Identification of Anthropogenic and Natural Inputs of Sulfate and Chloride into the Karstic Ground Water of Guiyang, SW China: Combined δ37Cl and δ34S Approach.

Because of active exchange between surface and groundwater of a karstic hydrological system, the groundwater of Guiyang, the capital city of Guizhou Province, southwest China, has been seriously polluted by anthropogenic inputs of NO3-, SO42-, CI-, and Na+. In this work, δ37CI of chloride and δ34S variations of sulfate in the karstic surface/groundwater system were studied, with a main focus to identify contaminant sources, including their origins. The surface, ground, rain, and sewage water studied showed variable δ37CI and δ34S values, in the range of -4.1 to +2.0%‰ and -20.4 to +20.9‰ for δ37CI and δ34S (SO42-), respectively. The rainwater samples yielded the lowest δ37CI values among those observed to date for aerosols and rainwater. Chloride in the Guiyang area rain waters emanated from anthropogenic sources rather than being of marine origin, probably derived from HCI (g) emitted by coal combustion. By plotting 1/SO42- vs δ34S and 1/Cl- vs δ37CI, respectively, we were able to identify some clusters of data, which were assigned as atmospheric deposition (acid rain component), discharge from municipal sewage, paleo-brine components in clastic sedimentary rocks, dissolution of gypsum mainly in dolomite, oxidation of sulfide minerals in coal-containing clastic rocks, and possibly degradation of chlorine-containing organic matter We conclude that human activities give a significant input of sulfate and chloride ions, as well as other contaminants, into the studied groundwater system through enhanced atmospheric deposition and municipal sewage, and that multiple isotopic tracers constitute a powerful tool to ascertain geochemical characteristics and origin of complex contaminants in groundwater. [ABSTRACT FROM AUTHOR]