recently

new species of phytoflagell ates , including some o f great rar i ty , have

b een des crib ed from humic , acidic Tasmanian coas tal lagoons whi ch o ccur

predominantly within this type of hab i tat (Croome and Tyler , 19 8 7 a , b ;

Croome et a Z o , 1 9 8 7 ; Croome et a l , , in pres s ) o Some were ob s erved in

this s tudy ( Se c t ion 4 o 3 . 10) . One , the dinoflagellate Proroc en trum

p Zayfairi , was r epor ted from the Sydney area ( as Exuviae l Za lima ( Ehr o )

S chutt . ) by Play fair ( 19 19 ) , and has been found in freshwat e r coas tal

dune lakes in north-eas t New South Wales (Chap ter Three) o Ano the r , the

chrysophyte Dynooryon unguentariforme , has been f ound in some Mor e ton

and Fras er Is land lakes and swamps (Croome et a l o , in press ) o The wide

dis tribution o f thes e two phy toplankters , and of the copepod Ca Zomoecia

tasmanica ( Smith ) , which is als o pres ent in wos t coas tal lagoons , s.uggests

that the freshw a ter coas tal lakes and lagoons o f western and south-wes t

Tasmania dis play s trong limno logical affinities with tho se f rom o ther

parts of eas tern Aus tr al i a .

4 . 5 CONCLUSIONS

1 3 7

The study shows tha t the water chemi s try o f the lagoons from

wes tern and south-w e s t Tasmania , and from the Bass S trait islands , is

s imilar to that shown by the maj ority of f reshwater coas tal dune lakes

o f th e eas tern Aus t r al ian s eabo ar d (e . g . B ayly , 19 6 4 ; Bensink and

Burton , 19 75 ; Timms , 1 9 6 9 , 19 8 2 , 1 9 86 a , b ) , a l though their s al inities ,

and in particular tho s e of King I s land , are s omewha t higher . Some

Flinders Island l agoons are saline , and resemb l e coas t al salt lakes

from South Aus tral i a and Wes tern Aus tralia ins tead. While some local ised

enr i chment with alkaline earth b ic arbonates o c cur in those located in

calc arious dunes , the maritime inf luences on the s t udy areas are

particularly stron g , and ions of o ceanic origin (Gibb s , 1 9 70 ) dominate

the water chemi s try . Many of the lagoons were h i gh ly dys trophic , far

more so than their mainlan d Aus tralian coun terp a rts (Bayly , 19 6 4 ; Timms

1 9 7 3 , 1982 , 1986b ) , and many were eutrophic , b ut f ew were turb id . HovJever ,

the lagoons displayed a considerab le var iab ili ty in their phy s iochemical

features , and even tho s e in c l o s e proximi ty could b e markedly different .

The high dys trophy of many of thes e waters s erves to highl ight the

maj or effects of dis solved humic s ubs tances wi th in them. Firs tly , it

cau s es the very rap id extinction o f solar radiation penetrating the

surfac e , resul t ing in turn in extr emely shall ow eupho tic depths and

spec tral dis trib u t ions centred on red l igh t . Severe the rmal gradients

may also res ul t f rom this , al though these are us ually o f a transient

nature , dependent o n prevail ing me teorolo gical con di t ions . Se condly ,

the high concentr a t ions of dis solved humic sub s t ances leads to a marked

reduction of pH in many of the s e waters , in p ar t i cular in the more dilute ,

and therefore unbuf f ered , o f them.

Al though subj e c t to th e l imit ations of the s ampl ing me thods employe d ,

a phytoplankton f l o ra dominated by desmids and f la gellates is mos t

probab le in the maj o r i ty o f dys trophic freshwater lagoons from wes tern

and south-west Tasmania . Some phytoflagellate s pecies are pos sib ly

virtually res tricted to such h ab i tats . Becaus e some o f these species als o

occur in similar coas tal l agoons elsewhere in eas tern Aus tralia , i t is

hypo thesized tha t all th ese waters may exhib i t flori s tic affinit ies ,

s imilar to those a t tributed to their fauna by Arthington (19 7 7 ) and

Timms ( 19 86a) . The s e woul d al s o include the lagoons from Kine;� and Fl inders

Is lands .

1 38

C HAPTER F I V E

DETAILED L IMNO LO GICAL STUDIES O F DYSTRO PHIC

LAKES AND RESER VO IRS FROM

WESTERN TASMANIA

5 . 1 INTRODUCTION

5 . 1 . 1 The Aims and Scope of these Studies

This chapter deals with three separate , detailed studies o f

dystrophic lakes and reservoir s from the western limnological province

of Tasmania (see Section 2 . 1 . 1 ) , and demonstrates the effects dis solved

humic substances have on the l imnology of such waterbodie s . Although

individual studies , when considered together they also represent a

p rogressive series illustrating many of the features r equired for the

establishment and maintenance o f meromixis .

Although Tasmania has many humic lakes ( Chap ter Two , Three and

Four ; and Buckney and Tyler , 1 9 7 3a , b) , few are as highly dystrophic

as the small forest lakes of Finland (Section 2 . 4 . 6 ) . Excep tions

include the lakes along the lower Gordon River ( see below) , and some

shallow coastal lagoons ( Chapter Four) . Lake Chisholm i s the only

non-meromi ctic , polyhumic forest l ake in Tasmania , and thus offers

an ideal site f or physicochemical and bio lo gical studies of highly

humic waters , comp arab l e t o the Finnish examp les . Other limnological

influences , such as basin morphometry and the shel ter afforded by

surrounding forest and hills , c an also be assessed . These studies

constitute the first p ar t of this chapter .

Investigation of f o ur humic reservoirs o f the Pieman River Power

Development form the second p ar t of this chap t er . Tyler ( 1 980)

predicted the onset of chemical stratification in impoundments

occupying steep sided , heavi ly vegetated river valleys , including

those of the P i eman River , and this study tes ts the accuracy of

that prediction . Comp arative data were also collected from Lake

Barrington , the first meromic tic Tasmanian reservoir (Tyler and

Buckney , 1 9 74) . Dissolved humic sub stances may play an important

role in the physicochemical l imnology of these reservoir s , and this

too was considered during this study .

139

Three of the four small , highly dystrophic lakes on the

eastern bank of the l ower Gordon River were found to be ectogenically

meromi ctic by King ( 1 9 80 ) and King and Tyler ( 1 98 1a , 1 982a , 1 983) .

Changes in the f low regime o f the Gordon River , caused by the

commissioning of a large hydro-electric dam on its middle reaches

(King and Tyler , 1 982b ) has lead to the decline o f meromixis in

these lakes . By 1 986 , only one , Lake Fidler , remained meromictic ,

and even this had changed considerably from its original condition

(Tyler , 1 9 8 6 ; C r o ome and Tyler , in press ) . The b e s t manifestation

of their meromi c tic condition was the extremely rap id change in

apparent redox p otential , from oxygenated to reducing condit;...ions (l?e,lO)I:c

over a dep th of j ust centimetres , within the chemocline . ThisAhas

progressively deepened over a p eriod of years , as meromixis has been

erroded away , and therefore is a very good indicator o f the demise o f

meromixis i n the lakes . Additionally , the meromictic stabilities of

the lakes also f all as the chemical stratification of the lakes decay s .

The third section o f this chapter emp loys these features to Sfi:,,hl'''

detail the demis e of meromixis in these lakes . This /also allows 1\ refinement of the theory of the origins o f their chemical stratif ication

(King and Tyler , 1 98 1 a ; Bowling , 1 9 81 ; Tyler , 1 98 6 ) . However , the

effects of other factors , such as lake morphology , shelter , and

p articularly the role of humic s in the limnology of the lakes are

also demonstrate d . These factors may assist the maintenance of

meromixis within the lakes , and therefore slow its demise . Thus ,

the lakes p rovid e a counter-point for those o f the chemically

s tratif ied reservoirs of the P ieman River , and polyhumic Lake

Chisholm . The great signif icance of the Gordon River lakes to the

World Heritage Area is also highlighted , and a knowledge o f the factors

affecting the dynamics of these humic , meromictic lakes is sought from

this study , to enable their effective management .

5 . 1 . 2 The Study Areas

The locations of the three study areas are shown in Figure 5 . 1 .

Lake Chisholm i s situated in the far north-west o f Tasmania , close

to the southern bank of the Arthur River , 9 0 metres above river level II). !\.;>,

and 1 20 metres above sealevel . � is well shel tered by surrounding 1\

hills , which f o rm its small catchment . There are no inflow creeks ,

but a s ingle out flow drains the lake northwards to the r iver . The

lake is a s inkhol e , a depression caused by a collap se in a local area

N

L 3 0 lun

140

S rn i t l > t o n _}J� �� A r th ur R · ' V a r

o 'f I L a k e C h i s h o l m

• s o · a v a g e , . J v e r

\ Figure 5 . 1 Map of Tasmania , showing the locations of the lakes and

reservoirs of this s tudy . See Figure 5 . 3 for more detail of the Pieman

River Power Development .

l) 0

IL :;; UJ f->-:c f-z 0 :;; z < UJ :;;

E E

2 0

1 5

1 0

0

3 0 0 ..1 ..1 <( u.

:: 2 0 0 < ti:

:r: f­z 0 ::;:

F igure 5 . 2

141

S M I T H T Q N �lax

2 0

1 5

!-.lin 1 0

0

3 0 0

2 0 0

1 0 0 l-

S A V A G E R I V E R

� Max

� v

J F M A M J J t. S O N D J F M A M J J A S O N D 1 9 8 4 1 9 8 5

Mean monthly maximum and minimum air temperatures , and

mean monthly rainfall for two stations in the v i c inity of Lake Chisholm

( see Figure 5 . 1 ) . X = no data . Data courtesy of Commonwealth Bureau

of Meteorology , Hobart .

142

of lime stone . The area has a moist , maritime climate typ ical o f all

western Tasmania , with p revailing westerly winds . Available climatic

data for the nearest stations ( Smithton and Savage River - see Figure

5 . 1 ) are given in Figure 5 . 2 .

Lake Chisholm is surrounded by thick "mixed" forest (sensu

Gilber t , 1 95 9 ) , with the dominant trees being Eucalyptus obliqua

L ' Herit . and E. v iminalis Labill . , and a secondary tree layer of

cool temp erate r a inforest specie s , in particular Nothofagus cunninghamii

(Hook . ) Oerst . , but also with some Atherosperma moschatwn Labill . ,

Eucryphia lucida (Labill . ) Baill . , Phy Uoc ladus asp leniifo lius (Lab i l l . )

Hook. F . , and Acacia me lanoxy lon R . Br . The shrub layer c ontains

Anopterus glandulosus Labill . , Cenarrhenes nitida Labil l . , Me la leuca

squarrosa Donn . ex . Sm . , Cyathodes juniperina (Forst . ) Druce ; Monotoca

glauca (Labill . ) Druce , and the tree fern Dicksonia antarctica Lab ill .

The ground cover is composed almost entirely of the fern B lechnum

wattsii T indale . This forest produces a deep peat which i s r esponsible

for the allochthonous organic material giving the lake its d ark brown

colourat ion . There is no emergent or aquatic vegetation around the

waters edge .

The P ieman River is one o f the main river sys tems of western

Tasmania , being formed by the confluence of the Mackintosh and

Murchison Rivers . Their source in the Cradle Mountain - Lake S t . Clair

National Park receives an annual rainfall in excess of 2 0 0 0 mm , often

as heavy winter snowfalls . Before impoundment the river v alleys were

narrow , s teep sided , and heav i ly vegetated . Pre-impoundment water

chemis try (Buckney and Tyler , 1 9 7 3a ; King and Civil Investigation

Division , Hydro-Electric Commis sion , 1 97 8a) showed their waters to

be humic and of low salinity , with pH values between 6 . 0 and 7 . 5 .

Murchison River waters were dominated by sodium and chlor ide , but

those of the Mackintosh and P ieman Rivers were considerab ly enriched

with calcium and bicarbonate .

Of the f our impoundment s (Figure 5 . 3a) , Lake Mackintosh , formed

in August , 1 980 , occupies the f o rmer valleys o f the Mackintosh and

Sophia R ivers, while Lake Mur chison was created in August , 1 982 , by

darning the Murchison River . Lake Rosebery occupies the upper reaches

o f the P ieman R iver and the l ower reaches of the Mackin t o sh and

Murchison Rivers , and first f illed in Augus t , 1 9 83 , while Lake P ieman ,

further downstream, commenced spilling in May , 1 986 . All the

143

A

N lake Mack intosh r

0 2 4 6 ���J

Km

B

Lake Mackintosh

Figure 5 . 3 A . Map of the impoundments of the Pieman River Power Development .

B . Vertical prof i le . Note the presence of high- level offtakes at each

dam . Vertical s cale 1 : 2000 , horizontal not to s cale ( after C ivil Eng ineer ing

Branch , Hydro-Electr i c Commiss ion of Tasmania , 1 9 80 ) .

144

reservoir s have high level o f f t akes , leaving a considerable amount

o f dead water b etween these and their bottoms (Figure 5 . 3b ) .

Morphometric dat a is given by P eterson and Mis s en ( 1 9 7 9 ) .

Lake Barr ington , on the Forth River in nor th-west Tasmania , is

not part of the P ieman River Power Development , but also o ccup ies a

narrow s teep.sided river valley which was heavily vegetated p rior to �n, �, 1'<!. '

flooding . receives water from Lake Cethana , another hydro-. i$ .. ,· r i��>fl�>.,�., electric impoundment immediately up stream . A chemical strat ification

has been describ e d by Tyler and Buckney ( 1 9 7 4 ) , Tyler ( 1 9 8 0 ) , and Fast

and Tyler ( 1 981 ) .

The po lyhum i c lakes of the Gordon River have been descr ibed by

King and Tyler ( 1 98 1 a , b ; 1 9 82a , 1 9 83) . The three meromictic lakes

are backswamp lakes , at river level , but sep arated from it by silt

levee banks , whil e the fourth , P erch�d Lake , is of uncert ain origin ,

seventeen metres above sealevel . ill are surrounded b y cool-temperate

rainfores t . Vegetat ional and c l imatic details of the area were given

by King and Tyler ( 1 9 8la) .

5 . 2 METHODS

5 . 2 . 1 Data Collection and Analysis

Thermal p r o f i le s were measured in situ with calibrated thermistors .

Water samp les wer e ob tained by Van Dorn water b o t t le for dissolved

oxygen determinations by the azide modification o f the Winkler method

(A . P . H . A . , 1 9 7 1 ) , or for dissolved sulphides by the method of Tyler

and Buckney ( 1 9 7 4 ) . Aliquot s of these samp les were taken for immediate

electrometric measurement of app arent redox p otential (Eh) , p H , and

electrical conduc tiv i ty (as Kl s) . Additional samples were obtained

from across the chemoclines of the Gordon River meromi ct ic lakes for

similar chemi cal analyses using c lose interval samp lers (po ints five

centimetres apart ) d e scribed by Baker et al ( 1 985b) and Croome and

Tyler ( 1 9 84a) . Join t use has been made with Croome ( 1 9 8 4 ) o f data

sets for 1 982 and 1 98 3 from Lake Fidler and Sulphide Poo l .

Additional water samples were taken from Lake Chisho lm and the

P ieman River r e servoirs for ionic analysis using the proceedures

described in Chap ter Four . Samp les for iron and manganese were

stored in ground- glass s toppered glass bottles , with all air bubbles

excluded , until analysis by atomic absorp tion spectrophometry . Two

drop s of concent r ated nitric acid were added to prevent the iron and

145

manganese precip itating . Turbidity , gilvin , and o ther optical

parameters were measured by the proceedures detai led in Chap ter Three ,

as were the phytop lankton .

Samples from Lake Chisholm for P 04-P and N03-N ( including any N0 2)

where filtered immediately a fter sampling through acid cellulose

f ilters and pres erved with HgCl2 on ice . P 04-P was measured colour­

metrically within two hours o f samp ling by the ascorbic acid method

(A . P . H . A . , 1 9 7 1 ) , and N03-N within twelve hour s with sulphanilamide

and N- ( 1 -naphtyl ) e thylenediamine dihydrochloride after colour removal

with aluminium hydroxide suspension and refiltrat ion , and reduction in

copper-cadmium c olumns (A . P . H . A . , 1 9 7 1 ) . Total-P was determined from

additional unf i ltered samples , also by the ascorbic acid method , but

after p redigesti on with potassium persulphate and sulphuric acid

(A . P . H . A . , 1 9 7 1 ) .

A bathymet r i c map was also constructed for this lake from line

soundings taken on theodo lite b earings with e lectro-magnetic distance

measurement s . Hyp s ographic curves and o ther morphometric p arameters

were then calculated by p lanimetry from this map , following the

methods of Wet z e l and Likens ( 1 97 9 ) .

Because o f wat er level fluctuations , all data for Lake Fidler

and Sulphide Poo l were p lotted to an arbitary datum level , 0 . 70 metres

on the gaugeboar d in Lake Fidler , and 0 . 60 metres on that in Sulphide

Pool . Similarily , all measurements from Lake Murchison have been

referenced again st a datum level o f 225 metres above mean sealevel .

The heat c ontent , thermal stability (for clo sed lakes - Walker ,

1 97 4) , Birgean Wind Work, and volume weighed averages of temp erature

(and oxygen in s ome lakes) were calculated for all lakes using the

computer program LIMN0 /2 (Ferris , 1 985) . This is a modif ied version

of the original LIMNO program of D . H . Merritt (Johnson � al , 1 97 8) .

An initial den s i ty o f 1 g cm-3 (pure water at 4 ° C ) was assumed for

wind work calculations .

Bowling ( 1 9 81 ) found a highly significant linear relationship

between condu c t iv ity at 1 8 ° C and density at 2 0 ° C [ p = 0 . 99 8244 +

( 4 . 867 x 1 0-7 ) K1 8 • r 2 = 0 . 9 98 , n = 92 ] for samp les from all three

Gordon River meromic t ic lakes . · Thi����permit s the calculation o f \

chemical s tabilities for these lakes for any occasion when a

conduct ivity p r of ile is availab le . Data o f King ( 1 9 80 ) , King and

Tyler ( 1 9 82a , 1 9 83) , Baker et al ( 1 985a) and unpub lished , Bowling

146

( 1 981 ) , and Croome ( 1 984 ) were used , additional to that collected for

this study , to c a l culate meromi ctic stabilities for the entire p eriod

the lakes have b e en s tudied , using the formula o f Walker ( 1 9 7 4 ) for

an open lake .

5 . 3 RESULTS

PART A LAKE CHISHOLM

5 . 3 . 1 Physicochemd.cal Features of Lake Chisholm

(a) Morphometr i c p ar ameters

A b athymetri c map o f Lake Chisholm is p r esented in Figure 5 . 4 ,

and derived morphometric parameters given in Figure 5 . 5 and Table 5 . 1 .

The lake is roughly c ir cular , covers an area o f almos t 4 . 5 hectares ,

and has a maximum depth o f 1 3 . 1 metres , although the water level varies

considerably , b e ing l owest in late summer and early autumn , and

highest during spr ing ( s ee Figures 5 . 6 and 5 . 8 ) . The lake contains

three small , ste ep sided basins with shallower r idges between them .

80% o f the lake i s less than 7 . 5 metres deep (Figure 5 . 5 ) , and over

80% of the lake vo lume o ccup ies the surface 5 . 5 metres . Despite this ,

Lake Chisholm s t i ll has a mean dep th of 4 . 6 metres , and a relative

dep th of 5 . 5% , indicating that the maximum dep th is considerab le for

a lake of its s iz e . Lakes such as this are more l ikely to have

retarded circul at ion and greater stability than large , shallow lakes

(Wetzel and Likens , 1 97 9) .

(b ) Water colour and light penetration

Sur face g4 40 value s of Lake Chisholm ranged between 24 . 0 m- 1 and

3 1 . 5 m- 1 , equiv alent to 300- 3 85 mg Pt L- 1 on the Hazen scale ( see

Chap ter Three) . Wat er colour varied sligh t ly b o th temporally and

with dep th (Figure 5 . 6) , being least from midsummer to early winter ,

but increasing d ur ing the second half o f the year . Colour was uniform

with depth during p e r iods of circulation , but usually increased with

dep th over mo st o f the stratif ied period .

P .A . R . is v ery r ap idly diminished with dep th in the p olyhumic

waters o f this l ake , and the euphotic dep th is extremely shallow ,

usually less than one metre b elow the surface (Figure 5 . 7 ) . Mean

downwelling vert ical attenuation coefficients , Kd (av) • were relatively

high (Table 5 . 2 ) , and downwelling P . A . R . also undergoes marked spectral

modification to produce a predominantly red underwater light-field by

147

Table 5 . 1 : Morphometric p arameters of Lake Chisholm derived

from the bathymetric map (Figure 5 . 4 )

Elevation 1 20 . 0 m Area 4 . 48 6

Maximum length 2 9 0 . 0 m Volume 207 , 340

Maximum width 2 38 . 0 m Shoreline 886

Maximum dep th 1 3 . 1 m Shoreline development 1 . 2

Mean dep th 4 . 6 m

Relativ e depth 5 . 5%

ha

m3

m

F igure 5 . 4

148

Bathymetri c map o f Lake Chisholm .

0

2

4-

;c � 6 -w 0

1 0

1 2

0

I I I

I I I

20

I

/ /

A R E A ( h a ) 3

' '

/

/ / /

' / /

-- A r e a

/

_ _ _ _ ?;, A r e a

4 0 6 0

% A R E A

4

/ / /

8 0

/ / /

5 0

1 0 0 0 2 0

N r O u t f l o w I / / ,

0

/ - - / \ I I

I

5 0 m s c a l e

b a r

Contours in metres .

V O L U M E ( m3 x 1 0.;)

/

1 0 1 5 2 0

' ' /

-- V olume

- - - - % V o l u m e

4 0 6 0 8 0

% V O L U M E

2 5

1 0 0

Figure 5 . 5 Depth-area and depth-volume relationships of Lake Chisholm .

0 2 3 'ii\ "' .t:l 4 · ()J .§ .!: 15. "' Cl 6 8 9 10 J

149

28 26 ·F M JMc�J M A 5 0

Figure 5 . 6

units ) .

0 . 1 0 -

2 0

4 o -

E u

G O -

I ·-0. UJ Cl

1 0 0

1 2 0

1984 1985 Isopleths of g440 in Lake Chisholm . Values in m- 1 ( ln

% I N C I D E N T P A R

1 . 0 1 0 0

F igure 5 . 7 Selected profiles of downwelling P . A . R . (400 - 7 00 nm . ) in

Lake Chisholm , highlighting the rap id attenuation and sha llow euphotic

depth in the lake .

( 32 F ' M 1 986

Table 5 . 2 :

D ate

1 8-2-84

1 6- 4- 84

1 0- 6-84

1 3- 8-8 4

9-9-8 4

7- 1 0- 8 4

6- 1 1 - 8 4

1 1- 1 -8 5

6- 2-85

4-8-85

2 2- 3- 8 6

150

Measured euphot ic depths ( Zeu) and mean vert ical

att enuation coefficients for downwelling P . A . R .

(Kd ( av) ) for Lake Chisholm

Zeu (m) Kd (av) (m- 1 )

0 . 80 4 . 88

0 . 90 4 . 5 1

0 . 70 5 . 37

1 . 00 3 . 82

0 . 80 4 . 60

0 . 80 4 . 34

0 . 80 5 . 1 0

0 . 80 4 . 80

0 . 70 5 . 1 0

0 . 75 4 . 45

0 . 75 5 . 1 5

151

0 . 5 metres deep (see Chap ter Three) . Turbidity has little effect as

values were always b elow 1 . 0 N . T . U . , and usually b elow 0 . 5 N . T . U . in

the surface waters . Secchi disc dep ths ranged from 0 . 8 to 1 . 2 metres .

