Influencing factors and evaluation of land degradation of 12 coal mine areas in Western China

The ecological environment in western China is extremely fragile. The land degradation caused by coal re- source exploitation and natural factors cannot be ignored in Coal Mine Area ( CMA). This paper aims to reveal the causes,degree,distribution and trend of land degradation in CMAs in western China,and to provide basis for land deg- radation prevention and land space ecological restoration in CMAs. The concept of land degradation in CMAa is proposed,and the affecting factors are categorized into direct and indirect factors (or external manifestations). Direct fac- tors include excavation,occupation,and subsidence. Indirect factors include soil erosion,vegetation degradation,and desertification or stony desertification. These land degradation factors are obtained by combining field survey data and supplementary interpretation of high-resolution and hyperspectral remote sensing data. Moreover,a comprehensive eval- uation model for land degradation in western CMA is constructed based on the grading evaluation criteria for the indi- rect factors of land degradation. Finally,an empirical study was carried out on 12 key CMAs in the Loess Plateau Re- gion (LPR),Southwest Mountain and Hilly Region ( SMHR),Northern Steppe Region ( NSR) and Northwest Arid Region (NAR). The results show that:① the subsidence rate of per 10 000 tons is mainly affected by factors such as mining thickness,burial depth,dip angle and overlying lithology,while the damage rate of per 10 000 tons is mainly af- fected by factors including coal seam thickness,stripped rock and soil thickness,and rock and soil stacking methods. ② Different regions have different main manifestations of land degradation. Among them,LPR is vegetation degradation and soil erosion,SMHR is soil erosion,while NSR and NAR are vegetation degradation,soil erosion,and desertifica- tion. ③ The land degradation of mine-scale is far more severe than CMA-scale,and the impact open-pit mining is more severe than underground mining. In addition,the degree of land degradation on the CMA scale is related to the Coal Resource Development Intensity (Referred to as CRDI,expressed as the ratio of the disturbance area of the coal mine to the total area of the CMA). Among them,the greater the CRDI,the more severe the land degradation in the mining area. However,the degree of land degradation is not directly proportional to CRDI,and it is also related to the ecologi- cal vulnerability or carrying capacity of the CMA. In conclusion,as the forms and degrees of land degradation are dif- ferent due to diverse methods of coal mining in different regions,it requires to take corresponding stategies of land res- toration. In order to prevent the excessive land degradation,it’s necessary to determine the rational exploitation inten- sity according to the ecological carrying capacity of CMAs.