Groundwater quality deterioration and recharge modes in a semi-arid coastal aquifer: Essaouira Aquifer case study (Morocco)

The sources of groundwater salinization, as well as the recharge modes in the Essaouira coastal aquifer, were investigated using a multi-assessment approach that combines hydrogeochemical, multivariate statistical, and isotopic analyses along with geostatistical and remote sensing tools. The multivariate statistical assessment reveals three types of parameters inducing groundwater degradation in the studied aquifer: (1) natural parameters (Na, Cl, NO₃, HCO₃, Ca, SO₄, K, and Mg), (2) the anthropogenic impact represented by NO₃, and (3) the processes controlling HCO₃ concentration in groundwater. The hydrogeochemical analyses denote the predominance of Ca-Mg-Cl and Na-Cl chemical facies and implicate a multitude of processes that induce groundwater mineralization in the Essaouira coastal aquifer. The stable isotope analyses identify recharge modes, and reveal a recharge dilution effect on groundwater quality close to the river. The interpretation of nitrate levels associated with different land uses suggests that domestic sewer leakage and livestock activities are the major sources of nitrate pollution in the studied aquifer. The adopted multi-assessment approach reveals the complexity and the interconnectivity between the different processes controlling groundwater quality in the Essaouira coastal aquifer.