The hydrogeology of the deep groundwater system in the Hammamet–Nabeul regional basin, north-eastern Tunisia: a hydrochemical and isotopic approach

Abstract

The scarcity of surface water in the Hammamet–Nabeul regional basin has imposed an over-abstraction of groundwater resources to meet the population demand for touristic and agricultural sectors. The impact of such a groundwater management on the aquifer system hydrodynamics and water quality has been investigated using a set of hydrochemical and isotopic data. Furthermore, a better understanding of the mineralization processes, the groundwater origins and the sources of recharge have been provided. Four water types were recognized; Na–HCO3, Ca–HCO3, Ca–SO4–Cl and Na–Cl. They are in relation with water–rock interaction processes i.e. the dissolution of evaporates and the cation exchange. Stable isotopes of water molecule (18O and δ2H) permit to identify three different groups. The first is characterized by relatively enriched isotope contents lending support to the important infiltration of recent rainwater in the foot of mountains. The second is distinguished by relatively depleted contents of stable isotopes reflecting a paleoclimatic origin. The third is marked by a significant enrichment of deuterium, which suggests a significant exchange with H2S in relation with the bacterial reduction of sulfate.