Source and distribution of organic matter in seabed sediments of the Changjiang River Estuary and its adjacent sea area

In this paper, 34 superficial sediment samples were collected in Changjiang River Estuary and its adjacent sea area. Subsequently, grain size, total organic carbon, total nitrogen, carbon and nitrogen isotope compositions were also analysized. Finally, organic carbon and nitrogen spatial distribution patterns in Changjiang River Estuary and its adjacent sea area were studied; characteristics of stable carbon and nitrogen isotope in seabed sediments and their implications for tracing organic matter source were discussed; and contributions of different organic matter sources in seabed sediment were calculated. The spatial distribution patterns of total organic carbon and total nitrogen show apparent correlation with currents of East China Sea shelf. Corresponding to distributions of these currents, the study area could be divided into four different parts. Total organic carbon, total nitrogen, and organic carbon and nitrogen stable isotope in sediments shows linear correlation with mean grain size, respectively, thus "grain size effect" is an important factor that influences their distributions. C/N ratio can reflect source information of organic matter to a certain degree. In contrast, nitrogen stable isotope shows different spatial distribution patterns with C/N and organic carbon stable isotope, according to their relationships and regional distributions. The highest contribution (more than 50%) of the terrestrial organic carbon appears near the Changjiang River Estuary, and their isolines project towards northeast, indicating the influence of Changjiang dilution water. The terrestrial particulate organic matter suffers from effects of diagenesis, benthos and incessant inputting of dead organic matter of plankton, after depositing in seabed. Therefore, the contribution of terrestrial organic carbon to particulate organic matter is obviously greater than that to organic matter in sediments in the same place.