The aquifer system of Essaouira basin is recognized as one of the most important aquifers in Morocco. The purpose of this study is to highlight the origin and the mechanisms responsible for the salinization of this aquifer system, thus based on the two hydrogeochemical and isotopic approaches. The results indicate that the central and downstream parts are dominated by the facies Cl-Ca-Mg and SO4-Ca-Mg with the dominance of the first facies, while the facies Cl-Ca-Mg, SO4-Ca-Mg, and HCO3-Ca-Mg dominate the upstream part with the dominance of the list facies. Hydrochemical approach shows that the groundwater mineralization in the study area is controlled by (i) the ion exchange phenomenon, under the marine intrusion and (ii) the dissolution of carbonate minerals (calcite, dolomite, and aragonite) and evaporate minerals (halite, gypsum, and anhydrite). High levels of NO3 would come from domestic pollutants, including livestock waste during water withdrawal. The isotopic method shows (i) aquifers recharge in the study area is provided by Atlantic precipitation without significant evaporation, (ii) the presence of recent water (after nuclear tests) and other (before nuclear tests), and (iii) various recharge altitudes from 300 to 1150 m asl. However, this investigation provides a foundation for effective groundwater management and effective mitigation of aquifer impacts.
Keywords: Essaouira basin; Groundwater; Hydrochemistry; Semi-arid climate; Stables isotope.