(c ) Thermal stratification , dissolved oxygen , and dissolved sulphides

The attenuat ion of most solar energy close to the surface has a

cons iderable effect o n the thermal stratificat ion o f Lake Chisholm .

Isopleths o f temperature (Figure 5 . 8) show the lake t o b e warm

monomi ctic , by Lewis ' s ( 1 983 ) c lassification . Stratification commences

early in spring ( Sept ember) , and cooling does not commence until mid

autumn , with overturn only o ccurring in late May , so that the p eriod

of winter c irculation is three months or less . The isopleths and

selected profiles (Figure 5 . 9 ) highlight the intense shallow thermal

gradients presen t during the summer months , which span a temp erature

differ ence of 1 0- 1 2 ° C , with an ep ilimnion only one to two metres deep .

The monthly volume weighed average lake temperatures and heat

contents (Figure 5 . 1 0� reveal the lake ' s annual heating cycle . These

closely follow the local climatic conditions (Figure 5 . 2 ) , being

lowest dur ing July and August , b ut rise rap idly in resp onse to warming

air temp erature s and increasing solar radiation in spr ing , reaching

a maximum dur ing mid-summer before declining again throughout autumn .

There were only s light variations between the maximum and minimum

average temp eratures and heat contents of the two study year s . The

annual heat budge t , 8ba • for the 1 984-85 heating period was 2 4 1 0

cal cm-2 ; that for 1 985- 1 986 2 1 24 cal cm-2 .

The year ly v ar iation in dissolved oxygen and sulphides is shown

in Figure 5 . 1 1 , along with some monthly profiles in Figure 5 . 9 .

These closely f ollow the regular cycle of the thermal regime . The

onset o f hypolimnetic anoxia lags b ehind the onset o f thermal

stratification , with small amount s of oxygen being present to the

sediments into November . However the hypolimnion is anoxic , with

considerab l e amo unts of dissolved sulphides present , for six to

seven months of the year . Oxic waters descend with the deepening

thermocline in late autumn , but the lake is not oxygenated throughout

its entire dep th unti l after overturn , in June .

The o xy gen content in Lake Chisholm rarely exceeded 75% o f the

saturation value , even in the surface water s . This decreases even

further in winter when anoxic bottom waters mix with the oxygenated

152

1 9 11 4 1 9 8 5

Figure 5 . 8 Isotherms ( ° C ) , showing the warm monomictic nature of Lake

Chisholm .

o2 % Svt 0 2 0 � 0 GO flO

o2x Sat 0 2 0 4 0 60 8 0

Oz % .Sat 0 2 0 · 4 0 . GO · 80

T ° C

1 1'1 8 6

T °C 7 2 1,1 �3 115

2 1 7 9 ' i 1 1 3 1 5 1 7 1 9

2

! I

" r2 .. ,.

(J)

1 4 1 �61

I

o1�j T�

I n2 I

Oi % Sat 20 4 0 ' 60 I ! l

T

I I I I '

\ 05·03· 1 935

1 0-, or-' -z'' -, .. 4..,..· -.-.6-'8 ' . ,_ ' · 1 � (mg I ) .

1 0

o2 % Sat a · 20 �o GO

T ° C

u · ;. · q . 6 5'--.(,:ng [1)

·'"02 % Sat 0 20 40 6 0

( ( 1 '0 6-07·1985

T \Oz"

Figure 5 . 9 Thermal , oxygen , and dissolved sulphide profiles , at two

monthly intervals , for Lake Chisholm . These highlight the annual s tratification

cycle of the lake .

' c.<i:' 4000 .'[

vr· ·

] 5 ,3000 .,.., c:: 0 u � :t

2000

1000·

.... 8 ... ,_ 01 • .§ } = "' c 6 _8 � 5 � � "' :> 4 <C � .c 01 3 ·� s: "' 2 e :l 0 :> l

A

.... .... _ - -, '

B

' I I

I

153

1-leat Content

� ... /"- _,.

..... ..... -... _\ \ r \

\./\ , �' Average Temperature\ I / I ' r \

\ / \ � � - \

\ ' \ ' './

/ /

I

I ( I

/ " r / "' - - - ...

F M A 1986

J 1 F 1 M r A 1 M 1 J ' J. 1 A 1 s. 1 0.1 rt 1 0 I J .I .. F 1 M 1 A 1 M 1 J 1 J . 1 A 1 5 1 0 1 N 1 0 l J ·' F 1 M , A , 1984 1985 . 1986 .

Figure 5 . 10 A . Monthly values of heat content ( solid line ) ( cals cm- 2 )

and volume weighed average temperature ( dashed line ) ( ° C ) for Lake

Chisholm . B . Thos e for volume weighed average oxygen content (mg 1 - 1 ) .

154

surface layer s . Because a large volume o f the lake is o ccupied by

the anoxic hypo l imnion during summer , the who le lake average for - 1 oxygen falls below 2 mg 1 , but the maximum value was still only

a little above 6 mg 1- l during winter , when c irculation was at its

greatest extent (Figure 5 . 1 0� . This is less than 55% o f the

saturation possible at the average lake temp erature at the time .

( d ) App arent r edox potentials (Eh) , p H , and conduct ivity (Kl 8)

Isopleths for apparent redox potent ials (Eh) are shown in Figure

5 . 1 2 . These c lo sely follow those for oxygen . Summer surface values

were around 400 mv . , but these fell rap idly to 40 mv . b elow the

thermocline , due to the reducing nature of the anoxic , hypolimnetic

wat ers . During winter values remain at 400 mv . at all dep ths . Due

to equipment breakage , little data were available for 1 985 .

pH varied b e tween 4 . 8 and 5 . 8 throughout the study period , with

values usually b e tween 5 . 2 and 5 . 6 (Figure 5 . 1 3 ) . pH was lowest in

spring and early summer each year , but changed by as much as 0 . 8 of

a unit b elow the thermocline . Sometimes this change represented an

increase in pH , but at o ther t imes PH decreas ed . Dur ing p er iods of

circulation pH was constant with depth .

There was only s light vertical variat ion in the concentrations

of ionic solutes during the study , as indicated by the isop leths for

electrical conductivity (Figure 5 . 1 4) . K1 8 was usually clo se to 100

�S cm- 1 , but surface values tended to increase slightly during periods

o :8. maximum thermal s tratification , when any s light dens ity increases

due to small increases in solutes would be counteracted by the

decreased density of the warmer water . The cells of sur face water

of higher than normal conduct ivity appear to be inflows which

depressed the t hermocline and oxycline to slight ly deeper levels .

(e ) Maj or ions , iron , and manganese

Few differences were shown in the ionic characteris tics of Lake

Chisholm water s , e ither in dep th or time . The distributions of the

maj or ions are giv en in the ternary diagrams of Figur e 5 . 1 5 . Despite

the karstic nature o f the lake ' s formation , the water chemistry tends

towards d ilute sea water , being dominated by sodium and chloride , with

little enrichment from alkaline earth bicarbonates .

0

E 3

;: 4 11. w 0 5 -

7

8

9

0

1 -

2

] 3

I 4 t-11. w 0 5

�� 8

g

1 0

OXYGEN ('iO Sat .) HiJ (mg 1- �

1 55

Figure 5 . 1 1 I sopleths of dissolved oxygen ( % saturat ion ) and total

dissolved sulphides ( mg 1 - 1 ) in Lake Chisholm . The s tippled areas

indi cate anoxia and the presence of H2S .

_4 0 0 4 0 0

400 4 0 0 4 0 0 '. 4 0

-4 4 0

3 8 0 40

- n o d a t a -

F igure 5 . 12 Isopleths of apparent redox potential , Eh ( mv , not corrected

for pH ) in Lake Chisholm .

I M 1 9 8 6

Figure 5 . 1 3

0

2 -

� E J I f- 4 0.. w ,a D 5 -

0

l .

0 ·

D

1 0 J

Figure 5 . 14

Lake Chisholm .

156

Isop leths of pH in Lake Chisholm .

0

\

, ! l I 6 \ . :: �'

0 0

I sopleths of electrical conductivity at 1 8 ° C ( K1 8 ) (!II:S cm- 1 ) in

M f 1 9 0 6

157

Iron never exceeded 0 . 2 mg L- 1 in the surface water s , and 0 . 5

mg 1- 1 in the hypolimnion ; while manganese was not measurable , even

at the height o f thermal stratif ication and hypolimnetic anoxia .

( f ) Nutrient chemistry

Both N03-N ( including N02-N ) and Total-P were uniformly

distributed with dep th during circulation in August , but there is

evidence o f a modest accumulation of nutrients in hypolimnetic waters

during the stratified p2riod f rom September onwards (Table 5 . 3 ) .

Epilimnetic nitrate levels also decreased following the onset o f

thermal s tratif i cation , a s d i d levels o f To tal-P . Orthophosphate

forms about 50% of the Total-P in Lake Chisholm .

5 . 3 . 2 Thermal Stabilities and Birgean Wind Work for Lake Chisholm

The monthly values of thermal stability are p lotted in Figure

5 . 1 6 . Annual change in thermal stability closely resemb les those o f

heat content and average temperature ( see Figure 5 . 1 0a) , with a summer

maximum o f 50 to 6 0 gm-cm cm-2 , and winter minimums below 2 gm-cm cm-2 .

The marked d ip s in s tabi lity that occurred in January and March , 1 9 85 ,

correspond to t imes of considerab le cooling o f the surface waters and

deepening o f the thermocline , caused by poss ible inf lows (see Figure

5 . 8 and Section 5 . 3 . 1 (d ) , above ) .

Bir gean Wind Work (Figure 5 . 1 6 ) also follows the monthly p at terns

set by heat content , average temperature , and stability . The maximum

values declined over the three successive summers , and winter values

in 1 9 85 were mar kedly lower than those o f midwinter , 1 9 84 , resulting

from the cooler average temperatures of the lake during 1 985 . The

unusual marked increase in June , 1 984 , corresponds with a rapid

deep ening of the thermocline j us t prior to overturn , at that t ime .

Direct monthly work curves show exactly where energy has been

expended in the water column (Johnson � al , 1 9 7 8) . Examp les of

these , at three-monthly periods during 1 985 , are given in Figure 5 . 1 7 ,

and shown as isopleths for the whole s tudy period in Figure 5 . 1 8 .

Mo st energy exerted on the lake to achieve the observed thermal

gradients is distributed in the surface 2- 3 metres . Only in winter

dur ing circulation i s energy distributed more or less evenly throughout

the water column .

Table 5 . 3 : The distribut ion o f nutrients (pg L- 1 ) in Lake Chisholm in 1 985 . N = N03-N + No2-N ;

P = P 04-P ; TP = Total-P

Dep th Augus t September Octob er November December (m)

N p TP N p TP N p TP N p TP N p

0 5 6 6 2 5 8 0 3 1 1 0 1 8 2 8 1 3 1 5 38 1 0 5 3

1 . 0 - - - - - - - - - - - 6 35

2 . 0 50 53 6 5 2 52 1 1 2 6 4 6 4 32 57 5 49

4 . 0 - 5 7 1 0 6 5 4 6 3 4 3 1 48 44 32 73 1 7 5 3

6 . 0 5 7 57 95 1 7 45 - 30 6 1 6 8 35 5 3

7 . 0 - - - - - - - - - - - - 4 8

8 . 0 6 5 5 3 6 8 5 5 0 4 0 3 5 4 9 7 0 3 9 6 0

bott om 5 8 6 3 1 7 6 4 6 5 4 3 3 3 5 8 6 3 4 2 8 8 20 4 9

TP ..... "' 00

40

46

48

5 5

6 2

5 3

159

s

C a:t+

' . • e • •

•

• •

••• .

G9 ....

Figure 5 . 15 Ternary d iagrams of ionic composition of Lake Chisholm

waters from various depths and times . f = World Average Freshwater ,

s = seawater . 60

E i' E ..'?) 40

1 0

\ \ I \

\ \ I I I

I \ I I I I \ I I I

\

' I I \ \ \ I

I

I I I r I I I

I r

I

\ )Wind, Work \ � �

1\ I I I I I I

I

I \ I \ I \ I \., � - .1

J1i:i'M'A'M"J' J ' A I s .' 0 I N ' D J E ·M A 1\1 J J ' A 1 984 1985

I I

I

I I

I I

I (

I I I I I

I I I I

r -1 \

I \ \ \ I "\

\ \

\ \

F 1\1 A

F igure 5 . 1 6 Monthly values of thermal stability ( so lid line ) and

B irgean Wind Work ( dashed l ine ) ( both gm- cm cm- 2 ) for Lake Chisholm .

1 6 0

Differential work curves ( LiB , the direct \vork curve for one mon th

ninus that of the previous month - Johnson et a l . , 1 9 7 8 ) are shown in

Figure 5 . 1 7 . Pos it ive work ( 6B > 0 ) is done over mos t dep th s o f the

lake during sprin g and summer as the l ake waters are warmed , but the

curves b ecome negative ( 6B < 0) during autumn and winter as the l ake

coo ls . F igure 5 . 19 gives isopleth details of 6B , and highlights three

features . F ir s tl y , the lake undergoes extens ive periods during the

year when pos itiv e work is acting to dis tribute energy throughout the

l ake , but only short periods o f negative work exis t , when the l ake looses

heat to the surro unding environmen t . These brief coo l ing periods o c cur

mainly in winter , b u t even then can be interrupted by periods when

positive work again warms the lake . Secondly , in autumn , al though

negative wo rk c auses cool ing to take place close to the surface , deeper

within the lake pos it ive wo rk is s till o ccurring as cooler hypol imne tic

water is replaced by the warmer overlying waters of the s inking thermocline .

The third , and mos t s ignificant feature is that mos t o f the deeper

waters exp erien c e very little work , either posi tive or negat ive , acting

upon them during the course of a year , and thos e c lo se s t to the b o t tom

are ob s tens ibly s ta gn an t (when 6B = 0 ) for much of the time .

5 . 3 . 3 . B iological Features o f Lake Chisholm

Tows us ing a 20 �m plankton net indicate that flagell ates are the

dominant phytopl ankton o f L ake Chisholm, al though some s pecies , especially

tho s e of small s ize , may have been missed by this sampl ing me thod . A

numb er of taxa o f Chrysophyceae occurred as virtually monospecific . blooms

on o ccas ions . S everal s pecies of Ma Z Zomonas , espec ially M. morrisonensis

Groome and Tyl er , and a col onial green fl agel late , possib ly Conium socia Z e

(Duj . ) Warmin g , wer e ab undant in the l a te summer and early autumn o f 1984 .

Thes e had dis ap p e ared by May , when the non-mo tile green alga Crucigenia

quadrata Morren was very plentiful in the epilimnion , and the few flagel­

lates present were mainly Peridinium sp . A b loom of Synu�a mami Z Zosa

Takahaski o c curred in Augus t , 1984 , while the fol lowing mon th Peridinium

s p . was the dominant f l agellat e , with some S. mamiZ Zosa and Dynobryon

cy Zindricum Imh o f f als o b e ing pres en t .

Chrysophy t e s dominated the phytoplankton for the remainder o f the

s tudy . Blooms o f M. morrisonensis occurred in November , 19 84 ; of D.

cy Z indricum in O ct ob er 19 85 and January , 1986 ; wh ile M. sp Zendens ( G . S .

Wes t) Playfair were pres en t in large numbers in Decemb er , 19 84 ; and from

May to July o f 1 9 8 5 • Attendant sp ecies recorded in small numb ers either

o c c a s ionally o r c ons tan t ly included M. adamas Harris and Bradley em.

� �

B /LIB (gm·cm cnf2)

·1L�- 3� -�- sp , 71o I ... --,.

2 - 1-"f<j�- - - - - • - ·' • ,rJanuary 1985 • December 1984

' , ' '

'• 4 - IL)B B

I I

I I I

161

9(? 1{0

<<�'""\

B /4B (gm-cm cm2) . 3

<April 1985 • March 1985 '

I

' I �n

1 l I

B

· 90

., ! 6 · I I I \

'

f5 0. ., 0 I I t

8 . I

1 0 ·

1 2 -

B. /.OB .(gm�cm cnf2) -2 0

' r I I

z� /� July 1985 , June; 1985

I ( 4- �B I

] \ ..§ 6� f5 0. \ 8 I

I 8• I

\

10-

12-

' \ I ' \

' ' I I

�I 1

Figure 5 . 1 7 Direct work curves ( B ) ( solid l ines ) , and differential

work curves (� B ) in summer , autumn , winter , and spring , for Lake Chisholm . ).

in 1 98 5 .

· o

1 1

1 2-

' I ' I

'- -

162

_,,',. - ..

... , ... ... ... .. .. '

20

. ... "" '

' '

. �\ ' ' ' ' 1 0 ,_

l 2 .

... "' .... ... .. - - - ... - - . ' , '- - .. ... ,.. ..

1 3 r--.--,--.--.---.--.--.--.---.--.--.--.--.---.--.--.--.--.�·-.�.--.--.--.--- ---,--,-� J F M A M J ,J A S 0 N D J 1 F M A 1 M N D, l J F M

0

1 984 1 985

Figure 5 . 1 8 Isopleths of direct work ( B ) ( gm- cm cm- 2 ) done by wind

to distribute energy within Lake Chisholm . B v d'1 X i<:i:l.

LlU > 0

M A ·M .J

D

A 1984

LI U ::: 0

s

0

0 .N D I J I F . . :M I A .M A s 0

- 'r

� ' '"' '

' · : '..

'N

1986.

F M, 1 986

F igure 5 . 19

Chisholm .

D if ferential work (tl B ) isopleths ( gm - cm cm- 2 ) for Lake

Dllrrs chmidt and Groome ; M. tasmanica (Croome and Tyler) Asmund and

Kri s t iansen , Mero trichia baci l lata Meres chkowsky , Prorocentrum p layfairi

Croome and Tyl er , Botryococcus braunii Kllt z ing , and Anabaena s p . Desmids

were unus ual in the lake , the mos t common being Cosmarium s p . , and

diatoms were rare .

Zooplankton comprised mainly o f a calanoid copepod ( prob ab ly

Ca lamoecia tasmanica ( Smith) ) , and s everal species o f ro tifers were

als o common . Chaoborus s p . l arvae , no tonectids , and tadpoles (species

unknown) were als o very common during summer . There was n o evidence

of fish in the l ake , which however supports a small popul ation of

duckb illed platypus ( Ornithorhynchus anatinus Shaw and Nodder) . The

l ak e and its surrounding forest also provides a hab itat for s everal

s pecies o f waterb i rds .

5 . 3 . 4 ,

PART B ; THE RESERVOIRS OF THE PIEMAN RIVER , AND LAKE BARRINGTON

Phy sico chemical Features of Lake Mackin to sh.

Lake Mackint o sh is humic and non- turb id . Surface gilvin values

were bet\Veen 7 . 8 and 8 . 3 m- 1 , while turb idity was around 0 . 5 N . T . U .

Bo th colour and turb id i ty increas.ed dramatically with depth in March ,

19 8 1 , (Hydro l o gy Section , H . E . C . , unpublished) , al though this may b e

due t o iron and manganes e rather than t o dis s olved humus ( s ee Section

5 • 3 • 5 ( a) , be 1 ow) •

Chemical s tratification had developed by March , 19 8 1 , s ix months

af ter the sealing of the dam ( Tab le 5 . 4) . The lake was thermally

s tratified and anoxi c b elow twelve metres , while conduct ivity , magnes ium ,

po tassium , b ic arbonate , iron , manganes e , and dis solved sulphides all

increase d b el ow this depth . Cal cium and bicarb onate were the dominant

ions , apart from in the surface waters .

The chemical s tratification had weakened cons iderably by June ,

19 8 1 , and occup ied only the b ottom few me tres ( Tab l e 5 . 4) . I t had

dis appeared entirely by Augus t , 1 9 8 1 , when smal l amounts o f oxygen were

present at the b o ttom , and sodium and chloride \.Jere the dominant i ons

throughout . Subs equent data collected in 1 9 8 2 and 1 9 83 ( Tab le 5 . 4

and F i gure 5 . 20 ) indic a te that chemical s tratification did no t redevelop .

In November , 1 9 8 3 . th ere were no s ignificant changes in

Table 5 . 4 : Chemical data f o r Lake Mackin tosh f o r the f ir s t year o f impoundment ( 1 9 8 1 - 8 2 ) ( d a t a f r om Hyd rology S e c t ion , Hyd ro-El e c t r i c Comm i s s ion o f Tasmania , unpublish e d )

Dep th Ca++ ++ K+ Ma.'\:imum Temp . Oxygen K1 3 Mg HC0 3 Fe Mn s

Dep th

(m) (m) ( o C) ( % S a t . ) (pScm- 1 ) meq L- 1 meq L- 1 meq L- 1 meq L- 1 mg L- 1 mg L- 1 mg L- 1

1 1 -0 3-8 1

3 49 l 7 . 8 6 8 . 4 3 9 . 8 0 . 1 50 0 . 0 8 3 0 . 0 1 7 0 . 1 2 5 0 . 1 4 0 . 0 3 3 < 0 . 1 0

1 2 1 2 . 0 0 . 9 40 . 5 0 . 1 85 0 . 0 8 3 0 . 0 1 6 0 . 1 6 1 0 . 5 6 0 . 0 6 0 0 . 39

4 3 . 5 8 . 0 0 . 0 5 7 . 7 0 . 30 5 0 . 1 65 0 . 0 4 6 0 . 2 6 2 8 . 1 0 0 . 630 0 . 40 4 8 7 . 9 0 . 0 5 9 . 6 0 . 3 2 5 0 . 1 7 4 0 . 05 0 0 . 2 6 9 8 . 50 0 . 7 3 0 0 . 36

1 0- 0 6- 8 1

3 43 1 0 . 7 6 3 . 1 3 7 . 1 0 . 1 40 0 . 08 3 0 . 0 1 8 0 . 1 3 8 0 . 2 7 0 . 0 2 7 < 0 . 0 5 '""'

1 2 1 0 . 3 4 4 . 6 3 8 . 1 0 . 1 35 0 . 08 3 0 . 02 4 0 . 1 4 4 0 . 34 0 . 0 28 < 0 . 0 5 � 3 8 8 . 4 0 . 0 3 9 . 0 0 . 1 55 0 . 0 9 1 0 . 0 1 7 0 . 1 9 7 0 . 8 1 0 . 0 4 3 < 0 . 0 5 4 2 . 5 8 . 4 2 . 6 4 6 . 7 0 . 25 0 0 . 1 0 7 0 . 0 1 8 0 . 2 3 0 1 . 7 3 0 . 1 81 0 . 25

2 0- 0 8- 8 1

3 5 0 8 . 2 5 0 . 1 3 7 . 1 0 . 1 2 5 0 . 0 8 3 0 . 02 1 0 . 0 9 2 0 . 34 0 . 0 2 5 0 . 1 6

1 2 8 . 2 !+ 5 . 8 ) 7 . l () . 1 2 5 0 . 0 8 3 0 . 0 2 2 0 . 1 0 5 0 . 32 0 . 0 2 7 0 . 1 6 4 5 . 5 6 . 8 4 . 9 3 7 . 1 0 . l /fQ 0 . 0 7 1. 0 . 0 1 6 0 . 1 0 5 l . 0 9 0 . 08 5 0 . 0 3

4 9 . 5 6 . 5 2 . 4 3 7 . 1 O . l ff 0 0 . 0 7 4 0 . 0 1 6 0 . 08 5 0 . 9 9 0 . 05 9 0 . 1 6

2 0 - 0 4- 8 2

3 39 . 1 1 4 . 2 7 4 . 6 40 . 0 0 . 1 45 0 . 0 8 3 0 . 02 6 0 . 1 6 4 0 . 1 5 1 . 1 30 < 0 . 0 8

1 2 1 4 . 0 5 4 . 5 6 0 . 0 0 . 1 5 5 0 . 1 2 4 0 . 02 9 0 . 1 3 1 1 . 0 7 1 . 2 2 6 <. 0 . 0 8

3 4 . 5 7 . 1 0 3 8 . 1 0 . 1 35 0 . 0 7 4 0 . 02 7 0 . 1 9 7 1 . 0 8 1 . 1 5 8 0 . 20 3 8 . 5 7 . 0 0 3 8 . 1 0 . 1 35 0 . 0 7 4 0 . 02 4 0 . 1 9 7 1 . 1 2 1 . 1 35 0 . 30

e ..... ..c: .... c. 0.)

