赣江上游河流水化学的影响因素及DIC 来源

对赣江上游38 处水体采样点的水化学特征和溶解无机碳稳定同位素的分析, 发现其总溶解质浓度较低, 其中, 阳离子以Na⁺、Ca²⁺ 为主, 阴离子以Cl^- 和HCO₃ ^- 为主, Si 的浓度较高, 表征了典型硅酸盐地区河流的水化学组成特征。通过海盐校正分析得出, 研究区大气降水对河水溶解质的贡献率为11.5%, 扣除降水的贡献部分, 利用主成分分析的方法, 计算得出赣南流域受硅酸盐岩风化作用强烈, 同时由于受附近盐矿的影响, 蒸发盐岩的风化作用显著。另外, 根据δ¹³C 溶解无机碳DIC 的测量值约为-8.35‰~-13.74‰, 平均为-11.65‰, 利用质量平衡计算得出, 研究区DIC 的主要来源, 约68.5%来自于土壤CO₂, 31.5%来自于碳酸盐矿物的溶解, 进而得出流域岩石化学风化过程消耗的土壤CO₂ 为2.11×105 mol/yr·km², 来自碳酸盐本身的HCO₃ ^-含量为9.6×104 mol/yr·km²。由于地理位置和流域环境以及人为因素的差异, 各支流DIC 来源的比例亦有所差异。

Hydro- geochemistry and the Sour ces of DIC in the Upr iver Tr ibutar ies of the Ganjiang River

Testing and analyzing the samples collected from the upriver tributaries of Ganjiang, we found that the river and its tributaries have low total dissolved solids concentrations and the chemical composition of river water is dominated by Na⁺, Ca²⁺, Cl^-,HCO₃^- and Si, representing that of the river water from the typical silicate rock areas. Seawater correction approach (Cl^- normalized seawater ratios) was used to estimate the contribution proportions of local precipitation to the solutes, we found that most watersheds of southern Jiangxi province were evidently influenced by precipitation. After the contributions of precipitation deducted from the total dissolved solids, on the basis of the principal composition analysis and factor analysis, the watersheds of Ganjiang were influenced strongly by silicate weathering. At the same time, the watersheds are evidently influenced by evaporates under the influence of the mineral resources. In this paper, the upriver tributaries of Ganjiang were selected for analyzing the dissolved inorganic carbon isotope composition of it. It has δ¹³C_DIC of -8.35 to -13.74‰, with an average of -11.65‰. The key source of DIC is soil CO₂ and carbonate weathering. According to carbon isotopic composition of soil CO₂ and carbonate rock, 68.5% of the DIC is calculated to originate from soil CO₂, respectively, and 31.5% of the DIC is calculated to originate from carbon rock. The soil CO₂ consumption of chemical weathering processes is 2.11 ×10⁵ mol/yr·km², and about 9.6 ×10⁴ mol/yr·km² is from carbonate. At the same time, the tributaries have different δ13CDIC values each because of different environments and the human interference.