Use of stable and radioactive isotopes in the determination of the recharge rate in Djeffara aquifer system southern Tunisia

Southern Tunisia is characterized by the presence of several hydrogeological basins, which extend over Tunisian borders. The Djeffara aquifer is one of the most important aquifer systems n this area and contains several interconnected aquifer levels. Stable (δ2H, δ18O and δ13C) and radioactive isotopes (14C, 3H) have been used to evaluate recharge mechanisms and groundwater residence time in the Djeffara multi-aquifer. Thesis aquifer presents two compartments, the first one ( west of the Medenine fault system) is unconfined with a well defined isotope fingerprint, the second compartment is deeper and confined multi- tracer results show groundwater of different origins, and ages , and that tectonic features control ground water flows. The unconfined part was mostly recharged during the Holocene. The recharge rates of this aquifer, inferred by 14C ages, are variable and could reach 3.5 mm/year. However, stable isotope composition and 14'C content of the confined groundwater indicates carrier recharge during late pelistocene cold periods. (Author)