Cl

165

Ox ygen (% Sat) 0 20 40 60 80 100

5 7 1 1 1 3 t'c 6 8 1 0 1 2 14 T°C 0 ,...... _ ____._ _L_�K-:-1

8

-::�3�'3;-�-;:;:S-c-m-;:::-_11--------L---'----+-·-j)-;'..1../:,. --rt;K�18-:=::-;:s'fi" i-;;�:F"S em -r-·

'20-

30-

40 1< 1 8 :: 36 11S cm-1 7-1 1-82

50..:

' I /, )' l(i;!

(,

,

'�1

8 = 33 �s em- '

24...:1 1 - 83

Figure 5 . 20 Temperature and dissolved oxygen profiles from Lake Mackintosh .

Conduct ivity is also indicated .

166

K1 s • concentrations o f the maj or ions , or of iron and manganese

between the surface and the bottom waters .

5 . 3 . 5 Physicochemical Features o f Lake Murchison

(a) Colour and Turbidity

Lake Murchison surface waters are also humic and non-turbid .

Gilvin ranged from 4 . 1 to 8 . 9 m- 1 , and turbidity was generally below

1 . 0 N . T . U . Both tended to increase with depth , especially near the

bottom of the reservo ir , where a localized monimolimnetic pool was

present . However such data must be treated with caut ion . Both

dissolved and fine precip itates ( those not adequately f iltered out ,

even with a 0 . 22 pm membrane filter ) o f iron and manganese considerably

increases measurements of water colour and turbidity , making such

measurements highly suspect .

(b ) Temperature , Oxygen , and Dissolved Sulphides

Thermal , oxygen , and dissolved sulphide p rofiles are shown in

Figure 5 . 2 1 . Initial investigations four months after the creation

of the reservoir , in November , 1 98 2 , revealed a slight thermal

s tratification , and oxygen present close to the bottom . A possible

warming o f O . l ° C below 45 metres datum is insufficient indication of

the onset o f chemical stratific ation . By March , 1 98 3 , the l ake was

s trongly stratified thermally , with temperature declining rap idly

through the surf ace ten metres , followed by a more gradual decl ine

to almo st 35 metres datum . A definite increase of 0 . 2 ° C o ccurred

over the bottom 20 metres . Oxygen values were low near the sur face ,

but increased in the mid-dep ths o f the reservo ir , before fall ing t o

zero by 40 metres datum. Hydrogen sulphide was smelt in waters

below this depth . Results from July , 1 98 3 , when thermal s tratification

was absent , confirmed the existance of a stable monimol imnetic pool .

Considerable mixing is apparent throughout the upper 50 metres of

the reservoir , but below this water temperature suddenly increased

by more than 1 . 0 ° C , oxygen fell from 64% saturation to zero in the

space of two metres , and hydrogen sulphide was present .

Marked dichothermal temp erature profiles , with concomitant rap id

changes from oxic to anoxic , sulpheretted waters were present over the

next two years (Figure 5 . 2 1 ) . A yearly trend is apparent , with the

bottom of the oxycline and the thermal inversion increasing in depth ,

relative to datum , between March and November , during winter

167

c irculation , b u t becoming shallower again over summer when thermal

s tratification was present . In July , 1 98 5 , oxygen at almost 20%

saturation was measured near the bottom , but dissolved sulphides

were again present at these dep ths the following November .

Dichothermy p e rsisted throughout .

(c ) Redox p o tentials (Eh) , and pH

App arent r edox potentials (Eh) further highlight the r apid change

from oxic wate r s through out mos t dep ths of the reservoir to the

anoxic , reduc in g , sulphide laden waters of the monimolimnetic pool

(Figure 5 . 22) .

pH values were usually between 5 . 0 to 6 . 0 throughout most of the

water column , but gradually increased towards 7 . 0 within the monimol­

imnetic pool (Figure 5 . 22 ) . The magnitude o f this pH change was

greatest in the first half of the study .

The positi ons o f both the pH and redoxclines al so varied during

each year , in a s imilar manner to the thermal inversions and the onset

of anoxia ( see Section 5 . 3 . 5 (b) , above ) .

(d ) Electrical Conductivity

The presence o f chemical stratification in Lake Murchison is

highlighted by the electrical conductiv ity measurements in Figure

5 . 2 3 . K1 8 incr eased slightly from 25 to 37 .� S cm- 1 between the

surface and 50 metres datum , in November , 1 9 82 , and this may indicate

the onset of chemical stratification . The magnitude of the K1 8 differences with depth had increased by March , 1 98 3 , in p articular

from below 35 metres datum . Subsequent data f o r 1 983 and 1 984 show

a well dev elope d , sharp , conduct ivity cline o ccurring near the bottom

o f the reservo i r , at depths identical to tho se of the temperature

increases , and of the redox changes . A maximum K1 8 value of 303 ,.�,s cm- 1

was measured f r om the bottom waters in Novemb er , 1 98 3 , but conductivity

subsequently d eclined , and the cline had sunk to below 60 metres datum ,

by the f ir s t half o f 1 985 . In July , 1 985 , there was little

difference in K1 8 between the surface and the bottom water s ,

al though by November , conduct iv ity at 60 metres datum had again

increased sligh t ly .

Par t o f the variation seen in conduct ivity (Figure 5 . 23 ) (and in

the maj or ions - see below) close to the bottom of the reservo ir mus t

-10

70

] 10 s .a .g !:! 30 .£ 1l -5 50. 0. 8

T

5

I (J /; '

9

T 0£ Preserit I I I os-;u-s2

I J JOz

..-:;' 1 1-07-84 \

4

T

0

·. 8p �

8 12

/:_;;:==-l ( /

I 102 I . 08·11·84 I

i '

4 8

0 I '

168 o2 (% Sat) · - 40 �o: ?L. --L--l4�---L--'so_c_j·

' ' I j I

9 I

13

I I I J

I .

I T :o2 T. /02 I I 24-11-8_3_ )

-1Hz5 Present

16 13 17 . 4 8. •--J-��--L-�-· � / �

,---, 0 2 $-"'"(mg ill

0

I I J I Joz

I I I I

80

4. 8.

.... ... - /

0 4

12

' .. I

/l9-11-85 I

F igure 5 . 2 1 Thermal , d i s s o lved oxygen , and dissolved sulphide pro f i les for

Lake Murchison .

-10

] 10 s .a l1l "' 30 !:! 0 "(;) .0 -5 50 . 0. <l! Q

70

-10

70

Eh (mv)

pH 5 7 l___l__l

0 200 400 0 200 400 . 0 200 400 0 200 400

(� Eh

3o-03-83

� · o zoo 400

J

pi-JEh

) ' / \ n-o7-84

1--'---'---'----' '--'--J---'--J '--'---'-----''---'---'

0

I I

I pH I , I IEh pH � /Eh . pH l, ---/Eh

' I I

21-07-83

L___] 200

I I

. ' ) '

(\' ?4-11-83 pH

�7 Eh (mv) 400

pH; Ia pH: L; t -- ' : 08-11-84 09-07-85

(\., 1 7-03-84

� 100 ' 300 500

; oH· Eli i ) �//

1 9-11-85

F igure 5 . 22

Murchison .

Apparent redox potential ( Eh ) and pH profiles for Lake

16

-10

] E 10 :l '-i "0 30 � .£ c.J .f:! ..c 50 0.

169

0 08·1 1-82 30-Q3·83 21·07-83 24·1 1-83 1 7-Q3-84 . 70

-10 ] E 10 :::: '-i

"0 30 -3 c Qj .f:! 50-£ c. c.J 0 70

I

~ 1 1-Q7-84 08-l l-84

60 ' 100 I I4o ' do ' z2o I z6o ' 300 ' 30'70'110' K1 s (f.J? cm·l)

\ 09-03·85 09-{)7-85 19-ll-85

' 3'o 1 7b 1 1i0 I 2b 1 610 1 , 160 1 140 2'0'60 z'or-Go K1g (fJS, cm·l )

z'o 61:1 ' 160 I I4o · I 180 I zzo I -260

Figure 5 . 23 Profiles of e lectrical conductivity at l 8 ° C ( Kl g ) for Lake Murchison .

170

b e at tributed to sampl ing error . Large water level fluctuat ions ,

combined with the steep , narrow nature of the original r iver course ,

made sampl ing at exactly the s ame l ocation every time very diff icul t ,

and not being exactly in the same posit ion could result in an error

of several metres in the maximum depth attained . This is v iv idly

demonstrated by the profiles for 1 985 . In July , a maximum depth o f

only 6 1 metres datum was obtained , and chemical stratification

appeared to have almost disappeared . However the following November ,

the maximum dep th sampled was 6 5 metres datum , with resul t s showing a

rap id increase in Kl 8 over the last two metres . The chemical

stratificat ion r evealed by this increasing K1 8 was probably al so

present in July , but missed on that occasion as the maximum depth

sampled was shal lower than the s tratification itself .

( e ) Dissolved s o lutes

The dominant solutes of the monimol imnetic poo l were calcium ,

magnesium , bicarbonate , iron , and manganese . Depth pro f iles for these

(Figures 5 . 24 and 5 . 25 ) resembl e tho se for K1 8 (Figure 5 . 2 3 ) , with

concentrat ions increasing rapidly near the bottom of the reservoir .

The concentrations o f these solutes in the monimolimnet ic pool

increased gradually after formation of the reservoir , reach ing a

maximum in November , 1 98 3 . Subsequent profiles then show decreases ,

apart from in November , 1 985 , when the maximum values for iron ( 5 1 mg L - 1 )

and manganese ( 7 . 7 mg L-1 ) were recorded for the study . Concentrations

of the o th er ions also increased on that occasion . However ,

comparisons are difficul t due to the dep th o f measurement problems

d iscussed in Sec t ion 5 . 3 . 5 (d ) , above .

Potassium prof iles (Figure 5 . 26 ) resemble those of cal c ium ,

magnes ium , bicarbonate , iron , and manganese , but its concentrations

are too l ow to add s ignificantly to the chemical stratif ication . In

comp arison , concentrations o f the minor anion , sulphate , fell to z ero

below the chemoc l ine , due to reduction to sulphides (Figure 5 . 2 6 ) ,

and sodium and chloride displayed little change in concentrat ion

throughout the dep th of the reservoir (Figure 5 . 27 ) .

Ternary diagrams showing ionic propor t ions from three o ccasions

in 1 9 8 3 , reveal the chemistry of Lake Murchison changed markedly with

dep th . The surf ace waters h ad p roportions akin to seawater , but once

below the chemocline , these changed towards World Average Freshwater ,

as cal c ium and b icarbonate became the dominant ions (Figure 5 . 28 ) .

A

-1

1 0 § e z "' Cl .. 30 "' .,

""

.c -"" � 50

70

B

-1 0 0 A

8

0 ·2 ·6 I

c

0 · 1 · 2 0

I ·1 ·2 · 1 I

·2 I

1 7 1 c}+ c� nccntr�tion [meq 1- 1]

c 0 G •2 0 ·2 .j ·6 ·8 L.....-J L_,_,___.__,___l

·4 ·6 ·8 }{) 1·2 }4. 1·6 1·8 20 2·2 :.?-4 F L.l__:_,

0 H ·2

M g 2 + C o n c e n t r at i o n [meq . l-1 1

D 9 · 1 ·2 0 ·1

I I

c E <} ·f · 5 Q ·1 <i! I I

0 G ·1 '---' F

8 ·2 ·3 9 ·1 I

I ·2

I

l.-.-J

I

L_

·3 ·4 I _J_

�----�---+----------�--------+-----+---�------·------------------'iii 1 0 E .s "' "' 3 30 " ;;:; lXI -" -"" � 50

70

c

-101 I I

'E I Oj E z "' "'

30� ;!: 0 ;;:; ""

.c: -0. ., 50 ""

70

9 A

B 0 ·4 '4 ·8 I I

Figure 5 . 24

B

c

·8

0

H C O j' C o n centrat i o n (meq l-1)

D F 0 •4 ·8 0 •4 C E

o, ·4 ·8 1·2 1'6 2-0 2·4 n 3·2 o ·4 ·8 1.--��--J�--��--��

I I I

\,____ Profile s o f calcium (A) , magnesium ( B ) , and bicarbonate

( C ) ion concentrations in Lake Murchison . A = 3 0 - 03 - 19 8 3 , B = 2 1 - 07 - 19 8 3 ,

C = 24- 1 1 - 1 9 8 3 , D = 1 7 - 0 3 - 1984 , E = 1 1 - 0 7 - 1 984 , F = 0 8 - 1 1 - 1984 , G =

0 9 - 0 3 - 1 98 5 , H = 09-0 7 - 1 98 5 , I = 1 9- 1 1 - 1985 .

172

A I r o n C o n ce n t ration (mg 1-1 ) I 0 10 20 30 40 50 60

-10

� 10 e !l "' "' 01: 30 "'

iil' ""

70

B

-10

� 10 E ,;; "' C> !!: 30 "' w ""

""' "'" � 50

70

A 0 10 ...............

·\

0 A

B

B 9 f 2

....____.

)

� B 1

c 9� 20 30 40 0 10 20

G

4 I c 9 2 4 6

c�

D E \ F

� �

Mang a n ese C o n centrat ion (mg 1- 1 ) D

0 2 4 1--'---'

8 ? I

\ I I I I I

\ ( I

2 I

F 0 2 4 4 I

\ E�F �

G

0 G 2 1--J

'\

0 10 L__._J

H

�

0 2 '---'

H

\

I

\

I 0 2 4 6

I

8

F igure 5 . 25 Profi les of dissolved iron ( A ) and manganese ( B ) concentrations

in Lake Murchison . A = 3 0 - 0 3 - 1983 , B = 2 1 - 07 - 1 9 8 3 , C = 24- 1 1 - 1 98 3 ,

D = 1 7 - 03 - 1 984 , E = 1 1 - 0 7 - 1984 , F = 0 8 - 1 1 - 1 984 , G = 0 9 - 0 3 - 1 985 , H =

0 9 -0 7 - 1 985 , I = 1 9- 1 1 - 1 985 .

A

-10

:§.: 10 E z "'

t::l

3: 3 1 2 cu "" ""'

0..

� 5

70

B

� 10 E E "' .,. 3: 30 t:l QJ "" -;; "'" .; 50

70

B Q 2p 4p

A ��0 q 20

·\

B 0 20 L--.1 A 20 40 0

I

0 c 4p 60 80 I .

c

173

K+ Conce n t rat ion (�-eq 1-1 )

0 F 20 .dQ 0 20 40 0 E

0 20 40

\ S04�- Concent ration (p -eq 1-1)

D F

G 20

0 20 40 0 20 40? 20 40 60 80 100 0 E '20 '----'

40 0 H 'L__20

H j �-

G 20 40 60 1 I I

H

I 20 40

I

�

Figure 5 . 26 Prof iles of potass ium (A ) and sulphate ( B ) ion concentrations

in Lake Murchison . A = 3 0 - 0 3 - 1 9 83 , B = 2 1 - 0 7 - 1 983 , C = 24- 1 1 - 1 98 3 ,

D = 1 7 - 03 - 1 98 4 , E = 1 1 - 07 - 1 984 , F = 0 8 - 1 1 - 1 984, G = 0 9 - 03 - 1 98 5 , H =

09 - 0 7 - 1 98 5 , I = 1 9 - 1 1 - 1 98 5 .

A

B 0 ·2

1-..--)

-1 0 A 0 ·2 0 L...........-1

§ 1 0

E ::. ..... ctJ

Q � 30 0 Qj 1:0

..t::

A\ .... t:l. II)

CJ 50 B

70

B

0 B ·2

i._J

-1 0 - 0 A ·2 0

c

c ·2

c

174

Na+ C o nc en t ra.t i o n (m e q 1 - 1 )

0 0 ·2

F u 0 ·2 0 ·2

L--J E

·2 ·4 0 t..............

0 E

L----1 L--J

F G

C l- C o n c en t ra t i o n (meq J - 1)

D F G 0 ·2 0 ·2 0 ·2 L_._.._) L.__J I_J

E

0 H

·2 L--J

H

H ·2 •4 0 ·2 0 ·2

l---l L----1--.--J L-J 1...--l

....... 1 0 8 E :::l .... "'

Cl � 3 0 "' Cll

tc ..r:: .... 0. w 50 A B c D E F G H c:J

70

d

I

\

·4 )

I

� F igure 5 . 27 Profiles of sodium ( A ) and chloride ( B ) ion concentrations

in Lake Murchison . A = 3 0 - 0 3 - 1983 , B = 2 1 - 0 7 - 1 9 8 3 , C = 24- 1 1 - 1 9 8 3 ,

D = 1 7 - 0 3 - 1984 , E = 1 1 - 0 7 - 1 9 8 4 , F = 0 8 - 1 1 - 1 98 4 , G = 0 9 - 03 - 1 985 , H =

0 9 -0 7 - 1 98 5 , I = 1 9 - 1 1 - 1 9 8 5 .

1 75

s or H GOj �---------------------------------------ry

+

a .. .. b

f

Figure 5 . 28 Ternary diagrams showing the ionic proporti ons of the

maj or ions at various depths for the three samp l ing occas ions in 198 3 .

a to e = 3 0 - 0 3 - 1 983 . a = 40m, b = 4 5m , c = S Om, d = S Sm , e = 5 7m .

f to i == 2 1 - 0 7 - 1 98 3 . f = Om, g = SOm, h == 55m, i = 6 0m .

j to 0 = 24- 1 1 - 1 98 3 . j = Om, k = 25m , 1 == SOm, m = 6 0m, n = 65m, 0 :::: ?Om .

x = seawater and + = World Average Freshwater .

1 76

Lake Murchison remained chemically s tratified throughout the

three years of the s tudy , but thi s gradually diminished , with the

concentrat ions of cal cium , b icarbonate , and manganese 60 metres

dep th , r e �tive t o datum , ste adily declining s ince their maximum

l evel s in November , 1 9 83 (Figure 5 . 29 ) . Conductivity remained fairly

c onstant at this dep th for the f irst two years , but th is too began to

decl ine after Jul y , 1 9 84 . The concentration o f dissolved iron , on

the o ther hand , increased sl ightl y until early 1 985 , but declined

after that , while sodium and chloride remained at relatively constant

levels throughout the study p eriod . The increasing concentrations of

dissolved iron may have offset the falling levels of cal c ium and

bicarbonate until Jul y , 1 98 4 , so that conductivity remained fairly

cons t ant . The ionic composit ion o f the waters at this depth moved

progressively away from the World Average Freshwater t yp e towards

proport ions s imilar to seawater (Figure 5 . 30) , as the dep th of the

chemocline sank through this l evel of the reservo ir . There was a

slight reversal o f this trend in November , 1 98 5 .

( f ) The upstream ext ent of chemical stratification

The up stream extent of the chemical s tratificat ion in Lake Murchison

was investig ated in July , 1 98 4 , with measurement s of water temperature

and dissolved oxyg en being made at points approximately 500 and 1 000

metres up stream o f the normal sampling point . Chemical stratification

was s t il l present 1 000 metres up stream , with an increase in water

t emp er atur e of 0 . 4 °C close t o the bottom (Figure 5 . 3 1) . However trace

amounts o f oxygen (0 . 65% saturation) were present r ight to the bottom

at thi s location , 58 metres b el ow the surface . A thermal inver sion of

1 . 2 ° C occurred close to the bottom at the point only 500 metres

up stream , and oxygen was present 5 4 metres below the surface , but

deeper waters were anoxic . A s imilar thermal invers ion was present

at the bot tom clo se to the dam wall , but anoxia here began 52 metres

below the surface .

These data reveal a wedge o f colder water intruding close to the

bottom o f the res ervo ir from up s tream . This cold density current ,

probably orig inating as snow-mel t in the catchment and flowing down

the dro\vned river channel , was being forced upwards and over the

denser , but warmer , waters o f the monimolimnet ic pool , depressing

its up stream end and t il t ing the chemocline away from the horizontal ,

rather than underflowing or o therwise disrupt ing the chemical

T E

200

.::: 1 0 0 ::::L.

2

T g l E

3

2 I = E

20

Cl

1 F e -;;, 10 E

177

1 983 1 984 1 985

F igure 5. 29 Dec l in e in electrical conduct ivity at 1 8 ° C (Kl s ) and in the

concentrations of various solutes at 6 0 metres depth , relative to datum ,

in Lake Murchison , over the study period .

178

so.( HCOj"

X

i • i .

h

- - --- - ---------------

MgH

Figure 5 . 30 Ternary diagrams showing the temporal changes in the

ionic proportions o f waters from 60 metres depth, re lative to datum,

in Lake Murchison . Proportions have changed from c lose to World Average

Freshwater (+) early in the study to close to seawater (X) three years

later . a = 30-03- 1 9 8 3 , b = 2 1 - 0 7 - 1 983 , c = 24- 1 1 - 1 983 , d = 1 7 - 03 - 1 98 4 ,

e = 1 1 - 0 7 - 1 984 , f = 0 8 - 1 1 - 1 984 , g = 09-03 - 1 985 , h = 09 - 0 7 - 1 985 , i =

1 9 - 1 1 - 1 985 .

179

t-(-- U P S T R E A M. c a . 1 0 0 m T O W A R D S D A M -

6 . 6 6 . 4 6 . 2

1 0

2 0

I � 3 0����--�---------------------0

4 0

6 0

F igure 5 . 3 1 Thermal stratification in LakP Murchison over a c a . one

k i lometre section immediately upstream of the regular samp ling location ,

July , 1 98 4 . An inverse thermal profile exists , indicat ing the presence

of the monimolimneti c pool over this distance . A cold dens ity current

i s overflowing the pool from upstream .

1 80

strat if ication . This is shown b y both dichothermy and anoxia

commencing at greater depth s as distance up stream increases .

5 . 3 . 6 Physicochemical Features of Lake Rosebery

Lake Rosebery is also a humic reservoir , with surface g440 values

of between 7 . 20 and 1 0 . 20 m- 1 . Turbidity was always below 0 . 5 N . T . U .

Both increased sl ightly near the bottom in November , 1 98 3 and July ,

1 98 4 , when inter ference from dissolved iron and manganese was

negl ibable , as the waters were oxygenated .

This reservoir also exhibited initial chemical stratification

af ter it was formed (Figures 5 . 32 , 5 . 3 3) . It <was thermally stratified

in November , 1 98 3 , four months after its format ion , but oxygen was

present to the bot tom . p H , calcium , bicarbonate , magnesium , and K1 8 all increased sl ightly with depth , particularly below 30 metres .

