Study On The Comprehensive Evaluation Of Water Quality Of Dongting Lake

Dongting Lake, the first Great Lakes in Hunan, can be described as the “Mother Lake” in Hunan. In recent years, with the rapid development of economic and the rapid increase of population, Dongting Lake appears a series of water environment problems, threatening human health and social development. In order to better understand the water quality situation of Dongting Lake basin, effectively control pollution of Dongting Lake, we first need to evaluate the water quality of Dongting Lake. Through the water quality evalution to determine the pollution level of water quality in Dongting Lake, find out the main pollution factors and the more serious pollution area, understand water quality variation, so as to provide some guidance to lake pollution remediation work.Based on the water quality data of 14 monitoring sections of Dongting Lake in 2005-2011, respectively using the principal component analysis method and the improved fuzzy comprehensive evaluation method on the 14 monitoring sections water quality analysis of space, find out the main pollution factors of each monitoring section, determine the relatively serious pollution section. Then the most polluted section were on time dimension analysis for water quality trends. Finally, according to the different water regime, analyze the similarities and the differences of water quality of 14 monitoring sections. The main contents are as follows:(1)With the aid of SPSS 19.0 software, the water quality of 14 monitoring sections of Dongting Lake in 2011 was evaluated by using principal component analysis method, the results show that the water quality of east Dongting Lake is the worst in the 14 monitoring sections, and the water quality of the river mouth section is the best. The main pollution factors in the lake area are organic pollution and eutrophication. Combined with these sections of the monitored area and the principal component analysis results of each section, can explain that the water quality of the lake center is worse than the water quality of the lake entrance, the water quality of the lake entrance is worse than the water quality of the lake outlet. In the three lakes, the water quality of east Dongting Lake is the worst, the water quality of west Dongting Lake is the best.(2)In view of the most serious pollution of east Dongting Lake section, use principal component analysis method to analyze the time variation characteristics of the water quality of east Dongting Lake in 2005-2011. It was found that the water quality of this section is generally good, and then it presents a trend of variation. The main pollution factors of east Dongting Lake are also changing, and not all the pollution levels are increasing.(3)With the aid of MATLAB R2012 b software, the weight assignment method of traditional fuzzy comprehensive evaluation method is improved, combination weighting method based on entropy method and analytic hierarchy process nethod, using the improved fuzzy comprehensive evalution method to evaluate the water quality grade of 14 monitoring sections of Dongting Lake in 2011. The results showed that in 14 monitoring sections, only the wanter quality grade of Zhang Shu Gang section, Wang Zi Hu section, east Dongting Lake section, Yue Yang Tower section is grade Ⅲ, other sections are gradeⅡ, this shows that the overall good water quality of Dongting Lake.(4)According to the different water regime, divided into high flow period, normal flow period, Low water period, analyze the water quality of Dongting Lake 14 monitoring sectiongs in space respectively. Integrated three different period of water, found that the overall water quality of east Dongting Lake section and Zhang Shu Gang setion is poor.