Assessing Contamination Sources by Using Sulfur and Oxygen Isotopes of Sulfate Ions in Xijiang River Basin, Southwest China.

The chemical and stable isotopic compositions (δS and δO) of Xijiang River water in southwest China, were measured to determine the extent of rock weathering and associated CO consumption rates, and to assess the contamination sources of river water. The SO concentration in the river water was in the range of 0.05 to 0.96 mmol L (mean value = 0.32 mmol L) and was characterized by δS values ranging from -9.1 to 5.1‰ (mean value = -2.1‰) and δO values ranging from -0.4 to 10.8‰ (mean value = 5.0‰). The δS and δO values ranged from high to low from the upper reaches to the lower reaches in all the river water samples. The results indicate that the oxidation of sulfide and anthropogenic inputs are the dominant processes affecting SO sources and S cycling of the Xijiang River during high-discharge conditions, which are controlled by regional hydrological processes that are affected by natural processes and anthropogenic inputs.