In this study we describe the degradation of groundwater quality in the Sichuan Basin, one of the most heavily populated and industrialized areas in China. We analyzed the major element chemistry and stable isotopic ratios of H, O, and S from groundwater and surface-water samples collected from four cities along the Minjiang and Yangtze Rivers. On the basis of these data, we examined the sources and downstream variations in groundwater pollutants in relation to increasing human activity in the basin.
Ca²⁺ and HCO₃^- were the dominant ions within groundwater analyzed in this study, although the proportions of Cl^- and SO₄^2- + NO₃^- progressively increased from the source area downstream along the Minjiang River to the Yangtze River. The degradation of groundwater quality was due to anthropogenic sulfur and nitrogen contamination within the basin. Sulfate δ³⁴S values indicated that the primary source of sulfur in contaminated groundwater was air pollutants derived mainly from the combustion of coal, while contamination by household detergents and industrial waste acted to increase SO₄^2- concentrations further downstream. Fertilizer also contributed to elevated SO₄^2- concentrations; however, the area affected by fertilizer contamination was small in comparison with the area affected by other pollutant sources.