Unveiling provenance of salinity and groundwater quality appraisal using hydrogeochemical, stable isotopes (δ2H, δ18O, δ13C) and multivariate statistical tools in the sedimentary rocks-pleistocene Epoch, Mirpur, Azad Jammu Kashmir

Abstract Groundwater is an important natural resource currently used for drinking, irrigation and industrial purposes, being deteriorated by natural and anthropogenic sources of pollution. The main aim of this is to assess groundwater hydrochemistry, salinity origins, recharge sources, and water quality in the Kashmir basin using geochemical modeling and multivariate statistics. The observed range of total dissolved solids (140 ≤ TDS ≤ 2226 mg/L) and chloride (10.3 ≤ Cl− ≤ 408.5 mg/L) in groundwater specify a mixed source of salinity, stemming from both natural geological formations and human activities. The average concentrations of cations and anions in groundwater are in order of Na+  > Ca2+  > Mg2+  > K+ and HCO3 − > SO4 2− > Cl− > NO3 −, respectively. The groundwater is categorized as fresh to very hard water in study area. Hydrochemistry, based on major ions were predominantly; Ca-HCO3 (40%), mixed Ca–Mg–Cl-SO₄ (30%), Na-Cl (10%), Na–K-HCO3 (15%) and Ca–Cl (5%) in study area. Stable isotopic and hydrochemical signatures clearly explained recharge of groundwater from rain and surface water, and origin of salinity in aquifer by dissolution of salts and rock-water interaction processes. Lower values of δ13CDIC, in groundwater is interpreted as evidence that biogenic CO₂, produced by the microbial oxidation of organic matter within the aquifer, is a significant source contributing to the dissolved inorganic carbon pool in groundwater. Geochemical modeling of groundwater indicates the water is under-saturated with respect to gypsum, anhydride, halite, and sylvite minerals, while being at equilibrium or slightly over-saturated with respect to carbonate minerals, suggesting significant water–rock interactions. Multivariate statistical analyses show natural weathering processes as well as anthropogenic sources of contamination in groundwater. Overall, computed water quality indices (WQIs) demonstrated that 12.5% and 85% water samples come under “excellent “ and “good “ quality, however 2.5% sample exhibited poor category. Irrigation water quality indices (IWQIs) appeared that groundwater in the study area is good quality to support the irrigation needs of crops, opening up opportunities for diverse and potentially more profitable agricultural activities.