Ecological and Environmental Impacts of Large Volume Groundwater

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 Cold spring (water table)

Alluvium/colluvium Bokkeveld (shale) Nardouw (quartzite) + f Cedarberg (shale) Peninsula (quartzite) Kaimans/Cango (metased) Production boreholes

Spring Valley floor Hot spring (artesian) Piezometric surface Cold spring Cold spring

f + + + + + f +

+ + + TMG Potential impacts Ecosystem components potentially affected

Direct and Indirect Impacts Drivers and Responses Biodiversity Coastal & Marine Estuarin e In-aquifer

Dry Lands Rivers & Riparia nWetland s& Seeps Ecosystem Processes 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 Low Resilience to natural climatic variation 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

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