Classification, hydrochemical characterization, and quality assessment of groundwater of coastal aquifer at Sari–Neka plain, Northern Iran

Lack of data on the hydrogeochemistry of coastal aquifers around the south Caspian Sea warranted the present hydrochemical and quality assessment studies. The study involving classical integrated methods, multivariate statistical analyses, and GIS applications was carried out on the groundwater encountered in coastal Sari–Neka plain, Mazandaran Province, Northern Iran. The present survey indicates that the groundwater encountered at majority (~ 68%) of the sampling locations is of Na⁺–SO4²⁻ category and constitutes deep meteoric percolation type and the same at the remaining ~ 32% of the sampling locations relates to Na⁺–HCO₃⁻ category and belongs to shallow meteoric percolation class. The groundwater situated at ~ 64% and ~ 36% of the sampling locations belongs, respectively, to freshwater and brackish water categories. The groundwater is specified by Na⁺ > Ca²⁺ > Mg²⁺ > K⁺ and HCO₃⁻ > Cl⁻ > SO₄²⁻ > NO₃⁻. It pertains to Ca²⁺-Mg²⁺-HCO₃⁻, mixed, and Na⁺-Cl⁻ hydrochemical facies. Reverse cation–anion-exchange process was found dominant at majority (~ 76%) of the sampling sites. Dissolved solids were originated chiefly from connate brine water confined to the aquifer sedimentary beds, dissolution of aquifer materials, ion-exchange, and different anthropogenic sources. Groundwater encountered at ~ 71% and ~ 27% of the bore well locations belongs to good and excellent categories of drinking water, while that at ~ 73% of the sampling locations pertains to (C3S1) irrigation water class of Richards (Diagnosis and improvement of saline and alkali soils (USDA. Agriculture handbook, Vol. 60). U.S. Department of Agriculture, Washington DC, 1954). The results of the present study are useful for planning sustainable management and protection of the groundwater in coastal areas, especially around the Caspian Sea, and serve as a database for international researchers.