Sulfur isotopic signatures of water-soluble sulfate in needles of Pinus Massoniana Lamb in two Chinese areas

Abstract

This study analyzed the water-soluble sulfate (SSO4) and total sulfur (ST) concentrations and their isotopic signatures (δ34SSO4 and δ34ST) in needles of Pinus massoniana Lamb collected from Guiyang (seriously affected by acid rain) and Yunnan areas (acid rain did not occur), China SW. The results indicated that the SSO4 concentrations in needles of Pinus massoniana Lamb collected from several Chinese areas were found to be significantly correlated to ambient sulfur dioxide (R2 = 0.9176, p = 0.01), showing that SSO4 concentrations in needles were more reliable to indicate atmospheric sulfur. The average δ34SSO4 (−7.2 ‰) and δ34STS (−5.1 ‰) in needles in Guiyang areas were significantly lower than those in Yunnan areas (+3.9 and +5.7 ‰, respectively), which were in accordance with the lower δ34S of coals in Guiyang areas than in Yunnan areas. The δ34SSO4 and δ34STS in needles became less positive with a distance from a plant combusted 34S-enriched coals while for another plant combusted 34S-depleted coals, more positive was observed. These results indicated that δ34SSO4 in needles was also a good indicator of atmospheric sulfur sources. A very small difference between δ34 ST and δ34 SSO4 for most needle samples suggested that little isotopic fractionation accompanies sulfur assimilation processes.