Evaluating groundwater salinity patterns and spatiotemporal dynamics in complex endorheic aquifer systems

Understanding salinity dynamics in endorheic aquifer systems is crucial for effective water resource management in arid regions. These environments, often characterized by intense agriculture and limited freshwater availability, are particularly vulnerable to water scarcity and salinity. The Bahira plain in central Morocco exemplifies such conditions, where groundwater salinity threatens both water quality and agricultural productivity. This research provides a comprehensive geochemical and isotopic assessment of salinity sources and evolution in both unconfined and confined aquifers within an endorheic basin. 213 groundwater samples from two aquifers were analyzed for major ions and stable isotopes. The findings reveal contrasting salinity levels, with the unconfined aquifer exhibiting hyper-salinity (EC up to 60,000 μS.cm^-1) attributed to excessive evaporation and soil leaching, whereas the confined aquifer displays comparatively lower EC levels (500 to 3000 μS.cm^-1). The spatial distribution of salinity reflects underlying variability in recharge and hydrogeological connectivity across the basin. To evaluate salinity variation and ionic imbalances, a binary mixing model was applied, providing insights into dominant hydrogeochemical processes. Geochemical observations emphasize the importance of water-rock interactions in controlling groundwater salinity, further intensified by high evaporation rates. Stable isotopic studies corroborate these observations, demonstrating evaporative enrichment and distinguishing between local recharge sources for the unconfined aquifer and regional input from high-elevation precipitation in the confined aquifer. These observations sharpen notions of hydrogeochemical processes in endorheic basins, emphasizing the array of climatic, geologic, and anthropogenic factors that control groundwater quality. The findings have broader implications for sustainable water management in similar dryland ecosystems worldwide.