黔中小流域水体C、S同位素特征及主要风化过程

Dissolved carbon and sulfur isotopic characteristics and major weathering processes in a small watershed of central Guizhou Province

选取贵州省红枫湖流域四条支流为研究对象,通过对水体中C、S元素浓度及稳定同位素特征的分析,探讨了典型碳酸盐小流域的主要风化过程对流域C、S循环的贡献。红枫湖流域河水中的C同位素组成在-7.47‰～-11.68‰之间,硫酸根浓度为295.5～1315.6μmol/L,除受当地煤矿影响较大的区域外,其余部分水体中离子的δ34S值在-3‰～-7‰之内,反映了这些河段中硫化物矿物的氧化的影响。通过质量守恒的方法,得到硫化物的氧化、蒸发岩溶解以及大气输入对河水硫酸根离子的贡献率分别为63.8%、30.8%和5.4%。来自硫酸对碳酸盐岩、碳酸对碳酸盐岩以及碳酸对硅酸盐岩风化的DIC比例为1∶3.58∶1.37,三种不同的风化过程对区域二氧化碳的净吸收量为7.97×109mol/a。

We studied the contributions of major weathering processes to regional carbon cycle in typical small carbonate watersheds, based on carbon and sulfur concentrations and isotopic compositions in river water samples from four small tributary rivers of Hongfeng Lake in Guizhou Province. The carbon isotopic compositions range between -7.74‰ - - 11.68‰, and the sulfate concentrations between 295.5 - 1315.6 μmol/L. With the exception of samples influenced greatly by local coal mines, most of the δ^34S values vary between - 3‰ - 7‰, reflecting the impact of sulfide mineral oxidation. Based on mass balance calculations, the contributions to the sulfate ions in the river water from sulfide oxidation, evaporite dissolution and the atmospheric input are estimated to be 63.8%, 30. 8% and 5.4%, respectively. The estimated ratio of DIC from carbonate weathered by sulfur acid versus carbonate weathered by carbonic acid, and silicate weathered by carbonic acid is 1 ： 3.58 ： 1.37, with a net CO2 consumption of 7.97 × 10^9 mol/a by these three different weathering processes.