中文摘要：

为了探讨珠江流域西江、北江河流溶解无机碳（DIC）及其稳定同位素组成（δ13CDIC）特征，分别于2007年春季和夏季对流域低水期、高水期的西、北江及思贤溶河道DIC及其稳定同位素组成进行了实测调查。结合实测河道水体理化参数，采用碳的稳定同位素示踪技术和多参数相关分析法，对西、北江流域及其涪口的河流DIC组成、性质及其碳源汇机制进行了分析。结果表明，西、北江的河流DIC的组成、性质都有明显的差异且存在显著的季节变化。春季，西、北江的河道DIC浓度及其δ13CDIC分别为1942μmol／L、1637μmol／L和-11．75‰、-12．44‰；而夏季，西、北江的河道DIC浓度及其δ13CDIC分别为1986μmol／L、1383μmol／L和-13．03‰、-12．77‰。河道DIC浓度及其δ13CDIC的这种差异反映出西、北江流域结构特性对DIC侵蚀、输移的显著影响。夏季汛期，流域的高温多雨环境致使大量有机质汇入河道、强烈分解、释放大量轻碳，使得西、北江河道δ13CDIC都低于春季；由于汛期高温和径流的共同作用使得北江DIC远远小于春季，而西江DIC却略高于春季。思贤溜水道的DIC浓度及其δ13CDIC受西、北江来水的控制发生季节变化。

英文摘要：

In order to research the characteristics of the riverine DIC and δ13CDIC of the Xijiang and the Beijiang tributaries in the Pearl River, investigations were carried out in the spring and summer 2007, corresponding to the low flow and high flow periods, respectively. The riverine DIC and its sources in the Xijiang, Sixianjiao and the Beijiang tributaries were analyzed by using tracing technique of carbon stable isotopic composition and physicochemical parameters. The research shows that there are striking variations in the properties of riverine DIC with seasonal changes of runoffs. The concentrations of DIC in the Xijiang River and the Beijiang River are 1 942μmol/L and 1 637 μmol/L, respectively, and δ13CDIC values are -11.75 ‰ and -12. 44 ‰, respectively, in spring, while the concentrations of DIC in the Xijiang River and the Beijiang River are 1 986 μmol/L and 1 383μmol/L, respectively, and δ13CDIC values are - 13.03‰ and - 12. 77‰, respectively, in summer. The variations of DIC and δ13CDIC are consistent with the basin characteristics impacting the weathering and transporting of DIC in the Xijiang and the Beijiang tributaries. The concentrations of DIC are slightly higher and δ13CDIC values are much lower in summer than in spring in the Xijiang tributary. The concentrations of DIC and δ13CDIC in summer are slightly lower than those in spring in the Beijiang tributary. This result from organic matter decomposition, higher temperature and the dilution of high water flow. The DIC concentrations and δ13CDIC in the Sixianjiao water way were controlled by the discharge of the Xijiang River and the Beijiang tributaries.