Potas sium and sulphate also increased with dep th , but sodium and

chl or ide remained constant . I onic proportions changed from a seawater

type order of dominance near the surface to one resembl ing World

Average Freshwater at the bottom . Due to oxidizing conditions ,

dissolved iron and manganese r emained below 1 . 0 mg L- 1 .

Lake Rosebery was still strongly thermally strat ified in March ,

1 98 4 . Redox chemistry changed from oxidiz ing to reducing conditions

ten to twenty metres below the surface , coinciding with the thermocline ,

and waters below this were anoxic and sulpheret ted . Dissolved iron

and manganese concentrations increased with dep th from below the

thermocline , but p H , Kl 8 • calc ium , magnes ium , and bicarbonate only

showed rapid increases below 4 0 metres . Thus the maj or stratification

of solutes began at this depth rather than from immediately below the

thermocline and redoxcl ine . Again , potassium increased sl ightly with

dep th , while sodium and chloride remained at f airly constant levels ;

however sulphat e concentrat ions fell to zero below 40 metres . Ionic

p roportions also changed from a seawater type order of dominance to

a World Average Freshwater type below 40 metres .

This incipient monimolimnetic pool had vanished by July , 1 9 84 ,

when the lake was isothermal with almo st 50% saturation dis solved

oxygen near the bottom . Maj or ions changed little with dep th , and

sodium and chloride were always dominant .

5 . 3 . 7 Physicochemical Features of Lake Pieman

Limnological investigations o f this fourth humic reservoir

commenced in mid S ep t ember , 1 98 6 . Thermal s t atification was j ust

A

1 0 Vi' 0) .b 0) a 30 - .

cS 0. 0) Q 50

70

B

1 0 -g; .b 0) _§ 30

cS 0. 0) Cl 50

70-

c

10 -rn 0) .b 0) _§ 30 ..:: ..... 0. 0) Cl 50

70

� 40 80

181 . 02 (% Sat) ·

o · · 40

T °C.

80

7 11 1 5 1 9 5 9' 1 3 · I [' 1 .� 1

[7' ' / �·o

2 I

25-1 1-83

I I �pH

I I I

25-1 1-83 , 5 7

' 20 60

25-1 1.:.;.83

l I '

' _ _ 1)1J - - - - - - __;-r

o- - ( �-----2

s::�-

' 1�3-84 ,---, g2-(mg f�� 0

Eh( I I lpH I l l ' ' ' I

I

1 8-{)3-84 5 pH 7

. Kls (PS c�-1) 20 60 100

1 8-03-84

I

�20

50 90

6 16.

I r) ) )�02

l ; I I I 1 I

12-{)7-84 .

; pH I · '

12-{)7-84 ,--r . 5 6

6()

12-{)7-84

Figure 5 . 32 Thermal , dissolved oxygen , and dissolved sulphide profi les

( A ) ; pH and apparent redox potential ( Eh ) prof iles ( B ) ; and electrical

conductivity at l 8 ° C ( Kl s ) prof i les ( C ) , for Lake Rosebery .

A 2

1 0 ,-...· !/) Q) tl Q) ..§ 30 •

.J:: Mnl Fe · +-' I 0. Q) I 0 50

70 25-1 1-83

B

-· 10 !/) Q) ;.. I +-' Q) '

..§ 3 0 l I

.J:: Mr/+\ c.r +-' 0. Q) 0 5 0

7 0 25-1 1-83

c 0 0.4

. I I

1 0 _...... !/) Q) tl . Q) ..§ 30.

� 0. Q) 0 5 0 ·

70 25-1 1-83

1 82

Fe/Mn (mgf1) 0

\ I I \

Mn • I . \

\ \

Fe

1 8..03-84

Ca')'Mg2+ (meq i� 0 0.1 0.2

l \ ' H �Mg ' . \

I \

1 8..03-84

HCOj (meq f 1)

0 · •0.4 r

. Mn : Fe

12..07-84

i I I

C , .. M l. + a 1 g

1 2..07-84

0 ' 0.4

. 1 2..0:7-84.

Figure 5 . 33 Dissolved iron and manganese profiles ( A ) ; calcium and

magnes ium ion profiles ( B ) ; and bicarbonate ion profiles ( C ) for Lake

Rosebery .

start ing , and p r o bably the reservoir had been circulating since

impoundment . However , temp eratures increased 0 . 1 °C below 80 metres ,

whil e d is solved oxygen diminished from 84% saturation at the surface

to 27% at 94 met res , and K1 8 increased from 49 to 64 � S cm- 1 (Figure

5 . 3 4) . Concentrations o f cal cium , magnesium , sulph ate , b icarbonate ,

iron , and manganese also increased slightly b etween these depth s ,

indicating the onset o f chemical stratification .

Measurement s at the height o f thermal stratif ication , at the end

of January , 1 98 7 , confirmed the development o f incipient meromixis in

Lake P ieman (Figure 5 . 3 4 , 5 . 3 5) . The reservoir was anoxic and reducing ,

with considerab l e amounts o f dis solved sulphides present , below 60

metres . Conduct ivity and d is solved iron and manganese also began

increasing b el ow this dep th , although rises in temper ature and

concentrations o f magnesium , calcium , and bicarbonate d id no t o ccur

until deeper , in a manner similar to Lake Rosebery . However , this

chemical s tratif ication did not persist . Measurements in September ,

1 987 , showed no trace of a dichothermal temperature profile or

conductivity differences with dep th , and oxygen was present right to

the bottom .

5 . 3 . 8 Physicochemical Features o f Lake Barrington

Lake Barr ington is a moderately humic reservoir , with surface

g ilvin level s b e tween 2 . 00 and 3 . 60 m- 1 . Colour increases slightly

in the mid- dep th s , but decreases below the chemocline to as low as

1 . 50 m- 1 . Sur f ace turb idities are low ( 1 . 2 N . T . U . ) , but measurements

of turbidity in the :bottom waters were impossible due to interference

by p recip itates o f iron and manganese .

This reserv o ir was sampl ed annually between 1 982 and 1 985 , and

the resul t s are shown in Figures 5 . 36 , 5 . 3] , and 5 , 3 8 . The reservoir

d isplayed stron g localized merontixis throughout the study period ,

with a monimol imnetic pool three to four metres deep .

Thermal p r o f iles (Figure 5 . 3 6a) were markedly dichothermal , with

temperature inc r eases of over 1 . 0 °C close to the reservo ir bottom .

Concomitant wit h this , oxygen c oncentrations f e l l from greater than

60% saturation t o z ero in less than one metre , and up to 1 3 mg L- 1

of dissolved sulphid es were present within the monimolimnetic pool .

Very rap id changes in redox potential (Eh) al so took place , from

oxidiz ing to reducing conditions , and pH increased sl ightly .

20

o2x Sat �o 4p �6P

10

K;i8" 48.7 s,cni1 I

I I

I

I I I I I I

{ T ' Oz.· I

I I

I I

100 1 1-()9-1986 . 3(}-01·1987

184

ft.

o2)1; Sat· ���_!JO·

/ ,' T /'02

' I • I \ ' I l (

I I

'

,/ K18::69.6 ps cnl . I

( f 1

,. -1 · K18�G7.6 }JS em .

24-()9-1987

Figure 5 . 34 Thermal , dissolved oxygen , and dissolved sulphide pro f i les

for Lake Pieman . K1 8 i s also indicated on two occas ions .

t I

I 20 I I

I I \ Vi I

� I "' 40 pH I _§ I

.s · I "' 8 60

pH

Eh

7

Kt8q;s Cll)-1) 40 60 80· 0 '

I \ Mn 1 Fe

2 I

0.0

d.o .o!z . �� o!6 Mn (mg f )

HCOf

F igure 5 . 35 Depth profi les of pH ; apparent redox potential (Eh ) ;

e lectrical conductivity ( K1 8 ) ; calcium, magnes ium , and bicarbonate ion

concentrat ions ; and dissolved iron and manganese concentrations in

Lake Pieman for 3 0 - 0 1 - 1 9 8 7 .

185

The p resence of chemical s tratification in L ake Barrington is

highlighted by r ises in electrical conductivity (K1 3 ) , and by the

concentrat ions o f some maj or ions and dissolved iron and manganes e .

The K1 8 increase i s extremely sharp and rapid , o ccurring over a

s trat•.u\\ only one metre deep (Figure 5 . 37a) , and then increasing to

almos t 500 t� S cm- 1 at the bottom . Identical patterns are shown by

dissolved iron and manganese , which increase from almost zero to

80 mg L- 1 and 1 0 mg L- 1 respectively (Figure 5 . 37b ,q . In September , 1 - 1 1 984 , dissolved iron exceeded 1 20 mg L- and manganese 1 2 mg L

at the deepest p o int s ampled .

Figure 5 . 33 gives depth profiles for calcium , magnesium , and

bicarbonate . Lake B arrington differs from the reservoirs of the

Pieman s cheme in that magnes ium rather than calcium is the dominant

cation . Concentrations of thes e two ions also increased rap idly

within the monimol imnetic pool , as did bicarbonate . Thes e ions , along

with dissolved i r on and manganes e , were the maj or solutes cau s ing the

chemical s tratif ication . Levels of sodium , potassium , and chloride

increased only s l i ghtly , while sulphate values fell to zero below

the chemo cline .

5 . 3 .9 Volume Weighed Average Temperature and Oxygen; Heat Contents , Thermal Stabilities and Birgean Wind Work in the Five Reservoirs

The result s o f thes e parameters , calculated for all f ive reservoir s ,

are given in Tabl e 5 . 5 . The volume weighed average temperatures show

the impoundment s , and especially Lake Murchison , are quite cold . This

is so even in summer , af ter considerable amount s of heat have been

absorbed , mainly by the humic surface water s , because the hypolimnion

remains cold and this lowers the volume weighed mean temperature .

Although s amplin g was too infrequent to allow accurate calculat ions

of the annual heat budgets , e ba • some estimate s of the amount of heat

gained or lost by s ome of the reservoir s are s t il l possible . For Lake -2

Murchison thi s was at least 1 00 85 cals em for the 1 983- 84 heating

period , and 1 0 8 9 1 cal s cm-2 for the 1 984- 85 period , while that for

Lake Rosebery , e s t imated from heat lost during autumn , 1 98 4 , was - 2

1 0635 cals em The variability in the heat contents o f the other

reservoirs indicate considerable heat exchange by their water s , too .

Volume weighed average oxygen contents showed the reverse trend to

that for temperature , being highes t during winter measurements and

lowes t in summer due to hypolimnetic oxygen demand .

A

10

70

B 9

10 � Q) .... ... Q) g 30 ..c: 0. Q) Cl 50

70

410

j 02-10-82

8,0·

' \

, I I

I I /Oz I

. - - - - _ }

2QO I I 400

pH : Eh I

02:10-82

,------, 6 7

Q 410 810

8

I

T /o2 I 26�1 1-83/

I . ' I - -l- - -y-.i

0 4

I pH:

I L :::..,.--

,__,_.._, ·s 7

186

� (% Sat) Q 1 4,0

r

I I I I I \Oz

29-09-84 / I

j I I

1 Q 1 410 8,0 I

I I � - - - -- � ��s·,-

i - - - - -· .......-------. s:-

pH

4 ' 8 . 12 0

i I I

jEh ! I

I ' I pH r

. I I I

4 ,I ' 8 I 112 I

4QO

Eh

29-o9-s4\ 2s-o9l-ss I I

I I I j

. ·r---1 6 ' 7

F igure 5 . 36 Thermal , dissolved oxygen , and dissolved sulphide prof iles

( A ) ; and of pH and apparent redox potential (Eh) ( B ) in Lake Barrington .

A

10

gJ j 30

£ 0. 0 50

70·

B

10 In Q) .... ] 30 .0: 15. Q) 50 Ci

70

c

10 In Q) ... � 30 ..::> £ g. Ci 50

70

1$7

K18()JS cnfl) 200 4�'-------------------o���zo�o�.��lo �-2�oo�-4�

No Data 02-lo-82 26·11·83 29-09-84 28-09·85

----"---- l_ Fe(mg f1)

0 ' i--��4L0-L�80��--�0��4�0�.�8�0--_,0r-��4 0 __ �8�0--�1�2_0 ___ 0r-�-!�--8�0�--

0 2- 1 0·82 26·1 1-83

· -------- \

29-09·84 28-Q9·85

-----

28-Q9-85

Figure 5 . 3 7 Profiles of electrical conduct ivity ( Kl g ) ( A ) , dissolved iron

( B ) , and dissolved manganese ( C ) in Lake Barrington .

A

10 _.;...._ (/) Ill )., .....

s 3o ........ ..!:: ..... 0. Q)

50 0

70

B

10 · ,....._ [/)

Q) I-< .....

_§ 30

..!:: ....., 0. 8 50

70

c

10

� ... � 30 _§ ..!:: .... 0. 8 50

.70

0 0.4

26-1 1-83:

0 0.4 0.8

26-11-83

. 188

u. .. -1 ca · (meq 1 ) 0 . 0.4

. 29-09-84

29..09-84

HC03 (meq f1) 0

r----'-r---'--1'-.0---''---'----'-t--'- 1. 0 2.0

26-1 1-83 29..09-84

0 0.4

28..09-�5

0.4

28..09-85

0 . 1 0 2.0

28..0�85

Figure 5 . 38 Calcium (A ) , magnes ium ( B ) , and bicarbonate ( C ) ion concentration

profiles for Lake Barrington .

189

Table 5 . 5 : Volume weighted mean temperat ures and oxygen contents , heat contents , thermal s tabilities , and Birgean Wind Work values for Lake Barrington and the Pieman River reservoirs , N . S . = Not Stratified

Lake D a t e Average Average Heat Thermal Birgean Oxygen Temp . · Content S t ability Wind Work

mg L- 1 o c Cals cm-2 gm-cm cm-2 gm-cm cm-2

Barrington 0 2- 1 0- 82 1 0 . 48 7 . 0 1 89 1 9 1 39 2 3 3 2 6- 1 1-8 3 9 . 20 9 . 9 2 6 603 7 9 1 7 5 1 2 9-0 9-84 1 0 . 3 9 6 . 9 1 89 6 4 N . S . N . S . 2 8-0 9-85 1 0 . 3 9 7 . 6 2 1 866 261 3 6 6

Murchison 0 8- 1 1-82 7 . 1 1 4633 1 45 1 4 9 30-0 3-83 4 . 7 7 8 . 8 1 7 9 36 450 2 8 9 2 1 -0 7-83 9 . 59 4 . 3 883 1 N . S . N . S . 2 4- 1 1-8 3 8 . 3 1 7 . 5 1 5 8 1 8 2 80 1 6 3 1 7-0 3-84 4 . 04 8 . 9 1 8 9 1 6 660 293 1 1-0 7 -84 9 . 1 1 5 . 5 1 1 1 43 N . S . N . S . 0 8- 1 1- 84 9 . 2 9 7 . 2 1 5 1 30 3 7 8 1 06 0 9-0 3-85 4 . 7 8 9 . 6 22034 7 3 8 505 0 9-0 7-85 1 0 . 22 5 . 8 1 2 1 37 44 5 8 1 9- 1 1 -85 8 . 1 1 8 . 7 1 75 86 5 46 238

Rosebery 2 5- 1 1 -8 3 5 . 7 9 1 1 . 0 1 89 65 4 0 1 5 6 7 1 8-0 3-84 4 . 6 7 1 4 . 1 23382 558 1 1 86 1 2- 0 7- 84 7 . 7 1 27 4 7 1 3 . 5 22 1

Mackintosh 1 1 -0 3-8 1 1 . 25 1 2 . 1 28496 6 4 9 1 1 7 9 1 0- 06-8 1 4 . 36 1 0 . 0 20238 83 6 1 4 20-0 8-8 1 4 . 37 7 . 9 1 9036 50 3 7 9 20-0 4- 82 5 . 02 1 2 . 8 2 3 369 2 5 7 928 0 7- 1 1 -82 8 . 7 1 6 933 1 5 4 2 7 5 2 4- 1 1 -83 2 . 99 1 1 . 1 1 6 840 1 9 1 3 7 3

Pieman 1 1 -0 9-8 6 8 . 1 2 7 . 8 2 2403 1 37 6 2 1 30- 0 1 -8 7 3 . 36 1 0 . 9 3 1 1 40 1 07 7 1 49 5 2 4-0 9-8 7 8 . 2 2 1 7 9 6 222 592

190

All the reservoirs d evelop quite high summer thermal stabilities ,

and large input s of energy would be required at these t imes to

completely homogeniz e them . Lake Mackintosh is possibly the least

s table of them. Thermal stabilities are low during winter

circulation , and could not be calculated for two occasions for Lake

Murchison and o nce for Lake Barrington , because of insufficient

density d ifferences .

Birgean Wind Work calculations foll ow those for stab ility . However

values for Lakes Mackintosh , Rosebery and P ieman were generally higher

than thos e for Lake Murchison , and possibly Lake Barrington . This

indicates more energy is expended to produce the thermal s trat ification

p atterns observ ed within these three reservoirs , than in the o ther two .

PART C THE LAKES OF THE LOWER GORDON RIVER AREA

5 . 3 . 1 0 PhysicochEmical Features of Lake Fidler

Thermal and chemical pro f iles for Lake Fidler from 1 98 3 onwards

are given in F igure 5 . 39 . All depths are relative to the gaugeboard

datum for this l ake . Thermal stratif ication is evident in the mixo­

limnion of the l ake during summer . A slight mes othermal bul ge , of

less than 1 ° C , was present centred 3 . 5 metres deep in April , 1 983 , and

at 3 . 0 metres in both April 1 986 and April 1 9 87 . However , the dep th

of the oxycline varied from 1 985 onwards . The lake became anoxic

3 . 30 , 3 . 45 , and 3 . 55 metres deep in January and March , 1 985 , and

April , 1 986 , respectively , but the maximum dep th of the oxic zone was

shallower , at 3 . 0 metres , during early 1 98 7 .

The considerabl e discont inuity in the pH profile in January 1 985

(Figure 5 . 39 ) is indicative o f the abruptness of the chemocline on

t hat occasion , but usually pH changes were less dramatic , and so were

not good ind icators of chemocline position . The depth of maj o r redox

changes from oxidizing to reducing values , increased from about 3 . 5

metres in early 1 983 , to below 3 . 7 5 metres in 1 986 . However in

February and April , 1 987 , the redoxcline was again positioned at a

depth of 3 . 0 metres . The progressive deepening of the redoxcl ine

s ince 1 98 1 , and its dramatic elevation again by 1 9 87 , is shown in

Figure 5 . 40 .

Profiles o f conductivity (Figure 5 . 39 ) show little evidence of

increased depth in the conductivity cline . However two s ignif icant

"' � " .§ E! "' "' ., � 0 " .0

.c co. " 0

-200 -100

191 Eh (mv) Eh (mv)

0 100 200 300 400 -HiO , 0 100 .200 . 300 400 · 500 L ________ t _t L.,__---'------'---'-------'------'------'

1.oc "? lp'

---------------

4.0

5. 0

6.0

2S·02-l983 . 12-04-1983 1 9-o1-1985

-.------, l r---.--·-.--�--�---, sooo o · 100"0. zooo . 3ooo 4ooo 5ooo 1000 2000 3000 4000 5000 ·K1 8 (ps cm"1)

Tile � l.Q 12 � '?:?

0 1000, 2000 3000 4000 Kl·sqJ� c�·l)

·200 I

I I

0

·1?0 9

K18(ps crri1) ,_1

--·�----. 5.0 r,:o 7!o pH

Eh (mv) . �0 100 290

T"-c LO 15 20

'''1 .0- -� I "' \l) j:l 2.0 " .§ E

---a;- I .E T I " K1s / ., .?-s 0 OJ 4.0 .0 -:5 l\1 8 0. · pH " Cl 5.0

6.0

7. u-os-1985 ·-0_7-oS-1985' 14-o4-19�6.

" iS 1 obo 2obo 3obo .11obo 5000 10 0 2000 300.0 4000 5000 0 1000 - 2000 3000 4000 5000 Kls(US cm'l) K18(US cm-1) K1g(US- cm·l)

5.0 .6.0 · 7.0 6�o:--7:o pH . pH

6 lb 2'0 b fo zo 310 ciz% sat -o2 % Sat

F igure 5 . 39 Depth prof i les of vari ous phys ico- chemical parameters

from Lake Fidler , plotted relative to datum to show f luctuations in

water level ( The figure is continued next page ) .

6.0

7.0

Eh (mv) Q 190 2QO 390 4QO 5QO rc· . 1�C

192

1&___:.1,5 L.�1,3::__----"'J,s

04-()2·1987

1000 2000 3000 4000 Kls(l!S cm"1).

0 ' . 1000 2000 3000 4000 �8(US cnili

z'o ·4b do . Oz % S�t

s'o ' 6 20 4.b do so o2.% Sat

-12.2.__ Q i''t l,Q______J,5

T

Eh (mv) 1po 290 3QO 4QO

15-04-1987 1 b 1o'oo zo'oo 3ooo 400o

K18(US cml)

do

Figure 5 . 39 ( continued ) . Further depth profiles of various physico- chemical

parameters from Lake F idler , p lotted relative to datum .

193

«i\119 �}, changes are apparent . Firstly , the�conductivity gradually

thickened , and spanned an approximately 2 . 75 metre stratum in 1 987 ,

compared

conductivity J, metre stratum in January , 1 985 . The

was also 0 . 75 metres shallower in 1 9 87 , and

conductivity at 3 . 00 metres had increased by about 300- 400 }AS cm-1

(Figure 5 . 40) . This change in the thickness and depth o,;� v

conductivity indicates the possib le intrusion of an interflow

more saline and d enser than the mixolimnetic waters , but l e s s saline

and dense than the monimolimnetic waters , positioning itself in the

vicinity of the chemocline . However in May , 1 985 , mixolimnetic

conduct ivities g enerally exceeded 500 p S cm- 1 , and were considerably

higher than tho s e of the previous March . conductivity also

occupied a narrower stratum typical of earlier measurement s . This

suggests an inf low of higher sal inity water into the mixol imnion ,

elevating its conduct ivity on this occasion .

The second s ignif icant change is the decline of conductivities

(and therefore salinities ) in the bottom wat ers of Lake Fidler , from

4 7 �0 Pl S cm- 1 at 7 . 0 metres in January , 1 985 , to 3 940 JlAS cm- 1 in

April 1 98 7 (Figure 5 . 3 9) . This dilution mus t result from wat er

movement s across the chemocline , perhaps in response to the salinity

gradient , and may also cause the increased thickness of the

conductivity cline .

5 . 3 . 1 1 Physicochemical Features of Sulphide Pool

Physicochemical profiles for Sulphide Pool are shown in Figure

5 . 4 1 . All depths reported below are relative to the gaugeboard datum

for this lake , too . Considerable changes in its meromi ctic condition

are apparent from December , 1 9 8 1 , onwards . At that t ime , and in

February , 1 9 82 , the lake was thermally stratified , and the redoxcline

was less than 2 . 0 metres deep . This stratum , occupying the mid depths

of the lake , was also a zone of considerable pH and conduc t ivity

change . The K1 8 of the monimol imnetic water s exceeded 1 600 S cm- 1 .

