Relationship between shallow and deep aquifers in the Sfax basin (Tunisia).

The study the isotopic composition (O-18 and H-2) of groundwater collected in the Sfax basin (Tunisia), helped to understand the behaviour of the diff erent aquifers. It showed that the groundwater in the deep aquifer is old, probably slow moving and recharged under a colder climate than at present. The increasing exploitation of the shallow aquifers probably favoured upwar d leakage from the deep aquifer. Isotope balance equations allowed us to es timate the contribution of the deep aquifer to the shallow aquifer recharge . (C) 2000 Acadimie des sciences/Editions scientifiques et medicales Elsevi er SAS.