Source of ?SO2-4?in karst groundwater in the Liulin spring area

The karst groundwater in the Liulin spring area is characterized by higher SO2-4- concentrations. It is important to understand the hydrogeochemical processes of karst groundwater to explore the source of SO2-4?Based on analysis of regional geologic and hydrogeologic conditions and spatial distribution of SO2-4concentrations in the karst groundwater, the methods for stoichiometry, isotopic mass balance model and Rayleigh distillation model are used to analyze the source of SO2-4, and to calculate the ratio of variable sources and the reduction ratio for SO2-4in stagnant areas. The results show that SO2-4 in the karst groundwater primarily stems from dissolution of gypsum and oxidation of pyrite. The percentages of SO2-4?from dissolution of gypsum range from 73% to 88% with a mean value of 81% in the discharge area, while those from oxidation of pyrite range from 12% to 27% with a mean value of 19%. The reduction of SO2-4occurs in the stagnant area, and the reduction ratios are in the ranges 9%~15% with the higher ratios close to the western boundary.