| Coal gangue is a kind of solid waste discharged from coal mining and washing and processing.Because of the low industrial utilization rate,it is mainly stacked in the form of coal gangue mountain,which will have a series of effects on the ecological environment of mining area.It is necessary to renovate the gangue mountain so that it can be used.The treatment of coal gangue mountain in the north of China is usually carried out by vegetation greening after leveling the soil,but the reconstructed soil is often affected by the downward leaching of heavy metals in the surface layer and the upward migration of the heavy metals in the coal gangue in the bottom layer.This to the coal gangue mountain vegetation restoration and reclamation land use form the barrier.Therefore,the study of soil available heavy metals content and its influencing factors in different years of reclamation in coal gangue mountain is helpful to find out the characteristics of toxicity and bioavailability of heavy metals,and to reveal the key factors influencing the migration and transformation of heavy metals in soils.It is very necessary for guiding the coal and gangue mountain to carry out vegetation reclamation according to the circumstances,and it also has important theoretical guiding value for the rational agricultural production of the mining area reclamation land.In this study,Wangzhuang Coal Mine and Caocun Coal Mine in Tunliu County,Shanxi Province,were selected to reclaim 3a10 a and 16 years irrigated grassland in gangue Mountain,and the normal irrigated land of the original landform in the mining area was used as the control.The physical and chemical properties of soil Hg,As Pb,Cd,Ni,Cu in soil and Cd,Pb and Cu contents in soil were measured respectively in the soil layer of 0-20 and 20-40 cm.The bioavailability coefficient was calculated,the risk grade was evaluated by using single factor pollution index and potential ecological hazard index method,and the key influencing factors of available heavy metal content were analyzed.The main results were as follows:(1)According to the difference of soil physical and chemical properties in three kinds of reclamation years:In the soil layers of 0-20 cm and 20-40 cm,the EC value and content of silt did not change significantly with the increase of reclamation years,but the pH value,content of organic matter,alkali-hydrolyzed nitrogen and sand increased significantly with the increase of reclamation years.The content of available potassium and clay decreased significantly with the increase of reclamation years.Compared with CK,there was no significant difference in soil pH value,silt content and EC value and organic matter between soil and CK.The content of alkaline hydrolyzed nitrogen and available phosphorus was significantly lower than that of CK,the content of sand was higher than that of CK,The content of clay particles is WV-3a plots,which is higher than that of CK.There was no significant change in WV-10 a plots.HV-16 a plots is lower than CK.Available potassium content in 0-20 cm soil layer is lower than CK,but higher in 20-40 cm soil layer.(2)From the differences of total heavy metals in soils of three kinds of reclamation years,In 0-40 cm soil layer,with the increase of reclamation years,the mass fraction of Hg,Pb and Cd decreased,and the content of As and Ni increased,and there was no obvious change in Cu content.Compared with CK,the content of heavy metal in 20-40 cm soil layer was higher than that in 0-20 cm soil layer.(3)The difference of the total pollution degree of heavy metals in the soil of three kinds of reclaimed years is as follows:The evaluation of single factor pollution index and single factor potential hazard index showed that in 0-20 cm and 20-40 cm soil layers,with the increase of reclamation years from 3 years to 16 years,the pollution index of Hg,Pb and Cd showed a gradual decreasing trend,and As,Nisho wed a gradual increase trend,but there was no obvious difference between Cu.Based on the background value of soil environment in Shanxi Province,the single factor evaluation shows that: in the soil layer of 0-20 cm and 20-40 cm,Hg in the samples of WV-3a and WV-10 a are heavily polluted and HV-16 a are moderately pollut ed.As,Pb,Cd,Ni and Cu were all slightly polluted in 3 kinds of reclaimed land.Single factor potential hazard assessment showed that Hg was a very strong ecological hazard in WV-3a and WV-10 a plot.HV-16 a sample was a very strong ecological hazard.Cd is a medium ecological hazard in three types of reclamation samples.As,Pb,Ni,Cu is a minor ecological hazard.Both the Nemero Composite Pollution Index and the Potential Ecological Hazard Index show that :in 0-20 cm and 20-40 cm soil layers,the pollution index of the three reclaimed plots decreased with the increase of reclamation years.Based on the background value of soil environment in Shanxi Province,the comprehensive pollution index evaluation of Nemero shows that:in 0-20 cm and 20-40 cm soil layers,the samples of WV-3a and WV-10 a were heavily polluted and HV-16 a were moderately polluted.The evaluation of the potential ecological hazard index indicates that WV-3a and WV-10 a like sites are very strong ecological hazards,and HV-16 a like sites are medium ecological hazards.The comprehensive damage degree of three reclaimed plots in 0-20 cm and 20-40 cm soil layers was WV-3a > WV-10 a > HV-16 a.(4)According to the differences of available heavy metal contents in the soil of three reclaimed plots:In the soil layers of 0-20 cm and 20-40 cm,the contents of Cd,Pb,Cu increased with the increase of reclamation years.All of them showed that the HV-16 a plots were significantly higher than those of WV-3a and WV-10 a plots.The bioavailability coefficient of Cd is higher than that of Pb,Cu in general.Moreover,the bioavailability of Cd and Pb has a tendency to increase with the years.The same trend of Cu is found in 20-40 cm soil layer.Compared with CK,the available contents of heavy metals in the three reclaimed plots were significantly lower than those in CK,and the bioavailability of CK was higher than that of the three reclaimed plots.(5)According to the influence factors of soil heavy metal available state in three kinds of reclamation years,the soil pH value,EC value,organic matter,CEC value and clay content all affect the Cd,Pb and Cu available state of soil in the reclamation of coal and gangue mountain to varying degrees.The content of organic matter CEC and clay are the key factors. |
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