Assessments of groundwater recharge process and residence time using hydrochemical and isotopic tracers under arid climate: Insights from Errachidia basin (Central-East Morocco)

The aquifer systems in the Errachidia basin, located to the south of the High Atlas limestone, are constituted by three superimposed and exploitable aquifers (Senonian, Turonian, and Infracenomanian). These aquifers hold economic significance for the central-east region of Morocco. This area experiences an arid to Saharan climate characterized by low precipitation, high temperatures, and very high evaporation. It is one of the most exposed and vulnerable regions to climate change in Morocco. The low local rainfall cannot explain the recharge of the deep aquifers. However, the significant spring discharges from these aquifers indicate the existence of other recharge contributions. The aim of this study is to elucidate the recharge processes of the Cretaceous aquifers in the investigated basin, clarify hydraulic relationships between them and the Jurassic aquifers of the High Atlas Mountains and estimate the residence time of groundwaters. Water samples from aquifers are collected and analyzed for chemical and isotopic elements. Several statistical methods (SOM, discriminant factorial analysis, CPA) are employed. The results reveal that many samples from different aquifers exhibit clear similarities in chemical characteristics, providing evidence of water transfer between aquifers. Isotopic findings are consistent with chemical characterization and mineralization anomalies. Recharge of the investigated aquifers originates from the Jurassic limestone of the High Atlas Mountains, facilitated by the karstic nature of the Jurassic in contact with the permeable formations of the Cretaceous basin. Age dating results, using 3H and 14C values, confirm that most of the investigated groundwater results from a mixing of old and recent recharges. This process of groundwater renewability is relevant. All the findings are valuable for decision-makers to enhance their understanding of the aquifer system's functioning and inform sustainable management strategies for future sustainability.