THE ECOLOGICAL IMPACTS OF LARGE SCALE ABSTRACTION...

WATER RESEARCH COMMISSION

ECOLOGICAL AND ENVIRONMENTAL IMPACTS OF LARGE VOLUME GROUNDWATER ABSTRACTION ON

ECOSYSTEMS LINKED TO THE TABLE MOUNTAIN GROUP AQUIFER

FINAL SCOPING WORKSHOP REPORT

July 2003

WRC project K5/1327

WATER RESEARCH COMMISSION

ECOLOGICAL AND ENVIRONMENTAL IMPACTS OF LARGE VOLUME GROUNDWATER ABSTRACTION ON

ECOSYSTEMS LINKED TO THE TABLE MOUNTAIN GROUP AQUIFER

FINAL SCOPING WORKSHOP REPORT

July 2003

WRC project K5/1327

REVIEWED BY WORKSHOP PARTICIPANTS

Authors of this Report (in alphabetical order):Cate Brown – Southern Waters

Christine Colvin - CSIRDavid le Maitre - CSIRPaul Lochner - CSIR

Derrick Netshitungulu - CSIRKornelius Riemann - Umvoto

Report published by:CSIR-Environmentek

P O Box 320Stellenbosch 7599

South AfricaTel: (021) 888 2400Fax: (021) 888 2693

Southern WatersP O Box 13280Mowbray 7705

South AfricaTel: (021) 685 4166Fax: (021) 685 4630

Umvoto Africa (Pty) LtdP O Box 61

Muizenberg 7950South Africa

Tel: (021) 788 8031Fax: (021) 788 6742

This report is to be cited as: Water Research Commission (WRC), 2003. Ecological and environmental impacts of large volume groundwater abstraction on ecosystems linked to the Table Mountain Group (TMG) aquifer: Final Scoping Workshop Report. WRC Project K5/1327. Published by CSIR-Environmentek, Southern Waters and Umvoto Africa. CSIR Report Number: ENV-S-C 2003-095, Stellenbosch.

CSIR Report Number: ENV-S-C 2003-095

Ecological and Environmental Impacts of Large Volume Groundwater Abstraction on Ecosystems linked to the Table Mountain Group Aquifer

CONTENTS

1. INTRODUCTION________________________________________11.1 AGENDA OF THE WORKSHOP________________________________________11.2 PARTICIPATION IN THE WORKSHOP__________________________________2

2. POTENTIAL ECOLOGICAL IMPACTS OF LARGE–SCALE GROUNDWATER ABSTRACTION_________________________32.1 RIVERS, STREAMS AND ESTUARIES___________________________________32.2 WETLANDS________________________________________________________42.3 DRYLAND__________________________________________________________42.4 BIODIVERSITY_____________________________________________________52.5 IN-AQUIFER ECOSYSTEM____________________________________________52.6 GENERAL__________________________________________________________6

2.6.1 Impacts of construction of boreholes______________________________62.6.2 Knock-on impacts of increased water supply________________________62.6.3 Benefits for water use management_______________________________62.6.4 Prediction uncertainties_________________________________________62.6.5 Legal_______________________________________________________6

3. ANALYSIS AND PRIORITISATION OF ISSUES/ IMPACTS AND PRELIMINARY RECOMMENDATIONS FOR MONITORING_____63.1 CLASSIFICATION OF THE ECOSYSTEMS BASED ON THE SUGGESTED

ECOLOGICAL IMPACTS OF LARGE ABSTRACTION OF GROUNDWATER IN THE TMG AQUIFER_________________________________________________6

3.2 RIVERS, STREAMS, RIPARIAN HABITATS, ESTUARIES, COASTAL AND MARINE ENVIRONMENTS____________________________________________73.2.1 Drivers and responses_________________________________________83.2.2 Prioritisation__________________________________________________93.2.3 Monitoring recommendations____________________________________9

3.3 WETLANDS AND SEEPS_____________________________________________103.3.1 Categorisation of TMG-related wetlands___________________________103.3.2 Drivers and responses________________________________________113.3.3 Prioritisation_________________________________________________113.3.4 Monitoring Recommendations__________________________________12

3.4 IN-AQUIFER ECOSYSTEMS__________________________________________123.5 BIODIVERSITY____________________________________________________13

3.5.1 Drivers and responses________________________________________133.5.2 Prioritisation_________________________________________________143.5.3 Monitoring and recommendations________________________________15

4. GENERAL DISCUSSIONS_______________________________15

5. OUTCOMES AND CONCLUSIONS________________________16

Final Scoping Workshop Reportpage i


6. WAY FORWARD______________________________________17

7. REFERENCES________________________________________17

8. GLOSSARY AND ABBREVIATIONS (BROWN ET AL. 2003)___17

TABLES

Table 3.1: Riverine, estuarine and coastal ecosystem drivers and responses___8Table 3.2: Wetland and seep ecosystem drivers and responses____________11Table 3.3: Monitoring procedures____________________________________12Table 3.4: Key ecosystem drivers for biodiversity and ecosystem responses__13Table 3.5: Direct and indirect impacts on biodiversity_____________________14

FIGURES

Figure 1: Ecosystem components and linkages potentially affected by groundwater abstraction._________________________________7

Final Scoping Workshop Reportpage ii


1. INTRODUCTION

The workshop was held at the CSIR (seminar room), Jan Celliers Street, Stellenbosch from 8.30 am to 4.30 pm on Friday 28th March 2003.

