Hydrochemical and isotope evidence of groundwater salinization processes on the coastal plain of Hammamet–Nabeul, north-eastern Tunisia

Major elements concentration, stable (δ18O, δ2H) and radiogenic (3H, 14C) isotopes are known to provide important additional information to more traditional hydrological data and unravel the processes that underpin the large variations in chemical composition within the Hammamet–Nabeul shallow aquifer, north-eastern Tunisia (Cap Bon peninsula).The hydrogeochemical investigations of Hammamet–Nabeul shallow aquifer show that groundwaters can be classified into two major water facies: Ca–SO4–Cl and Na–Cl. The main hydrogeochemical processes that typically control the groundwater mineralization are dissolution of evaporates (halite, gypsum and anhydrite), cation exchange and mixing processes related to the return flow of irrigation waters. The stable isotope signatures reveal that the main part of groundwater are not significantly affected by evaporation, which give evidence of a recharge mostly from the foot hill zone in the north of the basin. The tritium and carbon-14 data show mixing processes between modern and old water and suggest that groundwaters recharge occurs according to a long flow path. Nevertheless, moderated evaporation of waters was observed in the southern part of the basin, especially in the agricultural areas.