Research On Nutrients Fluxes At Sediment-Water Interface Of Mariculture Zone

In recent decades, the offshore aquaculture industry has developed rapidly, and, in consequence, the eutrophication problem has become serious. Serving as the source and sink of nutrients in marine ecosystem, sediment has an important impact on nutrients balance, dynamics of nutrients recycling and the eutrophication process. Across the sediment-water interface transferring and transformation of nutrients are hotspots of environmental science. It is not only urgent to know the exchange fluxes of nutrients between the sediment-water interface, but also to find theoretical basis for eutrophication control and ecologically restoration of eutrophicated bay.For the purpose to supply necessary data information of nutrients fluxes between sediment-water interface in eutrophicated bay, the typical mariculture zone Huangdungang Bay where the eutrophication is very serious and the water exchange is very slow was selected to study including:(1) The nutrient distribution on vertical section;(2)Nutrients exchange fluxes between sediment-water interface of columnar sediment samples in simulating different eutrophication degree seawater;(3)The influences of sediment dredging depth on nitrogen and phosphorus exchange fluxes across sediment-water interface.The main research results and conclusions were as followed:(1) A large amount of N, P and C elements were accumulated in the original columnar sediment samples of Huangdungang Bay, and they were uneven distributed on the vertical section, The nutrients that accumulated in the sediments will be harmful for Huangdungang bay water eutrophication.(2) When the DIN concentration of the overlying water were high, the nitrogen and phosphorus of sediments will be rapidly released to the overlying water at the first6hours, while during the6to9hours, they began to be accumulated to the sediments, and after1day, the releasing and the accumulating reached equilibrium. When the overlying water was polluted by DIN, the concentration of NO3--N decreased over time during one week’s experiment culture, it means that a part of NO3--N transformed into NO2--N and NH4+-N through the denitrification, and some other part of the NO3--N was accumulated to the sediments.(3) When the DIP concentration of the overlying water were high, the nitrogen and phosphorus of sediments will be rapidly released to the overlying water at the first6hours, while during the6to9hours, they began to be accumulated to the sediments, and after1day, the releasing and the accumulating reached equilibrium. When the DIP concentration was not so high(0.015mg/L) in the overlying water, sediments performed as the "source" of the DIP, while the DIP concentration was high (0.15mg/L and0.30mg/L) in the overlying water, sediments performed as the "sink " of the DIP.(4) Sediments were regarded as the "sink" of DIN and DIP of the overlying water, the DIN and DIP concentration can be effectively controlled by sediment dredging. Different dredging depth for DIN and DIP has a little influence on the exchange rate between the sediment and water interface.(5) The exchange rate of DIN and DIP after sediment dredging is higher than that of overlying water seriously polluted, at the both cases, the sediment were characterized as the "sink "of the DIN and DIP of the overlying water.