The main objectives of the workshop were to:

Scope the full range and types of potential ecological impacts of large scale groundwater abstraction from the TMG aquifer;

Identify geographical areas and ecosystems considered likely to be dependent on groundwater;

Prioritise areas for future monitoring and research.

This workshop was being undertaken as part of the scoping phase of a WRC funded project (K5/1327) on the ecological role of the Table Mountain Group (TMG) aquifer.

1.1 AGENDA OF THE WORKSHOP

8:30 Arrive, tea and coffee8:45 Welcome, introductions, apologies and ground-rules (Irene Saayman)8:55 Overview of the project and purpose of this workshop (Paul Lochner)9:05 Overview of TMG hydrogeology and abstraction target areas for the City

of Cape Town groundwater project (Chris Hartnady)9:25 Generic groundwater dependent ecosystem (GDE) concepts for the TMG

(David le Maitre)9:35 Questions of clarification10:15 Tea and coffee10:30 Workshop topic 1: What are the potential ecological impacts of large-scale

groundwater abstraction?12:45 Lunch13:15 Workshop topic 2 (small groups): How to better understand and monitor

these impacts? prioritisation of issues/impacts criteria for prioritisation (e.g. relevance of ecosystem in

wider environment, degree of ecosystem dependency on groundwater, potential ecosystem responses to changes in the hydro-geological regime, sensitivity of groundwater discharge zones to abstraction and climatic variations, capacity to monitor and evaluate changes in the ecosystem)

additional data sources monitoring recommendations

14:30 Small group report back session15:30 Tea and coffee13:45 Wrap up and way forward16:30 Closure

Final Scoping Workshop Reportpage 1


1.2 PARTICIPATION IN THE WORKSHOP

ATTENDANCE LIST

1. Verno Jonker Ninham Shand2. Cate Brown Southern Waters3. Charlie Boucher University of Stellenbosch 4. Chris Hartnady Umvoto5. Christine Colvin CSIR6. Dave Le Maitre CSIR7. Dave Ward University of Stellenbosch8. Derrick Netshitungulu CSIR9. Godfrey Moses CSIR10. Paul Lochner CSIR11. Irene Saayman CSIR12. John Roberts DWAF13. John Weaver CSIR14. Julian Conrad GEOSS15. Kornelius Riemann Umvoto16. Lara van Niekerk CSIR17. Mark Gush CSIR18. Mike Luger Ninham Shand19. Mike Smart DWAF20. Simon Hughes CSIR21. Wietsche Roets WCNCB22. William Bond University of Cape Town 23. Rob Taylor University of Cape Town 24. Mokete Sebogo University of the Western Cape25. Urgo Nzotta University of the Western Cape26. Feziwe Mabuto University of the Western Cape

APOLOGIES

1. Hans Beekman CSIR2. Lisa Cavé CSIR3. Dean Impson WCNCB4. Jeremy Midgely University of Cape Town5. Rowena Hay Umvoto6. Kevin Petersen WRC7. Heather Mackay WRC8. Ed February University of Cape Town9. Jan Vlok Private consultant10. Andre Görgens Ninham Shand11. Bill Harding Southern Waters12. Yongxin Xu University of the Western Cape



2. POTENTIAL ECOLOGICAL IMPACTS OF LARGE–SCALE GROUNDWATER ABSTRACTION

The following impacts or issues were raised in response to the question “what are the potential ecological impacts of large – scale groundwater abstraction?”

2.1 RIVERS, STREAMS AND ESTUARIES

Headwater streams most vulnerable Change river life Riparian Vegetation Change Riparian species stressed by low flow and discharge Aquatic species influenced by change in surface flow volumes and patterns Reduced freshwater input into Rivers, Estuaries and alluvial aquifers (flow) Effects on aquatic habitat- availability, quality, variability in rivers. Environmental flow impacts Change in Riparian communities with lower base flow Reduced base flow and thus stream flow Base flow might be reduced Base flow chemistry, temperature and dissolved oxygen change, Surface water temperature changes (hot/warm water discharges cease) Effects on riparian vegetation during dry season Effect on temperature and nutrients regimes of rivers Might implicate recharge estimation if spring flow is affected Impact on hot water springs Reduction in the river flow Improved induced recharge thus reduced surface run-off Water quality in rivers during the dry season Changing the water quality Water quality and flow, causing impacts on downstream system Water table lowering leads to increased recharge lower storm flow Extension of special protection zones Reduction in spring flow and associated dependencies Reduction of spring/stream flow in particular setting Postponed flood’s frequency and magnitudes Water quality reduction because reduction in extent of purifying wetlands Morphological changes in rivers as result of changes in riparian vegetation

Questions raised: Can we distinguish between continuous and discontinuous ecosystem

responses? How critical are hyporhoeic and surface water links in TMG streams?

2.2 WETLANDS



Increase in destruction of wetlands Social implications of changes to wetlands and flows Dry land terrestrialization of wetlands and rivers Erosion and reduction of peatlands because of drying and lack of wetland vegetation covers Vegetation change through drying and consequences of change Wetland vegetation change Change in botanical species Change in species numbers through drying Wetland degradation Hydrogeochemical environmental change in wetlands Threat to palaeo-endemic species Loss of frogs, snails, earthworms etc Desiccations of seeps, sponges etc (pieziometric head drops) Complete loss of wetland Wetland gets more salt Pollinator loss The wetland dependent ecosystems can be acutely affected Reduce the species diversity in wetlands areas Implications of drying of wetlands for impacts of fires Big increase of wetland monitoring lead to mechanical damage by monitoring scientist

Question: How mobile are these communities?

