中文摘要：

选取西江下游干支流6个样点进行一个完整水文年度的观测分析，利用基本水文水化学参数来揭示河水溶解无机碳（DIC）含量的时空变异特征，并估算流域DIC输出通量。结果表明，西江下游干支流DIE含量受控于流域地质环境和水热条件，变化于0．74—2．40mmol／L，之间，存在明显的时空变异。干支流DIC含量季节变化模式基本一致，呈现汛期（不包括受洪水影响极强的时段）较高、非汛期较低而洪水期最低的变化特征，流域水热条件的季节变化是其根本原因；河水DIC含量的空间变异基本与流域碳酸盐岩空间分布格局一致，干流DIC含量明显高于支流，且向下游呈减小趋势。西江流域DIC输出通量约4．57×10^12g／a，汛期和6月洪水贡献分别达84％和40％。全流域DIC侵蚀通量约12．95g／（m^2·a），在世界各流域中居中上水平。

英文摘要：

Water sampling and field measurements were conducted at 6 sites along the entire length of the lower reaches of the Xijiang River and from the mouths of its major tributaries across a whole hydrological year from April 2005 to March 2006, to reveal seasonal and spatial variations of riverine dissolved inorganic carbon （DIC）, as well as to estimate riverine DIC export flux, using the water hydrochemical parameters. The results indicate that DIC concentration in the Xijiang River is controlled by basin geology and climate, and presents obvious seasonal and spatial variations, ranging from 0. 74 mmol/L to 2. 40 mmol/L. The seasonal changing patterns of DIC concentration in the Xijiang River and its tributaries were nearly consistent with each other. The DIC concentrations in the dry season were lower than those in the wet season （exclude period of floods）, and the minimum values almost occurred during the flood. This seasonal variation mainly results from seasonal variation of bacterial activity and CO2 content in soil, as well as of carbonate/silicate mineral weathering, which caused by seasonal variation of precipitation and temperature in basin. The spatial variation of riverine DIC concentration was consistent with the distribution of carbonate rocks in basin. DIC concentration in the mainstream of the lower reaches of the Xijiang River was obviously higher than that in its tributaries, and for the mainstream, DIC concentration was downstream decreasing. DIC yield in the Xijiang River basin is about 12. 95 g/（m^2 · a）, slightly higher than global mean level. The Xijiang River annually exports DIC about 4. 57 ×10^12 g, in which, 84% occurred in the wet season and 40% during the flood in June.