Considerable instability o f the water column was app arent in

April , 1 9 82 . Eh fell suddenly to near reducing conditions at 1 . 95

metres , returned rapidly to oxidized values at 2 . 00 metres , b efore

changing once again to reducing conditions at 2 . 1 0 metres . These

changes were accompanied by irregularities in the conductivity prof ile

and decreasing pH. This pattern was conf irmed by another prof ile ,

taken with a second close-interval sampler , at a different posit ion

2.5

3.0

.:: I 0. I 8 3.5 I

; -

...... _ - - - - - - -

I -·

I I /

I I

I I I

I I

I I

I

194

,, I \. I ' '

' ,, _ _ _ K�s _ _ _ . - - ·! /- ---· - -\

Redoxcline

\ )'(' , i f.-. ' / v '- I \ ' \/

0

..;; "' :': "' 0

000 � ::t � g 0 " a. "' 2 s

-c Vl 1"\ 3, rooo ·.:::

I I 4•0 J l F I M {A I Ml J l.i""!ATSIOJNTDl'-J'I-r 'IM....,.IA-,1:-.M-ri-J 'I J-,lrA•I-srJo"lr. N-rl-:-o'j J:-Jr:F:-r.(:-MTj A--ri M-:-rj-JTI--�

1981 1982 1983· '' ' ' '" ' ' '"' "'T+'�l . 1985 Apdl 1987·. 198Q

Figure 5 . 40 The vari ation in the depth , relative to datum, of the

(redoxcl ine) 1 and in the electrical conductivity (Klg ) at a depth of 3 . 0 metres

( relative to datum) in Lake Fidler . Data from 1 9 8 1 from Bowling ( 1 9 8 1 ) ;

and for 1 982 from Croome ( 19 84 ) .

195

in the l ake . A mesothermal bulge was also present between 1 . 75 and

2 . 4 0 metres . The se data indicate a considerable drop in the chemoc line

posit ion t ook place b etween February and April , 1 982 . The chemo cline

was even deep er in November , 1 98 2 , and consider able ins t ab ility was

again app arent in the Eh and K1 8 profiles , this t ime within the

monimol imnion .

Marked irregularities were also present in the conduct ivity

profiles of both February and April , 1 983 , although the •

remained at a fairly constant depth during this t ime . The chemoc line

may have been protected from erro s ive mixing by the thermal

stratification present over summer . However , the concentrations o f

monimol imnetic s o lutes continually declined , and b y Augu st , 1 98 3 ,

the chemoc line had s unk to about 2 . 40 metres . A slight temp erature

inversion and a s harp increase in K1 8 took place at thi s depth on

this occasion .

The next data , from January , 1 985 , show considerable changes had

taken p lace in Sulphide Pool , with the K1 s at mos t depths being

considerably higher than in August , 1 983 . The gradual increase in

K1 8 from surface to bottom , rather than a sharp increas e at dep th ,

and the p er s i stance o f oxygen at trace amounts almos t t o the bottom

is indicative of an inf low of slightly saline Gordon River water ,

not much prior to the sampling t ime . By March , 1 985 , the conduct ivity

cline had been eroded considerably , and greater amount s of oxygen were

present , e sp ecially in the mid-dep ths of the lake , due to mixing in

the surface water s . A fur ther s al ine inf low had occurred by May 1 985 ,

again raising the conduct ivity o f the whole water column , e specially

below 0 . 5 metre s . The increased K1 8 below this dep th was accompanied

by increases in p H , decreases in g440 • and increases in oxygen , to

level s greater than 80% s aturation close to the bottom . The lake

was iso thermal .

Sulphide Pool was again s ampled in April 1 986 , and in February

1 9 87 , and was very s imilar on b o th occas ions . w��

about 2 . 00 metre s , and conductivity increased steadily from this

depth to the bot t om . K1 8 data for 1 986 shows two step-like increases

with d ep th , indicatin g two s ep arate strata of differin g s alinity

water . The conductivity o f the bo ttom waters had declined by

February 1 9 87 .

Changes in the meromixis o f Sulphide Pool are summarised in

Figure 5 . 4 2 . Thi s illustrates a s inking redoxcline between 1 98 1 and

'-:j) 0.5 t � s ! .0

3.0 .

3.0-

'pH

1 3- J 2- 1 Y8 1

�����·-·--1 tJ 5 f) pH

Eh lmd - 1 fL0

___ 2 ___ _ 1

_ _9��___::_�_j

T"c L __ �_!2____3o

0 5- 1 1 - 1982

0 4oo 8oo 12lio- -16'oo 6 !<1 8 I�S cm- 1)

196 Eh (mv)

100 200 300 400 0 Eh (mv)

1 00 200 300 400 --L----L ____ L__ __ , L_ __ _L ____ L_ __ _L ___ _j

1 0-02-1982

i I I 400 800 1200

I\18 lfJS cm-1) 1 600

1 05-04-1982 2000 o--4il()Bcl0 1 200 16bo

I<1 8qJs cm-11

Eh (mv) t�o ___ 2..J.o_o ___ 3_ln_o __ 4_o_jo ? 1 00

23-02-1 98.3

Eh (mv) 200 300

14-04-1 983

40o 8di:J IZlio 1 6oo 040il80o120o I<1 8ifJS cni1 ) I<1 s i}JS cm-1)

6 pH

400 500

7

Figure 5 . 41 Depth profiles of various phys ico-chemical parameters

from Sulphide Poo l , p lotted relative to datum to show fluctuations

in water level . (The f i gure is continued next page . )

-;; OJ .t: ,,_, _§ E 2 "' "" ;! .Q "' .0

-= 15. "' Cl

-;; "" l::; c;

_s § � � 0

o2 % Sat 0 1 0 20 197

T°C -5 1 0 1 5

0 . 0

0.5-

1.0-

1.5-' "1 2.5-i

J

I i .1.0-j

I

T

09-D8-1983 r

0 400 800 K18q.Js cm·1)

62_ 02 7.; St1t

70 8 0 90 T''c

1 0 1 5 �-------'

' I I

''" I(, h i "' ' '-._ 0.5� 1

1 .0� I i i

l .SJ

2.0·'

2.5�

I 3.oJ \

T l I I

\ \ 0�/ pi I

g4·10 \ I I

07-05-1985 �(Jo"""""BOo

1<1 s(US cni1)

5

5"""""""""iDJ:'s �!40(m" l)

G pli 7

20-{)1-1985 �,...----..,

0 400 800

?

I<1 8(j.JS cm1 )

1,0

,. ---, 1 5 20 25 g440(ni l )

,--,-� 4 6 5

pH

0 % Sat 20 40 60

T°C 1 5 20

0

1 0 l

0

o2 % $at 1 0 2 0

T°C 1 5 . 2 0

3 0

2 5 J___�_,..............

20

1 0-03·1 985

o2 ?,; Sat 40

0 400 800 K1 8 (pS crn" 1 )

GO 80 ____ .... L. __ ___,

T't " J 0 1 5 �

Figure 5 . 4 1 ( continued ) Further depth profi les o f various phys ico-chemical

parameters from Sulphi de Poo l , p lotted relat ive to datum .

� l:l· "' _g El E "' 'tl

1 .

r

I I

I

198

- - - - - - - - - - -,, " I I I '/f I I ' I I

' -.. .;

i3 2.0 0 I

I I

I 1000 -.; . .o .c 15. "' Cl I

I /

I /

Redoxcline

2000

Figure 5 . 42 The variation in the depth , relative to datum , of the

(redoxclin�.) 1 and in the electrical ronduct ivity ( K 1 8 ) at a depth of 2 . 0 metres

( relative to datum) in Sulphide Pool . No further redox data was available

after August , 1983 . Data from 1 9 8 1 from Bowling ( 19 8 1 ) .

,..r co . � !" 0 ii: <;' "' v. c. "' 2 a

-c (j) n ?.

199

we.r� 1 9 83 (no redox d a taAavailable after that date) , while the conductivity

at 2 . 00 metres a l so decreased as the chemocline sank through this

depth . Data since 1 98 3 show K1 8 varied at this dep th due to saline

inflows , but desp ite these , it never reached the values first

recorded in early 1 9 8 1 .

5 . 3 . 1 2 Physicochemical Features of Lake Morrison

The meromi ct ic condition of Lake Morrison decayed following the

commissioning o f a hydro-electric power stat ion on the mid-r eaches o f

the Gordon River , and its evenutal holomixis occurred in April 1 97 8

(King , 1 9 80 ; King and Tyler , 1 982b , 1 983) . The lake has s ince

vacillated between holomixi s , when it is completely isohaline , and

incipient meromixis , when conduct ivity clines are present (Bowling ,

1 981 ) . Subsequent data from the lake are shown in Figure 5 . 43 . It

was chemically s tratified from the end o f 1 98 1 to mid 1 98 2 , as

evidenced by the ano xic , sulpheretted bottom waters of December , 1 98 1 ,

and the weak con duct ivity gradient present in April , 1 982 . However ,

the lake was ho l omi ctic again in November , 1 98 2 .

The three s amp l ings in 1 985 and 1 9 86 all showed chemical

stratif ication . Conductivity increased gradually from surface to

bottom in March , 1 9 85 , while gilvin decreased with dep th , and

dissolved oxygen persisted almos t to the sediment s . The conductivity

cline was s imilar in May , 1 985 , but values were higher than two months

earlier . g440 a gain declined slightly with dep t h , while oxygen was at

a minimum 1 . 50 metres deep , but increased markedly to almost 6 5 %

saturation near the bottom . Th�s� data sugges t a large inflow o f

saline water , w i th conductivities up t o 1 645 �S cm-1 , causing chemical

s tratification , somet ime prior t o the sampling o ccasion . The incipient Of f\Pri I i ii;�, meromixis�was accompanied on this occasion by anoxia and hydrogen

sulphide , and a slight increase in temperature , in the bottom waters .

.5 . 3 . 1 3 Calculations of Meromictic Stability

Meromictic s tabil ities in Lake Fidler h ave f allen gradually since

1 9 7 7 (Figure 5 . 4 4 ) . Initially this was fairly r apid , decreas ing from - 2 2 9 2 . 0 1 gm- cm em in January 1 9 7 7 , to 67 . 42 gm- cm em- in Apr il , 1 9 7 8 .

This represents an average decl ine o f 1 . 54 gm-cm cm-2 per month during

this period . D e spite the rap id drop in meromictic stability b etween

May and July , 1 980 , cal cul ations for the next series o f s ampling dates

( 1 9 80 to 1 98 3 ) show a slower rate of decline , e specially after July ,

1 98 0 . S t abili t y fell from 6 7 . 56 t o 42 . 92 gm-cm cm-2) an average

0.5

- 1 . 0 "' b '" E t . s

c. '" Cl .

2.0

T"c ____ 1p_---1

J1 5 __ 20

2.5-1 l j H2S Pr esf�ni

J 1 0-1 2- 1 9 8 1

0--400-flOO K1 5 ifJS cm-1)

1'01'2--14� Hil 4d"i l )

04-04-1982 �---.------j 0 400 800

1<1 8qJs cm-1)

,.-----,

2QO

6.0 7.0 pH

6 46o soo -izlJO I<1 8 ifJS cni1 )

,------, 6.0 7 .0

pH

06-l l-1982

6"4bo K1 8(ps cm·l)

1� 1 6 1 8

I i ' I I ! . ) \ \ 1,1 8 I

\_

·g (m'l) 4 4 0 .

��, 1 I SS Present

1 2·04·1986

\

Figure 5 . 43 Depth profiles of various physico- chemical parameters

from Lake Morrison .

201

-2 decline of 0 . 70 gm-cm em per month . In the third set of data

available (January , 1 985 to April , 1 9 8 7 ) , meromictic stabilities -2 -2 dropped from 46 . 39 to 3 7 . 22 gm-cm em , an average o f 0 . 33 gm-cm em

per month . The l owest meromictic stability cal culated , 28 . 32 -2 gm-cm em in May , 1 9 85 , probably results from the higher salinity

mixolimnion present on that o ccasion , which decreased the apparent

density difference between thi s and the monimol imnion , rather than

from o ther change s within the l ake . Since 1 98 6 , meromictic stabilities

here remained almost constant .

Meromi ctic stabilities in Sulphide Pool (Figure 5 . 45 ) were much 'ft,� �:»; l.<h «� lower than those o f Lake Fidler . � aeclined gradually from a

maximum of 9 . 44 gm- cm cm-2 in January 1 9 7 7 , to 6 . 02 gm-cm cm- 2 in

April 1 9 7 8 , a mean drop of 0 . 2 1 gm-cm cm-2 per month . The decl ine

continued , from 4 . 1 3 gm- cm cm- 2 in May 1 980 to 0 . 07 gm-cm cm- 2 in

August 1 98 3 , an average decrease of 0 . 1 0 gm-cm cm-2 per month .

Inflows of sal ine water on occas ions since 1 985 ( 5 . 3 . 1 1 , above) hav e

caused slight fluctuations i n the chemical s tabilities of the l ake .

However , apart f rom that of May , 1 985 , when the evidence suggests the

greatest inflow , stabilities have always been below 1 . 00 gm-cm cm- 2 .

The meromiCtic s tability o f Lake Morrison fluctuated markedly

during 1 9 7 7 and e arly 1 9 7 8 , prior to the onset of holomixis (Figure

5 . 46 ) . These ranged from a maximum of 6 . 60 grn-cm cm- 2 in June 1 9 7 7 ,

to a minimum of 2 . 1 0 gm-cm cm- 2 in December 1 9 7 7 . Data from the

following years reflect the periods when the l ake is isoh.aline , with

s tabil ities near zero , such as in July , 1 9 80 ; May , 1 9 8 1 , and November

1 982 ; and the intervening periods of incipient meromixis , when

conductivity gradients were present . However , stabilities s ince

1 9 7 8 have never exceeded 2 . 00 gm-cm cm-2 .

5 . 3 . 14 Thermal Stabilities , Birgean Wind Work, Heat Content , and Volume Weighed Average T emperatures

(a) Thermal stabilities

Thermal stabilities for Lake Fidler , Sulphide Pool , and Lake

Morrison are shown in Figures 5 . 4 4 , 5 , 4 5 , and 5 . 4 6 , respectively .

These vary depending on the season and the extent of thermal

s tratification p resent . The h ighest thermal s tabilities occurred

in summer , when they could exceed the corresponding meromictic

s tabilities of these months , and thus assist the maintenance of

meromixis . This was particularly so in Lake Morrison and Sulphide

Pool . In contrast , thermal s tabilities were lowest in winter . In

202

100

80 ~ ,I \�\ t:

I •I I I

II - 60 I I

<'i l i 's I I � I I E I i

j 40

: I I ' I l I t�

� t 1 :' � I ' , , 1 s ' I i l I I l j l 'f) I I li 1 20 I I I ,. I

I • , . I I '

I

0 I I

' I I I , , \' ·2

1976 1 1 �77 I . 1978

I I I I I I I

1979 ' 1980

1 I I I I I 1 I I I

I I I I I I I I I I I 1 I 1 I I I 1 I I

'

1981

·.�\

1982 1983 1984 1985 1986

A . . 1 \ Thetmal Stability I I

1987 l

F igure 5 . 44 Chemical stab ilities ( so lid line ) , and thermal stabilities

( dashed line ) calculated for Lake Fidler . Results prior to 1983 calculated

from data of King ( 1 9 80 ) , Bowling ( 1 9 8 1 ) , Croome ( 1 9 84 ) , and Baker

et al ( 19 8 6 a ; and unpublished ) .

30

25

20

N' 'E u

E 1 5 � u i:

-.9 ,q :E J::l 10 (j)

5 I I I ' I : �

-2

" , , ' I ' • : I ' I I I , , I I I I I I

'I lj , , , , , , : I • ' , , I ' , , I I

I ' ' l ' , I . , , . I' j

t I :I I ' , I , , I \ ' I I l I ,I , , ,, 1 \ I I 1 1 I I (·) I I ' I I I Theff1lill Stability

I I I ; I • 1 1 1 I I I , I I I I I 1 1/ I I I I

I I v I I i I \ I I ::·: - - - ,� I �Stability

.-----.------.------.------r------.-----.------.------,------.------.-----. 1977 i97S. 1979 1980 1981 1982 1983 1984 1985 ' 1986 19$7

Figure 5 . 45 Chemical stabilities ( solid line ) and thermal stabilities

( dashed line ) calculated for Sulphide Poo l . ( Results pr ior to 1982

calculated from data of King ( 1 980 ) and Bowling ( 1 9 8 1 ) )

'7

5

4 T c'f' I

I ' § I I E I ' � I j 3 I

I � · I rE "' I 19 I iJ) I

2 I I I

I I I I' I II I I I : 1 : I 1 1 , 1 1 l 1 1 I I 1 1

0 I l l '

I • ' I ' ll I• I . -I

1977

IJ I I I I I I I I I I '

I

:

1978 1979 1980

'· ' I I I ' I : I

I I I I I I I I

203

1981 1982 1983 1984

I I I I Thermal Stability I I I I I I I I I ::;':· I I I

\� Chemical Stability

1985 1986 1987

F igure 5 . 46 Chemical stabi lities ( so lid line ) and thermal stabi lities

( dashed line ) calculated for Lake Morrison . (Results pr1or to 1 9 8 2

calculated from data of King ( 1 9 8 0 ) and Bowllng \ 1 9 � 1 ) )

I '.. I :. \

': \ ·. \ · .. I

:. I ·. I ·. I ·. \

• •• \ -..., I . \ "' ....; / ... /' ;,.,f ...

liea Content

8000

\ t: 7000 \" I \

6000

5000

��-,.-.-.-.. -.-,.-.-,r.�.-.-��·4000 o · N, D l J F M A f•l F M A .M J

1976 l'ITI 1978.

::J: & (") 0 " " ·g

f v; " s . y

Figure 5 . 47 Thermal stab i l ities ( so lid line ) , Birgean Wind Work ( dashed

line ) , and Heat Content ( dotted line ) calculated for Perched Lake

from October , 1 9 7 6 to Apr i l , 1 9 7 8 , from the raw data of King ( 1 9 80 ) .

204

1 9 7 7 , when marke d d i chothermal temperature profiles were measured ,

negative thermal s t abilities were calculated for all three meromi ctic

lakes . At time s , however , the normal seasonal pattern was distorted

with marked fluctuat ions in thermal stability . These would probably

be due t o p eriod s o f hot ter or colder weather causing warmer or cooler

lake surface waters , and stronger or weaker thermal gradients than

usual . The range s c al culated are given for each lake in Table 5 . 6 .

Thermal stabilities were al so calculated for nearby warm

monomictic and mesohumic Perched Lake , using King ' s ( 1 980) data for

1 9 77 and 1 9 7 8 . The range in thermal stabilities is shown in Figure

5 . 47. The seasonal pattern of change was more regul ar than shown by

the other three l ake s , for the s ame period . Climatic differences

probably account for the much lower stabilities of early 1 97 8 than

for the corresp onding p eriod o f 1 977 .

(b ) Birgean Wind Work

Birgean Wind Work values calculated for Lake Fidler , Sulphide

Pool , and Lake Morrison are shown in Figures 5 . 4 8, 5 . 4 9 , and 5 . 50 , respectively , while those for P erched Lake from October , 1 9 7 6 until

April 1 9 7 8 , are shown in Figure 5 . 4 7 . Ranges for the four lakes are

g iven in Table 5 . 6 . Birgean Wind Work generally showed smoother

seasonal variations o f l ess amplitude than thermal stability calculations ,

ap art from the sudden increase in July 1 9 7 7 , in Lake Fidler , which

possibly resul ted from its severe dichothermal stratificat ion at that

time .

The values o f Birgean Wind Work for Lake Fidler are l ower from

1 980 onwards (Figure 5 . 48 ) . However , the data , e specially f rom 1 9 83

onwards , is too fragmentary to ascertain whether this is indicative

of changes within the l ake itself , or due to t emporal diff erences .

In comparison , r ecent v alues for both Sulphide Pool and Lake Morrison

f all within the r anges cal culated for these l akes for 1 9 7 7 and 1 9 78 .

The mo st complete monthly data set for all f our lakes was from

January 1 9 7 7 unt i l April 1 9 7 8 . Direct work curves for selected month s

during this period are shown in Figure 5 . 51 , and all resul ts are shown

plotted as isolines in Figure 5 . 5 2. Mesohumic Perched Lake exwmplifies

how work d istributes energy in a warm monomictic lake dur ing a year .

In mid- summer , most energy is distributed within the surface two to

four metres , but this distribution deepens in autumn , and during

winter the little remaining ener gy is fairly evenly distributed

6000

5000 ., / \ ,, I 1 } I

I �-· I

/ I : ' I I I I ' I I

205

11 Heat Content I I I I I � 'S 4000 u ' I I I \ :\ I

I I I I \ ; \ I I I I I

/ I so

]

<'-I­' S u

.!!l _§

1000

I I I I t '

1976 1977 i978

' \

1979 1980

II I ' I \ '

·.:

\ /\Birgean Wind Work v \ 0

1981 1983

/

1984 1985 1986 1987

Ol

60 �· " :,:: 5' "'

40 � I "" "' 3 r\

20· 3 3, .19

F igure 5 . 48 Heat content ( dashed line ) and Birgean Wind Work ( solid

l ine ) values calculated for Lake Fidler . (Results prior to 1983 calculated

us ing data of King ( 1 9 80 ) ; Bowling ( 1 9 8 1 ) ; Croome ( 1 984 ) , and Baker

etal ( 1 986a , and unpub lished ) ) .

3000

2500 I '

2000

" ' I

\

>tl I '

; I , i I

h l-leat·Content

,' I I I I I I I

,\ 1 1 , I

I I I I I

14

12

10

8 c 1500 $.

I / I I { I �,' f I c: 0

u

1 1000

500

1977 1978 1979' •1980 1981

.-. · .. ·.�

0 · Birgean Wind Work

1982· 1983

6

0 0 4

2

1984 1985 1986 1987

F igure 5 . 49 Heat content ( dashed l ine ) and Birgean Wind Work ( solid

l ine ) values calculated for Sulphide Pool . ( Results prior to 1982 calculated from data o f King ( 1980 ) and Bowling ( 1 9 8 1 ) ) .

2500

' r ' ' 2000 '

� I , ' S I \) I

] I I I ' c I I � 1500 I I 0:: I I I 0 • f ' I u r '• I � I I I

i I :r: I

I I

1000 I

500

1977 1978 I 1979 1980 1981

206

,' Heat Co!!tent I [�·) I

I I

Birgean Wind Work 0

1982 1983

I

1984 1985

[14

12

10

f. o;J "" ::r (Q "' "' :0 s " 0.

G :E 6 0 :.1-

lEI � 3 4 " 3, J)'

1986 1987 1: F igure 5 . 50 Heat content ( dashed l ine ) and Birgean W ind Work ( solid

l ine ) values ca lculate d for Lake Morri son . (Results prior to 1982 calculated from data o f King ( 1 980 ) and Bowling ( 1 98 1 ) ) .

