Change in the Hydrological Functioning of Sand Dune Ponds in Doñana National Park (Southern Andalusia, Spain)

Anthropogenic pressure for groundwater resources in the Donana area (southern Spain) has caused concern in relation to the hydrological functioning of groundwater dependent ecosystems. In this study we have characterized the hydrological functioning of some of the most important dune ponds of the Donana Area: Santa Olalla (SOL), Zahillo (ZAH) and Sopeton (SOP). This characterization has been carried out applying different methodologies. The first one consisted in computing the daily volumetric water balance in Santa Olalla pond, during a period of two years (2015–2016), in order to determine to what extent is this ecosystem dependent on the input of groundwater from the aquifer. This balance, calculated from meteorological data and records of water level in the pond, has brought a significant improvement in the knowledge of the functioning of this water system thanks to the quantification of its main water inputs and outputs. Another methodology has consisted on a hydrological modeling of the three dune ponds during the dry season of 2016, when no precipitation occurred. Finally, temperature and electrical conductivity measurements of the water and the chemical analysis of the samples taken from the piezometers and ponds allowed us to characterize the physical-chemical signature of surface water and groundwater in the study zone.