As in many other semi-arid regions, the Plioquaternary aquifer of the eastern coast of Cap Bon peninsula (NE Tunisia) shows a parallel increase in overexploitation and mineralization of groundwater resources and so the water quality is deteriorating. Different methods using geochemistry (ions Na ? , Cl -, Ca 2? , Mg 2? , Br -) and stable isotopes ( 18 O, 2 H) are compared with the hydrodynamic information for identifying the main processes involved in the increase of salinization. Along the coast, intrusion of seawater resulting from groundwater overexploitation is identified, but is not the only cause of qualitative degradation: the development of irrigation that induces soil leaching and transfer of fertilizers to groundwater over the whole aquifer extent is another major reason for the increase in salinization. A total of 48 groundwater wells were sampled to obtain additional information on the hydrochemical characteristics of the groundwater defined in previous studies.

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Origin of the mineralization in the Plio-quaternary eastern coastal aquifer of cap Bon (Tunisia)In the Plio-quaternary aquifer of the eastern coast of cap Bon (Tunisia), the groundwater quality is deteriorating. Different methods using geochemistry (ions Na + , Cl − , Ca 2+ , Mg 2+ , Br − ) and isotopes ( 18 O, 2 H) are compared with the hydrodynamic information to identify the main processes involved in the increase in mineralization. Along the coast, seawater intrusion resulting from groundwater overexploitation has been identified but is not the only cause of the qualitative degradation: the irrigation development that induces soil leaching and fertilizer transfer to groundwater over the entire extent of the aquifer is another major reason for the increase in mineralization.

The northern Djeffara aquifer system is located in the southeast of Tunisia and extends over an area of 400 km 2 . This multilayer system of aquifers is essentially recharged by infiltration of rain and by groundwater of the Continental Inter-calaire aquifer, and occurs mainly at two levels between 0 and 180 m depth that belong to the Mio-Pliocene to form the aquifers. A combined hydrogeologic and isotopic investigation using several chemical and isotopic tracers', i.e., major ions, δ 18 O, δ 2 H and tritium, was carried out in order to determine the sources of water recharge to the aquifer and the origin of salinity. The results of geochemical and isotopic studies show that the groundwater in the south of the study area represents a mixture of the Djeffara aquifer groundwater and locally infiltrates modern recharge. In the northern part, the groundwater which resembles that of the Sekhira aquifer originates from locally infiltrated rain and runoff. The salinity of the groundwater is caused by dissolution of evaporate rocks (gypsum and halite minerals) in the aquifer system. The stable isotopes data do not support the hypothesis of mixing with seawater.

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