Heavy Metal Pollution In The Sedimnts Of Nanwan Reservoir And Assessment Of Its Potential Ecological Risk

Nanwan Reservoir is located in the south of Henan province in Xinyang.Nanwan Reservoir was once named as "the Pearl of Southern Henan".Before2000, the water quality of the reservoir basically kept the standard of the surface water Ⅰ class. However, in recent years, agriculture and tourism development have outstanding negative influence on the water quality of Nanwan Reservoir and the water quality has declined seriously, which has caught more attention from people. Some related departments have conducted various assessments on the water quality of Nanwan Resevoir, but reports about the heavy metal pollution in the sediment of the reservoir have not been covered.Consequently,sediment plays a special and important role in the study of heavy metal pollution. Study on the content,horizontal and vertical distribution,and the occurrence of heavy metals in water sediments is not only the key to assess the heavy metal pollution condition at present,but also the basis to trace the history of heavy metal pollution in the region. We have monitored five kinds of heavy metals with higher biological toxicity,including mercury(Hg),arsenic (As), copper(Cu), lead(Pb), and cadmium(Cd), and then estimated the ecological risk of the reservoir using the potential ecological risk index raised by Hakanson under the comprehensive effect of heavy metals so as to provide reference for the exploitation and prot-ection of the resources in Nanwan Reservoir.The results are as follows,in January2010,the contents of Hg,As,Cd,Cu,and Pb of the seven sampling points were respecti-vely0.13to0.31milligram per kilogram(mg/kg),10.01to19.45mg/kg,0.26to0.60mg/kg,24.17to39.67mg/kg,and10.20to19.60mg/kg.The water of Xishuanghe andMajiafan suffered moderate Hg polution;The water of Majiafan and Tanshizhui and Xiajiachong suffed moderate As Pollution;The water of Xishuanghe suffered moderat-e Cd Pollution;The water of Xishuanghe,Majiafan,and Tanshizhui suffered moderate Cu pollution.In July2010,the contents of Hg,As,Cd,Cu,and Pb of the seven samplingpoints were respectively 0.14-0.33mg/kg,10.21-20.01mg/kg,0.24-0.61mg/kg,26.47-36.82mg/kg and10.32-19.32mg/kg.The water of Xishuanghe,Majiafan and Tanshizhu-i suffered moderate Hg pollution.And the water of Ma-jiafan,Tanshizhui and Xiajiac-hong suffered moderate As pollution.And the water of Xishuanghe and Xiajiachong suffered moderate Cd pollution.And the water of Xishuanghe,Xiajiachong,Majiafan,Ta-shizhui and Damiao suffered moderate Cd pollution.The potential ecological risk of heavy metal pollution in Nanwan sediment was in amild level and some special pla-es suffered moderate heavy metal pollution according to the potential ecological ris-k index Ri, and the single factor potential ecological harm parameter Eri.Research res-ults suggest that tea production and livestock breeding near the reservoir have exert-ed some effect on the water qualty.To protect the water quality,exogenous pollutantsshould be prevented from going into the reservior.