The Exchange Rate and Flux of Macro-Nutrients and the Regulating Factors at the Seawater-Sediment Interface in the Bohai Sea

On-board sediment incubation was conducted on summer cruise in August 2002 in the Bohai Sea,for the purpose of evaluating the exchange rates and fluxes of the macro-nutrients(SiO3-Si,PO4-P,DIN) across the sediment seawater interface(SSI).The average exchange rates of the three macro-nutrients were 3?466,39 and 1?308 μmol m-2 d1 for SiO3-Si,PO4-P and DIN respectively.NH4-N and NO3-N were determined to comprise 48% and 47% of the DIN,separately.Further analysis of the exchange process with regard to the regulating factors had revealed that the exchange process of silicate across the SSI is controlled by dissolution and diffusion sub-process and the grain size and seawater temperature are the two dominant factors in the exchange rate.For phosphate,the adsorption effects at the SSI played an important role in the exchange process,and the grain size,temperature and the clay content were the controlling factors.The exchange process of DIN was multi-controlled and the strong bio-irrigation had re-enforced its complexity.The fluxes of the three macro-nutrients throughout summer at the Bohai Sea were calculated to be: 2.59×1013 for SiO3-Si,2.95×1011 for PO4-P,and 8.62×1012 mmol for DIN.The nutrients contribution from the sediment accounted for 65% of the SiO3-Si,12% of the PO4-P and 22% of the DIN demanded to maintain the primary productivity of the Bohai Sea in summer,which are far above the nutrients input from the peripheral rivers of Bohai Sea.