Temporal Spatial Distribution And Evaluation Of Water Quality In Nansi Lake

Nansi Lake is the largest freshwater lake in northern China,and an important lake for water transportation and storage in the East Route of the South-to-North Water Diversion Project.The water quality of the lake has been widely concerned.However,with the socio-economic development of the basin,the water quality of the Nansi Lake has deteriorated.This paper takes DO,COD,TN and TP as research objects.Based on the monitoring data in the past ten years,this paper analyzes the spatial and temporal distribution of water quality in Nansi Lake and its variation characteristics.The water quality labeling index method and fuzzy evaluation method are used to comprehensively evaluate the water quality.The results show that:(1)According to the water quality change data of the four lakes in the Nansi Lake,the water quality of the Nansi Lake has been significantly improved in the past ten years.Through the comparison of water quality indicators in the Nansi Lake during the year,the average COD concentration in the non-flood period of Nansi Lake in 2014 and 2016 is slightly higher than that in the flood season,which is 1.12 and 1.18 times of the flood season.The mean TN concentration in the non-flood period is 1.23 times and 1.26 times of the flood season,and the TP content in the non-flood period is also greater than the flood season,and the concentration of DO in the flood season is generally greater than that in the non-flood period.By comparing the concentrations of DO,COD,TN and TP in the flood seasons and non-flood seasons of the Nansi Lake in 2014 and 2016,it is shown that the water quality of the Nansi Lake is better than that of the non-flood period.(2)Among the four lakes in the Nansi Lake,the water pollution of Nanyang Lake is the heaviest,and the water quality of Weishan Lake is relatively good.The overall water quality in the south is better than that in the north.The concentration of COD,TN and TP in the area around Nansihu Lake is higher than that in the lake center,which is consistent with the distribution characteristics of water quality.The water quality of the lake is better than that around the lake.From the vertical direction,the concentration of each water quality index basically decreases with the increase of depth,indicating that the surface water quality of the Nansi Lake is inferior to the deep layer.(3)The water quality of Nansi Lake in 2006-2016 was evaluated by single factor water quality index,comprehensive water quality index and fuzzy evaluation.The results show that the comprehensive water quality index I of the four lakes in 2016 is 3.796,3.446,3.350 and3.128,and the water quality has reached the III standard.The overall optimization of 1-2water quality indicators in 2006.The water quality index of Nanyang Lake and Dushan Lake is higher than that of Zhaoyang Lake and Weishan Lake.The water quality of Weishan Lake is relatively better.The research of this paper can provide guidance for water environment management and water quality improvement of Nansi Lake since the water diversion of the South-to-North Water Diversion Project.It has important practical significance for the stability and safety of lake ecology.