硫化物风化产酸对流域岩石风化和碳循环的影响——以黄河支流三川河流域为例

The influence of sulfide acid on rock weathering and carbon cycle in catchment scale:A case study in Sanchuan River basin of Huanghe River tributary

硫化物风化产酸可加速岩溶作用但抑制大气二氧化碳参与流域碳循环,其复杂的地球化学机制和过程待阐明.本文以黄河二级支流三川河流域为例,通过采集20个三川河及其支流地表水点样和30个柳林泉地下水点样,经实验测试获得了流域比较系统的水化学资料和δ^13C、δ^34S数据,运用碳、硫同位素分析与水化学平衡计量方法,量化了流域硫化物风化产酸对岩石风化作用的贡献以及对碳循环的影响.计算结果表明:煤系地层硫化物和矿床硫化物的氧化及大气酸沉降所形成的硫酸明显促进了流域碳酸盐岩的溶蚀,对碳酸盐岩溶蚀的贡献约占64.59%;柳林泉水石膏溶解来源的SO2-4占69%,河水中石膏溶解来源的SO2-4占30%,但这些部分SO2-4没有参与溶蚀作用,应当扣除;三川河流域平均岩石风化速率为10.02 mm/ka,其中碳酸盐岩、 硅酸盐岩的风化速率分别为9.14 mm/ka和0.88 mm/ka,低于国内外很多流域;由于硫酸抵消了碳酸盐岩石风化作用对大气二氧化碳的吸收,流域岩石风化消耗大气/土壤CO2通量为116.58 mmol/(km^2·a),不足珠江流域的1/5,且硅酸盐岩风化的贡献占63.3%.

The sulfuric acid that generated from sulfide weathering can promote the dissolution of carbonate rocks and then influence the processes of atmospheric CO2 consumption during carbonate rocks erosion.However,its geochemical mechanisms are still unknown until now.To reveal this mechanism,Sanchuan River basin was selected.Sanchuan River,covering the drainage area of 4102 km2,is one of the tributaries of Huanghe River and locates in the slope areas between Lüliang Mountain and Ordos Basin in Northern China.The ranges of its latitude and longitude are 110°43'~111°35'and 37°3'~38°18'respectively.The basin is mainly covered by carbonate rocks and silicate rocks,as well as some coal,iron,bauxite and gypsum minerals that containing much sulfide inside.To clarify the influence of sulfide on both rock weathering and carbon cycle in catchment scale,20 surface water samples and 30 ground water samples were taken from Sanchuan River basin in August,2014.More eight ground water points and seven surface points were sampled in April,August,November,2014 and January,2015 to investigate their seasonal variations.All water samples were analyzed to obtain the water chemical and theδ^13C&δ^34 S isotope value.Based on the data,both contribution of sulfide on the rock weathering rate and estimation of carbon cycle under the influence of sulfide are calculated.The results show that the sulphuric acid that produced from the coal stadium sulfide,the oxidation of sulfide mineral deposit and the atmospheric deposit can evidently promote the dissolution of the carbonate rocks.The contribution rate of these three sulphuric acids to the carbonate rock erosion occupies about 64.59%.In which,30%of the sulphuric acid in river water are coming from the dissolution of gypsum.This part of SO42-does not take part in the carbonate rocks dissolution processes,so it should be taken out from the carbon cycle calculation.For the mean rock chemical weathering rate,it is 10.02 mm/ka in the Sanchuan River basin,which is much lower than that of most other river basins in the world.Moreover,the chemical weathering rate of the carbonate rocks is 9.14 mm/ka,which is 10 times of the chemical weathering rate of the silicate rocks(0.88 mm/ka).However,because the sulphuric acid would affect the processes of atmospheric CO2 consumption in dissolution of carbonate rocks,the atmospheric CO2 consumption rate in Sanchuan River basin is only 116.58×103 mol/(km^2·a),which is less than 1/5 of that in the Pearl River basin of South China.Meanwhile,under the influence of the sulphuric acid on the atmospheric CO2 consumption in dissolution processes of carbonate rocks,63.3%of the atmospheric CO2 flux of Sanchuan River basin is contributed by the silicate chemical weathering.