Transcript Ecosystem components potentially affected Ecosystem Processes

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
LEGEND
Cold
“perched”
spring
Cold
“perched”
spring
Alluvium/colluvium
Bokkeveld (shale)
Nardouw (quartzite)
Cedarberg (shale)
+
Cold spring
(water table)
f
Peninsula (quartzite)
Kaimans/Cango (metased)
Production boreholes
Spring
Valley floor
Piezometric surface
Hot spring
(artesian)
Cold
spring
Cold
spring
f
+
+
+
+
+
f
+
+
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+
TMG
Potential impacts
Ecosystem components potentially affected
Estuarine
Ecosystem Processes
Direct and Indirect Impacts
Drivers and Responses
Biodiversity
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
Perched springs & wetlands (type 1)
Fracture controlled springs & wetlands (type 2)
Lithology controlled (contact)
springs & wetlands (type 3)
Aquatic (riverine) ecosystems & estuaries
Terrestrial ecosystems
Cave
ecosystems
Resilience to natural climatic variation
Low
High
Species & ecosystems
Specialist
Generalist
System changes
• Continuous (e.g. proportional, linear, nonlinear)
• 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
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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
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Water Research Commission
City of Cape Town
Co-authors
Workshop participants
CSIR