Analysis Of Carbon And Nitrogen Stable Isotope Of Particulate Organic Matters And Plankton In South Yellow Sea In Summer

The source and distribution of organic matters in marine ecosystem is an outstanding issue in marine food web structure researches. Stable isotopes analysis, developed in recent years, is a brand-new method in this field. The fractionation of stable carbon and nitrogen isotopes (13C and 15N) in organic matters takes place in all kinds of biogeochemical process, making 13C and 15N indicators of sources of organic matters, food compositions of consumers, and trophic levels of organisms in a food web, which can provide valuable information for marine ecosystem studies. Therefore the stable isotope analysis method has a broad applicability in global or local ecosystem studies. In this study, in order to reveal the influence of two major hydrological characteristics in South Yellow Sea in summer (the Yellow Sea Cold Water Mass and the Changjiang Diluted Water) on the spatial distribution of the δ13C and δ15N composition of particulate organic matters (POM) and plankton, the concentration and stable isotope composition of particulate organic carbon and nitrogen on 123°E and 124°E sections in summer of 2013 is analyzed, together with the stable carbon and nitrogen isotope composition of plankton. The source of particulate organic carbon and nitrogen is also analyzed by comparing the isotope composition of particulate organic carbon and nitrogen from different water bodies, to demonstrate the biomass transportation and the ecosystem features on 123°E and 124°E sections in South Yellow Sea. Here are the main results and conclusions.1) From the variation in the carbon and nitrogen stable isotope composition of POM from 123°E and 124°E sections, it can be concluded that, in summer, the POM in different layers are mainly influenced by primary productivity, resuspension of sediments, mineralization and decomposition of organics and biological assimilation and absorption.2) Changjiang Diluted Water mainly affects the surface layer of the south area of 33.5°N in South Yellow Sea. The difference of δ13C of POM from different layers shows that the sources of particulate organic carbon vary among different layers. For surface layer, the main source of particulate organic carbon is marine phytoplankton, while for other layers it is resuspended sediments. A similar method is processed on δ15N of POM and results show that the PN in surface layer is mainly influenced by the biological assimilation and absorption, and for lower layers it is the mineralization of nitrogen-containing organics.3) The scope of Yellow Sea Cold Water Mass is the bottom layer of northern area of the South Yellow Sea. The discrepancy of δ13C and δ15N in POM among different layers in northern area reveals that above 30 m depth the particulate organic carbon is mainly composed by bio detritus (Plankton and its excretion and debris), and in bottom layer there are more resuspended organic sediments and the decomposition products, acting as another main component of particulate organic carbon. And the significant difference of δ13Cpoc in bottom water between south area and north area (p< 0.01) could reflect the migration of the terrigenous material to a certain extent. The main source of sediment in south area is from Changjiang, while in north area, the main source of sediment was Huanghe River. On the other hand,δ1NPN value decreases with the water depth and the mineralization of organics is the main source of particulate nitrogen in this area.4) The comparison of δ13C of phytoplankton and zooplankton collected by the three kinds of plankton nets shows that primary productivity and zooplankton abundance are the two main factors affecting plankton’s δ13C and δ15N. The δ1C of phytoplankton collected by microplankton net rises with the increase of phytoplankton abundance. The δ13C of zooplankton collected by meso-and macro-plankton nets rises with the increase of zooplankton abundance. Comparing the δ15N value of the three groups of plankton and the regular δ15N value of phytoplankton and zooplankton, it can be concluded that all three groups contain both phytoplankton and zooplankton. Moreover, microplankton net contains more phytoplankton, and zooplankton is more frequently found in macroplankton net.