Abstract : Groundwater from karst subterranean streams is among the world’s most important sources of drinking water supplies, and the hydrochemical characteristics of karst water are affected by both natural environment and people. Therefore, the study of karst groundwater hydro-chemistry and its solutes’ sources is very important to ensure the normal function of life support systems. This paper focused on the major ion chemistry and sulfate iso-tope of karst groundwater in Chongqing for tracing the sulfate sources and related hydrochemical processes. Hyd-rochemical types of karst groundwater in Chongqing were mainly of the Ca-HCO3 type or Ca(Mg)-HCO3 type. However, some hydrochemical types were the K+Na+ Ca-SO4type (G25 site) or Ca-HCO3+SO4type (G26 and G14 sites), indicating that the hydrochemistry of these sites may be strongly influenced by anthropogenic activities or unique geological characteristics. Theδ34 S-SO42- of collected karst groundwater sample fell into a range of -6.8 to 21.5%, with a mean value of 5.6 %. In dolomite aquifer, the δ34S-SO42- value ranges from -4.3 to 11.0%, and in limestone aquifer, it ranged from -6.8 to 21.5%. The groundwater samples from different land use types showed distinctive δ34 S-SO42- value. Theδ34 S-SO42- value of groundwater samples had range of-6.8 to 16.7%(mean 4.0%,n=11) in cultivated land areas, 1.5–21.5%(mean 7.2%, n=20) in forested land areas, and-4.3 to 0.8% (mean-1.7%, n=2) in coalmine areas. Theδ34 S-SO42- values of groundwater samples collected from factory area and town area were 2.2 and 9.9%, respectively. According to the d 34 S information of potential sulfate sources, this paper discussed the possible sulfate sources of collected karst groundwater samples in Chongqing. The variations of both δ34 S-SO42- and 1/SO42-values of the groundwater samples indicated that the atmospheric acid deposition (AAD), dissolution of gypsum (GD), oxidation of sulfide mineral (OS) or anthropogenic inputs (SF: sewage or fertilizer) contributed to sulfate in karst groundwater. The influence of oxidation of sulfide mineral, atmospheric acid deposit and anthropogenic inputs to groundwater in Chongqing karst areas was much widespread. For protecting, sustaining, and utilizing the groundwater resources, the sewage possibly originating from urban, mine or industrial area must be controlled and treated, and the use of fertilizer should be limited.
Keywords: Sulfate isotope; Hydrogeochemistry ; Karst groundwater; Chongqing Municipality