Study on hydrogeochemical connection and water quality assessment of subsidence lake and shallow groundwater in Luling coal-mining area of the Huaibei coalfield, Eastern China

The surface water from subsidence lakes and shallow groundwater plays an important role for agriculture, industry and local communities in coal mining areas. The connection between the two types of water and quality, however, remains unclear. In this study, 37 samples were collected from a subsidence lake and shallow groundwater around Luling coal mine. The hydrogeochemisty data and formation mechanisms were analyzed to reveal the connection proof. Compared with shallow groundwater, the surface water from the subsidence lake has a higher content of Na+ and HCO3−. For the two types of water samples, Na+ and Mg2+ are two most abundant cations, followed by Ca2+. The contents of anions followed the same order: HCO3− > SO42− > Cl−. The water samples were controlled by NaHCO3 (99.3%) type. The chemical composition of the two types of water were similar, which are all mainly influenced by silicate minerals weathering and ion-exchange interactions, among which ion-exchange interactions were more intense than in shallow groundwater. The recharging source of the two types of water mainly came from atmospheric precipitation. The two waters in the study area, in general, showed the risk of high salt and low-moderate alkali damage. The outcomes provide a better understanding of the subsidence lake and groundwater and it will help utilization of water resources.