2.3 DRYLAND

Impacts on vegetation Increased risk of veld fires Impacts on deep-rooted plants especially commercial afforestation Effects on the shallow rooted plants Terrestrial ecosystem (plants and animal drinking points) Stressing of sensitive rare plants Loss of important keystone species e.g. Pollinators Change in phonological responses of (keystone) plants Loose important elements that plants need Effects may be dependant on plant life history eg, lifespan, storage ability, and the rooting

strategy Nutrient and ion imbalance Loss of ecosystem resilience to drought Dependence of shallow-rooted species on deep species rooted species “Hydraulic lift” Trophic cascades Difference between bottom –up and top-down control of ecosystem Hydrological variability-influence on ecosystem Shifts in plant communities to more drought tolerant species



2.4 BIODIVERSITY

Reduction in biodiversity (botanical) Loss of groundwater dependent species/ communities Loss of indigenous species especially dependent on the groundwater availability Increase in alien invasion Effects on international commitment to pressure biodiversity Loss of biodiversity hot spot Headwaters fragmented population Habitat specialists, many of which are associated with the TMG Local extinctions of palaeo-endemic species and narrowly neo-endemic species Specialist pollinators invertebrates in streams Changes in fire pattern affecting the biodiversity

2.5 IN-AQUIFER ECOSYSTEM

In-Aquifer ecosystems comprises of both biological subsurface ecosystems, such as caves, and physical or chemical aquifer properties. The possible impacts of groundwater abstraction on these ecosystems are summarised below.

Aquifer properties Change in storage of TMG aquifers Collapsing of the aquifer Generation of sinkholes Subsidence of ground surface Vertical connections between independent groundwater flow/systems Induced (groundwater) seismic activity Reduction of seismic hazard (potentially reduced frequency but increased severity) Reduction in the water quality Salt-water intrusion

Subsurface ecosystems Loss of wet cave habitats and fauna

Since the aquifer properties are not ecosystems in the strict sense of the word and can have impacts on the other groundwater dependent ecosystems, these impacts are not considered further in the discussion.

2.6 GENERAL

2.6.1 Impacts of construction of boreholes

On-site during drilling and monitoring Development of roads, infrastructure can result in limited vegetation impacts



2.6.2 Knock-on impacts of increased water supply

Once resource is proven, more users will tap and increase impacts Urban and industrial development Commercial implications, e.g. reduction in hot-spring volumes and related impacts on the local

and international tourist industry Land use changes as a result of socio-economic change driven by increased water availability Increased stream flow (urban) Reduction in the water quality (waste water)

2.6.3 Benefits for water use management

Better control of water abstraction versus obligatory storage in dams Conjunctive use increases opportunities for meeting ecological reserve No more dams

2.6.4 Prediction uncertainties

Can we adequately predict the geometry of the drawdown

2.6.5 Legal

Legal implications attached to changes in upstream water flow

3. ANALYSIS AND PRIORITISATION OF ISSUES/ IMPACTS AND PRELIMINARY RECOMMENDATIONS FOR MONITORING

3.1 CLASSIFICATION OF THE ECOSYSTEMS BASED ON THE SUGGESTED ECOLOGICAL IMPACTS OF LARGE ABSTRACTION OF GROUNDWATER IN THE TMG AQUIFER

The following diagram (Figure 1) provides a conceptual map of the relationship between impacts identified in Section 2.



Figure 1: Ecosystem components and linkages potentially affected by groundwater abstraction.

Four groups were formed amongst the workshop participants with one hydrogeologist per group based on the above ecosystem categories. The groups addressing dryland GDEs, biodiversity and ecosystem processes merged to form a single biodiversity discussion group. The group discussions were led by the following topics:

General clarification of impacts raised Drivers and responses Prioritisation of issues / impacts and what criteria to apply Additional data sources (with reference to the data catalogue provided)

3.2 RIVERS, STREAMS, RIPARIAN HABITATS, ESTUARIES, COASTAL AND MARINE ENVIRONMENTS

The group that was tasked with consideration of riverine, estuarine and marine environments summarised the potential impacts on those ecosystems as a result of groundwater abstraction as impacts relating to changes in water flow (i.e. environmental flow impacts), and quality. It was considered that these impacts could be dealt with under the Ecological Reserve legislation (National Water Act 1998), but that the potentially diffuse nature of the changes in groundwater supplied to these ecosystems, combined with other possibly overriding water abstraction and disposal activities in many catchments, would be extremely difficult to: 1) detect; 2) quantify and 3) manage.



3.2.1 Drivers and responses

There was general agreement that monitoring of the potential impacts of groundwater abstraction on riverine, estuarine and marine environments should concentrate on the physical variables most likely to change, as changes in these variables would drive the changes in other ecosystem components. In the case of impacts related to groundwater abstraction, changes to the systems are likely to be driven by changes in the overall quantity of water reaching the ecosystems, changes in the temporal distribution of that water, changes in the physico-chemical properties of the groundwater itself and/or changes in the physico-chemical properties of the water in the ecosystems as a result of a reduced contribution from groundwater.

