Understanding salinity evolution in the Moroccan Ghiss-Nekor aquifer using differential mapping technique

Abstract

Assessing spatiotemporal groundwater hydrochemistry evolution is crucial for sustainable aquifer management. The Ghiss-Nekor aquifer, located in a semi-arid coastal region, requires a comprehensive grasp of hydrochemical shifts for proactive degradation mitigation. Accordingly, the differential mapping technique (DMT) has been employed to assess the salinity evolution in the study area. In 2015 and 2022, 48 and 52 groundwater samples were respectively analyzed. As a result, an overall increase in salinity was observed within the Ghiss-Nekor aquifer, particularly near the shoreline, where in some areas the TDS variations (ΔTDS) exceeded +7000 mg/L. ΔCl- reached up to +129 meq/L near the coast. Similarly, ΔNa+, ΔSO42-, ΔMg2+, ΔCa2+, ΔK+, and ΔHCO3-, showed values up to +94 meq/L, +22 meq/L, +17 meq/L, +10 meq/L, +1 meq/L, and +5 meq/L, respectively, along the coast. In contrast, a decline in the levels of these ions was noted across most of the plain, especially in the southern portion. Positive major ions levels near the sea indicate ongoing freshwater degradation due to seawater intrusion. DMT approach showed its effectiveness in assessing the spatiotemporal changes occurring within aquifers. These findings advocate for broader DMT application in safeguarding aquifers impacted by salinization, promoting sustainable development.