Nutrients Exchange At The Sediment-water Interface Along The Tidal Flat Of Yangtze Estuary

As an interface of land-ocean interaction, estuaries are characterized by strong water dynamic action, frequent sediment transportation, constant variations in deposition and erosion, and abundant biodiversity, et al., At the same time, estuaries, which widely affected and regulated by the increasing anthropogenic activities, are considered as the most fragile ecological environments. Tidal flat is a especial ecosystem that between land ecosystem and water ecosystem, which benefit great to the weather regulation, bio-diversity and ecosystem equilibrium. Tidal flat is a kind of ecosystem that have the highly productivity, its' economic value and potential economic value quicken the utilize of the resource. Therefore, it is of vital significance to natural science and social economy to develop environmental and ecological researches on estuarine tidal flat. As a sort of environment boundary between water and sediment, the sediment-water interface is a very important region where physical, chemical and biological parameters of nature water vary sharply. Simultaneously, numerous substance transportation and exchange take place in this interface. Nowadays, researches on the tidal flat sediment-water interface is a hotspot in environment science.Tidal Flat of Yangtze Estuary belongs to sub-tropics of east aisa, and the weather changes obviously. It's particular geographic position and river characteristics make the estuary very impor tant place of the study. Taking the tidal flat of Yangtze Estuary for example, we simulating the nutrient exchange in lab and in spot, based on the simulating result, the regulation of nutrient exchange of Yangtze Estuary were discussed.The result of these study not only enrich the theory of nutrients exchange of estuary, but also provide reliable and theoretical basis for environment management and pollution treatment. Through plenty of field sampling and observation, simulation and analysis in lab and in situ., we get following main results :(1) The result of simulation in lab shown: as an typical estuary in sub-tropics of east aisa, environmental factor changed frequently, then bring great influence to the nutrients exchange during seasons and different positions. The difference of river fluxes during the north and the south bring about the north of the river be of thesourse of the, but the south of the tidal flat NH4+-N were fluxes from the water into the sediments, the NO3--N were regulated by sediments' characteristics and environmental factors, the fluxes changes in the upper estuary and other places.(2) NH4+-N were affected by the concentration of NH4+-N in bottom water, when the concentration of NH4+-N in bottom water were higher than the concentration of pore water , the sediment were the end of the overlying water's NH4+-N ,on the other hand, when the concentration of NH4+-N in pore water were higher than the concentration in bottom water, the sediment would be the source of the overlying water. But we found, NO3'-N have little relationship with the overlying water. The concentration of inorganic P in bottom water were very low, and its' fluxes during the simulation was very weak.(3) The in situ simulation's result show: the concentration of DIN was mainly NO3-N, which was occupied 3 quarter of the total DIN. Different sample sites would have different contamination resource, and the input of the nutrients changes much. The nutrients exchanges at the sediment-water interface were affected by the sediments' characteristic, too. Many phytoplankton and autotroph absorb the DIN of the bottom water that decrease content of DIN in bottom water and change the fluxes of the DIN. And the activity of those phytoplankton and autotroph can even change the direction of DIN'S fluxes.