Table 3.1: Riverine, estuarine and coastal ecosystem drivers and responses

DRIVERS Water quantity and temporal distribution Water quality

RESPONSES

Geomorphology Vegetation Invertebrates Fish/amphibians Birds

There was some debate as to the likely impacts of groundwater abstraction on the temporal distribution of water entering the ecosystems. No resolution was reached on this issue but initial indications were that groundwater abstraction could potentially:

affect late summer flows delay the onset of higher winter flows, and possibly attenuate fairly large flood events (e.g. large annual flood events).

Examples of the response of other ecosystem components to the sorts of changes described above could include (see Section 2.1):

Rivers: reduction in transportation of sediments and changes in turbidity (geomorphology); channel degradation (geomorphology); bank erosion (vegetation and geomorphology); reduction in biodiversity (vegetation, invertebrates, fish, amphibians, birds); increase in alien and generalist species (vegetation, invertebrates, fish, amphibians,

birds); changes in species distribution (e.g. lateral riparian vegetation zones).

Estuaries: changes in mouth closure patterns; changes in estuarine vegetation, invertebrates, fish and ultimately birds; an increase in salinity penetration upstream, which in turn can lead to groundwater

contamination near an estuary;



reduction in the access of marine fish to the estuary, and thus reduction in population sizes of marine fishes;

changes in lateral and vertical distribution of salinity in soils (e.g. saltmarshes require groundwater to lower salinity in the soil alongside estuaries, and Phragmites roots need to be in fresh(er) groundwater);

reductions in biodiversity; reduction in the number and size of freshwater microhabitats which are important areas

for juvenile fish and invertebrates;

Note: The role of groundwater in the marine environment was not discussed.

3.2.2 Prioritisation

Priority areas where impacts should be avoided were identified as: Nature reserves, which are intended to protect habitat, including riverine, estuarine and

marine habitats; Areas rich in endemic fish, specifically mountain streams, the Olifants / Doring River

System, and the Molenaars / Elands / Krom River System; CAPE identified rivers, estuaries and wetlands; Estuaries with a high importance rating, such as the Olifants, Breede, Berg, Bot and Klein

estuaries, as well as some smaller estuaries as they are more sensitive to flow reduction than large estuaries.

It was noted that this list was incomplete, and that any exercise to map ‘red flag’ areas should take cognisance of other prioritisation initiatives that have been conducted in the study area.

3.2.3 Monitoring recommendations

The following monitoring recommendations were made: High frequency (i.e. daily or hourly) monitoring should be focused on the drivers to

establish the baseline data, while the response of the ecosystem components should be monitored less frequently.

DWAF gauging weirs should be used where possible, preferably after some assessment of their accuracy in terms of measuring very low flows, and large floods.

It will be essential to identify (at least in general terms) where the groundwater source is entering the river (see below re before-after sampling design) – the use of isotopes was suggested here;

In identifying the location of the groundwater sources to rivers, estuaries and the ocean that are likely to be impacted, cognisance should be taken of potential impacts related to both the cone of depression and a potential drop in the pieozometric head, as a result of abstraction pumping;

Data from sites likely to be impacted should be collected as soon as possible to allow for as long as possible record before groundwater abstraction commences (i.e. BACI design - verification of post-effect against pre-impact data);

In the case of rivers, try to select sampling sites upstream and downstream of the potential impacts (i.e. control vs treated), preferably in upstream reaches or relatively un-



impacted catchments, as otherwise there will be too much noise to determine any “signal” from groundwater abstraction (i.e. there will be numerous other external perturbations and variables to make it impossible to work out what changes are due to groundwater abstraction);

Rivers - although monitoring should ideally take place along the whole river length, it was recognised that difficulties with isolating groundwater abstraction impacts from a myriad of other impacts may render this pointless. Nonetheless, the costs and benefits of doing so should be explored.

The focus of the monitoring activities should be during the dry season (i.e. water stressed times) as this is the critical time (in terms of impacts on river ecology, peak abstraction period, etc.), and on quantifying the proportion of the flow contributed by the targeted groundwater sources to the ecosystem at risk (i.e. to enable determination and implementation of the Groundwater Reserve);

Water balances should be prepared for systems where groundwater abstraction is likely to have an impact (e.g. rain, surface flow, evaporation, interflow and groundwater) to enable researchers to understand the water dynamics in the catchment and to design their research accordingly.

Hydraulic data (e.g. depth and flow rates) will be required at each sampling site if changes in ecosystem components in response to changes in drivers, are to be explained.

Apart from the explicit identification of the location of groundwater sources, the monitoring required to quantify the impacts of groundwater abstraction on riverine, estuarine and marine ecosystems is identical to that required for compliance monitoring for the Ecological Reserve. A fair amount of work has been done on the design of compliance monitoring for the Ecological Reserve (currently led by Dr Neels Kleynhans at DWAF), and cognisance should be taken of that work in this project. Unfortunately, to date compliance monitoring for the Ecological Reserve has not been implemented anywhere in South Africa.

3.3 WETLANDS AND SEEPS

Much of what has been described for rivers above is also applicable to wetlands.

3.3.1 Categorisation of TMG-related wetlands

The wetlands were divided into four types:

Shallow perched: This is the type of wetland, which experiences rapid response to seasonality and the change in water quality.

