Benthic Exchange Rates And Fluxes Of Dissolved Nutrients At The Sediment-water Interface In The East China Sea

Intact sediment cores were sampled in the East China Sea in April-May 2002, August-September 2002, November 2002 and February-March 2003. During the laboratory incubation experiments, benthic exchange processes of nutrients at the sediment-water interface were measured. With the function method, the average exchange rates and the benthic fluxes of SiO3-Si, PO4-P, NHt-N, NO2-N and NO3-N at the sediment-water interface were calculated. The relationships between the nutrients exchange rates and the potential environmental controls were assessed. The benthic fluxes of different nutrients at the sediment-water interface were estimated by considering the weighted percentage of different patterns of sediment and the seasonal variations of these fluxes were studied. The main results are as follows:1. The exchange rates of SiO3-Si, PO4-P, NO2-N, NO3-N and NH4-N at thesediment-water interface in the East China SeaThe exchange rates of SiO3-Si were always in the direction from the sediment into the water column and ranged from 0.14 to 25.4 mmol-m-2-d-1. While the exchange rates of PO4-P, NO3-N, NO2-N and NH4-N varied in different seasons, ranging from -105.4 to -32.8 mol-m-2d-1, from -6632 to 132 oml-m-2-d-1, from -156 to 26.6 oml-m-2-d-1and from -927 to 2347 mol-m-2-d-1, respectively.2. The relationships between the nutrients exchange rates and the potentialenvironmental controlsIt was observed that the exchange rates of SiO3-Si were correlated with the temperature, DO, pH, salinity of the seawater, the water and clay contents of the sediments and the concentrations of SiO3-Si in the overlying water and pore water of the sediments. The dissolution and the diffusion were the key processes that influenced the exchange rates of SiO3-Si. The temperature was the main factor that controlled the exchange rates of SiO3-Si.The exchange rates of PO4-P in the East China Sea were correlated with the temperature, pH of the seawater and mainly influenced by the reaction at the surfaceof the sediments. The exchange rates were controlled by the DO and pH. It was shown that relationships between the exchange rates of NO3-N, NO2-N and NH4-N and the potential environmental controls were complicated. The exchange rates of NO3-N at the sediment-water interface were mainly controlled by the difference of the concentrations between the pore water and the overlying water. May be the nitrification or the denitrification and the degradation of organic matter were the key processes during the exchange of DIN and the processes were controlled by the temperature and the DO.3. The fluxes of nutrients at the sediment-water interface and their seasonalvariations in the East China SeaComparing the nutrients fluxes of the Chang) iang River with the fluxes at the sediment-water interface of the research areas, the interface was one of the most important ways for the exchange of SiO3-Si, PO4-P and DIN. It can provide 48% of SiO3-Si in spring, 35% of SiO3-Si in summer, 83% of SiO3-Si in autumn and 184% of SiO3-Si in winter that required by the primary productivity. But it can only provide 0.9% of PO4-P in spring. In the other three seasons the fluxes of PO4-P were in the direction from water column to the sediment. The fluxes of NH4-N contributed only 5.9% of N in spring, 3.0% of N in summer and 7.0% of N in autumn requirements for phytoplankton production. The bulk P and N required for phytoplankton production likely originates from microbial recycling in the water column.