| Dongting Lake, the second largest lake in China, is a wetland of international importance. It has an important ecological function and economic value, which is a habitat for many fish, birds and other wildlife. Recently, it has been experienced a serious pollution of heavy metals in Dongting Lake due to human activities. Heavy metals are toxic, persistent and non-biodegradable. They may accumulate through food chain in the ecosystem and have a potential effect on organisms. Therefore, ecological risk assessment and source apportionment are helpful for heavy metal control in Dongting Lake. In addition, exposure risk assessment of heavy metal to waterfowl is meaningful for waterfowl conservation and risk management.Firstly, surface sediments of Dongting Lake wetland were collected from ten sites to investigate variation trend, risk and sources of heavy metal distribution in dry seasons of 2011~2013. The three-year mean concentrations(mg/kg) of Cr, Cu, Pb, Cd, Hg and As were 91.33, 36.27, 54.82, 4.39, 0.19 and 25.67, respectively, which were all higher than the corresponding background values. Sediment quality guidelines(SQGs), Geo-accumulation index(Igeo) and potential ecological risk index(RI) were used for the assessment of pollution level of heavy metals. The pollution risk of Cd, Hg and As were great and that of Cr needed urgent attention because of its obvious increase. Pollution load index(PLI) and geographic information system(GIS) methods were conducted to assess spatial and temporal variation of heavy metal contamination. Results confirmed an increased contamination contribution inflow from Xiang River. Multivariate statistical analyses were applied to identify contribution sources of heavy metal, which showed anthropogenic origin mainly from mining, smelting, chemical industry and agricultural activity.Secondly, an exposure model was integrated for assessing heavy metal exposure risk to migratory birds in Dongting Lake Wetland. The concentrations of Cr, Cu, Pb, Cd, Hg and As in water, plant, soil and fish were investigated from 9 migratory bird habitats. The results showed that exposure doses from drinking water pathways were very low. There was a sensitive area that Cd and As exposure doses exceeded the most conservative tolerable daily intake, which is located at the estuary of Xiang River. In general, Dunlin had a greater risk than Eurasian Spoonbill. Hg, Pb and Cr were likely to have adverse effect on carnivorous migrants in Dongting Lake Wetland, while Cu and Cd were considered to be relatively safe. Almost all heavy metals were at no risk for Lesser White-fronted Goose in Dongting Lake Wetland.Thirdly, a method for exposure risk assessment of migratory herbivorous birds and identification of priority pollutants/areas was developed and employed in East Dongting Lake Wetland. Four heavy metals(Cr, Cu, Pb and Cd) in sedge and soil samples from 10 Anatidae habitats in East Dongting Lake Wetland were investigated. Results showed that negative effect of Cr and Pb on Anatidae may occur while Cu and Cd are considered to be relatively safe. Cr had the highest risk and was considered to be the priority pollutant. Pb was in a low risk. Spatial interpolation based on geostatistical methods showed that Spring Breeze Lake, with high integrated risk and relatively more Anatidae, should be payed much attention to. Furthermore, regions with high hazard index were identified to be priority areas of East Dongting Lake Wetland for risk management. The method proposed in this study is potentially useful for pollutant exposure risk assessment to wildlife and risk management around the world.Finally, according to the results of this study, some suggestions have been made for heavy metal contamination control and ecological environmental protection. |
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