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 - CSIR
David le Maitre - CSIR
Paul Lochner - CSIR
Derrick Netshitungulu - CSIR
Kornelius Riemann - Umvoto
Report published by:
CSIR-Environmentek
P O Box 320
Stellenbosch 7599
South Africa
Tel: (021) 888 2400
Fax: (021) 888 2693
Southern Waters
P O Box 13280
Mowbray 7705
South Africa
Tel: (021) 685 4166
Fax: (021) 685 4630
Umvoto Africa (Pty) Ltd
P O Box 61
Muizenberg 7950
South Africa
Tel: (021) 788 8031
Fax: (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 ____________________________________________1
1.1
1.2
2.
POTENTIAL ECOLOGICAL IMPACTS OF LARGE–SCALE
GROUNDWATER ABSTRACTION ______________________________3
2.1
2.2
2.3
2.4
2.5
2.6
3.
AGENDA OF THE WORKSHOP ______________________________________ 1
PARTICIPATION IN THE WORKSHOP ________________________________ 2
RIVERS, STREAMS AND ESTUARIES _________________________________
WETLANDS ______________________________________________________
DRYLAND _______________________________________________________
BIODIVERSITY ___________________________________________________
IN-AQUIFER ECOSYSTEM __________________________________________
GENERAL________________________________________________________
3
4
4
5
5
6
2.6.1
2.6.2
2.6.3
2.6.4
2.6.5
6
6
6
6
6
Impacts of construction of boreholes _____________________________
Knock-on impacts of increased water supply ______________________
Benefits for water use management _____________________________
Prediction uncertainties _______________________________________
Legal _____________________________________________________
ANALYSIS AND PRIORITISATION OF ISSUES/ IMPACTS AND
PRELIMINARY RECOMMENDATIONS FOR MONITORING __________6
3.1
3.2
CLASSIFICATION OF THE ECOSYSTEMS BASED ON THE SUGGESTED
ECOLOGICAL IMPACTS OF LARGE ABSTRACTION OF GROUNDWATER IN
THE TMG AQUIFER _______________________________________________ 6
RIVERS, STREAMS, RIPARIAN HABITATS, ESTUARIES, COASTAL AND
MARINE ENVIRONMENTS __________________________________________ 7
3.2.1
3.2.2
3.2.3
3.3
WETLANDS AND SEEPS___________________________________________ 10
3.3.1
3.3.2
3.3.3
3.3.4
3.4
3.5
Drivers and responses ________________________________________ 8
Prioritisation ________________________________________________ 9
Monitoring recommendations __________________________________ 9
Categorisation of TMG-related wetlands _________________________
Drivers and responses _______________________________________
Prioritisation _______________________________________________
Monitoring Recommendations _________________________________
10
11
11
12
IN-AQUIFER ECOSYSTEMS ________________________________________ 12
BIODIVERSITY __________________________________________________ 13
3.5.1
3.5.2
3.5.3
Drivers and responses _______________________________________ 13
Prioritisation _______________________________________________ 14
Monitoring and recommendations ______________________________ 15
4.
GENERAL DISCUSSIONS ___________________________________15
5.
OUTCOMES AND CONCLUSIONS ____________________________16
Final Scoping Workshop Report
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Ecological and Environmental Impacts of Large Volume Groundwater Abstraction on
Ecosystems linked to the Table Mountain Group Aquifer
6.
WAY FORWARD ___________________________________________17
7.
REFERENCES ____________________________________________17
8.
GLOSSARY AND ABBREVIATIONS (BROWN ET AL. 2003) ________17
TABLES
Table 3.1:
Table 3.2:
Table 3.3:
Table 3.4:
Table 3.5:
Riverine, estuarine and coastal ecosystem drivers and responses __________8
Wetland and seep ecosystem drivers and responses ___________________11
Monitoring procedures ___________________________________________12
