Effects Of Sediment Resuspension On Aqueous Nutrients Loading In The Changjiang Estuary And Its Adjacent Area

Whether in the shallow inshore area or in the deep ocean, sediment resuspension is a very common physical process. Especially in estuaries, sediment resuspension frequently occurs due to active hydrodynamic. Sediment resuspension will cause the redistribution of nutrients in sediment-water interface and significantly affect the nitrogen, phosphorus and silicon transfer, conversion and storage process. In the process of sediment resuspension, sediment can adsorb nutrients. At the same time, sediment can also release nutrients. Which is more important, it is influenced by many factors and vary widely in different regions and different conditions.In this paper, we took the Changjiang estuary and its adjacent area as study areas. Based on determining the contents of phosphorus in sediments and the concentrations of phosphate (PO4-P) in sediment pore water, we systematically discussed the effect on phosphate (PO4-P) in the overlying water when sediment resuspension occurred. And we studied preliminarily the effect on ammonium (NH4-N), nitrate (NO3-N), nitrite (NO2-N) and silicate (SiO3-Si) in the overlying water when sediment resuspension occurred. Primary conclusions are listed as follows:Detrital P (De-P) showed relatively higher concentrations in the Changjiang Estuary and its adjacent area, which accounted for above 50% of TP. The contents of organic P (Or-P) and refractory P (Re-P) are also higher. Bioavailable P (BAP), accounted for 21% of TP. Or-P was the major part of BAP. Or-P was significantly positively correlated with the BAP in sediment.Sediment resuspension led to the the concentrations of aqueous phosphate (PO4-P) increase or stay the same. In the processes of sediment resuspension, the concentrations of PO4-P in the overlying water had a significant increase, but the increase rate slowed down. In the later processes of sediment resuspension, the concentrations of PO4-P in the overlying water was tending towards stability. In the processes of sediment settlement, the concentrations of phosphate in the overlying water did not all reduced steadily, and it is also possible to rise.Sediment resuspension can not only change the intensity of dissolved inorganic nitrogen between sediment "source" and "sink", and it also can change behavior of exchange NH4-N, NO3-N, NO2-N at the sediment-water interface. The change law of the dissolved inorganic nitrogen in the overlying water was inconsistent in all stations, which showed some differences.Sediment resuspension led to the the concentrations of aqueous ammonium (NH4-N) increase, so sediment showed the NH4-N source. In the processes of sediment resuspension, the concentrations of NH4-N in the overlying water had a significant increase, but the increase rate slowed down. And in the processes of sediment settlement, the concentrations of NH4-N in the overlying water did not all reduced steadily, and it is also possible to rise. Sediment resuspension was not conducive to the release of NO3-N and NO2-N shows complicated transformation.Sediment resuspension led to the the concentrations of aqueous silicate (SiCb-Si) increase, so sediment showed the silicon source. In the processes of sediment resuspension, the concentrations of SiO3-Si in the overlying water had a significant increase. But in the processes of sediment settlement, the concentrations of SiO3-Si in the overlying water rised or remained the same, whichwas concerned with relative intense dissolution of biogenic silica (BSi).In aerobic conditions it was more beneficial to sediment SiO3-Si, NH4-N release than in anaerobic environment in the processes of sediment settlement, but it was against PO4-P, NO3-N release.