Ecological impacts on groundwaterdependent ecosystems

The ecological impacts of drawdown of the water table on surface water bodies and streams are increasingly constraining new groundwater developments (Llamas, 1992). Drying up of wetlands, disappearance of riparian vegetation because of decreased soil moisture and alteration of natural hydraulic river regimes can all be used as indicators of overexploitation. Reliable data on the ecological consequences of these changes are not always available, and the social perception of such impacts varies in response to the cultural and economic situation of each region. The lack of adequate scientific data to evaluate the impacts of groundwater abstraction on the hydrologic regime of surface water bodies makes the design of adequate restoration plans difficult. For instance, wetland restoration programmes often ignore the need to simulate the natural hydrologic regime of the wetlands, i.e. not only restore its form but also its hydrological function. Similar problems result in trying to restore minimum low flows to rivers and streams. Oftentimes minimum stream flows are determined as a percentage of average flows, without emulating natural seasonal and year-to-year fluctuations to which native organisms are adapted.

The social perception of the ecological impacts of groundwater abstraction may differ from region to region and result in very different management responses. GRAPES, an EU-funded project previously mentioned, looked at the effects of intensive groundwater pumping in three different areas: Greece, Great Britain and Spain (Acreman, 1999). In the Pang River in Britain, conservation groups and neighbourhood associations with an interest in conserving the environmental and amenity values of the river that had been affected by groundwater abstraction mainly drove management decisions. In the Upper Guadiana basin, dramatic drawdown in the water table (30-40 m) caused jointly by groundwater abstraction and drought (see Fig. 13.8) resulted in intense conflicts between nature conservation officials and environmental non-governmental organizations (NGOs), irrigation farmers and water authority officials. The conflicts have been ongoing for the last 20 years and have not yet been resolved. Management attempts to mitigate the impact of water level drops on the area's wetlands have so far had mixed results (Forn├ęs and Llamas, 1999; Bromley et al., 2001). On the other hand, in the Messara Valley in Greece, the wetland degradation caused by decline in the water table has not generated any social conflict. This situation seems to confirm that ecologi cal awareness is deeply related to economic value of water and to the cultural background of each region.

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