干旱区生态环境知识资源中心

The study based on the interpretation of geochemical (major elements) and isotopic data (O-18, H-2, H-3 and C-14) of the groundwater in the Djerid basin, Southwestern Tunisia, helped to understand the relationships between the different levels of the aquifer system in this basin. It indicates that the slow flowing groundwater of the deep Complex Terminal (CT) aquifer has been recharged under cooler palaeoclimatic conditions. In the present, this groundwater supplies the huge irrigation demands of the oases in the region. The excess irrigation water returns to the ground and recharges the phreatic water table of the Plio-Quaternary aquifer. This water table is not of great quantitative interest; however, it has an important influence in the recharge of the deep CT aquifer. Indeed, the return flow of the evaporated and CO2-equilibrated irrigation water of the phreatic aquifer leads, in some places, to a young bias of radiocarbon ages and a stable isotope enrichment of the deep CT groundwater.