Towards Sustainability in Dry land Oases: Water Challenges and Quality

Abstract

Drâa river basin (DRB) is a large arid area encompassing most important oases in the south of Morocco. Climate change, population growth and recently intensive agriculture activity have led to the overexploitation of limited groundwater resources aggravating the problem of water salinization. Therefore, this study aims to assess groundwater quality in the DRB using hydrochemical characteristics from various sources. The complex set of water quality information is simplified into two indicators namely the Water Quality Index (WQI) and Heavy Metal Pollution Index (HPI). Additionally, the suitability of groundwater for irrigation purposes are assessed using sodium absorption ratio (SAR), Residual Sodium Carbonate (RSC) and the permeability index (PI). The results show that the degradation of water quality is related to the high content of sodium and chloride which emerge as the predominant ions along the flow path. Fresher water (Ca-Mg-HCO₃ water type, low WQI and SAR scores), able to sustain local drinking and irrigation needs, are observed in the Upper DRB, while reducing ions excess and adopting agriculture tolerable to salinity become more imperative in downstream oases. The prevalence of hard, igneous and calcareous rocks imparts a general hardness character at a large scale and bicarbonates exceed the permissible limit in 82.30% of samples. However, sodium hazard was not associated with CaCO₃ and MgCO₃ precipitation (low PI and RSC). In some areas, nitrate contents imply anthropogenic contamination from local source of pollution, whereas the concentrations of heavy metals are more associated with the geological setting than anthropogenic activities.