Study On Ecological Cumulative Effects Of Mining Areas In Arid And Semi-Arid Grassland In Eastern Inner Mongolia

Grassland in eastern Inner Mongolia is not only an ecological security barrier region of“Two Screens and Three Belts”,but also the distributional area of large coal and coal power bases.Ecological problems,such as grassland degradation,groundwater level decline,and biodiversity reduction caused by coal mining,had a serious negative impact on the ecology of mining area and its surrounding after long-term cumulation and spatial expansion.Taking grassland mining area in eastern Inner Mongolia as an example and using geographic information technology,the paper quantitatively analysed the ecological effects of vegetation evolution,land cover and site surface quality on large-scale mining areas in tempo-spatial scale with remote sensing images and experimental detection data.The main conclusions are as follows.(1)Summarize ecological cumulative effect mechanism of grassland mining area based on the relationship between mining area development and grassland ecosystem evolution,the ecological effect cumulative characteristic of grassland mining area,and cumulative response of key ecological factors.The development periods of coal mine includes initial development,accelerating development,stable development and decline development,and each period affects the spatial evolution of grassland ecosystems through different disturbance methods.The ecological cumulative effect of grassland mining area has the characteristics of time cumulation,spatial expansibility,cumulative source overlaying or synergying,recessive and dominant,indirect effects,threshold sensitivity and poor recoverability of ecological functions.(2)Maximum value composites and trend line analysis were applied to analyze the ecological effects of vegetation evolution in 25 large-scale mining areas in eastern Inner Mongolia from 1981 to 2015.The vegetation coverage towards increasing in eastern Inner Mongolia decreased in the order of Tongliao>Hinggan League>Chifeng>Hulunbuir>Xilingol over the past 35 years.For the changes in vegetation coverage of 25 large-scale mining areas before and after mining,vegetation showed a decreasing tendency in 40%mining areas,but an increasing tendency in 60%mining areas after mining.Except Shengli No.1,an obvious correlation was found between vegetation change and precipitation in 45.83%mining areas after mining.Human activities had significant positive effects on vegetation growth in 25%mining areas.Significant negative effects of human activities were found in 8.34%mining areas,causing the vegetation degradation.However,there were 20.83%mining areas with vegetation changes not affected by precipitation and human activities.Vegetation change in Shengli No.1 had a significant correlation with precipitation and human activities after mining.(3)For Baorixile(mined for 20 years),Yimin(mined for 36 years),and Shengli No.1(mined for 45 years),their ecological sensitive areas were delineated and land cover changes and ecological cumulative effects were evaluated respectively.(1)The change ranges of ESV for Baorixile,Yimin,and Shengli No.1 were-4212.19,1915.68,and-2491.49 yuan/a,respectively.(2)Ecological storage status indicators showed that the ESV of mining area ecosystem per unit area in Baorixile,Yimin and Shengli No.1 tended to degenerate at a rate of 83.68,75.38,and 48.01 yuan/hm~2·a,respectively.The ecological storage transformation rates of these three mines were lower than 0,suggesting that ecological storage process shows a negative transformation trend.The ESC values of Baorixile,Yimin,and Shengli No.1 were-410,-310,and-240 yuan/hm~2·a,which indicates that there was a better ecological storage capacity for Shengli No.1.The EP values of these three mines were no obvious differences.The LC values of Baorixile,Yimin,and Shengli No.1 were0.37%,0.69%,and 0.62%.(3)The comprehensive indices of ecological storage effect for Yimin,Baorixile,and Shengli No.1 were 4.37,2.98,and 1.65,showing that the impact of land use on regional ecological storage is the smallest in Yimin and the largest in Shengli No.1.(4)According to ecological quality spatial changes of mining area site in different stages and soil quality status,we evaluated the ecological cumulative effects of surface mining area and delineated the ecological impact scope of Baorixile based on the life-cycle theory.Firstly,ecological situation was better for rising period(from2001 to 2017),was worse for reaching production period(from 2007 to 2011),tended to improve for high yield period(from 2011 to 2013),and showed a slight deterioration for stable production period(from 2013 to 2019).Secondly,the content of organic matter in mining area was lower than that of the Second National Soil Survey.The concentrations of Cr,Cd,Pb,Zn,Cu,As,and Ni did not exceed the national environmental quality standards(GB15618-2018).However,the concentrations of Cr,Cd,Zn,Cu,As,and Ni were higher than their corresponding background values.Cr and Zn showed a significant accumulation in soil.Soil heavy metal was at low risk level,and Cd is a main potential ecological risk element.Thirdly,results of mining site and soil ecological quality evaluation indicated that 0-2 km buffer zone in the southeast of mining area was significantly affected by mining activities,and 2-5 km buffer zone might be affected by mining activities.Finally,response strategies were proposed for ecological restoration of Baorixile,for example,"dynamic restoration",regional and phased key management,and planting of Medicago sativa L,Elymus dahuricus Turcz,Larch and Lespedeza bicolor Turcz.The thesis contains 63 figures,55 tables,and 235 references.