Assessment Of Sediment Quality For Metals And Nutrients In Major Freshwater Lakes Of China

Lake sediments are generally recognized as a sink for pollutants resulted from human activities,and a source to release substances to the water when physical and chemical conditions change,which may pose a significant threat to aquatic ecosystems.With the rapid industrial,agricultural development and urbanization occurring in China,geochemical patterns of lake sediments have been largely modified and lake sediment quality have been reported to deteriorate recently.However,the lack of a comparable geochemical dataset of lake sediments across the country has hindered the move to conduct a national assessment of environmental quality for lake sediments.A systmetic lake sediment geochemical survey across the major freshwater lakes,supported by the Multi-Purpose Regional Geochemical Survey(NMPRGS)project,has provided newer,higher density,more sensitive,more systematic geochemical data of lake sediments.This makes it possible to define meaningful measurements of background variation and assessing lake sediment quality on a national scale.This paper builds on the information obtained from the NMPRGS project to provide a consistent national geochemical overview and risk assessment for surface sediments in major freshwater lakes in China.(1)The natural background and baseline values of lake sediments for As,Cd,Cr,Cu,Hg,Ni,TOC,TN,TP,Pb,S,Sn,W,Zn and pH have been presented for national freshwater lakes and 13 major freshwater lakes in China.These values will be useful to identify the sources of enriched chemical elements and quatitatively assess the change trends of lake sediment quality.(2)The current ecological risk assessment of sediments in major freshwater lakes have been conducted in this study.The results showed that Cd,TOC and TN ranked as the most contaminated indexes for lake sediments on a national scale.Dongtinghu Lake,Dianchi and Taihu Lake are lakes with largest area of contamination.Among the surveyed freshwater lakes,Dianchi ranked as presenting the greatest ecological risk,which are followed by Yangzonghai Lake and Dongtinghu Lake.Ulansuhai Lake and Chaohu Lake are believed to be the safest lakes at present.(3)Uncertainties of risk assessment are also discussed by considering sampling methodology,geochemical background,the eco-toxicity of metals and the sensitivities of local benthic communities.Sampling depth of lake geochemical sediment is suggested to be 0-5 cm or 0-10 cm instead of 0-20cm in NMPRGS project.High natural background of Ni,Cr and As and large area with concentration levels above TEC or PEC make it necessary to investigate the biological effect for Ni,Cr and As in high background lakes,which will provide important information for establishing the reasonable sediment quality guidelines in China.Efforts should also be made on the geochemical monitoring of lake sediment quality,which will be a useful approach for improvement of lake management and pollution prevention and control in the country.