Water chemistry and stable isotope characteristics of subsidence lakes in coal mining areas, Eastern China

Many subsidence lakes have formed in eastern China as a result of underground coal mining. These coal mining-related subsidence lakes vary in their formation time and connectivity with rivers. These factors may influence the water chemistry and hydrogen and oxygen stable isotope characteristics of the lake water. This study collected and tested subsidence lake water, atmospheric precipitation, river water, and shallow groundwater in the study area. The results showed that the water chemical types of the subsidence lake water and river water are Cl-Na and HCO3 center dot Cl-Na and that the water chemical types of the shallow groundwater are mainly HCO3 center dot Cl-Na and HCO3 center dot Cl-Ca. There are no significant differences in the water chemical characteristics of subsidence lakes with different subsidence ages and types. The major ions in each water body mainly come from evaporite dissolution and silicate weathering, and ion exchange occurs. Reverse ion exchange occurs in some shallow groundwater samples. The stable isotopes of hydrogen and oxygen in the subsidence lake water, river water, and shallow groundwater are distributed along a straight line with a slope less than that of the LMWL, indicating that these water bodies have a common source, namely, precipitation. With increases in the formation time of the subsidence lakes, the heavy isotopes in the lake water gradually become depleted, and the d value gradually increases, mainly driven by precipitation dilution, weakening evaporation, river recharge, and groundwater recharge. The isotopic values of different types of lakes with the same subsidence time differ little. The research results may provide scientific guidance for the rational development and utilization of water resources in coal mining subsidence areas, enrich the study of the hydrological cycle in the area, and are of great significance for the protection of the local water balance and water environment.