Hydrochemical and isotopic investigations as indicators of recharge processes of the Continental Intercalaire aquifer (eastern piedmont of Dahar, southern Tunisia)

Abstract

Groundwaters of the Continental Intercalaire sandstone formations at the eastern piedmont of Dahar (southern Tunisia), where they outcrop, were analysed to study the mineralization, the water origin and the current recharge process. Hydrochemical study shows that these waters present a spatial variability of chemical facies which is linked to the lithology of the host rock. The factors contributing to the mineralization are mainly the water–rock interaction in particular the dissolution of evaporitic minerals and the cation exchange reactions. Stable isotopes show an enrichment in δ18O and δ2H contents principally for piezometric levels closest to the surface, reflecting measures found in the current rainfall subject to a semi-arid to arid context. These results are coherent with those of 14C and 3H that allow the qualitative identification of a current recharge which could probably be supplied by the recent infiltration of waters in Wadis and by the direct infiltration of meteoric water through the local sandstone outcrops of the basin. This concerns in particular the well of Salem ben Salem Dabbabi, showing a content of 1.03 TU, and its static level is controlled by the Tataouine Wadi, indicating therefore an evident sign of recent recharge.