207

B (gm-cm cni2 ) o . o 0.8 1 . 6 0 . 0 0 . 8

. . 0.0 0. 8 2 . 4 �-----! ___ _1_· ___ I _ ___..L___i ___ __ .l_ ___ j _________ k=--'----'---------',-=-'----'-' --'---____J..;.__-+-----1'

0.8 . 1 . 6 ----�- ->

1 0-{)4-1977

1 2

:5 0. \l)

a

2 /

OH14-� I

6 -

8 I.

o.o · o.4 o . 8 o . o

12-07-1977 25-10- 1 9 7 7

PER CHED LAKE

B (gm-cm cm2) 0 . 4

26· 1 0- 1 9 7 7

0 . 0 0 .4 --'------'------->L-- j ----- --'--------'------ 1�-- -'--""'

�"-"\ I

0 0 0 4 0 .8 0 0 ......-------L__.__..:_f __ L____. -L-·-·------·--"- __ ____)

-----------... ""'·

\ " '\ � 1

) \ \l) _§ I

I :5 �/ J e 2 a /

I /- 29-{)1-1977

1 2·07-1977

l '\ ' \

I \�

i llH 9 7 7

I / ' / SULPHIDE POOL 1/

B (gm·cm cm2J

0 4 0 0 � ------------�

14-{)7-1977 . 15-12-1977

LAKE MORRISON

'14-{)2-1978

(

0 0 0 4 "\ ' I ) ' J 06'{)4-1 978

F igure 5 . 5 1 Direct work ( B ) curves for the four lakes of the lower

Gordon River area , for summer , autumn , winter and spring periods , in

1 9 7 7 and 1 9 7 8 ( calculated from King ' s ( 1 980 ) raw data ) .

4-

]

PERCHED LAKE

- --/ "

'

' '

'

', · - - · · , · - - -10"

' ' '" , \

208

\ \.'· ... - -20'" ,;'

'• \

'

: "0 . -.s 6

' '

' '

.

c. ()) Q ' '

' \

' 8

5 I ' ' .

I . \ '·40 . ' " .. - ,.

10 '

2

4

' ' ' ' - - - - - - • - - . - - -' . . - - - - 20-- - - - - - - - - - - . - -

lAKE FIDLER L

I I F M A M r r

.. .. �- �

1977 A

1978

F igure 5 . 52 I sopleths of direct work ( B ) ( gm-cm cm- 2 ) done by wind

to d istribute energy within a lake - Perched Lake and Lake Fidler ,

October 1 97 6 to Apri l 1 9 7 8 . Arrows along bottom indi cate s amp l ing

o c cas ions ( calculated from raw data of King ( 1980 ) ) . ( This figure

continued next page . ) B \:S.

·. V) � (\) g ;S c. �

209

SULPHIDE POOL

3 ���--�1�--�1_,1L-r�t.--�-1�1_-r1_ 1. ,J F 1 M 1 A M J 1 J A S 0 N D J

19'17 F M A 1978

25 ---------25--'

- 50 �5 '

'

'

1 \ '

' '

' \ I '

' '

., 2 / ' -

t 1 I 'L 3 �J�r-

F-.-

M--.-

A-.�

M-.-LJ-.�J��A�-

S�r-O-.--N

--.-D�l�J-.�F��M��A�

1977 1978

Figure 5 . 52 ( continued ) I sopleths of direct work ( B ) ( gm- cm cm- 2 )

done by wind to distribute energy within a lake - Sulphide Pool and

Lake Morrison . Arrow a long bottom ind i cate samp l ing occas ions . ( Calculated

from raw data of King ( 1980 ) . B 'i/(d<H> )0'\1. tl-

210

throughout all d ep th s . The f ollowing spring wind work is again

effective in dist r ibuting incoming solar energy only a little below

the surface .

The direct work curves and isoline diagrams for the three

meromictic lakes p rovide a considerable contrast to thos e of Perched

Lake . Lake Fidler provides the best example . In autumn , maximum

energy distribution i s two metres below the surface o f the lake , but

in winter this drops to the mid-depths , due to the considerable amount

o f energy s till r emaining , stored as heat in the monimol imnion . The

spring p attern , b efore extensive surface heating commence s , i s s imilar ,

but by summer mos t energy is again distributed near t o the surface , a

little above the chemocl ine . S imilar patterns are also shown by both

Sulphide Pool and Lake Morrison , but to a lesser extent .

(c) Heat Content and Volume Weighed Average Temp erature

The heat contents calculated for the four lakes were also plotted

in Figures 5 . 4 7 , 5 . 4 8 , 5 . 4 9 , and 5 . 50 , and the ranges g iven in Table

5 . 6 . The marked s easonal changes in heat content are mo s t apparent ,

being greates t during the late summer months , and leas t in winter .

This allowed the estimation o f annual heat budgets , eba • for years

when sufficient data were available . These were 1 62 3 . 6 , 1 7 26 . 2 , and

1 720 . 0 cals cm-2 for Lake Fidler in 1 9 77 , 1 9 80 and 1 98 1 , respectively ;

1 1 9 7 . 3 and 1 0 1 1 . 4 cals cm-2 for Sulphide Pool for 1 9 7 7 and 1 98 1 ; and

1 02 1 . 7 and 1 37 8 . 5 cals cm-2 for Lake Morrison for 1 9 7 7 and 1 9 80 . The

heat budget for Perched Lake f or 1 977 was 3056 . 7 cal s cm-2 .

Volume weighed average temperatures for the four l akes are listed

in Table 5 . 7 . P erched Lake was always colder than the meromictic lakes

at the equivalent t imes of year , while summer average temp eratures

were generally l ower in Lake Fidler than in either Lake Morrison or

Sulphide Pool , but warmer during the winter . The average temperatures

of Lake Morrison generally exceeded those of Sulphide Pool . The

ranges recorded for the four l akes are given in Table 5 . 6 .

5 . 4 DISCUSSION

5 . 4 . 1 The Role of Humics in the Limnology of these Lakes

Dissolved humic substances play a dominant role in the l imnology

of all these lake s , and contr ibute s ignificantly to their meromictic

or near-meromic t ic conditions .

Lake

Fidler

Tab1e 5 . 6 : Range in Volume Wei ghed Average Temperatur e , Heat Content , Thermal Stabilities , and Birgean Wind Work for the four lakes o f the lower Gordon River area . Dates of o ccurrence are included .

Volume Weighed Heat Content Thermal S t ability Birgean Wind

Average Temp er ature Work

o c C a l s em - 2 - 2 - 2 gm-cm em gm-cm em

Max . Min . Max . Min . Max . Min . Max . Min .

1 6 . 1 9 . 0 5 1 89 . 6 2 9 0 9 . 6 8 1 . 1 1 - 1 6 . 58 5 5 . 4 1 1 4 . 37 ( 2 7-02- 7 7 ) (02-09- 7 7 ) ( 27-02- 7 7 ) (02-09- 8 1 ) ( 3 1 - 0 1 -8 1 ) ( 1 3-07-7 7 ) (2 7-02- 7 7 ) (02- 0 9- 8 1 )

Sulphide P o o l 1 8 . 4 7 . 6 2 9 1 0 . 5 1 1 99 . 1 30 . 56 -0 . 2 1 1 2 . 2 1 1 . 42 ( 0 3- 0 2- 8 1 ) (03- 0 9- 8 1 ) (03-02-81 ) ( 0 3-0 9- 8 1 ) ( 0 3-02- 8 1 ) ( 1 6-06- 7 7 ) (03-02- 8 1 ) ( 0 3-09-81 )

Morrison 1 7 . 5 7 . 6 2 386 . 5 1 00 8 . 0 5 . 7 1 -0 . 92 1 2 . 54 1 . 0 1 ( 2 9-0 1 - 7 7 ) ( 1 0- 0 7- 80 ) ( 30-0 1 - 8 1 ) ( 1 0-0 7-80 ) ( 1 2-03-85 ) ( 1 7-06- 7 7 ) ( 29-0 1 - 7 7 ) ( 1 0-07-80)

Perched 1 4 . 2 8 . 2 8 27 3 . 6 4 900 . 5 1 22 . 98 3 . 47 1 0 1 . 39 2 7 . 74 ( 2 3-02- 7 7 ) ( 1 2-07- 7 7 ) ( 2 3-02-7 7 ) ( 1 2-07- 7 7 ) ( 2 3-02- 7 7 ) ( 1 5-06- 7 7 ) ( 2 3-02-7 7 ) ( 24-08- 7 7 )

1-o) � �

212

Table 5 . 7 : Volume Weighed Average Temperatures C C C ) for the lakes o f the lower Gordon River

Date Perched Lake Sulp hide Lake

Lake Fidler Pool Morrison

October , 1 976 1 0 . 3 1 3 . 2

January , 1 97 7 1 4 . 0 1 4 . 9 1 5 . 6 1 7 . 5

February , 1 97 7 1 4 . 2 1 6 . 1

April , 1 9 7 7 1 2 . 4 1 4 . 1 1 3 . 6

June , 1 97 7 8 . 3 1 0 . 5 8 . 5 1 0 . 0

July , 1 97 7 8 . 2 1 2 . 2 9 . 8 1 0 . 8

August , 1 97 7 8 . 4 1 0 . 7 1 0 . 2 9 . 4

October , 1 97 7 1 0 . 5 1 2 . 8 1 2 . 1

December , 1 97 7 1 2 . 7 1 4 . 4 1 3 . 1 1 5 . 7

February , 1 97 8 1 3 . 3 1 4 . 3 1 3 . 8 1 5 . 9

March , 1 9 7 8 1 3 . 7 1 5 . 5 1 6 . 1 1 7 . 0

April , 1 9 7 8 1 2 . 1 1 3 . 6 1 2 . 8 1 2 . 9

April , 1 980 1 1 . 7

May , 1 980 10 . 7

July , 1 980 7 . 6

January , 1 98 1 1 6 . 0 1 8 . 4 1 7 . 9

March , 1 9 81 12 . 3 1 3 . 5

Apr il , 1 98 1 1 2 . 2

May , 1 9 8 1 1 0 . 7 9 . 7

Sep tember , 1 98 1 9 . 0 7 . 6 1 0 . 0

October , 1 981 l l . 5 1 1 . 1

December , 1 981 1 0 . 9 1 4 . 0

February , 1 9 82 14 . 4 1 3 . 9

April , 1 982 l l . 5 9 . 6

November , 1 982 9 . 7 1 3 . 2

April , 1 983 10 . 9

Augus t , 1 983 7 . 8

January , 1 985 1 2 . 0 1 2 . 1

March , 1 985 1 3 . 1 1 5 . 5 1 4 . 2

May , 1 985 1 1 . 2 1 4 . 4

April , 1 986 1 2 . 3 1 0 . 4 1 3 . 4

early February , 1 98 7 1 1 . 7 1 0 . 5

late February , 1 98 7 l l . 8

April , 1 987 1 1 . 0

213

Dys tr ophic waters rapidly absorb solar radiation (Chap t er Two ) ,

mos t of which is extinguished within the surface f ew metres o f these

l akes . 1his produces sharp , shallow , thermoclines which develop early

in spr ing and persis t well int o autumn . This is particularly so in

Lake Chisholm , where winter circulation lasts only three months ; a

much shorter period than in o ther Tasmanian lake s , such as the deep ,

exposed Risdon Brook Dam (Tyler , 1 9 74) , or even sheltered , mesohumic

Perched Lake , whi ch s tratifies for between seven and eight months o f

the year (King and Tyler , 1 98 1 b ) . Jones and Arvola ( 1 984) have

suggested a clos e inverse relat ionship exi s t s between water colour and

the dep th of mixing in small , sheltered , polyhumic forest lakes . The

high humus concentrat ions may p o s s ibly allow weak surface heating

even in winter . Temporary thermoclines with gradients of up to 5 ° C

can develop even on clear , calm winter day s in the Gordon River lakes

(Baker et al , 1 9 85a) , creating fur ther resistance t o circulation .

The s trong thermal s tratif ication resulting from dys trophy is

important in protecting the chemoclines and monimol imnions of the

meromic t ic lakes and reservoir s from the eros ive effects of circulat ion . . �f��t

Thiskwas shown p art icularly by Lakes Mackintosh , Ros ebery , and Pieman ,

,whe.r..-B chemical s tratificat ion disappeared once the l akes became

isothermal in the ir f irst winter . The maj or ero sion of the chemo­

clines and temporary s al inity gradients o f Lake Morrison and Sulphide

Pool also takes p lace in the abs ence of thermal stratificat ion , in

winter . P revention o f circulation , either by thermal stratification

or by ice cover , was an important cause of meromixi s in Czech reservoirs

(Fial a , 1 9 7 9 ) . Additionally , thermal grad ients may impart considerable

s tab il ity upon a lake , .which in summer may exceed that produced by any

sal inity gradien t present , and thus s ignificantly assist the develop­

ment and maintenance of meromixis .

A further e f fect of the l ong periods o f thermal stratif icat ion 'UitiXit��.

in dys tr ophic lakes is hypolimnetic anoxi a . Thiskresults from the

bacter ial decomposit ion o f alloch thonous humic subs tance s rather than

from autochthonous produ ction ( S alonen , 1 9 8 1 ; S alonen et al , 1 983) .

Hypolimnet ic anoxia may develop very rapidly af ter the onset of

thermal s tratification , as in Finnish polyhumic lakes ( Salonen , 1 9 8 4 ;

Salonen , Arvola , and Rask , 1 9 8 4 ; Jones and Arvola , 1 984) , al though

s everal weeks elapse before it o c cur s in Lake Chisholm and the Pieman

River reservoirs . A l arge volume , anoxic hypolimnion , present for

considerable period s , may cause the reduction and mobilizat ion of

solutes , and the ir accumulation in the bottom waters , leading to

meromixis , as happened in the P ieman River reservoirs , Lake Barring ton

(Tyler and Buckney , 1 9 74 ; Tyl er , 1 9 80) , and Klicava Reservo ir ,

Czechoslov akia (Fial a , 1 9 79 ) .

Dis solved humic substance s also lower the pH of the lakes and

reservoir s s tudied , as they do in humic coastal lakes (Chapters Three

and Four ) . Lake Chisholm waters are acidic , as were the surface

waters o f the Pieman River reserv o irs , and Lake Barrington , and those

of the Gordon River l akes (King and Tyler , 1 9 8 1 a ,b ; 1 982a , 1 9 8 3) .

This is in keep ing with other humic Tasmanian and Finnish waters

(�Buckney and Tyl er , 1 9 7 3a , b ; Arvol a , 1 98 5 ; Ilmavirta , 1 9 80 , 1 98 3 ;

Ilmavir t a e t al , 1 984 ) . The acidic nature o f the Lake Chisholm

waters , and its seawater ionic character , is unusual for a l ake

formed in a kar s t ic depression . One explanation may be that the

inflowing and res ident waters are isolated from rock contact by the

peat mantle of the forest floor and organic sediments of the l ake

bed . However , chelation and c o-precip itation of calcium with humic

subs tances ( Sholkovitz and Copeland , 1 98 1 ; O t suki and Wetzel , 1 9 7 3 ) ,

and the c onversion o f bicarbonat e ions to free carbon dioxide at l ow

pH (Wetzel , 1 9 7 5 ) such as tho s e created by dissolved humic substances ,

may also account for the low concentrations of these ions . If so ,

this may prevent a build-up o f these ions in the bottom waters o f

this lake , and biogenic meromixi s b y these ions .

Humic substances may als o p l ay a role in the redox equ il ibria of

the monimol imnetic pool s o f chemically stratified Tasmanian reservo irs .

Dickman and Hartman ( 1 9 7 9 ) proposed that b iogenically meromictic l akes

could be subdivided into two mutually exclusive categories ; those

with an accumul at ion of bicarbonate or carbonate ions , and tho se with

an accumulation of iron and manganese , in solut ion in their pro fund ial

water s . However , both metal s , plus bicarbonate and sulphides , were

present in solut ion in the monimol imnet ic pools of the Tasmanian

reservoirs of this s tudy ) without obvious precipitation of met al

sulph ides or carbonates . '' 'This may in p art be due to the sl ightly

acidic nature of thes e waters , cau sed by the presence of humic

substances . However , a similar s ituation occurs in the anoxic

hypol imnet ic waters o f dimictic Lake L�vBsundet , Sweden , which Liden

( 1 9 8 3 ) character ized as a mul ticomponent system dominated by H+

, e , 2+ 2+ .

Fe , Mn , HzS , HzC03 , and hum1c subs tances . He suggested a pH

dependant complexation of the metals with the humic sub s tances allows

215

the coexistance of all thes e c omponents at a redox equil ibrium . A

like redox chemis try is hypothesised for the Tasmanian reservoirs .

Additionally , humic substances als o increase the solu bility o f �

certain met al ions , including iron and manganese , even in the presence

of sulphides and carbonates (Rashid and Leonard , 1 9 7 3 ) .

5 . 4 . 2 The Influences o f Basin Morphometry , Alignment , and Shelter from Wind Action

t 1,�·.411{ Theserf;:,ctors exert a considerable influence on the l imnology of

some o f fhe l akes and reservoirs o f this study , and their importance

as aids to meromixis have been stressed in s tudies elsewhere

(Nor thcote and Hal sey , 1 9 6 9 ; Weimer and Lee , 1 9 7 3 ; Walker , 1 97 4 ;

Walker and Likens , 1 9 7 5 ; Culver , 1 975 , 1 9 77 ; Hongve , 1 9 80 ; Howell

and Ker eke s , 1 98 2 ) .

Lake Chisholm is shel tered from most wind by a natural ampitheatre

of fore s ted h il l s , and is small and of considerable dep th for it s

surf ace area . Both features impede circulation and favour s t ability

(Walker and Likens , 1 97 5 ) , so that turbulant mixing is weak . Solar

rad iation absorbed by the surface waters is not distributed deeper

within the lake by wind action , leading to a shallow epilimnion .

Addi tionally , thermal stratificat ion can develop early in spring and

persist late int o autumn , without destruction b y wind created

turbul� nce . The roles o f basin morphometry , and of shel ter provided

by surrounding hills and fore s t s , have also been recognized as being

l imnologically s ignificant in many Finnish polyhumic forest l akes

s imilar t o Lake Chisholm ( S al onen , Arvola and Rask , 1 984 ; Arvol a ,

1 9 8 3 , 1 984b) .

All four Pieman River reservoirs showed initial chemical

s tratification , but rhis pers isted beyond the first summer only in

Lake Murchison . 7his resul t s from differences in their basin

morphometry , alignment and shelter (Figure 5 . 3a) . Lake Murchison is

long , narrow , and sinuous , well p rotected by surrounding hills and

mountains , especially near the dam site , all of which reduce wind

mixing to a minimum . In c omp ar ison , Lake Mackintosh is much broader ,

especially in the arm o ccupying the valley of the Sophia River

(Peterson and Missen , 1 97 9 ) , and therefore much more prone to wind

action . Lakes Rosebery and Pieman are al so broader and more exposed

than Lake Murchison , and their wes t-east alignment would make them

mo re susceptable to mixing by the prevailing wes terly winds act ing

over their entire lengths . Thus depth , shelter , and the dendritic

nature of Lake Murchison , which limit s wind fetch , all allowed

meromixis to remain in this reservoir , as they did in Lake Barrington

(Tyler and Buckney , 1 9 7 4 ; Tyler , 1 980) .

The low meromi�tic stabilities calculated for the meromictic

Gordon River lake s point to the fragile nature o f this phenom�?Ilbn

within them , which , compared with stability results from meromi ctic

lakes el s ewhere (Table 5 . 8 ) , are more akin to biogenic r ather than

ectogenic meromixi s , e specially those of Lake Morrison and Sulphide

Pool . Campbell and Torgersen ( 1 980 ) have described meromictic

stabilities o f 5 . 5 to 9 . 5 gm-cm cm- 2 as "rather precarious " . Factors

other than the s a l inity gradients , such as basin morphometry and

shel t er , are therefore indicated a s being operative , and although

insufficient to f ully maintain meromixis , may aid to slow its rate

o f decline .

The different rates at whi ch the three meromic tic Gordon River

lakes have proceeded towards holomixis result principally f rom

difference s in basin morphometry , described in detail by King and

Tyler ( 1 98 1 a) , and shelter . Lake Fidler , though sheltered , is l arge

enough ( 1 . 2 8 ha) t o permit wind generated ripples , but is deep enough

(7 . 6 metres ) to p r event overturn . Its s teep sided bas in morphometry ,

plus its protected nature , has meant this lake proceeded more slowly than

the o thers toward s holomixis . As the chemocline sinks , it is pos s ible

that the resistance offered to mixing by its basin shape and the

salinity dens ity gradient may approach an equilibrium with the

circulatory effects of the weak wind action on the surface wat er s .

In comp ar ison , although highly sheltered and small (0 . 1 1 ha) ,

Sulphide Pool moved more rapidly towards holomixis , so that by

August , 1 98 3 , only a shallow monimolimnion remained . Subsequent

saline gradients created by more recent inflows also appear to be

eroded quickly . The shallownes s ( 2 . 7 metres) of Sulphide Pool allows

even the small amount of wind induced circulation to be effective , in

the abs ence o f a s trong s al inity gradient , over almos t its entire

dep th . Lake Mor rison is of similar depth to Sulphide Pool , but of

similar area to L ake Fidler , and is also the mos t expose d . I t

quickly became holomic tic once r iver regulation began (King and

Tyler , 1 982b , 1 98 3) , and periods o f incipient meromixis s ince have

also been rap idly destroyed . Thus , the favourable basin morphometry

and shelter of Lake Fidler allows only sluggish circulat ion there ,

217

Table 5 . 8 : Mer omictic Stabilities o f the Gordon River mer omictic lakes , compared with those for s e l ected meromictic lakes elsewhere

Lake S tability - 2 gm-cm em

Lake Fidler 9 2- 4 3

Lake Morrison 6 . 6-0 . 0 1

Sulphide Pool 9 . 4-0 . 07

Ecto g enic /Crenogenic Meromictic Lakes

Six Lakes in Central Washington , U . S .A . 4 1 0-4670

Big Soda Lake , Nevada , U . S . A 9 1 , 500-4 9 , 400

Wes t Basin Lake , Victoria , Aus tralia 87 8

Fayet teville Green Lake , New York , U . S . A .

Various Antarctic meromictic lakes

Laytons Lake , Nova S cotia , Canada

1 700

5 53-2609

88- 1 24

Biogenic Meromictic Lakes

Lake Mary , Wis c onsin , U . S . A

Hall Lake , Washington , U . S . A .

Lake 1 20 , Ont ar io , Canada

Eight lake s in the Romericke district , Norway

1 . 1

1 . 65

5 . 5- 9 . 5

Reference

This thesis

This thesis

This thesis

Walker , 1 97 4

Kimmel e t al , 1 9 7 8

Timms , 1 97 2

Brunskill and Ludlam , 1 96 9

Burton , 1 98 1

Howell and Kereke s , 1 982

Weimer and Lee , 1 97 3

Culver , 1 9 7 7

Campbell and Torgerson , 1 9 80

Hongve , 1 9 80

218

while the are a , shallowness , and exposure of Lake Morrison freely

enables mixing to all depth s . Sulphide Pool l ie s somewhere between

these two extremes .

5 . 4 . 3 Heating and Mixing Dynamics

The annual heat budgets o f Lake Chisholm and the Gordon River

lakes are small , and although tho se of the Pieman River reservoirs

were higher , thes e too were small for lakes of their size (Gorham ,

1 964) . These giv e s ome quantification of the influences o f shelter

on these lake s , s uggesting that }i�'W:! work has . been done by the wind (UI\(j,V. d· t '" e�·J;

to distribute hea t within them. This coupled with the high humus

content trapp ing mos t heat close to the surface , means that the

cap acity of the l akes to s tore heat is greatly reduced , as only the

epilimnetic or mixolimnetic waters p articipate in heat exchange with

the environment , and thus in the determination of annual heat budgets . �il:.:.t

Thll;. l stored in the monimolimnions of the meromi ctic lakes would also

have only l imited p articipation . Additionally , because mos t heat is

absorbed close t o the surface , it can be quickly l o s t back to the

atmo sphere at night , rather than being mixed to warm the deep er waters

of these lakes , and thus retained . Large diurnal temperature

fluctuations occur in the surface waters of the Gordon River lakes

(King and Tyler , 1 982a ; Baker � al , 1 985a ; Bowling , 1 9 8 1 ) . Similar

low annual heat b udgets have al so been reported for eight small ,

pro tected Norwegian meromi ctic lakes (Hongve , 1 980) , and for a

shel tered biogenically meromi ctic lake in Washington (Culver , 1 9 7 7 ) .

