Distribution Features Of Nutrient And Flux Between The Sediment And Water Interface Of East China Sea And Yellow Sea

The nutrients in the ocean are widely studied for its importance to support a high primary productivity, and the absence of any element may limit the growth of phytoplankton. At present, most studies are focused on the nutrient concentrations of the Yellow Sea and East China Sea,and little is known about the mechanisms of nutrient replenishment and recycle in the studied area. The nutrient concentrations and distribution in the East China Sea and Yellow Sea are discussed in this study, and the nutrient exchange fluxes between the sediment and water interface are evaluated based on incubation experiments on boat and pore water nutrient profiles as well. At the same time, Sanggou Bay is also studied for its nutrients dynamics.Based on the results of observations, the nutrient concentrations and distribution in the East China Sea and Yellow Sea show obvious temporal and spatial changes. In the Yellow Sea, the investigation in autumn of 2006 shows that the concentrations of NO3-, PO43-, SiO32-, DIN, TDP and TDN have similar distributions with the highest values in the surface layer in the southwest of the Yellow Sea, and decrease significantly from the south to the north and northeast. The nutrient concentrations also show high values around the Chengshan Cape, while the lowest values appear in the northeast of the south Yellow Sea. The nutrient concentrations in the near-bottom waters decrease from the west to the east, and show high values in the south part of this area. With respect to the DIN, NO3- is the major component. There is an obvious thermocline in the center part of the Yellow Sea influenced by the Yellow Sea Cold Water. As a result, nutrients show stratification distribution. The observation in the spring of 2007 also shows stratification distribution, when there is a phytoplankton bloom in the center part of the south Yellow Sea. The concentrations of nutrients are in a low level due to phytoplankton uptake. In the East China Sea, the distribution of nutrients is significantly influenced by the comprehensive current regime, i.e. the invasion of Kuroshio Subsurface Water, the Changjiang Diluted Water and Taiwan Current Warm Water. Two investigations in autumn and winter show similar distributions with high values in surface layer in the inner shelf of the East China Sea, and the contour is dense and parallel to the coast. From the inner shelf to the outer shelf, the concentrations of nutrients decrease quickly. In the near-bottom layer, the distribution of nutrients is similar to that of surface layer, except that there is another high-value area affected by the invasion of Kuroshio Subsurface Water. The vertical distribution of temperature, salinity and nutrients is well-mixed due to strong mixing of seawater in the inner shelf, and the concentrations of nutrients decreased from the inner shelf to outer shelf.The nutrient fluxes between sediment and water interface in the East China Sea based on laboratory incubations show that nutrient exchange rates are related to the sediment type, redox conditions, temperature etc. The NO3-, PO43-, TDP, SiO32- show a net exchange flux from water to sediment, while NH4+, DIN, DON are released from sediment to seawater, which will increase the imbalance of the nutrients structure in the East China Sea. The diffusive fluxes of nutrients obtained by pore water nutrient profiles are lower than that of laboratory incubations. The benthic nutrient fluxes in the East China Sea are compared to that in the other areas in the world.Four cruises are conducted in Sanggou Bay in April, July, November 2006 and January 2007. The result shows that nutrients show obvious seasonal changes. The concentrations of NO3-, NO2-, PO43-, DOP, TDP and SiO32- are the highest value in autumn, while the concentrations of NH4+-N, DON and TDN show the highest in summer. The lowest concentrations of nutrients appear in spring except DON. P is the potential limiting element for phytoplankton growth in spring and summer in Sanggou Bay. The contributions of NH4+, PO43- and SiO32- flux released from the sediment to primary production is quite limited. Comparing to other sallow sea environment, the benthic nutrient fluxes in Sanggou Bay are ranked in the lower end.