Abstract:

The Taihu watershed,one of the most developed regions in China,is in the lower reaches of the Yangtze River.The Taihu watershed includes parts of Jiangsu and Zhejiang Provinces and Shanghai municipality.The areas of lakes in the large drainage basin are approximately 1300 kilometers.Most of the lakes in Lake Taihu watershed are distributed in Suzhou,Wuxi and Changzhou.However,in recent years,because the rapid development of the local economy and enhancement of the urbanization level,the lakes in Lake Taihu watershed have been seriously plagued by pollutions from industrial wastewater,agricultural wastewater and city life sewage.Heavy metals naturally occur in the earth crust.However,human activities have introduced high loads of these elements in the environment,making the differentiation of natural and anthropogenic contributions difficult.Sediments provide a temporally integrated indication of the aquatic environment condition and act as a major reservoir for metals,though some sediment can also act as a source of contaminants.Furthermore,sediments have high physicalchemical stability and their characteristics usually represent the average condition of the system,often being representative of the average water quality.Therefore,the heavy metal pollution problems have already become one of the hot topics to the domestic and international research personnel.The aims of this paper are to investigate the spatial distribution characteristics and evaluate the pollutions of main heavy metals As and Hg in the sediments from lakes in Lake Taihu watershed.Five representative areas are selected for this research.The five selected research areas are Suzhou areas,Changzhou areas,Wuxi areas,Huzhou areas and Yixing areas in Lake Taihu watershed respectively.The spatial distributions of main heavy metals As and Hg in the sediments from lakes in Lake Taihu watershed,were analyzed with Hydride atomic fluorescence spectrometry analytical method.The pollution assessments of heavy metals were calculated by geoaccumulation index (Igeo) method on the background of the lakes in Lake Taihu watershed.The results showed that the highest concentrations of As and Hg in the Suzhou areas,Changzhou areas,Wuxi areas,Huzhou areas and Yixing areas were respectively 21.88 mg/kg,16.35 mg/kg,21.36 mg/kg,13.77 mg/kg and 13.97 mg/kg;1.50 mg/kg,1.42 mg/kg,1.01 mg/kg,1.65 mg/kg and 1.46 mg/kg.The lowest concentrations of As and Hg in Suzhou areas,Changzhou areas,Wuxi areas,Huzhou areas and Yixing areas were 2.92 mg/kg, 2.72 mg/kg,4.18 mg/kg,4.28 mg/kg and 2.47 mg/kg;0.34 mg/kg,0.03 mg/kg,0.23 mg/kg,0.29 mg/kg and 0.03 mg/kg respectively.The average concentrations of As in the sediments were relatively higher in Huzhou and Wuxi than other areas.The values exceeded environmental baseline in the basin of Lake Taihu.Average concentrations of Hg in the sediment from four areas (Huzhou,Suzhou,Wuxi and Yixing) were significantly higher than environmental baseline in the basin of Lake Taihu,except for Changzhou.The index Geoaccumulation (Igeo) values indicated that pollution intensity of As was unpolluted in all areas,but pollution intensity of Hg reached moderate level except for Changzhou.Therefore,the lakes from Lake Taihu watershed have been influenced by As and Hg,especially the heavy metal Hg pollution has been relatively serious