Risk Assessment Of Mercury Pollution And Magnetic Diagnosis In Surface Sediments Of Chaohu Lake

As an important natural resource,lakes play an important role in water storage,irrigation,tourism,fisheries and shipping.They also provide drinking water sources and improve the regional ecological environment.Lake sediment is a carrier of environmental information,recording regional and local environmental information.In this paper,the surface sediment of Chaohu Lake is taken as the research object,and uniform sampling is carried out according to the hydrological cycle and spatial distribution characteristics of Chaohu Lake.The physical and chemical properties,magnetic parameters（magnetic susceptibility,non-hysteresis remanent ARM,saturated isothermal remanent SIRM,hard remanent HIRM and S-ratio,etc.）and the spatial and temporal distribution characteristics of heavy metal mercury pollution are analyzed,and the main sources of magnetic minerals and mercury were identified.Finally,Three risk assessment methods（the cumulative index method,the potential ecological risk index method and the sediment quality guidelines method）were used to assess the ecological risk of heavy metal mercury in surface sediments.The main conclusions are as follows:（1）The average pH value of surface sediments in Chaohu Lake is weak alkaline,and the redox potential（Eh）of sediments is in the reductive state.The change trend of Eh value and pH value is consistent as a whole.Except for the high values at some points,the sediment EC values generally conform to the range of conductivity of natural waters.Long-term deposition and accumulation of dead algae are the main source of organic matter in Chaohu Lake sediments.（2）The concentration of Hg in surface sediments of Chaohu Lake ranges from 0.024 to 0.278 mg/kg,with an average value of 0.096 mg/kg.The maximum occurs in the Nanfei Estuary and the minimum occurs in the center of the lake.The spatial distribution of Hg in the West Chaohu Lake is higher than that in the East Chaohu Lake.The Hg concentration near the Nanfei River is higher,which may be related to the anthropogenic emission of large amounts of pollutants in the upper reaches of Hefei City.In terms of time,the concentration of mercury was the lowest in December（0.08 mg/kg）and the highest in September（0.114 mg/kg）.The mercury concentration tended to increase gradually.The mercury concentration was higher than that of the semi-closed shallow lakes of the same type.Physical and chemical properties of sediments have certain effects on heavy metals in sediments.The results of correlation analysis show that mercury concentration is highly correlated with conductivity and organic matter,negatively correlated with particle size,indicating that conductivity and organic matter have certain effects on mercury concentration of heavy metals in sediments.Ground Accumulation Index and Sediment Quality Criterion Method show that the risk of mercury pollution is low,while the potential ecological risk results show that the risk of mercury pollution is moderate.The risk of Xichao Lake is higher,and that of Nanfei Estuary is the highest（=229）.The results of risk assessment were higher than those of previous studies,indicating that the ecological risk of mercury pollution in surface sediments of Chaohu Lake tended to increase.（3）The main components of surface sediments in Chaohu Lake are silt,of which fine silt and medium silt distribute most widely in the lake,while the content of small-scale sand varies greatly in the coastal area.The average grain size of sediments ranges from3.27 to 6.64Φ,with an average of 5.62Φ.The grain size tends to decrease gradually with the increase of distance from the shore to the interior of the lake.However,in some near-shore areas,the concentration of rainwater into the lake results in drastic changes in grain size parameters.The frequency curve of surface sediments in Chaohu Lake shows an obvious peak value of components,and the corresponding particle size is 20 m,which indicates that the source of Chaohu Lake sediments is relatively single,which may be influenced by the coarse particles transported in close range.The average value of soil magnetic susceptibility（χ）in the study area is 66.89×10^-8m³/kg,which is higher than the background value,indicating that there is strong enrichment of magnetic minerals from artificial sources in the surface sediments of the study area.SOFT was positively correlated with SIRM,indicating that ferromagnetic materials in MD and PSD grains were the main contributors to the study of regional soil magnetism.The contents and results of this paper can provide reference for monitoring and controlling mercury pollution in surface sediments of Chaohu Lake.Figure 34 table14 reference147...