Very little is known about the hydrological functioning of plant communities that are dependent on groundwater in the fynbos biome* . Interactions between groundwater and vegetation are believed mostly to be limited to shallower-lying aquifers which discharge into springs, seeps and wetlands in mountain and valley environments. The potential impacts on vegetation of groundwater exploration in the much deeper Peninsula Formation are largely unknown.

It can be presumed from basic ecological principles that any abstraction of water from a previously unused source such as the TMG aquifer would have some effect on the ecosystems connected to it. It should be noted that shallow aquifers interact directly with surface ecosystems, whereas deep aquifer systems would only interact where the deep confined aquifer connects with the upper layers through a conduit or pathway. The ecological interactions are therefore expected to be less than those observed with shallow aquifer exploitation. The significance of this effect can only be determined, however, once the magnitude, extent and nature of the effects of these interactions are understood.

Map showing extent of Fynbos Biome

According to preliminary findings by the Council for Scientific and Industrial Research (CSIR), groundwater-dependent ecosystems in the Table Mountain Group are thought to be:

• The smaller seeps, springs and wetlands in the mountains;

• The larger bottomland wetlands, mostly in river valleys, where the relative contributions of surface and groundwater are unknown;
• Mountain plateaus with deep sandy soils;
• The long and extensive riparian (river bank) habitats and stream ecosystems that are dependent - to some extent and from various channel sections - on groundwater discharge during summer droughts; and
• Caves and other underground systems.
• Discharge zones along the coast where freshwater flowing from underground sources is thought to create less salty conditions in affected areas of coastal waters. It appears that freshwater input into the sea may be required for sustaining certain algae which in places underpin the food web.

One of the key issues that needs to be addressed is the extent to which the groundwater in one area may be connected to that in other areas, particularly along faults and major fault zones. This means that groundwater pumping in one area may affect groundwater flows such as spring discharges a substantial distance away, and this could affect the associated ecosystems.

The relationships between the different types of wetland and the type of groundwater discharge are not known, nor is the relative importance of groundwater in these systems understood. This is a key area that will have to be addressed in the Water Research Commission (WRC) funded project of the ecosystems and in the design of monitoring systems. The WRC has commissioned several studies that consider the environmental aspects of groundwater abstraction, these are listed in the bibliography of this document.

The studies initiated by the Water Research Commission, which are being run parallel to the TMG Aquifer Feasibility Study and Pilot Project, are expected to close many gaps in our knowledge about groundwater-ecosystem interactions. It is clear, though, that the precise ecological impacts of groundwater exploration and abstraction in the TMG aquifer can only be established once a carefully controlled and monitored drilling and abstraction experiment gets underway.