The values o f annual heat budgets are dep endant on both the size

and depth o f a l ake , increasing as lakes become larger or deeper , but

at a lessening rate (Gorham , 1 964) . Thus , the annual heat budgets of

the Pieman River reservoirs were highest , while tho s e of Lake Chisholm

and the Gordon River l akes were considerably les s . The calculations

are also dependqnt on the t iming of the thermal measurements used , as

the heat content s of l akes may vary significantly over a period of

j ust two or thr e e day s , making the spec.ific t ime o f maximum heat

content unpredic table (Stewart , 1 97 3 ) . This would al so be true for

the minimum heat content in warm monomi ctic lakes c irculating above

4 ° C in winter . With a sampling pattern of one measurement p er month ,

o r at even longer interval s , the periods of.maximum and minimum heat

c ontents of the s e l akes could very easily have been mis sed , l eading

to under-estimat ions of their annual heat budget s . Even the time of

219

day o f measurement may have some effect , if large diurnal t emperature

changes o ccur .

Because heat content i s a measure of the amount o f heat per unit

surface area , between lake c omp arisons cannot easily be mad e , due to

difference s in d ep th . However , volume weighed average temp eratures

allow this , bein g the equivalent of the heat content p er unit volume ,

calories cm- 3 ( Stewar t , 1 97 3 ) . Warm monomictic Perched Lake , Lake

Chisholm , and the Pieman River reservo irs were always cooler than the

Gordon River meromictic lake s , possibly because shallow thermal

stratification leaves a considerable volume of cold hypolimnetic wat er

which reduces the ir average summer temperature s , while they also lack

warm , s tagnant , monimolimnetic waters which could elevate average

winter temperatures in the Gordon River lake s . The shallownes s o f

both Sulphide Pool and Lake Morrison may have allowed greater summer

heating , and winter cooling , of the entire water columns of these l akes ,

so they were generally warmer in summer and colder in winter comp ared

to Lake Fidler . The larger surface area and exposure o f Lake Morrison

may al so have all owed greater opportunities for wind mixing to

distribute heat more equitably with depth , thus raising it s average

summer temp erature . Gorham ( 1 964) considered this the main function

of increasing lake area causing higher annual heat budget s . Since

1 9 7 8 , Sulphide Pool and Lake Morrison have shown greater extremes

than previously , but this may be due to temp oral differences between

years , rather than an effec t o f the demise of their meromixis in more

recent years . T emporal differences are apparent in Lakes Chisholm

and Murchison , too .

Birgean Wind Work may be used to show the exposure o f a l ake to

wind , and is the minimum amount o f work required to distribute a given

heat load from an initial condition (usually assumed to be an

unstratified lake at 4 . 0 ° C) to produce the observed density

s tratification (Idso , 1 9 7 3 ) . Low values indicate a predispos ition

toward s meromixis (Hongve , 1 980) . The values for Lake Chisholm are

very low , even in summer , a s are those for the Gordon River lakes ,

while warm monomic tic Perched Lake had the highest value s . These

also fall within the same order of magnitude as thos e reported by

Hongve ( 1 9 80) for highly s tratified Norwegian lakes , and result from

wind action having very little effect in distributing heat from the

surface to the d eeper parts of the lake s . Additionally , the

calculation does not differentiate between heat actually mixed

220

downwards by wind action and that generated at each depth by direct

solar heat ing , which may account for as much a s 50% of the heat

distribution in well p ro tected l akes (Hongve , 1 9 80 ) . Also , calculat ions

for meromi�tic Lakes Fidler , Morrison and Sulphide Pool may be

influenced by the amounts of heat stored within their monimolimnions ,

and not included in the mixing processes . Because of this , Bir gean

Wind Work may be of l imited value only in describing the mixing dynamics

of such l ake s . Wind Work values calculated for the Pieman River

reservoirs and L ake Barrington were higher than for th e o ther lakes

s tudied , but thos e for Lake Murchison especially were low for lakes

of this s ize and depth , indicating limited wind mixing there as well .

Thermal stabilities are e s t imates of the amount of work required

to mix a thermally s tratified lake to a new , uniform, isothermal

condition , without gain or loss o f heat (Idso , 1 973) . Tho s e o f Lake

Chisholm and the Gordon River lakes correspond well with tho se rep orted

for Norwegian lakes by Hongve ( 1 9 80) , but are much lower than tho se

calculated for the P ieman River reservoirs and Lake Barrington .

However , they are s till suf ficient to imp art considerable stability

to the water column during p er iods of thermal stratification , thus

aiding the devel opment and maintenance of meromictic or near-meromic tic

conditions in the lakes .

5 . 4 . 4 Meromictic Tendancies in the Lakes and Reservoirs

The warm monomic t ic stratif icat ion cycle of Lake Chisholm differ s ,'f i l ( ©t,d i �I\IHS

markedly from the A prevailing in Finnish polyhumic lake s , but

the effect of their humil1S content on heat absorption in early spring

is the s ame . With rap id heating of their surface waters , many

Finnish l akes transform swiftly from ice cover (which prevents winter

mixing) , to spring s t ratif ication , before full ventilation o f the

hypolimnion has b een achieved ; a condition known as " spring meromixis"

(Arvola and Rask , 1 9 8 4 ; Salonen , Arvola , and Rask , 1 9 84) . Dystrophy

al so creates a t endancy toward s incipient meromixis in Lake Chisholm ,

evidenced by the l ingering autumnal and early spring stratif ication ,

and even in winter circulat ion throughout the entire lake is slugg ish ,

and oxygen is distributed homog eneously for only four t o s ix weeks

during July and August . Desp ite changes in maj or solute concentrat ions

acros s the thermocline being minor , the water column none-the-les s

has considerable physiochemical s t ructure , p articular ly with respect

to temperature , oxygen , redox chemistry , and light . Thus , Lake

221

Chisholm closely resembles a Type IV meromictic lake of Walker and

Likens ( 1 9 7 5 ) .

There is l i t t le enrichment o f the hypolimnetic waters o f Lake

Chisholm , despite the long period availab le for mineral accret ion

during thermal s t ratification . The s carcity of iron and manganese

i s notable . Given the long period of anoxia , it is hypothesised

that , had thes e elements been present in the bedrock o f the lake ,

sufficient concent rations would be reduced and brought into solution

to create density dif ferences sufficient to resist the weak

circulat ion and r ender the lake permanently biogenically meromictic

in the manner of some Norwegian lakes (Kj ensmo , 1 96 8 ; Hongve , 1 980) .

Also , biological production is apparently too small for ions from

bio logical sources to accumulate during thermal stratification and

cause meromixis in the manner o f Lake Mary (Weimer and Lee , 1 97 3) ,

Sunfish Lake (Duthie and Carter , 1 970) and Hemlock Lake (Fast and

Tyler , 1 98 1 ) . Instead , the near meromictic condition of Lake

Chisholm is entirely due to its morphometry and shelter , so that it

tends towards "mo rphogenic meromixis " as described by Northcote and

Halsey ( 1 9 6 9 ) .

In keep ing with Tyler ' s ( 1 980) predict ion , chemical stratif ication

formed in all four Pieman River reservoirs , al though this was only a

fleeting ep isode early in the development o f Lakes Mackintosh ,

Rosebery , and P ieman . However , it p ersisted throughout the s tudy in

Lake Murchison , although a gradual decline was evident from mid 1 9 84

onwards . The meromixis was clearly of biogenic origin , with the

monimolimnetic waters dominated by calcium , magnesium , and bicarbonate ,

along with iron and manganese . These are typ ical o f biogenically

meromi ctic lake s (Dickman and Har tman , 1 9 7 9 ) . Other causes of

meromixis , such as triptogenesis , as occured in Hill s Creek Reservoir ,

Oregon (Larson , 1 9 7 9 ) , or annual saline inf lows l ike those

maintaining ectogenic meromixis in Lake Powell (Johnson and Merritt ,

1 9 79 ) are imp robable , as water entering the P ieman River reservo irs

is both dilute and non- turbid .

Chemical s tratification evolved quite rapidly after the formation

of each reservoir . It was incipient in Lakes Rosebery and Pieman only

three to four months after their creation , when increases in pH , K1 3 ,

and alkaline earth bicarbonates were evident in their bottom waters .

The early onset o f meromixis in Lake Murchison was les s marked , with

only s light increases in K1 8 , and temperature near the bottom .

222

Meromixis develo p ed f urther during the first sumner o f impoundment ,

after hypolimnet i c anoxia brought about by decaying vegetation from

the ·newly flooded river valleys under conditions o f thermal

s tratification a llowed the reduction and accumulation of dissolved

iron and manganes e at the base of the dam . Lake Mackintosh too was

meromi ctic seven months after i t s formation . The s e processes leading

to the early biog enic meromixis of the Pieman River reservoirs

closely follow those outlined by Tyler ( 1 9 80 ) .

All the reservoirs had high level off takes (Figure 3b) , leaving

a considerable d ep th of dead water below them for the establishment

of chemical gradi ents . The onset of triptogenic meromixis in Hills

Creek Reservoir was due p artly t o the dam lacking low level outlets

to purge highly tubid bottom waters (Larson , 1 9 7 9 ) , a s occurred in

Lake Rowallan , T a smania , where drawoff via low level outlets

destroyed incipi ent biogenic meromixis (Tyler and Buckney , 1 97 4 ) .

Withdrawal through high-level outlets also creates convective effects

which aid the e s t ablishment of meromixis in two way s . Fir stly , the

extraction via s uch outlets create extensive withdrawal currents at

depths corresponding to the outlet , removing the surface waters but

leaving the bot t om waters relatively undisturbed (Fiala , 1 9 65 ;

Johnstone and Mer rit t , 1 97 9 ; Welsh , 1 984) . Secondly , convect ive

circulation below the s e dep ths is blocked , further protecting the

monimolimnetic p ool . This effec t occurs in both Lake Powell , U . S . A .

(Johnstone and Merrit� 1 97 9 ) , and in Dartmouth Dam , Victoria (Welsh ,

1 9 84 ) .

Three p o s s ible methods for the initiation and maintenance of

meromixis in the Gordon River lakes were propo sed by King and Tyler

( 1 9 8 l a) ; f irstly , that the s al t s were relictual , trapped in the

bottom waters a f t er levee bank deposition ; secondly , that the salts

entered the lakes by p ercolation of s alt wedge waters through the

l evee banks ; and thirdly , saline waters could occasionally flow into

the lakes via creeks connec t ing them with the r iver .

The investigat ions reported here provide strong support for the

third alternativ e . The rapid demise and eventual elimination of

meromixis from L ake Morrison and possibly Sulphide Pool s ince 1 97 7

militates again s t their brackish monimolimnia being relictual .

Fossil pigment analys is of Lake Morrison sediments (Bowling , 1 98 1 )

indicate the lake had been meromic tic for a long p er iod o f time , so

clearly some form of maintenance of meromixis by sal t replenishment

223

is required . Limited data on ground water from bores along the r iver

bank (Kearsley , 1 9 78 ) show rapid declines in sodium and chloride

concentrations with distance from the river , so the s econd alternative

is also unlikely .

The third theory , that turbulent mixing raises the surface

s alinity o f the r iver whilst the salt wedge is present , and that this

then enters the l akes via the connecting creeks , also warrants

examination . Because they are infrequent events , no actual inflows

into the l akes have been observed , but the alternation o f holomixis

with p eriods of incip ient meromixis in Lake Morrison , and s imilar

inflows creating new conduct ivity gradients in Sulphide Pool , leaves

little doubt as t o their o ccurrence . Inflows also occur in Lake

Fidler , but are too d i lute to affect the monimol imnion , although they

may r ep lace the mixolimnion ins t ead . The marked conductivity gradients

present in both Lake Morrison and Sulphide Pool , and the considerably

e levated mixolimnetic conductivities in Lake Fidler, in May , 1 985 ,

indicate s imultaneous saline inflows into all three j us t p r ior to

this date . The creeks have sufficient cap acity to al low the rapid

exchange o f large volumes of water between the lakes and the r iver 0

(Bowling . 1 98 1 ) . Coastal meromictic lakes on Aland are also maintained

by s imilar occasional incursions of marine salts from the Bal tic Sea

(Lindholm , 1 975 , 1 9 82 ) , as is meromixis in the Swartvlei estuary ,

South Africa (Allanson and Howard-Williams , 1 9 84) .

5 . 4 . 5 The Future of Meromixis in Lake Murchison , Lake Barrington , and the Gordon River Lakes

Although mer omixis s t ill pers isted in Lake Murchison three years

af ter the formation o f this reservo ir , it app eared to be in decline ,

especially during 1 9 85 , when the chemocline sank below 60 metres .

Addit ional wind induced circulation that year may have caused the

erosion of the upper layers of the monimolimnetic pool . Climatic

data from Rosebery , the nearest meteorological station , indicate

1 9 85 was windier than e ither 1 9 83 or 1 9 84 , having eight days of strong

wind (mean wind speed in excess of 21 kno t s ) , compared to only one in

1 9 84 , and zero in 1 98 3 (Dat a from Commonwealth Bureau o f Meteorology ,

Hobar t ) .

Some shaving o f the monimol imnion by cold density currents

flowing over it , such as ob served in July , 1 9 84 , may als o have

occurred , increa s ing the dep th o f the chemocline , and removing

solutes . Cold d ensity currents may be frequent within the reservoir

224

during winter . Water at or clos e to maximum thermal density ( 4 . 0 ° C )

was present i n the mid-depths o f the reservoir in July , 1 9 8 3 , and

July 1 985 , overlying the warmer monimolimnetic waters and pointing

to their presence on these occas ions . Lake Murchison differs from

Lake Barrington in this regard , where few cold density currents would

exist to d isrup t the monimolimnet ic p oo l , due to this reservoir

receiving homogenized water from another impoundment immediately

up stream . However , cold density currents are insufficient by

themselves to totally disrupt the meromixis o f Lake Murchison . This

contrasts with Lake Gordon , Tasmania , and Dartmouth Dam , Victoria

(Steane and Tyler , 1 982 ; Welsh , 1 9 84) , where cold density currents

underflow and d e s troy any incip ient monimolimnetic water s . Ferri s

( 1 985 ) reported cold inflows causing s imilar strat ification

behaviour in Lake Burragorang , New South Wales .

I t is unlikely the decline o f meromixis in Lake Murchison resulted

from the exhaustion of organic materials remaining from the pre­

flooded r iver valley , the decay o f which would aid replenishment o f

the monimolimnet i c pool . Anoxia in the lower hypolimnion in March

and November 1 9 85 (Figure 5 . 2 1 ) suggests suff icient organics remaining

or produced within the reservoir f or this not to be so .

The declining meromixis in Lake Murchison may not necessarily

spell its end there . S imilar events occurred in the years following

the formation of Lake Barrington , where by 1 97 8 , the dramatic changes

associated with meromixis had all but disappeared (Steane , unpublished

data) . Tyler ( 1 9 8 1 ) predicted the end of meromixis in that reservoir .

However in October 1 9 82 , Lake Barrington was again intensely chemically

s tratified , with several p arameters being higher than ever recorded .

This condition was still being maintained in October 1 985 and the

p robability exis t s of its long- t erm presence . Similarily , meromixis

may also remain in Lake Murchison .

The re-emer gence of meromixis in Lake Barrington between 1 9 7 8 and

1 9 82 canno t be easily exp lained , although drought conditions in the

early 1 9 80 ' s resulted in lower average daily f low rates through the

reservoir (Hydro-Electric Commis s ion of Tasmania , per sonal communication)

which may have aided it . Fast and Tyler ( 1 9 8 1 ) have shown how rap id ly

b iogenic meromixis may become re-established in lakes under suitable

conditions , and Fiala ( 1 97 9 ) g av e evidence o f meteorological event s

causing the re-e stablishment o f meromixis in Czechoslovak reservoir s .

225

Favourable circumstances must have developed prior to 1 982 to trigger

the re-development o f meromixis in Lake Barrington .

Lake Fidler is the only one of the three Gordon River meromictic

lake s not t o hav e reverted to holomixis s ince the alteration o f the

flow regime of the r iver in 1 9 7 7 , although i t s meromixis , as measured

by meromic tic s t ab il ity , has declined 5 0% s ince then . Lake Morrison

quickly became holomictic in 1 9 7 8 (King and Tyler , 1 9 83) , while

meromixis in Sulphide Pool had declined by August , 1 9 83 , to a point

where it was ext r emely tenuous . Whether holomixis eventuated is

uncertain , as no further measurements were made for sixteen month s ,

by which t ime new saline inflows had occurred , but a period o f holomixis

during thi s t ime is possibl e . However , any remnants of the or iginal

meromixis s t ill p resent in 1 98 3 would have been swep t from the lake ,

and replaced by the newly created salinity gradients resul ting from

the more recent saline inflows .

Although s al t wedge intrus ions s till occur in the Gordon River ,

the h igher r iver flow rates now cause considerable dilution and

reduced mixing with the river surface water s . Consequently , inflows

of brackish wate r s into the l akes are now of insuff icient concentr at ion

to create density gradients of appropriate magnitude to resist even

the weak , wind- induced circulation . The sal inities of the bottom

waters of L ake Morrison during p eriods of inc ip ient meromixis are

only h alf o r l e s s o f those formerly recorded there by King and Tyler

( 1 9 8 3 ) , as are s al inities o f recent inflows into Sulphide Pool .

Further , salt wedge penetration is much l e s s frequent than prev iously

(Kearsley , 1 97 8 , 1 98 2 ) , so periods between s al t replenishment

in the l akes are longer .

The f uture o f meromixis in the Gordon River lakes under the

present r iver flow regime is now apparent . Lake Morrison should

c ontinue to vacillate between p eriods of holomixis and temporary

ectogenic merom ixis , as detailed previously (Bowling , 1 9 8 1 ) . Sulphide

Pool now d isplay s a similar limnological pattern of sal ine inf lows ,

but the decay o f the concentrat ion gradient s so created is considerably

slower than in Lake Morrison . Thus , new gradients may be established

by new inflows before the previous gradient has completely eroded and

the lake r endere d holomi ctic , although occasional holomixis should

eventuate in the event of long p eriods without inflows . Inflows

should b e l e s s f requent in Sulphide Pool than in Lake Morrison , due

to its location f urther ups tream . In comp ar ison , the rate o f demis e

226

of meromixis in Lake Fidler has slowed . This notion i s supported by

the diffuse nature of the halocl ine , and by the l ingering oxycline

within the lower mixolimnion , indicating very weak mixing at these

depths . I f so , meromixis should persist for a long t ime yet in Lake

Fidler , al though c ontinued loss of monimol imnetic s al t s will continue

to weaken it . However , the chemocline may s ink too deep to receive

adequate l ight t o ensure the continuance of the micro-organisms

s tratified about it . P arkin and Brock ( 1 9 80a , b ) have shown the

neces s ity of suf f icient l ight for the existance of bacterial p lates

in Wisconsin l akes .

5 . 4 . 6 Significance of the Gordon River Lakes to the World Heritage Area of South-west Tasmania

The Gordon River lakes have a special s i gnificance in that they

lie within the World Heritage Area of south-wes t Tasmania , and their

limnological p r op erties serve to enhance the conservation value of

the area (Tyl er , 1 98 6 ) . Firstly , the backswamp l akes are excellent

examples of meromixis , displaying p ronounced salinity gradients

accomp anied by o ther abrup t chemical changes , at shallow depths

(King and Tyler , 1 98 1 a , 1 982a , 1 98 3 ; Baker et al , 1 9 85a) . Meromixis

itself is an unusual l imnological phenomonena (Walker and Likens ,

1 9 7 5 ) . The lakes al so display unique biological feature s , including

a highly s tratif ied array of algal and bacterial micro-organisms

s traddling their chemocl ines , and other newly described or undescribed

species of micro-algae occur within their mixol imnetic waters , as

well as in near by Perched Lake (Croome , 1 98 6 ; Tyler , 1 9 86 ) . v

Additionally , the three meromic tic lakes , with their surrounding

marginal rafts o f herbfields , or "Schwingmore" , dramatically illustrate

ongoing proces s e s of terrestrializat ion (Tallis , 1 97 3 ) . Thus , they

mee t the World Her itage criteria (Mulvaney , 1 9 8 3 ) as outstanding

examples of ongoing p roces ses of biological evo lution , and of the

development of freshwater bodie s . Unfortunately , the means which

have brought about the demise of their meromixis also serves to

illustrate another World Heritage criterion ; that of Man ' s interaction

with his natural environment .

By chance , the lakes also have considerable cultural value .

The Gordon River area has rich archaeological cave s ites , indicating

aboriginal hab it at ion of south-wes t Tasmania during the last ice age ,

1 5 to 20 Kyr ago , when they were the mos t s outherly humans of those

t imes (Kiernan et al , 1 98 3 ) . The lakes are the only ones in this

2 2 7

a r ea , a n d their s e d im en t s o f f er a c orrob or a t ive chronol ogy o f c l im a t i c

a nd veg e t a t i v e cond i t io n s in t h e a r ea f o r a t l e a s t pa r t o f t h e per i o d o f

Aborigin a l o c cupa t io n . The s p ec i a l l imno l o g i c a l proper t i e s o f t h e me ro­

Jn :i c U c l a ke s ma ke them p a r t i c u l a r l y s u i t ed s i t e s f o r t h i s . Meromix i s ,

wi t h i t s perm a n en t s t r a t i f i c a t i on , a c compan i e d by ano x i a in t h e mon i ­

mo l imnion , m e a n s t ha t t h e s t r a t ig r a phy o f t h e b o t t om s ed imen t s i s

und i s t urbed by wa t er m ovemen t s or b y b u r r owing a n ima l s , s o th a t t h e y o f f e r

a microfo s s il c h r o no l o gy o f h i gh r e so1 u tion , A l tho ugh t h e meromic t i c

l akes prob a b l y da t e o n l y f r om t h e s t ab i l i za t ion o f s ea l ev e l a t i t s pr e s en t

po s i t ion , abou t 6 t o 8 Kyr B . P . , Perched Lake i s prob ab l y m u c h o l d er , and

woul d ex t end th e chrono l o gy , a l b i e t in a l e s s p r e c i s e m a nn e r , to even

e ar l i er per iod s . C ur r en t l y t h e p a s t c l im a t i c and v e ge t a t iona l h i s t o ry

o f the a r ea mu s t b e ex t r a po l a t ed f rom t h e po l l en r e co r d s o f h i gh l and

a r e a s o f C en t r a l a n d Sou thern Ta smania (Macph a il , 1 9 7 5 , 1 9 79 ) , whi ch may

d if f er g r e a t l y .

5 . 4 . 7 The E c o l ogy o f Phy to p l ank ton in L ak e Chisholm

Wh il e tlP Go r d on R i v e r l a k e s a r e of cons i d e r ab l e 1 inmol o g i c a l s i gn i f ­

i ca n c e , s o t o o i s L ak e Ch i s h o lm , a s i t is t h e on l y pol yhum i c f or e s t l a k e

o f i t s t ype in Ta sma n i a , a n d i t i s a l s o a r i ch ph y t o f l a ge l ] a t e h ab i t a t ,

e s p e c i a l l y f o r c h r y s o ph y t e s .

