Evaluating the groundwater salinization processes in Zarabad coastal aquifer (southeastern Iran) using hydrogeochemical and isotopic techniques

Hydrogeochemical, multivariate statistical analysis, and multi-isotopic (δ¹⁸O, δD, and δ³⁴S) approaches were used to identify the cause and process of groundwater salinization in the Zarabad coastal aquifer. The hydrochemical facies evolution (HFE) diagram suggests that the Na–Cl facies is the dominant hydrochemical facies. Groundwater chemistry is mostly influenced by cation exchange and its interaction with silicate rocks, as shown by the Gibbs plot. The isotopic composition of δ¹⁸O, δD, and δ³⁴S varies from −3.17‰ to −1.35‰ (with an average of −1.69‰), −25.5‰ to −9‰ VSMOW (with an average of −18.09‰) and −7.7‰–16.7‰ V-CDT (with an average of 0.54‰), respectively. The salinization of groundwater may be caused by the evaporation of water or the dissolution of evaporites. This can be inferred from the δ¹⁸O to δD data, which indicates that a majority of water falls below the GMWL, IMWL, and LMWL. The d-excess value, ranging from −19.8‰ to 5.36‰, further suggests that the groundwater has undergone evaporation before infiltration. In addition, the comparison between the δ³⁴S–SO₄^2- and SO₄²⁻ plots suggested that the dissolution of evaporites is the primary source of SO₄²⁻. Water chemistry changes in this aquifer is primarily caused by water-rock interaction, ion exchange, and evaporation.