贵州红枫湖硫酸盐来源及循环过程的硫同位素地球化学研究

Stable sulfur isotopic geochemistry to investigate potential sources and cycling behavior of sulfate in Lake Hongfeng,Guizhou Province

红枫湖是云贵高原上一个中等富营养化的季节性厌氧湖泊。对红枫湖流域湖水及其入湖河流河水一年内四个季节的水体硫酸盐硫同位素组成进行了系统研究,结果表明,红枫湖湖水硫酸盐的δ34S值介于-8.7‰～-4.9‰之间,平均-6.8‰,入湖河流的δ34S值变化范围为-14.7‰～+0.8‰。湖水的硫同位素组成主要受煤以及大气降水的控制,硫化物和蒸发岩的贡献较小。全年内湖水的δ34S值季节性变化明显,表现为夏季>秋季>冬季、春季的特征,反映了大气降水对湖水硫酸盐贡献的季节性差异。此外,湖水垂直剖面上呈现出明显的季节性差异,冬季、春季湖水的剖面上下δ34S值几乎没有变化,而夏季、秋季湖水表层和底层相对较高,呈规律性变化,这与湖水冬季混合、夏季分层的特点有关;夏季湖水分层期间雨水在湖泊表层的滞留,以及湖泊底层的硫酸盐细菌还原等相关生物地球化学过程是水体垂直剖面上δ34S值规律性变化的主要原因。

Lake Hongfeng Seasonal variation of sulfur tributaries were investigated is a seasonal physical stratification and anoxic lake showing slight eutrophication. isotopic composition of dissolved SO4^2- in Lake Hongfeng water and its inflowing in this paper. The results show that the δ34S value of dissolved SO4^2- in lake water ranges from - 8.7‰ to - 4. 9‰ with an average of - 6. 8‰. The δ^34S values of SO4^2- in the inflowing river water range from - 14. 7‰ to ＋ 0. 8‰. The sulfur isotopic compositions in lake and river water suggest that coal mining drainage and rainfall are the major sources of SO4^2- in the studied surface waters. Sulfide oxidation and gypsum dissolution have only limited relative contributions. Seasonal variation of δ^34S of dissolved SO4^2- in lake water, which shows the order of summer 〉 autumn 〉 winter and spring, was also clearly observed. This indicated variations of the relative contributions of rainfall in different seasons. Moreover, the δ^34S values of SO4^2- display homogenous vertical distributions in water columns in winter and spring due to water circulation and overturn mixing which caused a temporary equalization of chemical constituents in lake water. While in summer and autumn, the δ^34S values of SO4^2- of lake water display significant positive shift in epilimnion and hypolimnion layers mainly due to physical stratification of lake water in those seasons. The positive shift of δ^34S values maybe resulted from the retention of rainwater in the epilimnion and the biogeochemieal process such as sulfate reduction by bacteria in the hypolimnion.