Geochemical and isotopic investigation of groundwater mineralization process in the Zeroud basin, central Tunisia.

The determination of the origin of the salinity in the Zeroud aquifer (central of Tunisia) and the understanding of its hydrogeological and geochemical behaviors related to severe natural and anthropogenic constraints were approached by the combined survey of major element concentrations and stable isotopes (O, H). The hydrogeochemical investigations of the Zeroud aquifer show that groundwaters can be classified into two major water facies: Ca-SO-Cl and Na-Cl. The main hydrogeochemical processes that typically control the groundwater mineralization are dissolution of evaporates (halite, gypsum and anhydrite), dedolomitization, cation exchange and mixing processes related to the return flow of irrigation waters and the artificial recharge operations. The stable isotope signatures reveal that the first significant recharge origin is related to the direct infiltration of actual meteoric water particularly observed in the foot of hills bordering the basin and in the vicinity of the Zeroud Wady. A main part of groundwater is significantly affected by evaporation, giving evidence of a recharge mostly from the dam water during the artificial recharge operations. Moderated evaporation of waters was observed in the southern part of the basin, especially in the agricultural areas. [ABSTRACT FROM AUTHOR]