Exchange Rates Of Dissolved Nutrients At The Sediment-Water Interface Before And After Diatom Bloom In The Coastal Water Of Zhejiang In Spring

Exchange rates of dissolved nutrients at the sediment-water interface were studied before and after diatom bloom from March to May in the Coastal water of Zhejiang province in 2005. Intact sediment cores which were sampled at 10 sites were incubated on board, and exchange rates were calculated in the function method. Meanwhile setting particles were collected at ZA3 for the sedimentation flux.1. Exchange rates of Dissolved Nutrients at the Sediment-Water Interface before and after Diatom Bloom in SpringIt was shown that sediment absorbed NO3-N before bloom with the exchange rate ranging from-1.33 mmol/(m2·d) to -0.68mmol/(m2·d). The sediment released NO3-N after bloom with the exchange rate ranging from-0.69 mmol/(m2·d) to 0.82 mmol/(m2·d). NH4-N almost released from sediment with the exchange rate ranging from-0.65 mmol/(m2·d) to 1.46 mmol/(m2·d), and the rate was higher before bloom than that after bloom. NO2-N moved into sediment all along except at Zc17 with the exchange rate ranging from -0.09 mmol/(m2·d) to 0.05mmol/(m2·d), and the rate was little higher after bloom than that before bloom. The difference between pore-water and overlying water may control the process.SiO3-Si released from sediment all the time with the exchange rate ranging from 0.85 mmol/ (m2·d) to 9.23 mmol/(m2·d),and the rate was higher after bloom than that before bloom. The dissolving and diffusion of clay in sediment and the difference between pore-water and overlying water of SiO3-Si may control the process.The sediment absorbed PO4-P before bloom with the exchange rate ranging from -0.06 mmol/(m2·d) to -0.01mmol/(m2·d),but released PO4-P after bloom with the exchange rate ranging from 0 mmol/(m2·d) to 1.26 mmol/(m2·d) . The rising of temperature and reduction environment and difference between pore-water and overlying water of PO4-P may be the pivotal factor.2. Influence of Zoobenthos on nutrient fluxes The existence of bioturbation can increase the flux of SiO3-Si by 30%～50%.It also can reduce the flux of PO4-P by more than 90% and restrict the releasing of PO4-P effectively. The existence of Zoobenthos can restrict the releasing of NO2-N and NO3-N and NH4-N.3. Deposition flux and resuspension rate of setting particles in HABThe deposition flux of up layer was 4.2 g·m-2·d-1, and 13 g·m-2·d-1of bottom water . The deposition flux of POC was 0.59 g·m-2·d-1in up layer, and 0.20 g·m-2·d-1in bottom water. The deposition flux of PN was 0.031 g·m-2·d-1in up layer, and 0.027 g·m-2·d-1 in bottom water.Resuspension rate after emendation was 78%. It can be seen that resuspension of sediment may play an important role in contribution to deposition flux of bottom water. The main source of POC in bottom water may be the particles from upside.