Geochemical and isotopic constraints on the interaction between saline lakes and groundwater in southeast Australia

Abstract

Major ion and stable isotope geochemistry allow groundwater/surface-water interaction associated with saline to hypersaline lakes from the Willaura region of Australia to be understood. Ephemeral lakes lie above the water table and locally contain saline water (total dissolved solids, TDS, contents up to 119,000 mg/L). Saline lakes that lack halite crusts and which have Cl/Br ratios similar to local surface water and groundwater are throughflow lakes with high relative rates of groundwater outflows. Permanent hypersaline lakes contain brines with TDS contents of up to 280,000 mg/L and low Cl/Br ratios due to the formation of halite in evaporite crusts. These lakes are throughflow lakes with relatively low throughflow rates relative to evaporation or terminal discharge lakes. Variations in stable isotope and major ion geochemistry show that the hypersaline lakes undergo seasonal cycles of mineral dissolution and precipitation driven by the influx of surface water and evaporation. Despite the generation of highly saline brines in these lakes, leakage from the adjacent ephemeral lakes or saline throughflow lakes that lack evaporite crusts is mainly responsible for the high salinity of shallow groundwater in this region.