Evaluation Of Comprehensive Water Quality And Analysis Of The Improvement Effect In Nansi Lake During The Year 2006-2015

Nansi Lake is an important water transport channel and storage lake of the east route of South-to-North Water Diversion Project.Its water quality has been drawing wide public attention.This research investigated the monitoring data of 90 sites in the lake from 2006to 2015.The monitoring data was used to analyze and compare the water quality variation trends of the lake in different monitoring sites,annual and spring by using the water quality comprehensive pollution index,comprehensive water quality identification index and principal component analysis method of the analysis and evaluation method.At the same time,this research was to analyze the water quality variation trends of the lake and the water delivery channel after water diversion.Study show:?1?The water quality on the whole in Nansi Lake from 2006 to 2015 has been greatly improved and the overall water quality reaches the standard.On the basis of the water quality comprehensive pollution index method,the index P decreased from 1.75 to0.89.The water condition was basically up to standard.And the variation trend of the spring and autumn water quality was the same.The improvement effect of spring water was better than that in autumn.On the basis of the comprehensive water quality identification index method,the index I decreased from 4.620 to 3.200.Water quality reached III class.Water quality compliance rate was over 97%,and it was smaller than in autumn,the decrease rate of water quality I was 22%.Based on the principal component analysis,the main pollution factors of Nansi Lake were N and P,which are the dominant one,followed by organic pollution.The same sort of water in Nansi Lake with the above 2analysis methods,water quality fluctuation in autumn was improved greatly.?2?The reduction ratio of COD_Cr,COD_Mn,T-P,T-N and NH₃-N in Nansi Lake in October 2015 compared with October 2013 were 47%,-3%,36%,60%and 80%respectively.The average concentration of COD_Cr in spring was slightly higher than that in autumn,which was 1.02 times of that in autumn.The average concentrations of COD_Mn,T-P,T-N and NH₃-N in autumn were higher than those in spring,and the times respectively were 1.04,1.36,1.08 and 1.07 with spring.The water quality from north to south gradually became better,water quality was better in spring than in autumn.And the water quality of the environment in some areas still needed to be improved further.The worst water quality monitoring points in October 2015 mainly concentrated in the Nanyang lake and Xinxue river,Xuecheng Xiaoshahe and Panzhuang river near the estuary area.The best water quality monitoring points were Zhaoyang Lake?lower?and Weishan Lake.From the perspective of Nansi Lake,COD_Cr,COD_Mn,T-P,T-N and NH₃-N of water quality index from the north to south water became better.It fluctuated in the north of Zhaoyang Lake and the Weishan Lake.?3?The reduction ratio of NH₃-N,T-P and T-N of the lake were 56%,28%and 22%,and the reduction ratio of NH₃-N,T-P and T-N of the water delivery channel were 40%,11%and 31%in October 2015 compared with October 2013.The water quality in the Nansi Lake and its water delivery channel has been greatly improved as a whole,and the effect of continuous improvement of water quality was remarkable.On the basis of Nansi Lake and water channel quality comparative analysis,the variation trend of the 5indicators of water quality and the water quality comprehensive pollution index of P were basically the same with the Nansi Lake and water channel in October 2013 to October2015.And The water quality was continuously improved,and the concentrations of NH₃-N,T-P and T-N decreased significantly.The reduction ratio of COD_Cr and COD_Mn were slightly higher than the water channel,and the reduction ratio of T-P,T-N,NH₃-N were lower than the water channel.But the water level and transparency variation trend of the Nansi Lake and water channel were opposite.The variation trend of electrical conductivity was quite different.And the variation trend of dissolved oxygen was consistent.