Groundwater divide shifting due to pumping in a sector of the Doñana aquifer system (SW Spain): environmental implications.

The Doñana Natural Space (SW Spain) is considered one of the most important European wetlands, with many ecosystems depending on groundwater. As a consequence of intense groundwater withdrawals for urban use and, above all, irrigation, serious impacts have been observed in the eastern part of this aquifer, where the Doñana National Park is located. There is also groundwater exploitation in the western part of the aquifer, where a groundwater divide exists. The main goal of this work is to analyze the impact of groundwater withdrawals in this area. For this, the evolution of groundwater levels since 1968 in piezometers and pumping wells has been compiled and analyzed. This zone is characterized by the existence of a deep aquifer of high transmissivity, and a shallow aquifer with lower hydraulic conductivity, which behaves as an aquitard. Results show that pumping has caused a strong cone of depression in the deep aquifer, shifting the groundwater divide, and diverting water originally directed to the protected area, aggravating the overexploitation problems. Drawdowns in the shallow aquifer are lower and seem to be masked by the slow groundwater dynamic. However, a small lowering of the water table may cause severe impacts on such fragile ecosystems. The division of the aquifer for its management into six groundwater bodies belonging to two hydrographic districts has caused these important changes to go unnoticed until now. A proper coordination between the different water authorities managing groundwater and urgent adoption of remediation measures is essential.