Deep Cold Peninsula: This type of wetland has slower response, same seasonality, low pH and low TDS.

Deep Cold Nardouw: This is everything above Peninsula and it also has a slower response, same seasonality, pH varies, Higher TDS and iron often present.



Deep Hot spring: This is the type of wetland with constant flow, higher temperature, elevated silica and iron and the soils are rich in manganese. It was also added that, this wetland is Nardouw versus Peninsula).

These types are simply provisional high-level categories based largely on the argument that a key driver in wetlands is the flow (discharge) regime and the water chemistry. There will be considerable variation within these categories and they should be seen as a continuum rather than discrete groups. A survey of the wetlands in the Western Cape was done by Jackie King and students in the 1980s, but the results were not been written up because the Foundation for Research Development stopped funding the work. The data from the survey may help with refining this classification.


Table 3.2: Wetland and seep ecosystem drivers and responses

DRIVERS DIRECT RESPONSESReduction in flow Terrestrialisation due to the change in community

species and structure, change in phenology, change in number of species, loss of mesic species, loss of wetlands soils.

Seasonality of flow reduction Seasonal systems may be more resilient Threshold variable for different species Effects on the palaeo-endemics are critical

INDIRECT RESPONSESChange in temperature and/or chemistry

Biological community response variable and unknown, e.g. dispersion, mobility, uniqueness, location/distance separation

Riverine Variable inflow Change in the water quality (nutrients, sediments,

temperature, pH, DO, Fe, Mn and etc.) Biota affected Alien vegetation increases


This should be based on the following criteria: Palaeo-endemics and neo-endemics (uniqueness, irreplaceability) Loss of wetland structure and processes Type of wetland (see 3.2.1) Monitoring damage – need to be careful about damage during by monitoring procedures?

Monitoring of damage e.g changes in populations, soil loss, changes in nutrient cycling due to terrestrialisation?



3.3.4 Monitoring Recommendations

Three types of monitoring procedures were suggested by the group, and these include Physical, Chemical and biological monitoring.

Table 3.3: Monitoring procedures

PHYSICAL AND CHEMICAL MONITORING

QuantityV-notchWater level Piezometers (weekly / continuous)

QualitypH, temperature, EC, DO, these should be collected on the monthly or continuous babes from the boreholes

BIOLOGICAL MONITORING (Plants, Frogs and invertebrates)

Vegetation Extent (area / boundaries).Community structure and composition (monitoring should be conducted two years initially and then annually in dry season).Individual responses of selected species.

These should include long and short lived plants

To ascertain desiccation effects (physiological and phenological).

3.4 IN-AQUIFER ECOSYSTEMS

The group presenting about the in-aquifer ecosystem stressed the point that very little is known about the in aquifer ecosystems, the following points below were highlighted.

Hypogean or cave ecosystems in the TMG occur only in the vadose zone and mainly in the recharge areas. The fauna and flora in the caves are not groundwater dependent. Therefore they will not be considered further.

Very little is currently known about deep-aquifer microbiology in the TMG. However, the activating of existing bacteria could lead to clogging of the aquifer and or equipment, e.g. clogging due to iron-bacteria.

Water quality is identified as the main driver for these processes. Changes in temperature, increases in dissolved oxygen and other nutrients can lead to increased populations of bacteria, resulting in the above-mentioned effects of clogging.

Increased flow can also change the living conditions for the microorganisms and can bring the population to regions in the aquifer with different physico-chemical conditions.



Priority for further studies is the research about the occurrence and behaviour of deep-aquifer microbiology. Only then it is possible to develop a monitoring system for assessing the impacts of groundwater abstraction on these ecosystems.

3.5 BIODIVERSITY

The group recognised that we are considering an aspect of the biodiversity of the fynbos which is poorly understood even from a taxonomic point of view (compositional component of biodiversity); even less is known about the structural and functional components of that biodiversity. For example, there are indications that wetlands may function as keystone ecosystems by being the habitat for organisms (e.g. long-tongued flies) that are important or sole pollinators for plant species in adjacent environments. In addition to the insects, fynbos also has unique frogs, snails and crustaceans which may require groundwater dependent ecosystems as habitats. These unique components together with the (so-called) palaeo-endemic families suggest that these wetland environments have adapted to a stable groundwater discharge over many millennia and may be highly vulnerable to changes in groundwater discharge, particularly if these exceed the historical range of variability.


The key drivers are similar to those for the other components (Table 3.4). Both the change in the mean discharge and the discharge regime (e.g. frequency distribution of flow rates, discharge depths) can be important. The same applies to the water chemistry and temperature regimes.

Table 3.4: Key ecosystem drivers for biodiversity and ecosystem responses

DRIVERSChange in dischargeChange in chemistryChange in temperature etc.

RESPONSESChange in speciesChange in communityKnock-on / ripple effects

The group noted that there are two categories of concerns about the large scale of groundwater abstraction on the TMG aquifer, namely the direct and the indirect impacts (Table 3.5). The direct responses will involve impacts mainly on particular plant and animal species and may also become evident as changes in ecosystem size and structure. The changes in size and structure can become important if they affect the viability of populations of wetland dependent organisms. The indirect responses will be more evident through interdependencies such as key mutualisms (e.g. pollinators), which could also have effects on dryland ecosystems.

