Integration of multivariate statistical analysis, geochemical modeling, and irrigation water quality assessment in the aquifers of the South-Atlas Tinghir-Errachidia-Boudenib basin (Pre-African Trough, Morocco)

Irrigation development commonly results in the onset of salinization and soil alkalinization, to different degrees, and the irrigation water quality index (IWQI) is the main method utilized globally to assess water quality. This study aims to investigate the hydrogeochemical characteristics and irrigation suitability of groundwater in the South-Atlas region, one of the arid regions in the southeastern part of Morocco, using Principal Component Analysis (PCA) was applied to identify the main factors influencing groundwater quality and Hierarchical Cluster Analysis (HCA) was then used to classify the water samples into distinct groups based on their hydrogeochemical properties. The research also evaluates groundwater suitability for irrigation using several irrigation water quality indices (IWQIs) such as irrigation water quality index (IWQI), Sodium Adsorption Ratio (SAR), Percent Sodium (Na%), Permeability Index (PI), magnesium hazard (MH), and Potential salinity (PS) assisted by geochemical modeling and the Piper trilinear diagram. Fifty groundwater samples were systematically collected in February 2023 from various aquifers (Senonian, Infracenomanian, Quaternary, and Paleozoic) based on their geographical distribution and hydrogeological significance. The Piper diagram reflecting Ca-Mg-Cl-SO4 followed by Na-K-Cl-SO4 and Ca-Mg-HCO3 water facies under the stress of evaporation, saltwater intrusion and reverse ion exchange processes.

The results of the IWQI indicated that, roughly speaking, 0% of the samples fell into the unrestricted category, 46% had leaching restrictions ranging from low to moderate, and 54% of the samples were classified as high to severely limited, meaning that only high salt tolerance plants can be irrigated with groundwater.

The Senonian samples demonstrated excellent SAR, Na%, and PI, values, whereas most groundwater samples from other aquifers showed good to permissible suitability for irrigation. The study identified water-rock interactions, particularly in the Infracenomanian aquifer, and the use of agricultural fertilizers as significant factors affecting groundwater composition.