摘要
Abstract
Pollutants are deposited in the sediments of lakes and reservoirs but,under certain circumstances,nutri-ents and heavy metals can be released into the overlying water and lead to secondary pollution of the water environ-ment.Sediments directly reflect the pollution status of a water body.Dongting Lake,the second largest fresh water lake in China,is hydrologically connected with the middle reaches of the Yangtze River.Sedimentation of sand and mud and embankment construction has segmented the lake into three distinct water bodies:West Dongting Lake, South Dongting Lake and East Dongting Lake.The aim of this study was to explore the spatial distribution charac-teristics and ecological risk of nutrients and heavy metals in the surface sediments of Dongting Lake in order to bet-ter understand the endogenous loading of Dongting Lake and provide a reference and evidence needed to more effec-tively control eutrophication and heavy metal pollution.Nine representative sampling sites were selected in the Dongting Lake.Surface sediments were collected in triplicate at each site in February 2012 and April 2013,mixed and stored frozen at 4℃.The mixed samples were dried and detritus was removed.After grinding and sieving,the organic matter (OM),total nitrogen (TN),total phosphorus (TP),cadmium (Cd),mercury (Hg),arsenic (As),lead (Pb)and chromium (Cr)in the sediments were determined.The ranges of OM,TN and TP content in surface sediments were,respectively,1.48% -4.22%,382 mg/kg -2 217 mg/kg and 142 mg/kg -716 mg/kg.Compared with other lakes (reservoirs)in China,the content of OM and TN in Dongting Lake were mid-range,so the endogenous load is too large to ignore.Spatially,OMand TN displayed similar distribution pat-terns in the three sections:South Dongting Lake >East Dongting Lake >West Dongting Lake.The spatial distribu-tion of TP was East Dongting Lake >West Dongting Lake >South Dongting Lake.The ranges of Cd,Hg,As,Pb and Cr content in surface sediments were,respectively,0.60 -20.70 mg/kg,0.090 -0.640 mg/kg,10.4 -83.7 mg/kg,16.9 -95.8 mg/kg and 59.0 -199.0 mg/kg.The contents of Cd and As exceeded the environment quality class Ⅲ standard for soils in China and are the main heavy metal pollutants in Dongting Lake.The average contents of Cd and Hg showed similar spatial patterns South Dongting Lake >West Dongting Lake >East Dongting Lake.The spatial distributions of As,Pb and Cr were the same:South Dongting Lake >East Dongting Lake >West Dongting Lake.In conclusion,except TP the nutrients and heavy metals all have the possibility to pose low ecologi-cal risk to the ecosystem in the Dongting Lake.While Cd,As and Cr in Henglinghu and Yugongmiao and Cr in the estuary of Dongting Lake pose serious ecological threats to the system.High concentrations of Cd and As in South Dongting Lake also pose a high ecological risk.关键词
营养盐/重金属/生态风险/洞庭湖/表层沉积物Key words
nutrients/heavy metals/ecological risk/Dongting Lake/surface sediments分类
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