Table 3.5: Direct and indirect impacts on biodiversity

DIRECT Loss of species and changes in the extent



composition and structure of: Wetlands Seeps Springs Estuaries Marine

INDIRECT

Changes in functional biodiversity and ecosystem processes including:

Life cycle stages Up and down stream links Food wed-subsidies Top-down and bottom-up Increase in fire frequency and

intensity in sensitive ecosystems

An important element in understanding the responses is whether the controls on those systems are bottom-up (e.g. soil type, water supply) or top-down (e.g. herbivory, predation); the importance of herbivory on mature plants is generally regarded as low in fynbos but impacts on key life-stages such as seeds can be critical. Food web subsidies may also be important where a wetland system is the breeding habit for organisms (e.g. insects) which are an important food source for predators in the less productive adjacent environments. In low nutrient environments even a small change in nutrient availability can be significant.

A key concern is that the drying out of wetlands makes them more likely to burn whenever there is a fire. There is evidence that the inherently lower flammability of wetlands results in them burning less frequently than the adjacent environments. This enables species to survive in them which would not be able to survive the more frequent fires in dryland environments (e.g. Widdringtonia nodiflora). The other concern with fires is that many wetlands have soils which are peats or have a high percentage of organic material which would be burn-out if the wetlands dry out. This type of has a catastrophic impact on the ecosystem, resulting in little, or no, vegetation recovery and potentially major changes in biodiversity because the seed banks and sprouters are killed by these fires and the habitat for the fauna has been lost.


The basic approach should include characterising the GDEs in terms of their:

Water source type Water source use Species’ tolerance to loss/stress

The criteria for assigning priorities for protection and for research and monitoring should include:

Endemism – uniqueness Likelihood of impacts



Likelihood for knock on effects

3.5.3 Monitoring and recommendations

Monitoring techniques could include the use of remote sensing data (ranging from satellite images to aerial photography) which can be used to:

Identify Groundwater Dependent Ecosystems Quantify changes

A key constraint on this approach is that it needs to be matched to the size and shape of the GDEs to provide meaningful data.

Onsite monitoring should include:

Regular observations on selected species Quantification of patterns and trends in discharges and/or water table levels (depths)

The group concluded that the minimum requirement would involve the following 8 steps:

1. Site selection to obtain paired sites (affected and unaffected)2. Appropriate sample/monitoring point replication based on statistical power analysis3. Community characterisation and identification of response indicators4. Target species should include palaeo-endemics or other unique species 5. Use isotope analysis to determine Groundwater Dependent species6. Assess drought stress tolerance of groundwater species using standard physiological

techniques7. Demographic analyses and elasticity analyses of sensitive stages8. Link satellite remote sensing with points 1 and 3.

4. GENERAL DISCUSSIONS

The following topics of general discussion were noted:

Need for longer-term fieldwork that extends over several annual cycles, and not limited to one to two years.

This project should employ advanced techniques such as isotope analysis, as this is often not possible within conventional research budgets, and brings added value to the broader research in this arena.

Statistical power: There is no point collecting data if it is not statistically useful and conclusive. This needs to be checked before the data collection commences.

Will we get a null hypothesis? (i.e. what if we cannot conclude whether groundwater abstraction is having any affect on ecology, because of the “noise’ from numerous disturbances and surrounding perturbations). If the statistical power analysis is low (low “t” value) after one year of data collection, then consider stopping data collection for that particular item.



To what extent will we be able to develop a management tool for controlling abstraction of groundwater. For example, at Great Brak River the physical parameters at the mouth are monitoring (e.g. water levels, open or closed status of the mouth) and used to make decisions on the release of water from the upstream Wolwedans Dam. Will we be able to determine the rate flow from an abstraction borehole, so that when indicators reach critical thresholds (e.g. soil desiccation levels), then abstraction from the borehole is stopped? How will study help understand this situation?

How will the findings of this research be used for management control with regard to the reserve? For example, would it lead to the situation (as happens in Australia??) where groundwater is abstracted from aquifers and then directed into surface rivers, possible to meet surface flow targets (adaptive management approach).

There were also topics of general debate, such as:

Whether monitoring should focus on species or communities. Whether monitoring should be short term (e.g. in the dry season) to be more cost effective, or

undertaken on a more ongoing basis (e.g. water level recording in order to obtain accurate averages).

Whether we should go on a “fishing trip” to collect data or undertake a focused data collection based on a clear hypothesis or suite of hypotheses.

5. OUTCOMES AND CONCLUSIONS

There were no significant points of clarification required on the key concepts and generic principles as per the Scoping Document (Brown et al. 2003) and presentations. The participants, from a variety of specializations, used the terminology and concepts and therefore appear to be familiar and in agreement with the generic principles as set out by the project team.

The format of the workshop discussion fell naturally into different habitat types (river, wetlands, dryland, etc) as per the disciplines represented, but with additional overarching issues such as ecosystem processes and biodiversity clearly identified (Figure 1). The participants found it useful to address impact issues within the driver-pressure-response framework, and consider potential impacts, direct and indirect.

Practical scientific and technical guidance was given by the break-away groups on monitoring the different habitats. It was generally agreed that the design of the monitoring programme for the project will be critical and difficult. The issues of statistical power and dealing with natural complexity within limited time frames and at limited representative sites was raised. This highlights the need to source additional funding to continue monitoring after the life-time of the project.

