WATER QUALITY ASSESSMENT IN THE SURFACE WATERS FROM TAIHU LAKE AND ITS MAIN TRIBUTARIES

Water quality assessment is the basis of knowing of the water quality status,which plays an important role in the management of regional water environment.In this study,surface water samples were collected from Lake Taihu and its main tributary in even-water period.Grey clustering method was applied to evaluate regional water quality based on physical indicators(transparency,dissolved oxygen),nutrients(total nitrogen,total phosphorus,ammonia nitrogen),chlorophyll a and permanganate index.Multivariate statistical method was used to analyze and identify pollution factors.The results showed that the overall water quality of Lake Taihu and its main tributaries were in inferior status and the concentrations of pollutants in most of the sampling sites(63% of the river water and 36%of the lake water in Autumn,2012 and 100%of the river water and 64%of the lake water in Spring,2013)exceeded the established water quality standards(Ⅲ).The results indicated that pollutants from the input rivers contributed a lot to the algal bloom in Lake Taihu in spring.Hence,more consideration should be taken to manage the water input from the inflouv rivers before algal bloom in Lake Taihu.To help better manage water environment,the sampling sites were classified into high,middle and low standards.Principal component analysis showed that nitrogen and phosphorus were still the main factors that affected water quality in Taihu watershed.