Hydrochemical and isotopic characterization of groundwater in the Ghis-Nekor plain (northern Morocco)

Abstract The coastal aquifer of Ghis-Nekor (Morocco) was studied to identify the major processes causing salinization of groundwater. In fact, a geochemical approach multi tracer (general chemistry and isotopes - δ 2 H, δ 18 O- H2O , δ 34 S, δ 18 O- SO4 ) was utilized, with the hydrodynamics to explain the processes responsible for the salinization of groundwater, and for identttifying areas most vulnerable to seawater intrusion. The recharge of the aquifer is mainly by the Al-Khattabi dam, the Nekor River and the Ghis River, on the eastern border of the plain. The water that feeds the aquifer shows a relatively high level of salinity and for this reason, the majority of sampled wells indicate high values of electric conductivity and total salinity which arrives at 7.5 g L −1 . The plot of the geochemical results analyzes of groundwater in the Piper diagram shows two distinct chemical facies; sodium chloride-facies and chlorinated calcium and magnesium sulfated facies. The concentrations of 18 O range between −4.15‰ and −5.73‰, while the values of 2 H range between −28.4‰ and −41.7‰. The Nekor river water is depleted in heavy isotopes, and the isotopic compositions are in the order on −6‰ for 18 O and −40.5‰ for deuterium. Most of the wells have a slope 18 O- SO4 vary between 4.35‰ and 8.60‰, while the 34 S isotope values range from −4.3‰ to 9.9‰. For Ghis River, these values are between −4.4‰ and 4.95‰, respectively, for sulfur and oxygen. The interpretation of the chemical and isotopic results suggesting the intrusion of seawater to increase salinity of groundwater in the region is low. However, only the NE area shows probable contamination of seawater. In contrast, wells are saline independent of seawater intrusion, the origin of the high salinity can be related to: 1- the accumulation of rivers fluid intake and water dam rich dissolved salts and sulphates, 2- the anthropogenic pollution (domestic sewage, agricultural inputs, septic uses).