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David Le Maitre, C Brown, C Colvin, C Hartnady, R Hay, K Reimann

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

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David Le Maitre, C Brown, C Colvin, C Hartnady, R Hay, K Reimann

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  1. 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

  2. TMG-related studies • WRC funded • Research oriented • Experimental abstraction • CCT funded • Feasibility study • Pilot abstraction +/-5 x 106 m3 • > 500 m depth

  3. WRC Research Programme Objectives: • Develop an understanding of TMG aquifer systems (recharge & flow mechanisms) • Develop an understanding of the environmental impacts of exploitation • Integration of groundwater into IWRM

  4. 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

  5. Groundwater settings in the TMG

  6. Regional to landscape scale systems

  7. LEGEND Cold “perched” spring Cold “perched” spring Alluvium/colluvium Bokkeveld (shale) Nardouw (quartzite) TMG Cedarberg (shale) Peninsula (quartzite) Cold spring (water table) + Kaimans/Cango (metased) Production boreholes f Spring Valley floor Piezometric surface Hot spring (artesian) Cold spring Cold spring f + + + + + + + + + f Landscape to habitat scale systems

  8. Potential impacts

  9. Ecosystem components potentially affected Ecosystem Processes Wetlands & Seeps In-aquifer Dry Lands Estuarine Coastal & Marine Rivers & Riparian Direct and Indirect Impacts Drivers and Responses Biodiversity

  10. 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

  11. 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)

  12. 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

  13. 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

  14. 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?

  15. Provisional approach

  16. 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

  17. Monitoring • Depends on type of ecosystem • Abiotic • Discharges/levels • Chemistry • Groundwater contribution • Biotic • Indicator species populations • Unique species populations • Habitat extent and structure

  18. 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

  19. Acknowledgements • Water Research Commission • City of Cape Town • Co-authors • Workshop participants • CSIR

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