中文摘要：

根据对长江口水下三角洲上部（CJ16）和口门浅滩（CJ19）柱状样的粒度、总有机碳（TOC）、总氮（TN）和有机碳同位素（δ13C）以及长江口表层样TOC的测定, 得出其粒度及碳氮元素特征, 利用C/N和δ13C分析有机质来源及不同来源的贡献率。研究结果表明： （1）沉积物中有机碳含量在0.19%～1.17%之间, CJ16柱中有机碳含量比CJ19柱略高; 总氮含量均比较少, 且变化幅度小; C/N比值在5～17间变化; CJ16柱的δ13C值在-24.70‰～-22.86‰间变化, CJ19柱为-24.88‰～-22.37‰, 且CJ19柱δ13C值在36 cm以上段较下段明显增大, 推测可能与南汇边滩互花米草（C4植物）的引种有关; （2）长江口表层沉积物TOC的含量范围为0.17%～1.16%, 平均值为0.52%; （3）粒度特征显示长江口主要以粉砂和粘土为主, 砂含量较少, 粒度与长江口TN、TOC含量有较好的相关性; （4）C/N和δ13C值的特征均显示该区有机质为陆源和海洋混合, 利用C/N比值估算出来自陆源的有机碳比例在CJ16柱约为40%, 而在CJ19柱中约为60%; 根据δ13C值估算出CJ16柱陆源和海源两种有机质来源几乎是各占一半的比例, CJ19柱来自陆源的有机碳占总有机碳的60%, 与用C/N比值法测得的结果较一致。上述结果显示长江口的不同空间位置碳氮元素分布特征不同, 沉积记录受到粒度、河口区物源的影响, 还受到陆源和海源不同有机质来源输入的影响。

英文摘要：

Two cores, CJ16 and CJ19, were collected from upper subaqueous delta and river mouth shoal in the Changjiang estuary, respectively. Grain size, total organic carbon （TOC）, total nitrogen （TN） and carbon isotope （δ13C） values were measured to obtain the downward variations and to trace the change of organic matter sources in the two cores. Modern distribution of the TOC was also obtained in the Changjiang estuary. TOC ranges between 0.19% and 1.17%, with higher content in the CJ16. TN is low in the both cores. C/N varies in the scale of 5-17. The value of δ13C varies from -24.70‰ to -22.86‰ in the CJ16 and from -24.88‰ to -22.37‰ in the CJ19. The profile of the δ13C in the CJ19 shows higher values in the top 36 cm than the lower part. The change of the δ13C may be related to the introduction of Spartina alterniflora （a kind of C4 plant） on the Nanhui tidal flat adjacent to CJ19. The TOC in the surficial sediments in the Changjiang estuary is in the scale of 0.17%-1.16% with an average of 0.52%. Seabed materials in the Changjiang estuary consist of silt and clay, with less sand. The TN and TOC show good correlations with grain size. The different proportion of terrestrial organic sources might reflect the distance from the river mouth. The terrestrial organic sources in CJ19 are estimated to be 60% on the basis of C/N as well as δ13C, which is located at river mouth shoal. However, they are estimated to be 40% and 50% respectively by using C/N and δ13C in CJ16 at the upper part of the subaqueous delta far away from the river mouth. This study indicates that sedimentary records at different parts of the Changjiang Delta show discrepancy and this discrepancy is not just naturally influenced by the marine and terrigenous contribution of the organic matter, but also influenced by human activities, such as the colonization of Spartina alterniflora）.