Hydrogeochemical and Stable Isotope Processes of Groundwater in Laayoune-Dakhla (Southern Sahara, Morocco)

Abstract

In this study, to determine chemical elements and stable isotopes in 30 GW samples collected from SS Moroccan L-D region, various analytical techniques were used.Thus, the goal was to identify and understand different geochemical processes contributing to water mineralization in the study area.In fact, statistical results for major cations and anions indicated that they obeyed the following trend: Na + > Ca 2+ > Mg 2+ > K + , and Cl - > SO4 2-> HCO3 -> NO3 -, respectively.Additionally, it was found that water EC values varied from 1290 to 6895 s/cm.Indeed, pH values of investigated GW was from 6.88 to 7.75.Studied GW had HG facies with 86.66% Na-Cl and 13.33% Ca-SO4.This finding is explained by the dissolution of evaporative formations that characterizes Saharan sections.Additionally, ionic ratios analysis revealed that GW chemical evolution was influenced by processes such as rock weathering, mineral compounds dissolution and evaporation.Therefore, a better relationship between Ca and SO4 suggested gypsum and anhydrite leaching.It was found that stable isotopes ( 18 O and 2 H) values differed from -6.96 to -8.93 and from -51.5 to 65.56, respectively.These findings strongly suggest that waters in the region undergo significant evaporation before reaching the aquifer.In addition, the aquifer's recharge height was also predicted to be no higher than 300 m, with a latitudinal gradient of 18 O, including 0.52 per 100 m.These results can serve as valuable guidance for decision makers in optimizing exploitation and assessment processes in Moroccan SS area.