Temporal dynamics of inundation area, hydrochemistry and brine in Bakhtegan Lake, South-Central Iran

Study region: Bakhtegan Lake, southern Iran, is a “Wetland of International Importance” (Ramsar Site). Study focus: This study focuses on analyzing the time series of the lake's inundation area, identifying factors contributing to its shrinkage, and studying its hydrochemical characteristics. To map the inundation area, Landsat images from 1972 to 2019 were used and 64 water samples were collected from the lake during 2017–2019 for geochemical modeling. New hydrological insights for the region: The study reveals that the Bakhtegan Lake has become a seasonal lake with a long-term dry state since 2007. The lake's inundation area shows a significant correlation with the Kor River discharge, and the main reason for the lake's shrinkage is a decrease in river inflow due to over-exploitation in the basin and construction of two new dams since 2007. The lake water and brine below the lake bed have TDS concentrations varying between 70000 and 451000 mg/L and 118000–373000 mg/L, respectively. The Gibbs, Na-normalized ratio end-member diagrams show that the lake water chemistry is mainly controlled by evaporation. The saturation index indicates that brine samples were in an equilibrium state with gypsum, halite, and glauberite. The Spencer diagram and evolutionary pathway model suggest that water samples shifted toward natural sulfate-rich minerals during evaporation. The lake water evolution model predicts precipitation of halite, kieserite, and carnallite minerals during progressive evaporation.