Origin of the salinisation and hydrogeochemical behaviour of a phreatic aquifer suffering severe natural and anthropic constraints: an example from the Djebeniana aquifer (Tunisia).

The determination of the origin of the salinity in the superficial aquifer of Djebeniana (South-East of Tunisia), and the understanding of its hydroge ological and geochemical behaviours related to severe natural and anthropic constraints, were approached by the combined survey of some dissolved ions (especially the conservative elements: Br- and Cl-), and by oxygen-18, one of the stable isotopes of water molecules. These 'tracers' indicate that: (1) the present recharge during rainwater infiltration brings downward a hi gh content of nitrates and other dissolved salts; (2) two other sources of dissolved salts in groundwater exist, favoured by the intensive exploitatio n of the phreatic aquifer. The first one is due to mineralised water uprisi ng from a deep and confined aquifer. The sea intrusion is the second source of salinity. (C) 2001 Academic des sciences / Editions scientifiques et me dicales Elsevier SAS.