Water Ecological Comprehensive Assessment Reserch Of Downstream Lake Of Nansihu

With the rapid development of social economy, the water ecological environment problem is increasingly prominent and more and more people pay attention to it. The downstream lake of Nansihu is the lake that on the south of the Nansihu secondary dam. And it is one of the important regulation and storage lake of South-to-North water transfer project. So the water ecology of the lake not only affects the region’s social economy but also affects the water quality of the South-to-North water transfer project. For promoting the construction of downstream lake of Nansihu basin and ensure the water quality of South-to-North water transfer the water ecological comprehensive evaluation of downstream lake of Nansihu is necessary and urgent.The research contents, research methods and research results of this paper as follows:(1)Through combined with the system study of water ecological evaluation research results at home and abroad and the own characteristics of downstream lake of Nansihu and finally established water ecological evaluation system of downstream lake of Nansihu followed with scientific, systematic, dominant, combination of dynamic and static, combination of qualitative and quantitative, comparability and operability principles, etc. And made the analysis of water ecological of downstream lake of Nansihu from the aspect of water quantity, quality, eutrophication and water biological integrity.(2)This research established a criterion and ideal curve of water quantity of downstream lake of Nansihu. Improved the Projection Pursuit Technique and verified the preciseness and reliability and then used it on water quality evaluation of downstream lake of Nansihu. Chose comprehensive nutrition state index and trophic status index to analysis and compare the water eutrophication of downstream lake of Nansihu, and estimated the biological integrity of downstream lake of Nansihu from the five index of phytoplankton, zooplankton, zoobenthos, fish and aquatic macrophyte.(3)Established the variable weight comprehensive assessment method of water ecology of downstream lake of Nansihu and made comprehensive assessment of downstream lake of Nansihu from the four aspect of water quantity, quality, eutrophication and water biological integrity by variable weight method.(4)Get the conclusion of assessment that:The key influence factor of downstream lake of Nansihu water quality is BODs. The trophic state level is between mesotropher and light eutropher of the two monitor station in downstream lake of Nansihu. The water ecology situation from medium grade gradually increase to good grade. the water ecological restoration measures carried out on nansi lake basin have a significantly effect and nowadays the water ecology have become better than the end of the 20th century. The water ecology have a improve trend from 2008 to 2014, and can guarantee the water quality requirements of South-to-North water transfer project.