| The open-cut coal mining is a great threat to the tender grassland ecosystem in the arid and semi-arid area. A large number of stripping wastes are produced following the mining, and many spoibanks are formed. The spoibanks not only damage grassland but also accelerating water and soil loss under the effects of rain and wind on the untreated spoibank, and decreasing the quality of grassland ecological environment. Ecological environmental problem is one of the sustainable developmental problems of regional economy in open-cut coal mining area. Meanwhile, accurate understand of the heavy metals contamination and accumulation characteristics in the soil, and proceeding vegetation restore and rebuild in spoibank, which are the base of prevention and control of heavy metal contaminated soil in mining area,and which are also the keys to ease the ecological pressure and to solve environmental problems. So the study on the characteristics of soil heavy metal pollution in open-cut coal mining area and vegetation restoration in typical steppe, could provide scientific theory basis to soil heavy metal pollution prevention and grassland ecosystem sustainable development, meanwhile, which is very important to promote the healthy development of national economy.In this study, the research objects are the Western One and Two of Shengli coal field in Xilin Gol Prairie, and combining field sampling and laboratory analysis. Seven researching belt transects were set in the mining area to East, south, West, North, northeast, southeast and southwest direction. In mining area as the center, set a survey plot respectively in eastern belt transect, in the distance from the periphery of the mining boundary 0 km,0.5km, lkm,2 km and 4 km, and set a survey plot respectively in the distance from the periphery of the mining boundary 0 km,0.5km, lkm,2 km,4 km,6 km and 8 km, in other six belt transects. Meanwhile in southern, Western and northern belt transects, set a survey plot respectively as a control plots in the distance from the periphery of the mining boundary 10 km.On the basis of investigating community characteristics in 2014 from July to September, collected the surface soil in 0-10cm and analyzing the contents of Cr, Cu, Mn, Ni, Zn, Pb in soil. Using multivariate statistical analysis method, GIS spatial analysis method, and Geo-statistics Kriging interpolation method, and so on, to study on the following aspects:mining area soil heavy metal content in space distribution, migration and diffusion rules, and the effect of soil heavy metals on coal mining in typical grassland. To National Soil Environment Quality Standard (Secondary) and Inner Mongolia soil background value as a benchmark, using the single factor index method, the Nemerow index method and accumulation of quantitative index method to evaluate the pollution status of heavy metal in soil around the open-cut coal mining area in typical grassland. Study on the level of ecological risk and the grades of spatial distribution pattern by the potential ecological risk assessment method.In 2015, selection the plots had been restored for 2 years and 5 years in opencast coal mine dump both with biological Barbara vegetation restoration area and non-biological Barbara vegetation recovery area, to investigate the community characteristics, and collecting soil samples in 0-10cm to assess the content of soil heavy metals (Cr, Cu, Mn, Ni, Zn and Pb) and nutrient contents (organic matter, available nitrogen, available phosphorus and available potassium), and analyzing the influence of vegetation restoration measures on the vegetation and the soil physicochemical conditions.The following results were obtained:(1) The open-cut coal mining has a significant impact on the spatial distribution of heavy metals in the soil, which are affected by many factors on the influence degree and range. The content of soil heavy metal elements, Single Factor Pollution Index, Nemerow Comprehensive Pollution Index and Potential Ecological Risk Index are the highest in the center of the mining area, and gradually reduced to the mining area around.(2) The content of heavy metals in soil were higher than the soil background values of Inner Mongolia, the pollution index and comprehensive potential ecological risk index were at the light pollution level and moderate ecological risk level in the northeastern parts of the mining area.(3) Within 0.5 km of mining area, the content of soil heavy metals exceeded soil background values in Inner Mongolia that as reference values. Comprehensive pollution index and potential ecological risk index indicates that, the effect of mining area in the Western and Southern of mining area concentrated in range of 2 km, but the effect in the Eastern and Northern of mining area range up to 4 km.(4) The contents of Cu, Mn, Zn, Ni, P and Cr in the soil of mining area were at clean level in Inner Mongolia typical steppe, by assessed with The National Soil Environmental Quality Standards (Secondary). The Single Factor Pollution Index showed that the content of Cu in soil was at the light pollution level, compared with the soil background values of Inner Mongolia. The content of Cr, Mn, Ni, Zn and Pb in soil were at the clean level, but reached the level of light pollution within the mining area of 0.5 km; the result by Nemerow comprehensive pollution index suggested that all of the soil around mining area belong to the light pollution level. Index of geoaccumulation indicated the contents of heavy metals in soil of mining area were at non pollution level. Compared with the test control plots, the results evaluated by the Potential Ecological Risk Index showed that the highest soil pollution level was moderate ecological risk level in the study area, but the soil pollution level of most the areas were in the mild ecological risk level.(5) The results showed that Cr, Cu, Mn, Ni and Zn in the mining area soil come from the same source, while Pb came from the other source, by Correlation analysis, principal component analysis and cluster analysis.(6) With the vegetation restoration measures duration increasing, community species richness and diversity index gradually increased, the proportion of annual and biennial plant species and biomass in community decreased. Perennial forb and shrubs gradually become dominant species, which biomass accounted for the community of 70%, and this community has higher species diversity.(7) With the increase exposure time of waste soil, the content of heavy metals in the soil increased. Using the artificial vegetation restoration technology, could increase the content of soil organic matter, available nitrogen, available phosphorus and available potassium, and the effect was significantly improved with the increase of the recovery time. Except for the Pb, the contents of other 5 kinds of heavy metal in the soil were reduced significantly by vegetation restoration measures. After 5 years of vegetation restoration, the contents of heavy metal in the soil reached the level of control plot that was from 10 km around the mining area. Overall, biological Barbara vegetation restoration effect was significant. |
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