| Shallow lake of city has the characteristics of shallow water, poor liquidity and plenty of pollutants, which resultes in serious deterioration of water. Because of sediment deposition and the exchange between sediment and water, pollutants accumulate in the sediment of lake. Resuspension and material exchange between sediment and water worsen the situation. Therefore the diagnosis and treatment of sediment pollution in lake is becoming more and more important. Foreign scholars raise the idea of "Endogenous nutrient release". Afterwards relative research mostly based on the shallow lakes of city. "Endogenous nutrient release" is infulenced by various factors, such as concentration gradient of sediment-water interface, the dissolved oxygen content, temperature, PH value, mixing, exogenous input intensity and water disturbance,etc. Some research in this area has started at home and abroad.To know the nitrogen and phosphorus releasing process and patterns of the internal source in urban shallow lakes, sediment was collected at two spots at the inlet, one spots within the lake and other two spots at the outlet of Dianshan Lake. Through a laboratory simulation of the effects of three environmental factors (pH value, temperature and perturbance) on nitrogen and phosphorus releasing from sediment, the release mechanism in shallow lakes has been studied. The writer detennine the various parameters by experiment, and then do the simulation by using SedFlux model. The result of simulation is reasonable by comparing with measured data from Dian Shan lake.Finally,using the adjusted SedFlux model simulation annual nitrogen and phosphorus flux in Dianshan lake.The results are as follows:(1)It was indicated that sediment in Dianshan Lake had an evident feature to release phosphorus, in different points and under different environmental factors the range of TP flux is 0.21-26.39mg/m3.d,the range of TN is-55.74--2.98 mg/m3. (2)When the temperature increases,the flux of nitrogen and phosphorus releasing will be more, which tells that the temperature affects the releas of the flux of nitrogen and phosphorus. The higher the temperature, the greater the fluxes of nitrogen and phosphorus releasing could be.(3)Disturbance to the water column above sediment will speed up the release of nitrogen and phosphorus. The more the perturbation in the water column above sediment, the greater the fluxes of nitrogen and phosphorus releasing could be.For such a shallow lake of Dianshan lake, the effect of disturbance is particularly significant.(4) The higher the pH value is, the greater the fluxes of nitrogen and phosphorus releasing could be.(5) In Dianshan Lake, sediment at the inlet has been seriously contaminated, and the centre of the lake has rather higher level of phosphorus. But in the outlet the situation become better.(6)In contrast with the experiment result of Yuandang, the pollution of sediment in Dianshan lake is more serious than Yuandang.(7)By using the SedFlux model calibrated by the experiment results to simulate the release flux of nitrogen and phosphorus in Dianshan lake around the year.The calculated results is:the release flux of NH3-N is-727.09kg/y; the release flux of NO3-N is-6.53kg/y;the release flux of DTP is 129.23kg/y. The results showes the SedFlux model can be used as a tool to simulate water environment in Dianshan lake.Through simulation on SedFlux model and the study on the influence factors of the release of nitrogen and phosphorus in Dian Shan lake sediment, some theoretical idea to control Eutrophication of Dian Shan lake could be provided... |
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