中文摘要：

2007年夏季和冬季对长江干流悬浮物进行了季节性采样，系统分析了悬浮物颗粒有机碳含量及稳定碳同位素的组成，研究了其空间分布以及季节变化特征。结果显示，长江干流夏季颗粒有机碳含量在0．4％～1．3％，冬季含量在0．7%-2．2％。冬季和夏季颗粒有机碳平均δ^13C值分别为-24．74‰和～24．83‰，季节性差异不大，在空间分布上，冬季上游值要高于中、下游，而夏季不明显。长江干流悬浮物C／N比值的季节性变化不大，在空间上C／N比值有从上游向下游略微降低的趋势。长江上游悬浮物总体上具有较中下游略高的δ^13C值，在夏季主汛期，中下游悬浮物δ^13C值保留了较多的上游特征。而在冬季枯水期，中下游悬浮物占δ^13C值明显低于上游值，使入海悬浮物的δ^13C值相对减小，这可能是由于在枯水期中下游物质贡献量相对增加和中下游水生植物的相对增多造成的。最后，计算了2007年5月到2008年4月长江一年的颗粒有机碳通量为1．46Mt／a，相比长江三峡蓄水前有机碳的通量有较大减少。

英文摘要：

Suspended particulate matter （SPM） samples were collected along the Changjiang mainstream in summer and winter 2007 to investigate the distribution of organic particulate organic carbon （POC） concentra- tions and the stable isotopic composition of POC （813C） within the river system. The results indicate that the POC% has a range from 0.4% to 1.3% in summer and 0. 7% to 2. 2% in winter. The mean ^13C values of the POC in winter and summer are --24.74‰,--24. 83‰, respectively. The C/N ratio has no significant seasonal variability. The 813 C values of upper reaches are higher than the values of the middle and lower reaches in win ter （low flow season）, The relative decrease in δ^13C values during the low flow season from the upper to lower reaches could be interpreted as the result of an increase in the soil erosion rate and channel erosion in the middle and lower reaches after dam construction, except for flood events during which rivers are also strongly influ- enced by relative more contribution of phytoplankton from the middle and lower reaches. We got a total organic carbon flux of 1.46 Mt/a after impoundment of the Three Gorges Dam which could have caused a sharp reduction in sediment load of the Changjiang River.