[Exchange rates of dissolved nutrients at the sediment-water interface before and after diatom bloom in the East China Sea 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 East China Sea in 2005. Intact sediment cores which were sampled at 10 sites were incubated on board, and exchange rates were calculated in the function method. It was shown that sediment absorbed NO3(-) -N before bloom with the exchange rate ranging from - 1.33 mmol/(m2 d) to - 0.68 mmol/(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 was almost released from sediment with the exchange rate ranging from -0.65 mmol/(m 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 0.05 mmol/(m2 d), and the rate was a little higher after bloom than that before bloom. SiO3(2-) -Si was released from sediment all the time with the exchange rate ranging from 0.85 mmol/(m d) to 9.23 mmol/( m2 d), and the rate was higher after bloom than that before bloom. The sediment absorbed PO4(3-) -P before bloom with the exchange rate ranging from -0.06 mmol/(m2 d) to -0.01 mmol/(m2 d), but released PO4(3-) -P after bloom with the exchange rate ranging from 0 mmol/(m2 d) to 1.26 mmol/(m2 d). PO4(3-) -P and NO3(-) -N which were absorbed by sediment in spring restricted the diatom bloom, but their release from sediment after diatom bloom may make a great contribution to subsequent dinoflagellate bloom.