The main geochemical characteristics of surficial and groundwater were studied in Jarales area (Cordoba Province, South Spain), an evaporite karst plateau characterized by the presence of endorheic wetlands and drained by brine springs. For four years, routine sampling of groundwater (springs and wells), wetland, and rainwater was carried out. The major ion composition of the samples was determined, and the saturation indexes of the main mineral species were computed, using PHREEQC code. The main elements affecting the hydrochemical composition of the considered points were identified performing a Principal Component Analysis (PCA), and inverse geochemical modeling was executed by means of the NETPATH software to investigate the geochemical evolution of groundwater along a theoretical flowpath.
The chemical results and their latter statistical treatment show a high inverse relationship between the elevation of the outlets and their water temperature and mineralization mean values, which is associated to a transition of the main hydrochemical facies: from Ca-HCO3- to Na-Cl type, by way of Mg-SO4 waters. The analysis of ionic relationships in groundwater evidences that the main processes explaining the geochemical transition of groundwater from recharge to discharge areas are halite and gypsum dissolution and, to a lesser extent, dedolomitization and dissolution of other evaporite minerals. Other minor reactions identified in the area are calcite precipitation (triggered by common-ion effect) and ion-exchange. The information derived from geochemical modeling, together with the mineral saturation state of the samples and their increasing rCl /SO42- values, support the previous statements and suggests that the chemical composition of the NaCl-type groundwater is related not only with lithology but with their residence time within the media. All that combine suggests the existence of a large hierarchized gravity-driven groundwater flow system. Thus, the drainage taking place at higher altitudes (brackish water) may be associated with local flows of short residence time in the media. On the other hand, springs placed at lower positions would drain regional groundwater flows (brine water) of greater age. Lastly, outlets at intermediate positions do not constitute the last destination of groundwater flows, which rather go towards other areas situated at lower altitudes. The methods used in this research permits to better understanding the hydrogeological and hydrogeochemical processes occurring in the studied system, but also in equivalent evaporite environments worldwide.