Stable isotope and quality of groundwater around Ksob sub-basin, Essaouira, Morocco

Groundwater resources are playing an increasingly vital role in water supply for domestic and irrigation purposes in the Essaouira basin. The main objective of this study is to assess the quality of groundwater for the population of the Essaouira basin to determine its suitability for drinking and irrigation purposes. A total of 28 water samples were collected in March 2019 for chemical analysis. According to Piper trilinear diagram, two dominant hydrochemical facies, mixed Ca–Mg–Cl and Na–Cl type, were identified. The final integrated WQI map shows two priority classes such as poor and very poor groundwater quality zones of the study area and provides a guideline for the suitability of groundwater for domestic purposes. Results of WQI showed that 60.7% of the samples indicate poor water quality, while 28.6% of groundwater sampled in the field of research had very poor water quality, only 10.7% of samples are unsuitable for drinking. To test the suitability of groundwater for irrigation, four indices are used; they are sodium adsorption ratio (SAR), sodium percentage (Na%), magnesium hazard (MH), and permeability index (PI). For irrigation suitability, the study proved that most sampling sites are suitable while less than 3.57% are unsuitable for irrigation. The presence of evaporation and marine intrusion leading to an increase in salinity in the downstream part of the study area was confirmed by the content of stable isotopes (δ¹⁸O, δ²H), which demonstrated the role of recent precipitation in the recharge of the aquifer.