Study On Heavy Metal Pollution Characteristics And Plant Enrichment In Soil Of Wetlands At The South Feihe River Estuary

Located in central Anhui Province,Chaohu Lake is one of the five largest freshwater lakes in China.The Nanfei River,which originates in the northwest of Hefei,is an important tributary of Chaohu Lake.With the rapid development of Hefei in recent years,heavy metal pollution in the Chaohu Lake area has become increasingly serious.The wetland at the mouth of the South Feihe River is the intersection of the South Feihe River and the Chaohu Lake,and is the main site for heavy metal enrichment.Heavy metals have the characteristics of concealment,long-term,accumulation,and irreversibility,making it very difficult to control heavy metals in soil.Traditional control methods not only have high costs,but also have shortcomings such as small control area,and damage to soil structure.Under this background,phytoremediation emerged as a new ecological treatment method for heavy metal pollution.This thesis takes the wetland at the mouth of the South Feihe River as the research area,and takes the heavy metal elements Hg,As,Cd,Cr,and Pb as the research objects to analyze and evaluate the pollution situation,distribution characteristics,and potential ecological hazards of heavy metals.At the same time,seven local dominant wetland plants,Echinochloa caudata Roshev,Polygonum hydropiper,Phragmites australis,Typha orientalis,Alternanthera philoxeroides,Carex nemostachys,and Cyperus rotundus,were selected to comprehensively compare and analyze their enrichment ability to heavy metal elements,Explore local wetland plants with strong enrichment capacity for heavy metals.The research results can provide a reference basis for the prevention and control of heavy metal pollution in the soil of the South Feihe River and Chaohu Lake areas,as well as for plant selection in wetland construction.The research conclusions are as follows:(1)The sequence of the contents of five heavy metals in the wetland soil of the South Feihe River estuary is Cr>Pb>As>Cd>Hg.Compared with the background values of soil elements in the Jianghuai River Basin in Anhui Province,wetland soils have different degrees of enrichment of five heavy metal elements,with the highest concentration of Hg,which reaches 4.88 times the background value.Except that the content of Cd in some sample points is slightly higher than the screening value in the "Soil Environmental Quality Standard for Agricultural Land Pollution Risk Control Standard(GB15618-2018)",the content of the remaining four heavy metals are within the standard range.The correlation analysis shows that the correlation between heavy metals Hg,As,and Cd in the wetland soil environment in the study area is significant,and the pollution sources are similar,mainly from the electroplating industry,the use of pesticides,transportation,and domestic sewage discharge,which are significantly affected by human activities.The spatial distribution indicates that the sampling points close to the river location have high concentrations of heavy metals.(2)Based on the soil element background of the Jianghuai River Basin in Anhui ProvinceThe single factor index method,the Nemero comprehensive index method,the land accumulation index method,and the potential ecological risk index method were used to evaluate the heavy metal pollution status and potential ecological risk of the wetland soil in the estuary of the South Feihe River.Taking the background values of soil elements in the Jianghuai River Basin in Anhui Province as a reference,the results showed that there was a certain degree of pollution in the wetland soil environment in the study area,including Cr,Pb,which were slightly polluted,while Hg was heavily polluted.The evaluation result of the Nemero comprehensive index method shows that the wetland soil in the South Feihe River estuary is generally in a severe pollution level,mainly due to the high single pollution index of Hg.The evaluation results of heavy metal pollution in soil using the single factor index method are heavier than the results obtained by the ground accumulation index method.From the perspective of potential ecological risks,the wetland soil in the South Feihe River estuary is at a slight ecological hazard level,but the single potential ecological risk of Hg and Cd is at a very strong ecological hazard level and a strong ecological hazard level,respectively.(3)The study on the heavy metal content of dominant wetland plants in the study area found that there were differences in the heavy metal content of different wetland plants and different parts of plants.The overall order of the heavy metal content in the whole plant body was Cr>As>Pb>Cd>Hg,and the heavy metal content in the root of the plant was higher than that in the shoot.Different wetland plants have different enrichment abilities for heavy metal elements.Carex striatum has the strongest enrichment ability for Cr,with an average enrichment coefficient of 0.22.Peanut has the strongest enrichment ability for Hg and Cd,with an average enrichment coefficient of 0.69 and 9.46,respectively.Reed has the strongest enrichment ability for As and Pb,with an average enrichment coefficient of 0.63 and 0.44,respectively.Cypress has a strong enrichment ability for As,with an average enrichment coefficient of 0.61.Barnyardgrass has a strong enrichment ability for Hg,Cd,and Cr,The average enrichment coefficients are 0.62,4.17,and 0.20,respectively.Polygonum hydrophila has a strong enrichment ability for Cd,with an average enrichment coefficient of 4.94.Typha has a strong enrichment ability for Hg and Cd,with an average enrichment coefficient of 0.62 and 2.44,respectively.In general,reed,barnyard grass,and water peanut have the best enrichment ability,and can be prioritized when phytoremediation of heavy metal pollution in the soil of the wetland in the South Feihe River estuary.(4)The results of correlation analysis between different parts of wetland plants and heavy metals in the soil in the study area showed that the contents of five heavy metal elements in the roots of plants were positively correlated with the contents of heavy metals in the soil,with a very significant correlation between Cd and Hg,As,and Cr,while the correlation between Pb elements was poor,indicating that the toxicity of Pb may lead to stress resistance reactions in wetland plants,making it difficult to enrich Pb elements.The concentrations of the five heavy metals in the aboveground parts of wetland plants were also positively correlated with the concentrations in soil,but they did not show significant correlation.