6. WAY FORWARD

The following key steps were identified:



a) The data catalogue is to be emailed to the workshop participants to review and comment on key data sources that may have been overlooked

b) The presentations at the scoping workshop are to be placed on the ftp site for the project. The address is: http://fred.csir.co.za/extra/project/WRC TMG-Eco/index.htm

c) The draft workshop report (this document) is to be circulated to participants for comment, with comments submitted to Paul Lochner ([email protected]) by Friday 9 May 2003.

d) Members of the botanical/ecological component of the eco-impacts project team could join the hydrogeologists from the City of Cape Town project in their hydrocensus planned for April 2003. This could be linked with a student botany project (William Bond to discuss with Chris Hartnady and John Weaver).

e) Based on the results of the April 2003 hydrocensus and feedback on the draft workshop report (including the “general principles”), the fieldwork phase will be designed.

7. REFERENCES

Brown, C, Colvin, C, Hartnady, C, Hay, E, le Maitre, D & Reiman, K, 2003. Ecological and environmental impacts of large-scale groundwater development in the Table Mountain Group (TMG) aquifer system: Discussion Document for the Scoping Phase, prepared for WRC Project K5/1327. Stellenbosch.

8. GLOSSARY AND ABBREVIATIONS (BROWN ET AL. 2003)

Acidic Water with a low pH.

Alluvial Recent unconsolidated sediments, resulting from the operations of modern rivers, thus including the sediments laid down in the river beds, flood plains, lakes, fans at the foot of mountain slopes, and estuaries.

Anisotropic Having physical properties that vary in different directions.

Aquiclude An impermeable geological unit that cannot transmit water at all. (Very few natural geological materials are considered aquicludes.

Aquifer A saturated permeable geological unit that can transmit significant (economically useful) quantities of water under ordinary hydraulic gradients. Specific geologic materials are not innately defined as aquifers and aquitards, but within the context of the stratigraphic sequence in the subsurface area of interest.

Aquitard A saturated geological unit of relatively lower permeability within a stratigraphic sequence relative to the aquifer of interest. Its permeability is not sufficient to justify production wells being placed in it. (This terminology is used much more


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frequently in practice than aquiclude, in recognition of the rarity of natural aquicludes

CAPE Cape Action Plan for the Environment, a major collaborative initiative to implement a strategic plan to protect and conserve the Cape Floral Kingdom.

Capillary fringe

(a.k.a. tension-saturated zone) - The subsurface zone directly above the water table in which pores within the geologic matrix are saturated with water, but the fluid pressure is less than atmospheric. Water is held within pores of the geologic matrix by capillary forces

Cone of depression

The cone-shaped area around a well where the groundwater level is lowered by pumping. The shape of the cone is influenced by both the permeability and storativity of the aquifer, and the abstraction rate and time. In fractured-rock aquifers the geometry of the fracture network and the contrast between fractures and matrix have the main impact on the shape.

Confined aquifer

An aquifer that is physically located between two aquicludes, where the piezometric water level is above the upper boundary of the aquifer. The water level in a well tapping a confined aquifer usually rises above the level of the aquifer. If the water rises above ground level, the aquifer is called artesian.

Contact zone The join or interface between different geological units. Where a permeability contrast occurs, springs may form.

Discharge area The area or zone where ground water emerges from the aquifer naturally or artificially. Natural outflow may be into a stream, lake, spring, wetland, etc. Artificial outflow may occur via pump wells.

DO Dissolved Oxygen, the concentration of oxygen gas in the water.

Down gradient Direction toward lesser hydraulic head than point of origin, or point of interest

DWAF Department of Water Affairs and Forestry

EC Electrical conductivity a simple measure of the quality of the water based on its ability to conduct electricity

Endorheic A catchment area with a closed drainage system i.e. one with no outlets. Often with a perennial or seasonal water body (pan) at its lowest point.

Fe The chemical name for the element iron.

Fracture Breaks in rocks such as joints, due to intense folding or faulting.

Fracture connectivity

A measure of how well the individual fractures or fracture systems, are connected to each other and thus of the potential flows.

GDE Groundwater dependent ecosystem.

Groundwater Water in the subsurface, which is beneath the water table, and thus present within the saturated zone. In contrast, to water present in the unsaturated or vadose zone which is referred to as soil moisture.

Heterogeneous A characteristic of the geologic matrix of interest in which hydraulic conductivity is dependent upon position and or direction.

Homogeneous A characteristic of the geologic matrix of interest in which hydraulic conductivity is independent of position and or direction.



Hydraulic conductivity

The constant of proportionality in Darcy’s law. It is defined as the volume of water that will move through a porous medium in unit time under a unit hydraulic gradient through a unit area measured at right angles to the direction of flow. Hydraulic conductivity is a function of both the porous medium and the fluid flowing through the porous medium.

Hydraulic gradient

The difference in hydraulic head between two measuring points within an aquifer located to each other in the direction of flow, divided by the distance between the two points.

Hydraulic head The fluid potential for flow through porous media largely comprised of pressure head and elevation head. This satisfies the definition of potential in that it is a physical quantity capable of measurement (such as with manometers, piezometers, or wells tapping the porous medium), where flow always occurs from regions of higher values to regions of lower values.

Hydrotect High permeable fracture or fault zone that extends over a long distance.

