david le maitre, c brown, c colvin, c hartnady, r hay, k reimann
DESCRIPTION
Ecological and Environmental Impacts of Large Volume Groundwater Abstraction on Ecosystems Linked to the Table Mountain Group Aquifer. David Le Maitre, C Brown, C Colvin, C Hartnady, R Hay, K Reimann. TMG-related studies. WRC funded Research oriented Experimental abstraction CCT funded - PowerPoint PPT PresentationTRANSCRIPT
Ecological and Environmental Impacts
of Large Volume Groundwater Abstraction on Ecosystems Linked
to the Table Mountain Group Aquifer
David Le Maitre, C Brown, C Colvin, C Hartnady, R Hay, K Reimann
TMG-related studies
• WRC funded• Research oriented• Experimental abstraction
• CCT funded• Feasibility study• Pilot abstraction +/-5 x 106 m3
• > 500 m depth
WRC Research Programme
Objectives:
1. Develop an understanding of TMG aquifer systems (recharge & flow mechanisms)
2. Develop an understanding of the environmental impacts of exploitation
3. Integration of groundwater into IWRM
Environmental Project Objectives
• 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
Groundwater settings in the TMG
Regional to landscape scale systems
Landscape to habitat scale systems
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f
f
f
+ +
+
++
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Cold “perched” spring
Cold spring (water table)
Cold spring
Hot spring (artesian)
Cold “perched” spring
Cold spring
Bokkeveld (shale)
Alluvium/colluvium
+
LEGEND
Nardouw (quartzite)
Cedarberg (shale)
Peninsula (quartzite)
Kaimans/Cango (metased)
TMG
Production boreholes
Spring
Valley floor
Piezometric surface
Potential impacts
Ecosystem components potentially affected
Ecosystem Processes
Biodiversity
Direct and Indirect ImpactsDrivers and Responses
Riv
ers
& R
ipari
an W
etl
an
ds &
S
eep
s
Dry
Lan
ds
In-a
qu
ifer
Estu
ari
ne
Coasta
l &
Mari
ne
Key effects/drivers
• Changes in groundwater discharge/levels:• Quantity & timing
• Quality & timing
• Temperature
• Knock-on effects on (for example)• Ecosystem water regime (e.g. mix of surface and
groundwater)
• Terrestrialisation (e.g changes in fire frequency)
• Downstream environments
Responses
• Ecosystem itself:• Structure & composition
• Groundwater dependent species/communities• Unique species (e.g. endemics)
• Habitats• Habitat specialists
• Function and processes (e.g nutrient cycling)• Functional linkages with associated
ecosystems (e.g.keystone species, key processes)
Discharge regime (structurally controlled)
Constant Highly variable
Lithology controlled (contact) springs & wetlands (type 3)
Fracture controlled springs & wetlands (type 2)
Perched springs & wetlands (type 1)
Terrestrial ecosystems
Cave ecosystems
Aquatic (riverine) ecosystems & estuaries
Species & ecosystemsSpecialist Generalist
Low HighResilience to natural climatic variation
System changes
• Continuous (e.g. proportional, linear, non-linear)• point and diffuse discharge, stream/river
systems
• Discontinuous (e.g. threshold)• water table within rooting zone
Resilience
• How has the system varied over long time scales – years to aeons?
• How easily are these: • Species • Communities• Linked systems
able to re-colonise and re-establish?
Provisional approach
Prioritisation
• Areas rich in endemic/special species
• Potential knock-on effects
• Potential GDEs already IDed by CAPE
• Rivers with priority estuaries
• Existing conservation areas
• Existing threats
Monitoring
• Depends on type of ecosystem• Abiotic
• Discharges/levels• Chemistry• Groundwater contribution
• Biotic• Indicator species populations• Unique species populations• Habitat extent and structure
Key challenges
• Development of predictive tools, innovative techniques & indicators of impacts
• Enhanced understanding of TMG-related GDEs & sensitivity to variations in groundwater regimes• Annual & seasonal• Low & drought flows
• Developing a statistically sound and innovative sampling design to distinguish abstraction from natural background variability and trends
Acknowledgements
• Water Research Commission
• City of Cape Town
• Co-authors
• Workshop participants
• CSIR