Research On Sediment Phosphorus Release And Simulation With Water Quality Model In Estuary Of Taihu Lake

Water environmental pollution of Taihu Lake will directly affect the drinking water safety, water ecological safety and recycling of water resources, which will become a restricted bottleneck to the sustainable socio-economic basin development and the construction of a harmonious society. Phosphorus is the limiting factor of eutrophication problems in Taihu Lake. Phosphorus in water accumulates from two sources:the exogenous and endogenous polluting sources. Based on the characteristics of phosphorus pollution sources and sediment phosphorus release in the rivers around the Lake, the Water Quality Analysis and Simulation Program (WASP7.3) was revised and applied in the prediction of pollution control. The results was showed as following:(1) The non-point source pollution analysis of phosphorus showed that agricultural non-point source pollution is a major source of pollution in the regional total phosphorus, accounting for 61.47%, while domestic pollution accounts for 38.53%. Among the agricultural non-point sources, farming and livestock emissions relatively more than the aquaculture on total phosphorus. The spatial differences between the upstream and the downstream of the rivers around Taihu Lake indicated that the emission level of the downstream region were almost equal and low. The phosphorus distribution in water pollution is determined by exogenous load as well as the flow rate, flow and other hydrological terrain conditions. Spatial distribution of phosphorus in sediments was mainly determined by river width, flow conditions and other factors.(2) The start flow rate for sediments re-suspension is 0.10 m·s-1. When the flow rate of overlying water is less than 0.10 m·s-1, the release of phosphorus from sediment almost stay stable with a value as 0.580 mg·(m2·d)-1 for phosphate and 0.671 mg·(m2·d)-1 for total phosphorus. However, the flow rate of overlying water is less than 0.10m/s, there exists a corresponding mechanisms between the release flux and the flow rates as R=aeb(?) And as for phosphate, a=56.974, b=4.8486; while for TP a=63.161, b=4.9638 in this study.(3) The simulation results of phosphorus in Huzhou estuary with WASP7.3 on the reverse was slightly worse than the forward flow. The reason maybe the simplification of one-dimensional simulation and the ignoring of sediment flux. After the involving of sediment flux, the consistency index (d) increased the absolute error and the relative error dropped down. It indicates that it is a significant fact of sediment releasing in estuary which should be concerned in water quality simulation.(4) Application of the modified model revealed that under different scenario analysis that the non-point source pollution load reduction rate set as 10%,20%,30%, 50%, the non-point source pollutants should be cut more than 50% in order to achieve the control objectives of the functional areas requirements. Therefore, it is the point source that is the key point of watershed phosphorus pollution control. Further reduction of non-point source pollutants should be carried on based on the control of point-source pollution.