[Isotopic composition and isotope tracing of sulfur in atmospheric precipitation at the head area of the Three Gorges Reservoir, China].

Rainwater samples were collected in the head area of the Three Gorges Reservoir from June 2009 to July 2010. The SO4(2-) content and the characteristics of sulfur isotopic composition were determined. The results showed that the concentrations of SO4(2-) ranged from 31.4-668. 1 micromol x L(-1) with a weighted average of 161.9 micromol x L(-1), whereas the variation of delta34S values for SO4(2-) ranged from -2.14 per hundred to 6.07 per hundred with an annual average of 2.06 per hundred +/- 1.97 per hundred. Significant seasonal variations were found in the SO4(2-) content, which were higher in winter and spring and lower in summer and autumn. The delta34S values for SO4(2-) measured in winter were much higher than those in the other seasons. Analysis of the delta34S values showed that the biogenic sulfur might have significant contribution to the acidity of rainwater, especially in summer and autumn.