Study On Eutrophic Evaluation And Numerical Simulation Of Water Quality In Nansihu Lake

As an important transmission channel and storage lake of South To North Water Transfer Project in Shandong Province,Nansihu Lake is facing a great challenge to guarantee the water safety in this project, and the control of water pollution has become an urgent problem to solve. In this paper, mathematic methods are adopted to evaluate the water quality and eutrophication on the base of the investigation and inspecting, also the spatial distribution of the main pollutants is researched and analyzed, so that we can provide some useful control measures of the pollution in Nansihu Lake. The main contents of this research are as follows:(1) In this paper, fuzzy mathematics is adopted to evaluate the water quality, and select DO, CODMn, COD, NH3-N and TP as the evaluate indices. According to the standards of environmental water quality, the type of water quality is determined. The water quality of Lower Lake is better than Upper Lake. The water quality of Nanyanghu Lake isâ…¢-type water in Aug. 2008, while Dushanhu Lake and Zhaoyanghu Lake areâ…¡-type water. In Dec. 2008, the water quality of Dushanhu Lake is changed better which wasâ… -type water, Zhaoyanghu Lake is changed toâ…¢-type water. The water quality of Upper Lake is deteriorated in July 2009, and changes better in Oct. 2009, which isâ… -type water.(2) TSI method is adopted to evaluate the eutrophication in Nansihu Lake, and select Chl.a, TP, TN, SD and CODMn as the evaluate indices, also visualize the concentration of pollutants using the Surfer plotting software. According to the classificate criterion, the degree of eutrophication can determined. The Nanyanghu Lake is mesotrophication in 2008, and the degree of eutrophication is reduced in 2009, which is oligotrophication. The TSI of Dushanhu Lake in 2009 is larger than that in 2008, and it has become mesotrophication in Oct. 2009. Zhaoyanghu Lake and Weishanhu Lake are oligotrophication in 2008 and 2009, but the pollute degree of Zhaoyanghu Lake is more serious than Weishanhu Lake.(3) In order to study the main factors of influencing the water quality of Nansihu Lake,Surfer is adopted in this paper to visualize the spatial distribution of concentration of Chl.a,TP,TN,CODMn which affecting the level of eutrophication, and also analyze the distribution of the pollutants which will contribute to Nansihu Lake Pollution Control. In the figure of spatial distribution, the concentration of pollutants in Upper Lake is higher than the Lower Lake. Nanyanghu Lake has the highest concentration of the pollutants, then Dushanhu Lake and Weishanhu Lake, Zhaoyanghu Lake has the lowest pollutant concentration.(4) The hydrodynamic model and water quality simulation model are established using RMA2 and RMA4 modules of SMS basing on the actual situation of Upper Lake. Through the simulation of hydrodynamic and water quality in the flood season, we can realize the moving rules of the pollution. Seen from the analysis of pollutant concentration, the pollutants flowing into Lake is affected Nanyanghu Lake largely in the early time, and its concentration will reached to the largest soon. And it affects Dushanhu Lake and Zhaoyanghu Lake largely in the later time, the pollutant is enriched gradually.Pollution control countermeasures for Nansi Lake are presented in this paper from the aspects of pollutants reduction flowing in the lake, eutrophication control and sediment release control according to the moving rules of the pollution. Moreover,this paper provides technological support for pollution control in East Route Project of South To North Water Transfer Project in combination with the evaluation results of water quality and eutrophication.