Hydrochemical and isotopic assessment of groundwater quality in the Quaternary shallow aquifer, Tazoghrane region, north-eastern Tunisia

The major ion hydrochemistry and environmental isotope composition (18O, 2H) of the Tazoghrane shallow groundwaters were investigated to identify the sources and processes that affect the groundwater composition. The Quaternary shallow aquifer of Tazoghrane represents one of the most important aquifers in the Cap Bon peninsula. Groundwater from this aquifer is classified into two water types: Ca–SO4–Cl and Na–Cl. The groundwater composition is largely controlled by the water–rock interaction, particularly the dissolution of evaporate minerals and the ion exchange process. Elevated content of nitrates indicates that agricultural activities are probably the most significant anthropogenic sources of nitrogen contamination. The stable isotopic signatures reveal two water groups. Non-evaporated waters, which are distinguished by depleted d18O and d2H contents, indicate the significant recharge by modern rainfall from Mediterranean air masses. Evaporated waters that are characterized by relatively enriched d18O and d2H contents indicate an important component of recharge by return flow of irrigation waters.