Vegetation changes and groundwater abstraction in SW Donana, Spain

Several works carried out in Donana area have case predicted the groundwater abstraction for cropping and urban supply might affect the ponds and the vegetation of the wetter zones such as the riparian forests, and the ecotone between the clay marshes and the sand dunes. The present study examines the vegetation changes in the Naves, the driest area of the stabilized sands of Donana National Park, and the processes responsible for them. The long-term Vegetation changes showed a trend to more xerophytic communities over the last 30 yr due to a decrease in water availability. The age of the oldest pine trees growing in the bed of a dried pond suggest that the process started around 1973-1974. Among the possible reasons, the decline in water table level due to the pumping for urban water supply of a close tourist resort set up at the end of 1960s seem the most probable cause and, to a lesser degree, the transpiration of large pine plantations. The dynamics of the water table and the effects of groundwater abstraction are explained in terms of the geomorphologic structure of the area. The existence of a semi-permeable soil layer (fragipan) between two different superimposed dune episodes could separate a deeper, semi-confined layer from a superficial unconfined one. I suggest that this feature has strong implications at local scale, influencing both the water table fluctuations and the vegetation changes. (C) 2001 Elsevier Science B.V. All rights reserved.