Hydrogeochemical and isotopic characteristics to infer groundwater salinization in the Mauritanian coastal sedimentary aquifer basin

The Mauritanian Coastal Basin (MCB), located between the Mauritanides mountain chain and the Atlantic Ocean (14°–21°N, 12°–16°W), encompasses four main aquifer systems: alluvial, Continental Terminal (phreatic and sub-phreatic), and Eocene. This semi-arid region experiences demographic growth and increasing water demand, resulting in overexploitation of groundwater resources facing significant salinization challenges. This study elucidates groundwater mineralization and salinization processes using hydrogeochemical and isotopic analyses of 195 water samples collected between 2013 and 2019. We characterized hydrochemical facies, identified dominant geochemical processes through ion ratios and Gibbs diagrams, discriminated salinization mechanisms using bromide tracers and stable isotopes (δ¹⁸O, δ²H), and assessed spatial water quality variability against WHO standards across different aquifer systems. Results reveal diverse hydrochemical evolution from Ca-HCO₃ freshwaters in deeper aquifers to Na-Cl saline waters in shallow systems. Silicate weathering and carbonate dissolution control mineralization, while seawater intrusion affects 16.7 % of samples with evaporative concentration dominating 66.7 % of the sampled groundwaters. Stable isotopes confirm widespread evaporation effects (67.8 % samples with d-excess <5 ‰) and paleoclimatic recharge in deeper systems. The percentage of samples complying with WHO standards decreases from the Eocene aquifer (70 %) to the Continental Terminal groundwater aquifer (19 %), establishing a vulnerability gradient crucial for sustainable water management strategies in coastal sedimentary basins under increasing anthropogenic pressure. • Hydrogeochemical signatures differentiate marine vs continental groundwater sources. • Bromide ratios reveal seawater mixing (16.7 %) and evaporative concentration (66.7 %). • Stable isotopes confirm paleoclimatic recharge and widespread evaporation effects. • Water quality decreases from deep (70 % WHO compliant) to shallow aquifers (19 %). • Conceptual model guides depth-stratified extraction for sustainable management.