Groundwater hydro-geochemistry of Mateur Alluvial Aquifer (Northern Tunisia)

The sustainable management of the ground water resources of the Mateur alluvial aquifer (Northern Tunisia), which is threatened by salinization related to the infiltration of saline waters of Ichkeul lake in the discharge zone, is carried out by integrating, the geochemical data, presented in the form of GIS-based geochemical maps, the hydrogeochemical and the multivariate statistical methods, to understand the spatial and temporal vaiation of water mineralization and assign the major hydrochemical processes controlling its composition. Water samples were collected from 40 sites in wet and dry season, and analyzed for temperature, pH, salinity, dissolved oxygen, electrical conductivity and major ions. This study reveals that the origin of the groundwater mineralization was controlled by several coexisting processes, including : water origin (leaching of low mineralized water in the recharge zone and salt water into decharge zone), dilution in the wet season and evaporation in the dry season, thickness, grain size and lithology of the unsaturated zone. It’s noteworthy that the water-rock interaction does not contribute significantly to the solutes aquisition since minerals within aquifer are sparingly soluble. The spatial distribution maps of the major ions contents, especially Cl- and Na+, are similar with that of salinity, which increases down gradient. The principal component analysis (PCA), demonstrates that groundwaters are divided into two main groups: Moderately to weakly mineralized waters with Ca-Na-Cl and SO4 -Ca-Na-HCO3 -Cl facies, which are those of natural recharge area of the aquifer : Highly mineralized waters, with NaCl facies, characterizing the down Stream part, which is influenced by Salt water infiltration, from El Melah river, Ichkeul marshes and salty soils).