Th e c h a r a c t e r i s t i c phy s i o c h em i c a l fea t ur e s of pol yhumic l ak e s c r e a t e

a d if f i c u l t env i r o nmen t f o r phy t op l ank t on , g i v en t h e p o o r und erwa t er

l igh t c l ima t e s f o r pho t o s yn t h e s i s , th e l i m i t e d m i xi ng d u e t o weak wind

a c t ion and s t rong t h ermal s t r a t i f i c a t i on , th e l ow pH , a n d th e o f t en l ow

n u t r i en t l eve l s i n t h e s u r f a c e w a t e r s (Arvo l a , 1 9 8 5 ) . Th e s e c on d i t i o n s

ha v e b e en i d en t i f i e d a s f a vour ing f l ag e l l a t e s ( I l ma v i r t a , 1 9 80 , 1 9 8 2 ,

1 9 8 3 , 1 9 8 4 ; I lmav i r t a e t a Z . , 1 9 84 ) , a n d some may con t r ib u t e t o t h e i r

domina t i on o f Lak e Ch i s h o l m . F l a g e l l a t e s a l s o p r e d o m i n a t e in th e sma l l ,

b r own-wa t e r fores t l ak e s o f F i n l a n d ( I l ma v i r t a , 1 9 8 3 , 1 9 84 ; Arvo l a , 1 9 8 5 ,

1 9 8 6 ) , and in L a k e F i d l e r ( G ro ome and Tyler , 1 9 86 ) . The l im i t e d epil im­

n e t i c c i r c u l a t ion ma y a l s o e xp l a in t h e pau c i t y o f d e s m i d s and d i a toms in

La k e Ch i s ho l m .

The l im i t e d n u t r i en t d a t a f r om Lak e Ch i s h o l m s ug ge s t th a t ph o s phorus

i s u n l ike l y to be l imi t in g f o r phy t o p l a nk t on g rowth , a n d th e l a k e cou l d

b e r eg a r d e d a s rne s o t r o p h i c o r eu t rophic ( O . E . C . D , , 1 9 8 2 ) . N i t r a t e

c on c e n t r a t ions i n th e l a k e a r e m o r e ind i c a t ive o f l ow t roph i c s t a t us

( We t ze l , 1 9 7 5 ) . N u t r i en t l ev e l s we r e o f t h e s am e o r d e r o f m a gn i t u d e

a s t h o s e r e port ed f r om F i n l a n d ( I lmavir t a , 1 9 80 , 1 9 8 3 ; Arvo l a , 1 9 8 3 , 1 9 84a ,

2 2 8

b ; Rask et a Z . , 1 9 86 ; S a l o n e n et a Z . , 1 9 8 3 ; I l mav i r t a e t a Z . , 1 9 8 4 ) ,

a. l though or th o ph o s pha t e wa s mo r e r e ad i l y avai l ab l e in t h e e p i l imn io n ,

tnd changes in con c e nt r a t io n s o f n u t r i en t s a c ro s s the thermo c l in e w e r e

n. o t a s marked .

Mark e d s e a s ona l s u c ce s s i o n o f phy t o p l ankton i s a r e gu l ar o c c u r r e n c e

in Scand inav i an f o r e s t l a ke s . Th e s e h a v e b e en a t t r ib u t ed t o the v e r y

l ar ge t empo r a l v a r i a t i o n s i n t h e e f f ec t iv e l i gh t cl ima t e ; wide cha n g e s in

w a ter t emper a t u r e , inc l ud in g w i n t e r ice cover ; and n u t r ien t ava i l ab i l i t y

( Ramb erg , 1 9 7 9 ; Arvo l a and R a s k , 1 9 8Lf ; Arvo l a , 1 9 8 3 ) . D e s p i t e r egu l ar

non thly s ampl ing over a two-ye a r p er io d , ther e a p pe a r s to b e no r e gu l a r

s ea sonal s uc c e s s i o n wi thin t h e phy t o p l ank ton o f Lake Ch i sh o l m , i n k e e p ing

w i th mo s t T a smanian l a k e s ( Ty l e r , 1 9 7 4 ; King and Ty l e r , 1 9 8 lb - b u t s e e

a l s o Cheng and Ty l e r , 1 9 7 3 a ) . In s te a d , th e Lake C h i s h o l m phy t o p l a n k ton

wax and wane c a pr i c io u s l y w i th p e r i o d i c a l v i r t tJ a l mono s p e c i f i c b l oo m s .

I t is spec u l a t e d t h a t t h e d i f f er e n c e s b e tween Lake Ch i sholm a n d i t s

S c an d inavian c o un t er pa r t s may l i e in t h e i r con t r a s t in g t h erma l r e g im e s . 0 0

L ake Ch :l s h o l m , a t 1� 2 S , 20 l a t i tu d e c l o s e r to t h E� e q u a t o r t h an F i n n i s h

l akes , and expo s ed t o a m a r i t ime r a th e r t h a n c o n t inent a l c l im a t e , i s warm

monom i c t i c w i t h t a rdy ov e r - t urn a nd no win t er i c e . In F i n l and , in c ompa r i­

s o n , there i s r ig o r ou s d im ix i s . Even mid-win t er in T asman i a s e e s s u f f i c ien t

d ay l e ng th , wi t h a high e n o u gh s o l a r el eva t ion , f or s u f f :i e i e n t l :i gh t f o r

phy toplank ton grow th i n L ak e C h i s h o l m . Th e l ake ' s ex t en d e d s t r a t i f i c a t :ion

m e an s a r e l a t iv e l y s t ab l e l a k e and un i f o rm env i r o n me.n t f o r many mon ths of

the year . Th e ec o l o g i ca l p r e s s u r e s whi ch f avour phy t o p l ankton s u c c e s s i on

in F in n i s h and Swed i s h l ak e s may ther e f o r e b e con s i d er ab l y r ed u ce d in

Lake Ch isholm .

5 . 5 CONCLUS IONS

Lak e Ch isho lm , L a k e B a r r in g t o n , �h e Pieman R iver r e s ervo i r s , and the

l ak e s of the l ower Go r d on R i ve r , a l l d is p l a y s ever a .l f ea t ur e s in common .

Al l a re dy s t r o ph i c , w i th L ak e Ch i sholm � F i d l er , M o r r i s on , a n d S u l p h i d e Po o l

b e i ng po lyhurnic , and i p a l l l o c a t io n s th i s pro d u c e s s h a l l ow t h e rmo c l :in e s

w i t h s t eep therm a l g r a d i en t s . The humus l o a d in g h a s o th e r e f f e c t s too ,

s u ch a s l ower ing p H , e nh a n c i n g th e sol ub :i l i t y o f r e d u c e d me t a l ion s in

th e p r e s en c e o f s u l ph i d e s a nd b i c arb o n a t e , and pos s ib l y a d d i n g t o hypo­

l imn e t ic anoxia t h r o u g h i t s d e co mp o s i t ion .

The p re s e n c e o f mcrom l c t i c o r n c n r-mc rond . c t :l. c (' on d i t: J n n s w i t :l d n t i H' S ('

wa t erbo d i e s :i s l a r g el y a r e s u l t o f th e l on g p er io d s o f t h e rma l s i : r a t i f :i. c a t i o n

wh i ch c r e a t e s a c on s i d er ab l e s t a b i l i ty a g a in s t m :ix ing . The m o r phome t r y of

th e l ak e b a s in s a n d t h ei r d e g r e e o f shel t e r f rom wind a r e a l s o v e ry

imp o r t an t f e a t u r e s whi c h i n f l ue n c e the exten t o f

229

wind-induced mixing in these lakes and reservoirs , and whether the

buildup and maintenance of solutes in anoxic bottom waters , free

from disrupt ion by circulation , is pos sible . In those that are

shallow comp ared with their sur face area , such as Lakes Mackintosh

and Morrison , incip ient meromixis is quickly des troyed , as it is

where exposure to prevailing winds o ccur s , such as in Lakes Rosebery

and Pieman . However , where lakes are deep comp ared to their surface

area , and shelt ered by nearby hil l s and forests , such as Lakes

Fidler , Barrington and Murchison , even weak chemical s tratif ication

can p er s is t , or winter c irculat ion will be sluggish , as in Lake

Chisholm .

All the meromi ctic lakes and reservoirs had only small density

difference s due to solute concentration between their surface and

bottom water s . A sufficient loading of decaying organics , either

from pre-impoundment vegetation or from that produced within the

waterbody ; or o f reduced iron and manganese , is also essential to

create and later maintain an adequate density gradient to resist

the effects of mixing , as in Lakes Murchison and Barrington , o therwise

chemical stratif ication will break down , and holomixis

Likewise , the renewal of monimol imnetic salts by s al ine inflows

into the lakes of the lower Gordon River is also required to maintain

meromixis within them , and it is the inadequate supply o f these s ince

the river flow rates have been regulated that has caus ed it s eventual

demise . The original meromixis has now gone from bo th Lake Morrison

and Sulphide Pool , and these should vacillate between holomixis and

incipient meromixis in future , although changes in Sulphide Pool will

be slower ; while meromixis should remain in Lake Fidler for a long

t ime yet , but the chemocline may s ink too deep to support the array

of micro-organisms which once straddled it . In Lake Chisholm ,

which i s morphometrically predispo sed to meromixis , it is only the

lack of a solute-based density gradient in its bottom wa�:ers which

mitigates against it becoming meromictic .

The s tudy has shown three winter mixing or s tratif ication pat terns

are p o s s ible in reservoirs . Fir s t ly , chemical s tratif icat ion ,

morphometry , and shel ter between them may be insufficient to prevent

full winter circulation , as o ccurs in Lakes Mackintosh and Ro sebery .

The anamolous s tratif ication behaviour shown by Lake Gordon and

Dartmouth Dam (Steane and Tyler , 1 982 ; Welsh , 1 984) p rovides a second

pattern , where the morphometric restrictions imposed on mixing and on

230

the inf lowing cold d ensity currents allows for the undercutt ing of

pre-exis t ing bot tom waters , but comp lete , wind-induced circulation

is p revented . The third pattern , uninterup ted chemical s trat ification

all year , undi s t urbed by either winter circulation or density currents ,

is shown by Lakes Murchison and Barrington .

The dystrophic nature of these water s may favour a p redominantly

flagellate phytopl�nkton flora dominated by chrysophytes , as occurred

in Lake Chisholm. �his may result from their characteris tic array of

accessory photo s ynthetic p igments , an ecolo g ical tolerance to

dystrophic waters , and to their motility . Blooms are frequent , but

there is l it tl e evidence of s tructured seasonal successions of

phytoplankton c ommunities , possibly due to only limited environmental

stresses o ccurring over t ime within the lake .

2 3 1

CHAPTER SIX

THE L IMNOLOGY OF DY STROPH I C WATERS

6 , 1 CONCLUS IONS FROH THE STUDY

Th e s t udy ha s d emon s t ra te d th e s tr o n g inf l u en c e d i s s o l v e d humic

s ub s t an c e s have o n the l iMto l o gy o f dy s t r o ph i c w a t e r s , through t h e i r

e f f e c t s o n th e u n d e rw a t e r l i gh t c ondi t ions , a n d t h e i r in f l uence on

t hermal prope r t i e s and wa t e r chem i s try .

An ov era l l p e r s p e c t iv e o f the in f l uence o f g Li vin on un d e rwa t e r

l igh t cond i t ions c a n b e gained f r om the inv e s t i ga t ions o f s t anding

f r e shwa t e r s f rom Ta sman i a , ho r th-eas t New S o u t h Wa l e s ; and s ou th -e n s t

Queens l and . In a l l t h r e e s t udy a r e as i t was the domin ant a t t enua t o r

o f P . A . R . , a l tho u gh t r i p t o n d i d c on t r ib u t e s l i gh t l y i n the wa t e r s o f

no r th- e a s t New S o u th Wa l e s . G i l v in al s o c au s e s the marked s pe. c t r cJ l

mo d i f i c a t ion o f t h e in c i d e n t l igh t f ie l d , r a p i d l y r emoving the sho r t er

wave l en g th l i gh t . Even low gil vin concent r a t ions , at b a r e l y de tee t ab l e

l evel s , h ave n o t i c e ab l e e f f e c t s , ab s o rb in g b l u e l i gh t a t d ep th , wh i l e

i t s e f f e c t s in p o l yhumi c w a t e r s a re s ev e r e . L ikewi s e , gi l v in dominates

the o p t i c a l p r o p e r t i e s of mo s t f reshwa t e r c o a s t a ] l a goon wa t e r s f rom

the Bas s S t r a i t i s l an d s , and wes t e rn and s o u th-we s t Ta s mania ; as we 1 1

a s in L ak e Ch i sh o lm , Lak e B a r r in g t on , th e r e s e rvo irs o f the l' ieman

Rive r ( Ch a p t e r Th r e e ) , and in the Go rdon River l akes ( King ;:md Tyl e r ,

l 9 8 lb , 1 9 8 2 a , 1 9 8 3 ; Groome and Tyl er , 1 9 84a , 1 9 8 5 a , B ow l i n g and Ty l e r ,

1 9 86 ) . A l tho u gh t u rb i di t y may b e an impo r t an t a t t enu a t o r in s ome par ts

of Aus t r a l ia ( S e c t ion 2 . 5 . 5 ) , g J1 vin i s p rob ab l y the maj o r a t tenua t o r

o f l i gh t in mo s t Au s t r a l i an inl and wa t e r s .

The � [ f e e t o f h i gh g J l. v in l o a d in gs on the th erma l. p rope r U e s o f l n k e s

w a s shown b y t h e c o a s t a l l a goons o f t he S t r ahan a r ea o f we s t ern Ta sman i a ;

by Lake Ch i. s ho l in , t h e P i eman R iv er r es ervo i r s , and t h e Go rdon R i v e r l ak e s . In t he ab s e n c e o f wind ind u c e d mixing , s t rong t h erma l gr ad i en t s

qu ickly d ev e ] o p a s h e a t i s r a p id ly a b s orb ed b y t h eir b r own s u r f a c e wa t er s .

2 3 2

:) f •\ l:,h 'fhe s e�ar e o f a t r a n s i e n t n a t u r e o n l y in t h e mor e expo s ed o f t h e c o a s t a l

l agoons , which wou l d b e c l a s s i f i ed b y Lewis ' s ( 1 9 8 3 ) s y s t em a s d i s -

c on t inuous warm p o l ym i c t ic l ak e s . In compar i s o n , Lak e G a r c i a , a l ong

with Lake Chi sho l m , L ak e Bar r i n g t o n (Ty l er and Buckn ey , 1 9 7 4 ) t h e P i em a n

R iver res ervo ir s , and the G o r d on R iver l ak e s ( Ki n g and Ty l er , l 9 8 1 b ,

1 9 8 2a , 1 9 8 3 ) h av e t he rm a l s t r a t i f i c a t io n of the warm monom i c t: ic t yp e .

Their dys t r o ph i c n a t u r e and sh el t er c an r e s u l t i n e x t end ed p er i od s o f

s t ra t if ica t ion a n d ev en r ed u c ed win t er c i r cu l a t io n .

Dis s o lv e d humic s ub s t a nc e s b o t h d i r ec t l y an d ind i r e c t l y i n f l u e n c e

t: he chemis try o f d ys t r op h ic wat: er s . Hypo l imn e t ic. a n o x i r1 a n d sh a r p

c hanges in r e d o x chem i s t r y w i t h d ep th a r e p a r t l y c on s e q u en t u p o n t h e

long s t ab l e per io d s o f thermal s t r a t i f ic a t io n , and po s s ib l y the m i c r o­

b ial decompo s i t ion of s om e h umus in the wa t er ( Sa l o n en � 1 9 8 1 ; Sa l o n en

et aZ . , 1 9 8 3 ) . How e v er , oxygen n ever r eaches 1 0 0 % s a t ur a t io n in t h e

humic wa t e r s o f T a sman i a . B ec a t t s e gil v i n a l s o i n c r e a s e s t h e a c id i t y

of dys t r o phie w a t er s , ma ny d i s s o l v e d ehemi c a l s a r e in a r ed uc ed s ta t e

und er t h e s e c on d i t i o n s , and ex e r t an oxygen d emand , even in epi l im n e t ic

wa t er s ( Pa t d. ck e t a Z . , 1 9 8 1 ) . Hum ic sub s t an c e s prob i1 b l y enhn n e e t h e

r edue t ion and s o l ub i l i t y o f iron a n d man gan e s e i n the chem ic a l l y

s t r a t if i ed r e s e r v o i r s o f t h i s s t u d y , even i n the p r e s enc e o f a n ion s

which wou l d norm a l l y c a u s e t h e ir p r e c i p i t a t io n . A d d i t iona l l y , ch e l a t ion

and sub s equen t p r ec i p i t a t io n m a y l ower concen t r a t ions o f c a l c i um in

some hum ic wa t er s , s u eh a s L ake Ch isholm and t h e B a s s S t r a i t i s l a nd

l agoons ; wh il e b y d ec r ea s in g p H , g ilvin may l ower the b ic a rbona t e

concent ra t io n s o f d ilu t e , unb u f f er ed wa t er s . Some ch em i c a l d i f f e r ences

d o occur b e tween the c o a s t a l l a g oo n wat e r s o f the B a s s S t r a i t i s la n d s

and tho s e o f w e s t er n a n d sou th-we s t T a smania ( s u f f i c i e n t f o r Buckn ey

and Tyl er ( 1 9 7 3 a ) t o p l a c e t h em in d i f f erent l imno l o g i c a l ca t eg o r i e s ) ,

b u t this i s d u e mor e t o t h e h i gher s a l in i t i e s o f the King and F l ind er s

Is l and l ag o o n s , r a t h e r t h a n t o t h e e f f e c t s o f t h e ir d i s s o l v ed hum i c

sub s t an c e s .

Al t hough F i n n i s h d a t a s u gg e s t r e l a t ionships b e tween d i s s o l v ed hum ic

s ub s t an c e s a n d t h e t y p e s an d q u an t i t i e s of a l g a e p r e s e n t in d y s t rophic

f r eshwa t er s ( ll m av i r t: a , 1 9 80 , 1 9 8 2 , 1 9 83 , 1 9 8 4 ; I l mavi r t a ei; o Z. . , J 9 8l; ;

Arvo la 1 9 86 ) , th e s in g l e p l a nk ton net samp l e s f rom n o r th - e a s t New Sou t h

Wa l e s � s o u th-ea s t Q u e en s l a nd , a n d wes t e r n a n d s o u th-we s t Ta sma n i a n f r e sh­

w a t e r s are in s u f f i c i en t to show if s imil ar r e l a t io n s h i p s ex i s t in t h e s e

hum i c Aus t ra l i a n l a k e s . How ev er , t h e mo r e ex t en s iv e s a mpl ing und e r t nken

on Lake C h i s h o l m i nd i c a t e s th a t f l a g e l l a t e s � and in p a r t ic u l a r c:hrys ophy t e s

may p o s s ib l y d o m in a t e t h e p hy t o p l ank t on commun i t i e s o f t h i s l a k e . Howev er

2 3 3

Inllch more t horough me t ab ol i c inves t ig a t ions wo u l d b e r e qu i r ed to

det ermine if any r ea l d if f er en c e s do exi s t due to d y s t r o ph y .

The dys troph i c n a t u r e o f L a k e Ch isholm , t h e P i eman River r e s ervo ir s ,

�d t h e backs wamp l ak e s o f t h e l ower Gordon R iver i s an impo r t ant con t r ib ­

� ing f a c t o r in t h e i r t end enc i e s t oward s meromix i s , through the ef f e c t s

of humic sub s t a nc e s o n t h e t h ermal p r oper t ies and chem i s t ry o f t h e s e

-wa t er s . However o th er f ac t o r s , such a s she l t er an d b a s in morphom e t r y ,

and t h e a d e qu a t e r es up p l y o f s o l u t e s t o t h e b o t tom wa t er s , w i l l ev en t u a l l y

d e t ermin e whe ther m e r om i x i s w i l l b e a t t a in e d , main t a in ed , or d ec l in e back

t o h o l omixi s .

Thu s , t he s t u d y h a s s hown t h e con s id erab l e e f f e c t cli. s s o l v ccl humic

sub s t anc e s hav e o n many a s p ec t s of t he l imno l o gy of d y s t rophic wa t e r s ,

and e s pecial l y t ho s e o f t h e W (� s t e r n and c o n s t a l l i mn o l o g J c n l p r o v in c e s

o f Tasma n i a , w h e r e th e s e p r ed omina t e .

234

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P atrick , R . , B inetti , V .P . , and H alterman , S . G . ( 1 9 8 1 ) Acid lakes from natural and anth ropogenic cau s e s . S cience 2 1 1 , 4 4 6 -4 4 8 .

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Phillip s , D . M . , and Kirk , J .T . O . ( 1 9 8 4 ) S tudy of the s p e c tral v ariation of ab sorption and s c a t tering in some A u s tralian c o a s tal w ater s . A u s t . J . Mar . Fres hw . Res . 3 5 , 6 3 5 -6 44 .

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P layfair , G . I . ( 1 9 1 5 b ) F resh water algae of the Lismore dis trict ; with an appendix o n the alg al fungi and schizomycete s . Proc . L in n . Soc . N . s . W . 4 0 , 3 1 0 - 36 2 .

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P layfair , G . I . ( 1 9 1 8 ) N e w and rare fresh w ater alg ae . Proc. Lin n . Soc . N . S . W . 4 3 ' 4 9 7 - 5 4 3 .

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P lay fair , G . I . ( 19 2 1 ) A u s tralian fresh water flagellates . Proc . L inn . Soc . N . S . W . 4 6 , 9 9 - 14 6 .

P layfair , G . I . ( 1 9 2 3 ) N o te s on freshwater algae . Pro c . L inn . Soc . N . S . W . 4 8 , 2 0 6 - 2 2 8 .

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and Ojala , A . ( 19 8 6 ) T h e limnolo g y of a small , naturally acidic , highly humic fore s t lake . A r c h . Hydrobiol . 1 0 6 , 3 5 1 - 3 7 1 .

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APPENDIX ONE: PAP ERS RESULTING FROM THIS THESIS

The following i s a list o f p apers published or in pres s

result ing from research undertaken as part of this thesis . P lease

note that papers 1 ) and 2 ) also contain research from my B . Sc . (Hons)

thesis (Bowling , 1 98 1 ) . Photocopies of these papers are g iven in

the following p ages .

1 ) Bowling , L . C . and Tyler , P . A . ( 1 984) Endangered lakes of scient ific and cultural value in the Wor ld Her i t age Area of South--west Tasmania . Bio l . Conserv . 30 , 2 0 1 - 20 9 .

2 ) Bowling , L . C . and Tyler , P . A . ( 1 986 ) The d emise o f meromixis in riverine lakes o f the World Heritage wilderness of south-west Tasmania . Arch. Hydrobio l . 1 0 7 , 5 3- 7 3 .

3 ) Bowling , L . C . and Tyler , P . A . ( 1 984) Physicochemical differences between lagoons o f King and Flinders Islands , Bass Strai t . Aus t . J. Mar. Fres hw . Res . 35 , 6 5 5-662 .

4 ) Bowlin g , L . C . , S teane , M . S . and Tyler , P . A . ( 1 986 ) The spectral distribut ion and attenuation of underwater irradiance in Tasmanian inland waters . Freshwat . Bio l . 1 6 , 3 1 3- 335 .

5 ) Bowling , L . C . and Tyler , P . A . forest lake i n Tasmania .

( 1 988) Lake Chisholm , a po lyhumic Hydrobio logia . ( in press)

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