| A Tailings Pond is a dam body formed by the accumulation and rolling of tailing,which is divided into tailing accumulation dam and initial dam.It plays a very important role in the protection and treatment of mine environment,and is mainly used to store tailing or other industrial waste discharged after ore separation in metal and non-metal mines.Heavy metal elements in various forms will diffuse and permeate into soil and groundwater with time in the tailings pond where metal slag is accumulated,thus polluting soil and groundwater and finally entering the food chain to endanger human health.In this process,the heavy metal elements often change the physical and chemical properties of various nutrients and enzyme activities in the soil,affecting the soil quality.However,for microbial communities active in soil,heavy metal pollution in soil and changes in soil quality will bring about overall structural and functional changes.Especially in the process of soil remediation,microorganisms often reduce the toxicity of heavy metals by producing resistance to heavy metals,which in turn improve soil quality.Taking Majiatian tailings pond as the research object,this paper makes comparative analysis on the distribution of heavy metals,physical and chemical properties of soil and microbial diversity in different periods of tailings pond covering soil,slag and control soil.Through further correlation analysis,this paper explores the influence of heavy metal distribution characteristics in different periods of dam covering soil on the physical and chemical properties of soil and microbial community diversity,providing theoretical basis and technical support for the health monitoring of tailings pond soil quality and ecosystem restoration.1.Distribution characteristics and pollution risk assessment of heavy metals in tailings pondThe total content of heavy metals and the content of heavy metals in different forms were measured by collecting earth covering of dam body,slag and control soil far away from tailings pond area in different periods,and the possible environmental hazards were evaluated.The results showed that,with the increase of accumulation time,the total content of heavy metal Mn in the earth covering on the surface of tailings pond increased,while the total content of other heavy metals didn’t change significantly.Heavy metals Ti,V,Cr,Cu,Zn and Pb mainly exist as residues in soil.Heavy metal Cd mainly exists in oxidation state.The contents of heavy metals V,Cu and Mn in reducible state all increased with the accumulation time of slag.The assessment results of Contamination Factor CF and Risk Assessment Code RAC showed that the heavy metals Mn,Cu,Cd and Pb in the earth covering of the dam body had great potential environmental hazards,but they all belonged to low-risk types.2.Influence of heavy metal distribution in tailings pond on physical and chemical properties of soilPhysical and chemical indexes and enzyme activities of the soil covering the dam body,slag and control soil far away from the tailings pond area in different years were tested to obtain the data of soil physical and chemical properties.At the same time,the principal component analysis method was used to study the changes of soil physical and chemical properties in different accumulation years.The relationship between distribution characteristics of heavy metals and physical and chemical properties of soil was studied by Person correlation analysis method.The results showed that the contents of available potassium,available phosphorus,total N,total P and the activity of alkaline phosphatase in the earth cover of the dam decreased with the increase of the accumulation time of the earth cover of the dam.The contents of heavy metals such as V,Cr,Zn,Cd,Cu,Ti and their morphological distribution characteristics had great correlation with enzyme activity and physical and chemical indexes in soil,which can be used as potential detection indexes for soil quality control in the future.3.Influence of heavy metal distribution in tailings pond soil on soil microbial community structureHigh-throughput sequencing technology was used to analyze the microbial community structure in the dam casing soil,slag and control soil respectively.Bio-information analysis technology was used to predict its function.The correlation between the structural characteristics of microbial community and the distribution characteristics of heavy metals was analyzed,and the relationship between the form and total amount of heavy metals in soil and the structural characteristics and functions of microorganisms in the earth covering of dam body was discussed.The results showed that the microbial diversity in the soil changed to some extent during the accumulation process of the earth covering on the dam body.The level of microbial diversity in slag was the lowest.The expression abundance of bacteria in each sample was counted in different taxonomic levels.In terms of phylum,Proteobacteria had the highest abundance in all samples,followed by Actinobacteria,Acidobacteria,Chloroflexi and Gemmatimonadetes,etc.In terms of class,Gammaproteobacteria was the most abundant in slag and the earth covering of the dam body accumulated in 1977,followed by Gammaproteobacteria,Deltaproteobacteria,Alphaproteobacteria and Actinomycetes in slag.Actinobacteria had the highest abundance in the dam body covering soil,followed by Gammaproteobacteria and Alphaproteobacteria.In terms of order,the most abundant species was Pseudomonadales,followed by β Proteobacteria.In terms of family,Burkholderiaceae accounted for the largest proportion in slag,followed by Pseudomonas.In terms of genus,the most abundant species was Pseudomonas.COG(Clusters of Orthologous Groups of proteins)database was used to perform functional cluster analysis on the identified flora.The results showed that the identified flora was mainly related to metabolic pathway,genetic information processing,environmental information processing and cellular molecular biological processes.In terms of phylum,class,order,family and genus,the structural characteristics of flora were significantly correlated with the distribution characteristics of heavy metals.Moreover,the flora in the earth covering of the dam body was resistant to heavy metals.The distribution characteristics of heavy metals were significantly correlated with the formation of extracellular structure,glycolytic gluconeogenesis metabolism,citric acid cycle TCA cycle metabolism,pentose phosphate metabolic pathway,steroid biosynthesis metabolism,steroid hormone biosynthesis,tetracycline biosynthesis metabolism,transcription function,cell movement function,extracellular structure and flora cytoskeleton formation,etc.The metabolic function of the flora can effectively reduce the content of heavy metal active forms in the earth covering of the dam body. |
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