| The massive exploitation of mineral resources has not only greatly contributed to the rapid development of the local economy,but has also created a number of environmental problems.Each year,China’s mineral development of new destroyed land up to 1.5 million m~2,and mineral resources in the mining and smelting process generated by the tailing slag and other arbitrary pile abandonment.Under the action of natural conditions,a large number of toxic and harmful elements in the tailings are easily activated and released into the environment,and can even enter the human food chain,posing a health hazard to the surrounding residents.To address the current urgent problem of pollution management and ecological reconstruction of mine abandoned land.In this study,one new tailing pond area and one old tailing pond area within the Niujiaotang lead-zinc tailing concentration in Qiannan were selected as the study area,and eighteen 1m×1m samples were randomly laid on the tailing pond tailings and surrounding soil for natural recovery vegetation survey.A total of 122plant samples,22 tailing sand and soil samples,and 22 microbial samples were collected in two field sessions.The physicochemical characteristics,nutrient status,typical heavy metal content and fugacity patterns,and diversity of inter-root microbial communities of tailings and soils were analyzed.And combined with the enrichment effect of dominant plants on heavy metals.The influencing factors of natural vegetation restoration in the tailing pond area are explored.In order to provide basic support and practical value to the ecological restoration of the same type of waste land in karst areas.The main findings were as follows:(1)The plant community diversity in the old tailing pond area is better than that in the new tailing pond area,and the old tailing pond area is richer in plant species and has a more stable ecosystem.A total of 22 plant species,belonging to 11 families and 21 genera,were counted in the 18 randomly laid samples in the new and old tailing pond areas,mainly in the families Gramineae and Asteraceae.There are 11dominant plant species in the old tailings pond area,including Arundinella hirta,Eremochloa ciliaris,Imperata cylindrica,Equisetum hyemale,Indigofera tinctoria and Lonicera acuminata among others.There are 8 dominant plants in the new tailings pond area,including Saccharum arundinaceum,Miscanthus floridulus,Equisetum hyemale,Bidens pilosa,Ficus erecta and Parthenocissus quinquefolia,etc.And the dominant plants in the two tailing pond areas are mainly herbaceous plants.(2)The p H,conductivity,water content and organic matter content of the tailing sand and soil in the study area are suitable for the normal growth of vegetation.Among them,the tailing sand and the surrounding soil are neutral to alkaline environment as a whole,the conductivity is at a medium level,the water content and organic matter content are higher compared to similar mining areas,and the tailing sand particles are smaller in size,which is suitable for plant growth.The overall nitrogen,phosphorus and potassium contents of the tailings and surrounding soils are at low levels,but the nutrient content of the old tailings impoundment area is generally better than that of the new tailings impoundment area,making it easier for plants to settle naturally in the old tailings impoundment area.(3)None of the naturally restored dominant plants in the study area are super-enriched plants,but they exhibit a certain degree of heavy metal tolerance and accumulation characteristics compared with common plants,and have the potential to remediate complex heavy metal pollution.A variety of heavy metals with Cd and Zn as the main factors have been accumulated in the tailings and surrounding soil of the tailings pond,but the dominant plants have weak enrichment capacity for Cd and Zn,indicating that Cd and Zn have less influence on the initial plant growth in the tailings pond area.The dominant plants,such as Bidens pilosa,Saccharum arundinaceum,Miscanthus floridulus and Eremochloa ciliaris,showed better enrichment effects on Cu and As,and also had better transport properties for a variety of heavy metals,which have some potential value in remediation of soil heavy metal pollution.(4)The diversity index and richness index of inter-rooted microbial communities showed that the diversity of microbial communities in inter-rooted tailings with vegetation cover in the study area was higher compared with those without vegetation cover,but all of them had Proteobacteria as the most dominant group,which was also widely distributed in the surrounding soil.Environmental factors have a certain influence on the structure and diversity of microbial communities.Cyanobacteria Chloroplast,Planctomycetes and Candidatus Saccharibacteria have certain heavy metal tolerance ability and can be further screened and cultured,and are expected to become effective heavy metal tolerant groups. |
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