Nitrogen Forms In Sediment In The Yangtze River Estuary And Adjacent Area

Nitrogen is an essential kind of ingredient in the growth and reproduction of marine plankton, and is the foundation of marine primary productivity and food chain. The primary source of N in ocean is river input. Being important water sources and sinks of nitrogen in marine sediments, sediment is an important reservoir of nitrogen. Nitrogen in sediments exist in different forms, which represent different physical and chemical properties and bioavailability. The determination of the contents of different forms of nitrogen and the inquiry into their influencing factors are necessary in order to clarify the nitrogen biogeochemical cycle as well as to provide scientific basis for the study of biogeochemical characteristics in the Yangtze River estuary and adjacent waters.Two cruises were carried out in August 2013 and August 2014 in the Yangtze River estuary and adjacent area.An improved classification extraction Method was used to measure Ion-exchangeable form (IEF-N), Carbonate form (CF-N), Iron-manganese oxide form (IMOF-N) and Organic matter-sulfide form (OSF-N). To investigate the effects of different forms of nitrogen content, distribution of reasons, and the role of nitrogen in the cycle, the source of nitrogen in sediments, the relationship between sediments and phytoplankton total nitrogen were analyzed.In August 2013, the total nitrogen content in surface sediments of Yangtze River estuary and adjacent waters is 320-1356 μg/g, while the average content is 713.9 μg/g. In August 2014 the total nitrogen content in surface sediments of Yangtze River estuary and adjacent waters is 359-1468 μg/g, while the average content is 810.4 μg/g. The distribution of TN content show increase from north to south, and increase from the inshore to the seaside. The reason is that the organics in sediments increase significantly in the Yangtze River estuary and adjacent waters, accompanying with marine sediments TN content being increased. TN content of Argillaceous sediments are higher than in sandy sediments.The distribution of the forms of nitrogen are various differently in the area.This difference are mainly caused by reasones as follows, IEF-N mainly is affected by land-based sources containing large amounts of organic matter and sediment grain size and biological activity.The distribution of CF-N is mainly affected by the change of pH in the course of mineralization of organic matter in sediments. IMOF-N mainly affected by the deposits redox environmental conditions, OSF-N distribution is mainly affected by primary productivity.Vertical changes of TN content was found significantly in A8-6 station. On the surface, TN content increase significantly with increasing depth. While reaching the highest value, TN content decrease with increasing depth. Vertical changes of TN content was found significantly in A7-5 station. On the surface, TN content descerease significantly with increasing depth.While reaching thelowest value, TN content increase with increasing depth descreased eventually. Overall performance is decreasesing with increasing depth.The forms of nitrogen change in the research area significantly. This difference are mainly caused by reasones as follows, IEF-N is increasing with the increasing water depth, accompanying with complex of mixing water and disturbance from benthic organisms. CF-N descreases with the increasing water depth,because the Yangtze River Estuary and adjacent waters are coarse sediments, mainly including silty and fine sand. The change of IMOF-N is more complex, due to the majority of coarse clastic marine sediments, sediments gap between the relatively are large. The change of OSF-N was due to the sufficient oxygen of surface and most of the microorganisms live in the sediment surface with sufficiently.