Identifying the factors controlling surface water and groundwater chemical characteristics and suitability in the East Nile Delta Region, Egypt

In the East Nile Delta Region, Egypt, water scarcity is a major concern, as the shallow Quaternary aquifer has been observed to experience a persistent decline in groundwater levels alongside a deterioration in groundwater quality. The present study was carried out to identify the processes that control water quality mainly in relation to salinity sources and the suitability for drinking and irrigation purposes in the study area. To achieve this aim, 19 surface water and 110 groundwater samples were analyzed for physical parameters (TDS, pH, temperature, and EC), major ions (Na, Ca, K, Mg, Cl, SO₄, and HCO₃) along with spatial and multivariate statistical analysis. The geospatial distribution of the total dissolved solids (TDS) and majority of the major chemical ions show an evident increase toward the north and northeast parts of the study area. Graphical methods using Gibbs plot and Piper diagram showed that water chemistry was mainly affected by weathering and water rock interaction while the geochemical evolution results revealed the dissolution and precipitation of carbonates and silicates, ion exchange processes, dissolved evaporite minerals, and anthropogenic activities. Still, the geochemical processes of surface water and groundwater were different. Additionally, the chemical data were analyzed using factor analysis to identify the most important factors influencing the variation in water quality. In the present study, three main factors explaining 92.47 and 80.95% of the total variance were identified as responsible for the surface water and groundwater chemistry variations from which the first factor (53.79% and 54.08% for surface water and groundwater, respectively), represented a natural weathering and salt accumulations, the second factor (28.60 and 13.52% for both waters) constituted agricultural activities, and the third factor (10.9 and 13.89% for the two types of water) is a contribution from dissolution processes. The results also indicated that 66.3% of the samples fell into the excellent category, 16.4% were considered good, 11.8% were doubtful, and 5.5% were unsuitable. In terms of surface water, 89.5% were classified as excellent, with 10.5% rated as good for irrigation, because of their high sodium levels and salinity. The study results provide a basis for the sustainable utilization of regional water resources.