Discrimination of groundwater mineralization process in the Jemna oases (southwestern Tunisia) between anthropogenic effect and evaporate dissolution

Abstract

Abstract Southern Tunisia is characterized by high temperatures, scarcity of rainfall (less than 90 mm/year), and high evaporation. In such an arid environment, most oases are developed thanks to groundwater springs and deep wells in artesian aquifers. Located in the southwestern part of Tunisia, the Jemna oases are considered among the most important palm groves in the country. In recent years, various modernization interventions and significant financial resources have been mobilized in this area to produce groundwater from the Continental Intercalaire (CI) and the Complex Terminal (CT) aquifers to supply the ever- increasing demand for water for agricultural activities. However, the overexploitation of these aquifers has led to the decline of groundwater heads and, therefore, a drying up of most natural springs. The results show that the dissolution of evaporitic minerals constitutes the principal cause of the observed groundwater mineralization. These salinization problems were greatly accentuated by local corrosion of the casing of a central groundwater production well exploiting the CI 11 aquifer in 2014. Since this date, the problem of contamination seems to have reached all the surrounding shallower aquifers. Caused by several combined anthropogenic and geological factors, the degradation of groundwater quality in this arid region constitutes a serious risk of limitation of water resources and even the extinction of the Jemna oases. Combined isotopic and hydrochemical investigations were conducted to understand the hydrodynamic characteristics of the different aquifer systems in the Jemna area and identify the main factors and mechanisms that control groundwater mineralization.The isotopic data highlights the significant mixing of waters from underlying aquiferes in realtion to the geological complexity of the region.