Isotopic and Chemical Characterisation of shallow aquifer of Djeffara of Gabes (Southern Tunisia)

The Djeffara plain located south-eastern Tunisia, is characterized by the presence of important aquifer systems. The aquifer system of Djeffara of Gabes is one of the most significant and it is formed by a shallow and deep aquifers. However, urban and industrial developments have led to a sharp increase in the exploitation of groundwater resources especially in shallow aquifer. The intensive exploitation caused a decrease in piezometric level and the deterioration of groundwater quality with the increase in salinity. This study shows that groundwater flows from El Hamma region and Matmata relief to the Mediterranean Sea in the East. The hydrochemical analyses prove that the shallow aquifer groundwater is homogeneous and characterized by a Cl-(SO4)-Na-(Ca-Mg) water type. The water salinity increases near El Hamma sabkhas and in the coastal region. Isotopic approach using stable isotopes ( (18O, 2H) ) shows that the shallow aquifer is recharged by vertical leakage from the Continental Intercalaire aquifer in El Hamma region where groundwaters are depleted in stables isotopes, and by rain water infiltration in Matmata Mountains. These isotopic values confirm also the connection between the various aquifer levels through the existing faults and prove the influence of evaporation process in shallow groundwater. (author)