Accumulation And Migration Law Of Heavy Metal Pollution Fron Atmospheric Dust Fall By Biological Crust In Industrial And Mining Areas

With the rapid development of global industrialization and urbanization,atmospheric particulate pollution has become one of the serious urban environmental problems.Due to mining and production activities,industrial and mining areas will produce a large amount of atmospheric dust.Toxic heavy metal elements carried in atmospheric dust are easy to be deposited on the surface and accumulate in the surface soil to varying degrees,thus causing lasting effects on the ecosystem around the emission source and human health.Heavy metal pollution from atmospheric dust has the characteristics of wide pollution range,easy accumulation in soil and plants,and difficult degradation.Biological crust,as a common vegetation type in desert area,can effectively improve soil properties and enrich atmospheric dust.Biological soil crust can not only be used for dust control and remediation in coal mine area,but also for remediation of heavy metal pollution in coal mining areas and tailings areas.What harm will the heavy metals enriched in biological crust produce to biological crust?And what is the migration pattern of heavy metals enriched in biological crust under the background of alternating wet and dry climate,and how much of them will migrate to the subsoil?What are the effects of heavy metals migrating to deeper layers on substratum soil microbial communities?To what depth?To solve the above problems,it is necessary to carry out relevant research in typical areas.In this study,three types of biological crusts,including moss crusts,mixed crusts and algal crusts,naturally developed around thermal power plants that are prone to atmospheric dust fall,located in typical industrial and mining areas of desert steppe,and their underlying soil were taken as the objects,and the same kind of biological crusts were selected as the control in the widespread biological crusts with no industrial activities in the same type area.On the basis of statistical analysis of local atmospheric dust flux,the main components and pollution degree of atmospheric dust were analyzed.The accumulation law and comprehensive pollution degree of different types of biological crust on atmospheric dust fall were analyzed.The effects of heavy metals enriched in biological crust on bacterial community structure and diversity in soil were analyzed.Soil column simulation experiment was used to analyze the reduction rule and release amount of heavy metals from atmospheric dust fall caused by different types of biological crust under the background of alternating dry and wet cycles,in order to provide some reference for species selection and microbial cultivation of biological crust for ecological restoration in industrial and mining areas.The main conclusions are as follows:(1)The spatial and temporal distribution of atmospheric dust flux in industrial and mining areas shows that the dust flux in industrial and mining areas is significantly higher than the average level in industrial parks;It showed obvious seasonal dynamics:the four seasons dustfall showed spring>summer>winter>autumn.The main composition of atmospheric dust is similar to that of local soil parent material,but the heavy metal elements of dust mostly come from industrial emission sources.The results of pollution degree evaluation showed that the heavy metal pollution degree of dust removal showed a significant distance effect,that is,the closer the distance to the industrial emission source,the higher the heavy metal pollution degree.(2)The biological crust in industrial and mining areas has a certain ability to enrich heavy metal pollutants in atmospheric dust,and it increases with the succession of biological crust,that is,the moss crust in the late succession has a stronger ability to enrich heavy metal.The heavy metal content in the three types of biological crust is sorted as:moss crust>Mixed crust>Algae crust indicates that the higher the development degree of biological crust,the stronger the enrichment ability of heavy metals.At the same time,the three kinds of biological crust can also improve the physical and chemical properties of the underlying soil.(3)Considering that the three types of biological crust have significant surface enrichment of various heavy metal elements from atmospheric dust,and will cause a certain degree of pollution to the crust and subsoil;Affected by soil physical and chemical properties and heavy metal pollution,the relative abundance of dominant bacterial phyla was different in different habitats.Heavy metals As,Pb,soil clay content,electrical conductivity and pH were the main driving factors affecting the local bacterial community structure.(4)The results of soil column simulation showed that heavy metals enriched in biological crust migrated downward under the action of leaching under the background of alternating wetting and drying,and the depth of migration was closely related to the type of crust,the number of alternating wetting and drying cycles,and soil properties.