ECOLOGICAL IMPACT OF GROUNDWATER EXTRACTION ON WETLANDS (DOURO BASIN, SPAIN)

Declining water table levels in the Douro River basin, Central Spain, are caused by the extraction of groundwater from a relatively homogeneous aquifer, and results in several types of impact on local wetlands which vary according to their characteristics. These wetlands are local, intermediate and regional groundwater discharge sites, seepages from post-Tertiary deposits, and non-linked ponds to groundwater dynamics. The following important factors influence the type of impact: the recharge or discharge nature of the affected sector of landscape; the type of connection with the regional aquifer; flow lengths and residence time of the water; the interaction between the water and the surface material, particularly clay. A wide range of wetland values and functions are affected according to the type of impact. These include productivity, amenity, recreational, scientific, educational and conservation values.