Study On Enrichment, Source And Risk Assessment Of Pollutants In Chaohu Lake

Chaohu lake is the fourth largest freshwater lake in China. The lake plays an important role in the local economic growth through commercial fishing, water supply, irrigation navigation. In recent years, the water environment was deteriorated gradually by pollutions with the increases of population, economy, and urbanization in the area. On basis of a large number of domestic and international lakes literatures and statistics on hydrogeological and humanities socio-economic information in Chaohu lake basin,118surface water samples,62surface sediment (0-5cm) samples were collected from entire lake including its main river entrances. The aquatic pollution factor were investigated, heavy metals were analyzed with62surface water samples and surface sediment samples by ICP-OES respectively, A four-step sequential extraction was used for the partition of the heavy metals in40surface sediment samples. Temporal and spatial distribution characteristics of aquatic pollution factor, heavy metals, nitrogen and phosphorus of biogenic elements were studied, the correlation of heavy metals’speciation with their water contents were explored, the pollution source of Chaohu lake were systematically demostracted on basis of factor analysis, and the results indicate as follows.(1) The seriously polluted aquatic factor were Petroleum, TN, TP and Anionic surfactant, Season variation showed that contents of the aquatic pollution factors (except ammonia) were highest in autumn, while ammonia’ content was highest in winter. The Shiwuli river is the most polluted of the inflow rivers.(2) The mean content of heavy metals are lower than grade3of China surface water quality standards, and the highest contents mainly distributed in lake near Hefei city. The mean content of Hg was0.36μg/L, a little higher than Grade3of Chinese water quality.(3) The heavy metal contents in Chaohu lake sediment were higher than Chaohu lake background value. The element Cr contents between threshold effect level and probable effeet level were90.30%. The heavy polluted areas were mainly distributed in the estuaries.(4) The contents of organic matter(OM)、TN and TP in Chaohu lake sediment were high. The spacial distributions indicated that OM, TN,TP had similar trend, the patches of highest concentrations confined in the Chaohu valley of Feidong county which is near Nanfei river mouth, and the estuary of Hangbu river.(5) The highest concentration values for Cr and Ni were observed at the fourth stage of the extraction procedure. The elements Pb, Zn,Cu and Cd were mainly existed in the Non-residual forms The elements of Cd, Pb and Hg had a light potential ecological risk in Chaohu lake.(6) The values of C/N, correlations analysis and factor analysis showed that Chaohu pollution were mainly form domestic sewage, industrial source, agricultural non-point source.