Hydrochemical changes due to intensive use of groundwater in the carbonate aquifers of Sierra de Estepa (Seville, Southern Spain)

Abstract

Summary The carbonate aquifers of Sierra de Estepa, situated in southern Spain, are undergoing intensive groundwater exploitation. Consequently, the volume of pumping surpasses the average recharge for periods of several consecutive years. Under such conditions, nearby springs have either dried up or only function during short time periods, after very rainy episodes followed by long droughts. During the brief periods when the springs are active, their water and the water extracted by pumping are calcium bicarbonates, with a spatial–temporal variability of their physico-chemical characteristics that is mainly conditioned by the degree of functional karstification of each system. When the springs are inactive, the pumping water gradually increases in salinity and becomes HCO3ClCaNa, ClHCO3NaCa and ClNa. Under the new conditions caused by so much pumping, the main factors determining the hydrochemical changes are the mixing of waters and the subsequent reactions of dissolution–precipitation between (1) the recharge coming from rainwater, (2) the hypersaline inputs from the clay-evaporite aquitards situated on the edges and at the base of the aquifer, and (3) the water stored in each aquifer. The hydrochemical information acquired allowed us to characterize and model the groundwater of these aquifers, to study the causes of its great spatial and temporal variability, and explain the influence of exploitation. This research shows that making sustainable use of water resources associated with carbonate aquifers calls for sound knowledge of the relationship between the aquifer and other bodies of groundwater or surface water, the hydrochemical quality of these possible inputs, and the vulnerability of the aquifer to exploitation, which in turn is conditioned by the ratio between water reserves and recharge.