| The Poyang Lake Basin has been a relatively developed and affluent area in the country since ancient times.The lake area is rich in species and has a beautiful ecological environment.There is a joyous scene of "fishing boats singing late,sounding on the shore of Pengli",and the famous scenic name of "green mountains,vast water,and the middle of the river." Poyang Lake borders the Yangtze River,and the formation of the Yangtze River Economic Belt has promoted a faster development process in Jiangxi.In the process of economic prosperity,we must always put the protection of the ecological environment in the first place,and always respond that gold mountains and silver mountains are not as good as green mountains.The Poyang Lake water system is the source of life in Jiangxi.The lake area brings together the water sources of the five major river systems and various tributaries.The source of the sediments in the lake area is mainly water as the transport medium to carry pollutants,and through a series of physical and chemical reactions,the final migration and transformation,flocculation and sedimentation are formed.The pollution and harmful substances contained in its sediments include heavy metals.Heavy metals are metal elements with a density greater than 5,which not only cause carcinogenesis,teratogenicity,mutagenesis,and potential risks to animals and plants,but also affect the nature and ecological environment.It is difficult to degrade,easy to accumulate,and cause secondary pollution under certain conditions.By collecting 79 surface sediments and 28 marginal sediments in the study area,the Nanjishan Wetland,the largest wetland in Poyang Lake,was selected to collect 6columnar sediments,each 24 cm,and three types of sediments near 6 sampling points were collected.Water plants Phragmites australis,Neyraudia montana,Cymbopogon citratus.Determine the content of heavy metals As,Cd,Cr,Cu,Ni,Pb,Zn,Hg through laboratory treatment,and the physical and chemical indicators p H,Eh,SOM(soil organic matter),D(particle size),SSS(water-soluble salt content)Wait.Use Nemeiro composite index,geoaccumulation index method,potential ecological hazard index method and other methods.It also analyzes the accumulation and distribution of heavy metals in the surface,marginal,and profile lake sediments,discusses its potential ecological hazards,and conducts a rough assessment.At the same time,with the help of Arc GIS,Kriging interpolation analysis is used to analyze the distribution characteristics of heavy metals in the sediments of Poyang Lake area and the regional description of risks.Cluster analysis and correlation analysis are used to trace the source of heavy metal pollution in the sediments.After experimental determination of heavy metals in plants,the transfer coefficient and enrichment coefficient are mainly used for analysis to explore the accumulation degree and pollution characteristics of heavy metals in the wetland ecological environment by different tissues of plants.The target hazard coefficient and the composite target hazard coefficient are used to comprehensively evaluate the impact of a single heavy metal and multiple heavy metals in the plant on the health of adults and children.The main relevant research results are as follows:(1)The areas with high levels of heavy metals As,Cd,Cr,Cu,Ni,Pb,Zn,and Hg in the surface deposits of Poyang Lake are mainly concentrated in the southern part of Poyang Lake.The pollutants on the surface sediments of the lake area are mainly at the mouth of the lake.The tributary waters are the main transportation routes.The super-background value rate of heavy metals is divided into Cu>Cr=Pb>Zn>Ni>Hg>As>Cd.The average content of heavy metals Hg,Cu,Pb,Cd,Zn,As,Cr,and Ni in the marginal area of Poyang Lake are 1.71,5.61,2.29,5.83,2.10,0.85,2.20,1.40 times of the background value of Poyang Lake,respectively.Element Cu is the main pollution factor,the super-background value rate of the surface layer is 98.76%,and the surrounding area is 100% super-background value.There are 8 kinds of heavy metals accumulated in different degrees,and the sediments are polluted by heavy metals.(2)Principal component analysis and correlation show that the first principal component is As,Cr,Cu,Pb,Zn,and the correlation between As and Cr,Cu,Pb,Zn is significant,and the main source of pollution is agricultural production such as mining and smelting Live.The second principal component is Hg and Cd,the two have a significant correlation with a large coefficient of variation.The high content areas are located in the south and southwest,and the pollution source is mainly human activities.The third principal component is Hg and Cd.Ni,its pollution sources are mainly from the mining of mineral resources and the changes in natural rock and soil structure.Correlation analysis and cluster analysis show that with environmental changes,marginal heavy metal pollution may turn into non-point source pollution.(3)The content ranges of Hg,Pb,Cu,Cd and Zn in wetland sediment profiles are 0.075～0.340mg/kg,2.63～38.53 mg/kg,0.21～28.22 mg/kg,0.01～0.43 mg/kg,25.88～80.72 mg/kg,the rate of heavy metals exceeding the background value of Jiangxi Province is Hg>Cd>Pb>Cu>Zn,and their contents have a trend of enrichment.The results of the heavy metal content of the vertical profile show that the content of heavy metals Hg,Pb,Cu,Cd,and Zn is slightly higher in the depth range of 0 to 6 cm;the content of heavy metals in most sediments of 6 to 15 cm presents a sawtooth fluctuation state;at a depth of 15 cm There are peaks of Hg,Cd,and Pb content at20cm;after 20 cm,there is a downward trend.Excluding measurement errors may be related to the influence of human activities and the changing factors of the natural environment.Single heavy metal pollution may not be particularly harmful to the environment.The pollution index of heavy metal load on the overall columnar sediments shows that the pollution degree trend is an inverted U-shaped pattern from weak to strong to weak,that is,heavy metal pollution already exists on the profile.(4)In the experimental study,the three plants in the Nanji Mountain wetland all have different degrees of heavy metal enrichment and transfer.The relationship of heavy metal elements Cd and Hg in reeds,mountain reeds,and citronella grass is CF>TF,and the relationship of Zn,Cu,Pb is expressed TF>CF,but the relationship between heavy metal elements Cu and Pb in citronella grass is CF>TF.The comprehensive adsorption accumulation index shows that the relationship of the three plants to the heavy metals Hg,Pb,Cu,Cd and Zn is mountain reed> reed> citronella grass,reed>citronella>mountainreed,reed>mountainreed>citronella,Lemongrass>Mou ntain Reeds>Reeds,Phragmites>Lemongrass>Mountain Reeds.It can be seen that reed has the best adsorption and accumulation effect and is the plant of choice for adsorbing heavy metals,indicating that wetland plants can play an important role in purifying heavy metal polluted sediments.The single target hazard index indicates that there are health risks in the root and leaf tissues of reeds,mountain reeds,and citronella grass.The stem tissues of citronella grass can be eaten by adults without health risks,and children should eat with caution.The overall research shows that the composite target hazard index TTHQ of heavy metals is greater than 1,and accidental ingestion will cause cancer risk.(5)Comprehensive analysis results of multiple evaluation methods show that there are different levels of pollution of heavy metals in the sediments at the edge of Poyang Lake,the order of Pz is Cu>Zn>Ni>Cr>Pb>As>Hg>Cd,and the order of potential risks It is Cd>Hg>Cu>Pb>As>Ni>Cr>Zn.With the help of pollution elements combined with multi-dimensional analysis of sampling points,Hukou County and the edge of Poyang Lake are more polluted,with strong load and strong risk.Other lake areas bordering Poyang Lake such as Raohe,Ganjiang and Xinjiang are in serious condition.Pollution,there are intensity loads and risks.The accumulation of heavy metals in surface sediments is mostly mild to moderate accumulation,and very few are strong accumulation.The heavy metals Cr,Cu,Pb,Zn,and Hg are polluted more seriously,followed by Cd and Ni.The total ecological risk RI in the study area has two levels. |
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