ISOTOPIC COMPOSITION AND POTENTIAL SOURCES OF SULFATE IN TWO WATER SUPPLY RESERVOIRS OF THE GUIYANG CITY, SOUTHWESTERN CHINA

Sulfur isotopic composition of dissolved SO(4)(2-) in waters from the Hongfeng and Aha reservoirs and their inflowing tributaries in the Guizhou Province, southwestern China were investigated. The results show that delta(34)S values of SO(4)(2-) range from -6.07 +/- 0.10 parts per thousand to -7.8 +/- 0.01 parts per thousand, with the average SO(4)(2-) concentration of about 0.65 mM/L in the Hongfeng reservoir water but range from -10.00 +/- 0.08 parts per thousand to -10.53 +/- 0.05 parts per thousand, with the average SO(4)(2-) concentration of about 3 mM/L in the Aha reservoir water. delta(34)s values of SO42- in the river water samples from the inflowing tributaries also show relatively low values (-2.34 +/- 0.01 parts per thousand to -11.88 +/- 0.06 parts per thousand) compared to most of river waters of the world. According to the sulfur isotopic compositions and SO(4)(2-) concentrations in the studied reservoir and river waters, three potential sources of dissolved SO(4)(2-), including coal-mining, acid deposition and oxidation of sulfide were identified. Within these S sources, coal mining is the major source of SO(4)(2-) in surface waters of the studied drainage basins. The estimation for the relative contributions of the potential sources indicate that about 80-90% of the sulfate in the Aha reservoir and its inflowing river water and about 60-70% in the Hongfeng reservoir and its inflowing river water are derived from coal strata via the coal mining activities. Acid rainwater and oxidation of sulfide have only limited contributions.