Study On Environmental Behaviors And Source Analysis Of Heavy Metals In Sediments Of Luoma Lake

Luoma Lake,one of the four freshwater lakes in Jiangsu Province,it is not only an important floodwater lake and flood channel for the Huaihe River basins,but also an important regulating water source for the East Route of the South-to-North Water Diversion Project.It has special ecological location value and resource advantages.In recent years,it has been listed in the list of“Lakes with a water surface area of more than 50km~2 that carry out ecological environmental protection and have good water quality or important ecological functions”,but no researchers have so far polluted heavy metals in the sediments of Luoma Lake problem systematic research.This article makes an in-depth analysis of the environmental behaviors,potential risks and source identification of heavy metals in the sediments of Luoma Lake,aiming to scientifically and comprehensively understand the internal laws of the occurrence of heavy metal pollution in the lake area,and reveal the direction of prevention and control of heavy metal pollution,provide theoretical support and decision-making basis for water environment protection in Luoma Lake.Mainly draw the following conclusions:1)Pollution characteristics of heavy metals in the sediments of Luoma Lake:Cd exceeds the background value by at most 1.47 times,Cr,Pb,and Hg have not exceeded the background value,and the remaining elements are relatively close to the background value.Ni,Cu,as,Zn are respectively 1.27,1.22,1.12,1.12 times of the background value,which shows that most heavy metals in Luoma Lake suffer from the dual role of anthropogenic inputs and natural weathering.The pollution of heavy metals in the lake area is cleaner than that in the upstream and downstream waters.The overall distribution of metals is Southeast>Northeast>Lake Center>North>Southwest,with occasional high concentration distribution in the northwest.2)Environmental risks of heavy metals in sediments:Enrichment factors(EF),index of geoaccumulation(Igeo),Nemero index,and potential ecological risk assessment all show that Cd is currently the most polluted element,and Hg is the cleanest element in Luoma Lake.In addition,Ni,Cu,As and Zn are also in light pollution state through the evaluation of Nemero index.The evaluation of the toxic units showed that Ni is a higher risk element.From the perspective of element evaluation,Cd is the most polluted element in the lake area,but the pollution of Ni and Cu can not be ignored.The Nemero integrated pollution index(IPI)has an average value of 1.848,which is at the level of light pollution but half of the points reach the level of moderate pollution.The evaluation result of the pollution load method shows that the average value of the pollution load index(PLI)is 0.84 and it is still in a non-polluting state.The method of comprehensive potential ecological risk assessment shows that Luoma Lake is in a state of low potential ecological risk.According to the comprehensive evaluation of toxic units,11 sites in sediments of Luoma Lake have reached the level of moderate toxicity.The southeast of lake is the relatively high-risk location shown by all the comprehensive evaluation results,followed by the Northeast Lake area.Risk management and control should pay attention to the above areas.3)The dynamic development and changes of heavy metals in the lake area:The accumulation of Cd in the estuaries areas of the Yihe River,the Grand Canal and other lakes has been increasing in recent years.which may lead to the aggravation of heavy metal pollution in the lake area.Cr and Zn in the Yihe River Estuary also increased significantly in recent years,which may develop into the main risk element.The overall content of heavy metals in the lake area has gradually decreased in recent years,which indicates that the heavy metal pollution in the lake body is in the improvement stage.However,Cd is the more special element,which is still increasing in the southern and western lake areas,and its accumulation state may be further aggravated.The increasing trend of Cd,Cr and Zn may reverse the current state of improvement of lake heavy metal pollution in the near future.The continuous release characteristics of Cd,As and Cr at multiple points indicate that its fixation in the lake area is not stable,and it may release to the outside world when the environmental conditions of a certain intensity change,and then harm the ecology,become the main pollution elements in the lake area.4)Analysis of sources of heavy metals in Luoma Lake:The results of principal component analysis show that the sources of heavy metals in Luoma Lake are mainly industrial sources,followed by agricultural sources and transportation sources.According to the method of multiple linear regression,50.69%of industrial sources,48.21%of agricultural sources and 1.10%of transportation sources are determined.The results of Positive Matrix Factorization(PMF)show that heavy metals come from industrial sources(46.74%),agricultural sources(30.98%),transportation sources(11.97%)and natural sources(10.32%).Industrial sources are the first input source of heavy metals in Luoma Lake,followed by agriculture sources,and the third source of transportation sources.Map analysis shows that urban human activities and lake farming behaviors are important sources of heavy metals in Luoma Lake.In isotopic fingerprint analysis,32.97%of Pb element come from agricultural sources,19.05%from living sources,18.32%from traffic sources,16.12%from industrial sources,and13.55%from other sources.The direct discharge of human activity units in the Laoyi River and the lake is the main way for heavy metals to enter the lake.