西南三江(金沙江、澜沧江和怒江)流域化学风化过程

Chemical weathering in the Three Rivers( Jingshajiang,Lancangjiang,and Nujiang) Watershed,Southwest China

选择中国西南三江流域作为研究对象,结合水化学及溶解性无机碳碳同位素,借助正演模型,分析河水溶解性组分来源及混入比例,说明硫酸参与区域碳酸盐矿物风化过程及CO2净释放量。结果表明:(1)西南三江流域河水受复杂岩性控制,金沙江河水以Na-Ca-Cl-HCO3为主,与流域上游蒸发盐矿物溶解有关,澜沧江和怒江则以Ca-HCO3为主,显示碳酸盐和硅酸盐矿物溶解的影响;(2)蒸发盐矿物溶解是金沙江干流河水阳离子主要来源,其贡献均值为52%,对澜沧江和怒江河水贡献较小,平均值分别为11%和2%。碳酸盐矿物溶解是澜沧江和怒江干流河水阳离子主要来源,其贡献均值分别为70%和78%,对金沙江干流河水的贡献较小,平均为38%,但对金沙江支流河水的贡献较大,平均为74%。硅酸盐风化产物对金沙江、澜沧江和怒江干流的平均贡献分别为8%、16%和15%,对金沙江支流河水的贡献为15%;(3)金沙江、澜沧江和怒江流域硅酸盐矿物风化速率分别为1.39、3.27和4.27 t·km-2·a-1,CO2消耗速率分别为0.34×105、1.18×105和1.40×105mol·km-2·a-1,碳酸盐矿物风化速率分别为16.93、33.13和33.54 t·km-2·a-1,CO2消耗速率分别为1.40×105、2.47×105和2.22×105mol·km-2·a-1;(4)西南三江流域河水硫酸盐主要来源于硫化物矿物氧化,硫酸参与碳酸盐矿物风化净释放CO2量分别为0.73×105、3.01×105和4.27×105mol·km-2·a-1,高于中国贵州地区,应当在研究区域碳循环以及全球气候变化过程中引起重视。

The Three Rivers （Jinshajiang River, Lancangjiang River, and Nujiang River） region （TRR） in Southwest China was selected to study the characteristics of chemical weathering during river erosion. With the forward model, hydrochemical characters and dissolved inorganic carbon isotopes of river waters were used to interpret the sources and their corresponding contribu- tions to dissolved components, and to confirm the participation of sulfuric acid in carbonateweathering and the net release of CO2. The results showed that ： （ 1 ） Hydrochemical compositions of river water were controlled by complex lithology. The ions of Na-Ca-Cl-HCO3 were dominated in Jinshajiang River due to outcrop of evaporates in its upstream region, while Ca-HCO3 was dominated in Lancangjiang River and Nujiang River due to the existence of abundant carbonate and silicate minerals; （2） Sources and ratios of dissolved components in river waters in TRR were variable. The dissolution of evaporates might control the sources of ions in the main stream of Jinshajiang River with an average percentage of 52%, but was minor in Lancangjiang River and Nujiang River with an average percentage of 11% and 2%, respectively. On the contrary, the dissolution of carbonates controlled the sources of ions in the main stream of Lancangjiang River and Nujiang River with an average of 70% and 78%, respectively, and was minor in the main stream but considerable in major tributary drainage of Jinshajiang River with a corresponding av- erage of 38% and 74%. In addition, the contribution ratios of silicates weathering to the main streams of Jinshajiang River, Lancangjiang River and Nujiang River were 8%, 16%, and 15% respectively; （3） The weathering rates of silicates in the catchments of Jinshajiang River, Lan- cangjiang River and Nujiang River were 1.14, 3.32 and 4.32 t · km-2 · a-1, respectively, and the corresponding CO2 consumption rates were 0.35, 1.19 and 1.41× 10^5 mol· km-2 ·a-1. By contrast, the weathering rates of carbonates in the three studied rivers were 17.41, 34.04 and 34.84 t ·km-2 · a-1 with the C02 consumption rates of 1.46, 2.69 and 2.53×10^5 mol · km-2 ·a-1 respectively; （4） Sulfate in the TRR was mainly derived from sulfide oxidation which led to net release rates of CO2 as 0.87, 3.01 and 4.36×10^5 mol · km-2 ·a-1 in Jinshajiang River, Lan- cangjiang River and Nujiang River, respectively. These values were higher than those in Guizhou, China, so attention should be paid to the important role of sulfuric acid in rock weathe- ring during the study of regional carbon cycle and global climate change.