Key ecosystem drivers for biodiversity and ecosystem responses __________13
Direct and indirect impacts on biodiversity ____________________________14
FIGURES
Figure 1:
Ecosystem components and linkages potentially affected by
groundwater abstraction. ________________________________________7
Final Scoping Workshop Report
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Ecological and Environmental Impacts of Large Volume Groundwater Abstraction on
Ecosystems linked to the Table Mountain Group Aquifer
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
12:45
13:15
Arrive, tea and coffee
Welcome, introductions, apologies and ground-rules (Irene Saayman)
Overview of the project and purpose of this workshop (Paul Lochner)
Overview of TMG hydrogeology and abstraction target areas for the City
of Cape Town groundwater project (Chris Hartnady)
Generic groundwater dependent ecosystem (GDE) concepts for the TMG
(David le Maitre)
Questions of clarification
Tea and coffee
Workshop topic 1: What are the potential ecological impacts of large-scale
groundwater abstraction?
Lunch
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
15:30
13:45
16:30
Small group report back session
Tea and coffee
Wrap up and way forward
Closure
8:30
8:45
8:55
9:05
9:25
9:35
10:15
10:30
Final Scoping Workshop Report
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Ecological and Environmental Impacts of Large Volume Groundwater Abstraction on
Ecosystems linked to the Table Mountain Group Aquifer
1.2
PARTICIPATION IN THE WORKSHOP
ATTENDANCE LIST
1.
2.
3.
4.
5.
6.
7.
8.
9.
10.
11.
12.
13.
14.
15.
16.
17.
18.
19.
20.
21.
22.
23.
24.
25.
26.
Verno Jonker
Cate Brown
Charlie Boucher
Chris Hartnady
Christine Colvin
Dave Le Maitre
Dave Ward
Derrick Netshitungulu
Godfrey Moses
Paul Lochner
Irene Saayman
John Roberts
John Weaver
Julian Conrad
Kornelius Riemann
Lara van Niekerk
Mark Gush
Mike Luger
Mike Smart
Simon Hughes
Wietsche Roets
William Bond
Rob Taylor
Mokete Sebogo
Urgo Nzotta
Feziwe Mabuto
Ninham Shand
Southern Waters
University of Stellenbosch
Umvoto
CSIR
CSIR
University of Stellenbosch
CSIR
CSIR
CSIR
CSIR
DWAF
CSIR
GEOSS
Umvoto
CSIR
CSIR
Ninham Shand
DWAF
CSIR
WCNCB
University of Cape Town
University of Cape Town
University of the Western Cape
University of the Western Cape
University of the Western Cape
APOLOGIES
1.
2.
3.
4.
5.
6.
7.
8.
9.
10.
11.
12.
Hans Beekman
Lisa Cavé
Dean Impson
Jeremy Midgely
Rowena Hay
Kevin Petersen
Heather Mackay
Ed February
Jan Vlok
Andre Görgens
Bill Harding
Yongxin Xu
CSIR
CSIR
WCNCB
University of Cape Town
Umvoto
WRC
WRC
University of Cape Town
Private consultant
Ninham Shand
Southern Waters
University of the Western Cape
Final Scoping Workshop Report
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Ecological and Environmental Impacts of Large Volume Groundwater Abstraction on
Ecosystems linked to the Table Mountain Group Aquifer
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
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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?
Final Scoping Workshop Report
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Ecological and Environmental Impacts of Large Volume Groundwater Abstraction on
Ecosystems linked to the Table Mountain Group Aquifer
2.2
WETLANDS
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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
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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
Final Scoping Workshop Report
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Ecological and Environmental Impacts of Large Volume Groundwater Abstraction on
Ecosystems linked to the Table Mountain Group Aquifer



