Paticulate Organic Carbon and Its Role in Nutrient Biogeochemical Cycles under Anthtropogenic Activity Effects in The East China Sea

In the East China Sea, Changjiang Diluted Water (CDW) influenced area was characterized as eutrophic area with high anthropogenic nutrients inputs. Nutrients, POC and photosynthetic pigments were studied during the summer season in the East China Sea in 2011. Nutrients levels and ratios effects the phytoplankton growth and the structure of phytoplankton communities. Pigment results indicated that the phytoplankton community was characterized by high contribution of diatom followed by cryptophyta in the near shore. In the middle shelf, different water mass mixing zone( CDW, TWCW and Kuroshio current Water), the proportion of diatom to chl a decreased, while the proportions of dinoflagellate and prymnesophyta to chl a increased. In the outershelf, POC was low and prymnesiophyts or cyanobacteria dominated due to lack of N- as well as P. The nutrients was removed from the ehphotic layer with POC deposition in water column.The nutrients uptake ratio was discussed in the upper ocean according to a two- end member model. In the near shore, Under high nutrient levels and high N/P ratio, POC concentration was high and diatom dominated with relative high Si and P uptaken. The uptake of △N/△P ratio is about 30. The proportion of phytoplankton POC sinking removed water DIN in surface water was calculated. About 80% of DIN was removed from the euphotic zone and recycled in the bottom layer. This part of nutrients plays important role in supporting the following ecosystem in autumn and winter season in the East China Sea.