硫酸侵蚀碳酸盐岩对长江河水DIC循环的影响

The impacts of chemical weathering of carbonate rock by sulfuric acid on the cycling of dissolved inorganic carbon in Changjiang River water

对长江及其主要支流河水水化学和溶解无机碳(DIC)同位素组成(δ13CDIC)进行了研究。河水阳离子组成以Ca2+、Mg2+为主,阴离子以HCO 3-、SO42-为主,水化学组成主要受流域碳酸盐岩矿物的化学侵蚀控制。DIC含量为0.3～2.5 mmol/L,从上游到河口逐渐降低。δ13CDIC值为-12.0‰～-3.4‰,与DIC含量具有相似的变化趋势。H2CO3溶解碳酸盐岩是控制河水DIC来源及其δ13CDIC组成的主要机制。H2SO4溶解碳酸盐岩加剧了流域碳酸盐岩的化学侵蚀,一方面导致了河水的DIC含量增加,另一方面也使河水的δ13CDIC值升高。

The chemical and carbon isotopic draining the Changjiang River were measured compositions of dissolved inorganic carbon （δ13GDIC） in river water during August 2006. The results show that the chemical compositions of river water are dominated by Ca2＋, Mg2＋, HCO3- and SO4^2-, representing that of typical river water draining carbonate regions. Th DIC concentrations of the river water ranging from 0. 3 to 2.5 mmol/L, show a decrease trend from the upriver to the river mouth. While the δ13GDIC values of the river water vary from - 12.0‰ to - 3.4t/w, displaying a similar tendency to DIC concentrations. The end-member identification by the inter-correlations between chemical and isotopic ratios shows that weathering of carbonate rock by H2CO3 is the dominating reaction controlling both DIC sources and δ13GDIC compositions, and that weathering of carbonate rock by H2SO4 and weathering of silicate rock by H2CO3 alSO have significant impact on them. Weathering of carbonate rock by H2SO4 increases the weathering rate of carbonate rock in drainage basins, leading to the high concentrations of DIC and enriched δ13GDIC values in river water.