2.4
Difference between bottom –up and top-down control of ecosystem
Hydrological variability-influence on ecosystem
Shifts in plant communities to more drought tolerant species
BIODIVERSITY
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2.5
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
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
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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.
Final Scoping Workshop Report
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Ecological and Environmental Impacts of Large Volume Groundwater Abstraction on
Ecosystems linked to the Table Mountain Group Aquifer
2.6
GENERAL
2.6.1
Impacts of construction of boreholes
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2.6.2
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2.6.3
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2.6.4

2.6.5

On-site during drilling and monitoring
Development of roads, infrastructure can result in limited vegetation impacts
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)
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
Prediction uncertainties
Can we adequately predict the geometry of the drawdown
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.
Final Scoping Workshop Report
page 6
Ecological and Environmental Impacts of Large Volume Groundwater Abstraction on
Ecosystems linked to the Table Mountain Group Aquifer
Coastal &
Marine
Estuarine
In-aquifer
Dry Lands
Wetlands
& Seeps
Rivers &
Riparian
Ecosystem Processes
Direct and Indirect Impacts
Drivers and Responses
Biodiversity
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:




3.2
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)
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.
Final Scoping Workshop Report
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Ecological and Environmental Impacts of Large Volume Groundwater Abstraction on
Ecosystems linked to the Table Mountain Group Aquifer
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

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


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;
Final Scoping Workshop Report
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Ecological and Environmental Impacts of Large Volume Groundwater Abstraction on
Ecosystems linked to the Table Mountain Group Aquifer
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
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
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;
Final Scoping Workshop Report
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Ecological and Environmental Impacts of Large Volume Groundwater Abstraction on
Ecosystems linked to the Table Mountain Group Aquifer






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 unimpacted 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.
Final Scoping Workshop Report
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Ecological and Environmental Impacts of Large Volume Groundwater Abstraction on
Ecosystems linked to the Table Mountain Group Aquifer



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.
3.3.2
Drivers and responses
Table 3.2: Wetland and seep ecosystem drivers and responses
DRIVERS
Reduction in flow
DIRECT RESPONSES





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 RESPONSES
Change 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


3.3.3
Prioritisation
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)
Final Scoping Workshop Report
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Ecological and Environmental Impacts of Large Volume Groundwater Abstraction on
Ecosystems linked to the Table Mountain Group Aquifer

3.3.4
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?
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
V-notch
Water level
Piezometers (weekly / continuous)
pH, temperature, EC, DO, these should be collected
on the monthly or continuous babes from the
boreholes
Quantity
Quality
BIOLOGICAL MONITORING (Plants, Frogs and invertebrates)
Vegetation
These should include long and short
lived plants
3.4
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.
To ascertain desiccation effects (physiological and
phenological).
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.
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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.
3.5.1
Drivers and responses
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
DRIVERS
RESPONSES
Change in discharge
Change in chemistry
Change in temperature etc.
Change in species
Change in community
Knock-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.
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Table 3.5: Direct and indirect impacts on biodiversity
Loss of species and changes in the extent
composition and structure of:
 Wetlands
 Seeps
 Springs
 Estuaries
 Marine
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
DIRECT
INDIRECT
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.
3.5.2
Prioritisation
The basic approach should include characterising the GDEs in terms of their:



Water source type
Water source use
Species’ tolerance to loss/stress
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The criteria for assigning priorities for protection and for research and monitoring should include:



3.5.3
Endemism – uniqueness
Likelihood of impacts
Likelihood for knock on effects
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.
2.
3.
4.
5.
6.
Site selection to obtain paired sites (affected and unaffected)
Appropriate sample/monitoring point replication based on statistical power analysis
Community characterisation and identification of response indicators
Target species should include palaeo-endemics or other unique species
Use isotope analysis to determine Groundwater Dependent species
Assess drought stress tolerance of groundwater species using standard physiological
techniques
7. Demographic analyses and elasticity analyses of sensitive stages
8. 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
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

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:



5.
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.
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.
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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 (plochner@csir.co.za) 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
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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
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.
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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)
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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
or piezometric
surface
An imaginary surface formed by measuring the level to which water will rise in
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
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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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