Geochemical and isotopic study of phreatic aquifer in an arid area, case study of El Golea region (Algerian Sahara)

Abstract

Shallow groundwater is a major reservoir of water in arid areas. This water is characterized by strong mineralization which represents a major quality problem for human consumption and even for its use in agriculture. For this reason, geochemical, statistical and isotopic studies were conducted to obtain an overview of the processes that control water mineralization in the oasis of El Golea (Algerian Sahara). Spatial distributions of EC in this area show that the highest concentrations are situated close to the El Golea Lake formed by evaporitic rock. Geochemical and statistical analysis and data from 28 water points in the phreatic aquifer of the El Golea oasis show a strong correlation between electrical conductivity and the majority of chemical elements, indicating the influence of the interaction between fresh water and bed rock on this mineralization. The results obtained indicate that Carbonate minerals (calcite) are oversaturated in all groundwater samples. The ionic ratios demonstrate the role of weathering, dissolving, ion exchange, and evaporation procedures in mineralization acquisition. The scatter plot of that relates δ 2 H = f (δ 18 O) reveals that all of the samples were founds to be below both the GMWL of Craig (1961) and the Sfax local meteoric boundaries (South Tunisia) indicating that groundwater samples have an old origin. This isotopic composition depletion can be explained by the presence of mixes of phreatic groundwater and Continental Intercalaire (CI) (W2).