Tracing sulfate sources and transformations of surface water using multiple isotopes in a mining-rural-urban agglomeration area.

Rapid urbanization and mining activities are exacerbating sulfate (SO) pollution in surface water, and the information on its sources and transformations is crucial for understanding the sulphur cycle in mining areas. In this study, the SO in the surface water of Huaibei mining area were monitored and the main sources of pollution and biogeochemical processes were identified using stable isotopes (δD, δO-HO, δS-SO and δO-SO) and water chemistry. The results demonstrated the SO content in the Huihe River and Linhuan subsidence water area (SWA) is higher than that in other rivers and SWAs, which exceeded the environmental quality standard of surface water. The SO content of different rivers and SWAs showed seasonal differences, and the dry season was higher than the wet season. In addition, the SO in Tuohe River and Suihe River is primarily caused by urban sewage and agriculture activities, while in Zhonghu and Shuoxihu SWA is mainly contributed by natural evaporate dissolution. Notably, the input of SO in the Huihe River and Linhuan SWA caused by mining activities cannot be disregarded. The aerobic environment and isotopic fractionation of surface water indicate that sulfide oxidation is not the major cause of SO formation. This work has revealed the multiple sources and transformation mechanisms of SO, and provided a reference for the development of comprehensive management and effective remediation strategies of SO contamination in surface water around mining areas.