Identifying recharge and salinization sources of groundwater in the Oussja Ghar el Melah plain (northeast Tunisia) using geochemical tools and environmental isotopes

International audienceThe recharge sources and groundwater degradation in the coastal plain of Oussja Ghar el Melah were investigated using geochemical and isotopes tools. We demonstrate that the water quality of shallow groundwater in the phreatic aquifer is impacted by long-term intensive irrigation. We show that the factors controlling the salinity and composition of groundwater are the return flow of the irrigation water, the water\textendashrock interaction in the aquifer and salts formed on the surface by marine sprays. In the low plain where NO3 - content is of up to about 140 mg/L, groundwater is affected by diffuse pollution caused by intensive agricultural activities. In the upstream part of the plain and in the area situated in the SW, stable isotopes and tritium values indicate recent recharge by local precipitation