Hyporheic zone The saturated and biologically active zone in the unconsolidated material underlying and next to a water-course. The hyporhoeic zone is important in river system nutrient budgets as it acts as a nutrient storage system. It also provides a habitat and refuge for aquatic organisms, thus also serving a buffering function which promotes rapid recovery of aquatic ecosystems after floods or droughts.

Interflow The lateral movement of water through upper soil horizons, normally during or following significant precipitation events.

Lithology The description of the macroscale features of a rock, eg texture, grain type etc.

Mn The chemical name for the element manganese

Oligotrophic Refers to lakes with considerable oxygen in the bottom waters and with limited nutrient matter.

Orographic Related to elevation; orographic rainfall pattern means a strong relationship between amount of precipitation and elevation of the area.

Perched water Unconfined groundwater held above the water table by a layer of impermeable rock or sediment.

Percolate The downward flow of water through the pores or spaces of unsaturated rock or soil.

Permeability The capacity of rock or soil to transmit water. It is the portion of the hydraulic conductivity, which is a function of the porous medium alone. In primary aquifers permeability is an intrinsic property, which is a function of mean grain diameter, grain size distribution, sphericity and roundness of grains and the nature of grain packing.

pH A measure of the acidity or alkalinity of the solution (concentration of hydrogen ions)

Porosity The degree to which the total volume of soil or rock is permeated with spaces or cavities through which water or air can move.

Potable water Water, which is free from impurities that may cause disease or harmful physiological effects, such that the water is safe for human consumption

Potentiometric An imaginary surface formed by measuring the level to which water will rise in



or piezometric surface

wells of a particular aquifer. For an unconfined aquifer the potentiometric surface is the water table; for a confined aquifer it is the static level of water in the wells. (Also known as the piezometric surface.)

Primary aquifer

Aquifers in which the water moves through the spaces that were formed at the same time as the geological formation was formed, for instance intergranular porosity in sand (e.g. alluvial deposits).

Recharge areas Areas of land that allow groundwater to be replenished through infiltration or seepage from precipitation or surface runoff.

Rejected recharge

Groundwater discharge occurring relatively close to the recharge area of a regional aquifer system. The groundwater discharge has followed a flow path that is short in relation to the rest of the flow system.

Representative elementary volume

A volume of sufficient size where there are no longer any significant statistical variations in the value of a particular property with the increasing size of the element (Bear, 1972).

Salinity The concentration of dissolved salts in water. The most desirable drinking water contains 500 ppm or less of dissolved minerals. Saturated zone - The subsurface zone below the water table where pores within the geologic matrix are filled with water and fluid pressure is greater than atmospheric. Aquifers are located in this zone.

Secondary aquifer

(a.k.a. as fractured-rock aquifer) - Aquifers in which the water moves through spaces that were formed after the geological formation was formed, such as fractures in hard rock.

Semi-confined aquife

(a.k.a leaky aquifer) - An aquifer that is physically located between two aquitardes, and where the piezometric water level is above the upper boundary of the aquifer.

Storativity Capacity of the aquifer to store water in its pores, voids, fissures and fractures. It is given as the volume of water released from storage per unit surface area of the aquifer per unit decline in the hydraulic head (typically m3/m2/m, i.e. dimensionless).

Surface water Bodies of water, snow, or ice on the surface of the earth (such as lakes, streams, ponds, wetlands, etc.).

Syncline A fold in rocks in which the strata dip inward from both sides toward the axis, often forming a valley Tectonic – designating the rock structure and external forms resulting from the deformation of the earth’s crust.

TDS Total dissolved solids, a simple measure of the quality of the water based on the quantity of salts in solution.

TMG Table Mountain Group - this is a geological unit which forms the base and bulk of the Cape Supergroup and, thus, the Cape Fold Belt Mountains. It is formed from layers of mainly coarse grained sandstones alternating with shale layers grouped into two sub-groups, the Nardouw and the Peninsula, each of which includes a number of formations. The most important of these is the Peninsula formation which reaches a thickness of 1800 m.

Unconfined aquifer

(a.k.a. water table aquifer) - An aquifer which is not restricted by any confining layer above it. Its upper boundary is the water table, which is free to rise and fall.



The water level in a well tapping an unconfined aquifer is at atmospheric pressure and does not rise above the level of the water table within the aquifer. An unconfined aquifer is often near to the earth's surface and not protected by low permeable layers, causing it to be easily recharged as well as contaminated.

Unconsolidated Where the matrix of the aquifer is formed from un-cemented materials such as sand, gravel pebbles or mixtures of these.

Unsaturated zone

An area, usually between the land surface and the water table, where the openings or pores in the soil contain both air and water. (See also “vadose zone”)

Up gradient Direction toward greater hydraulic head than point of origin, or point of interest.

Vadose zone (a.k.a. unsaturated zone) - The subsurface zone above the water table and the capillary fringe in which pores within the geologic matrix are partially filled with air and partially filled with water, and fluid pressure is less than atmospheric.

Water table The top of an unconfined aquifer where water pressure is equal to atmospheric pressure. The water table depth fluctuates with climate conditions on the land surface above and is usually gently curved and follows a subdued version of the land surface topography.

Watershed All land and water within a drainage area, defined by topographic high points. Well - An opening in the surface of the earth for the purpose of removing fresh water.

WCNCB Western Cape Nature Conservation Board

WRC Water Research Commission


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