Damage Characteristics Of Soil Properties Under Different Land Use Types In Loess-gully Coal Mining Subsidence Are

After coal mining,the overlying rock damage in the goaf is transmitted to the surface,and geological environmental damage such as cracks,step-shaped fractures and collapse pits will appear,which will damage the surface ecosystem.At present,there have been many studies on the degree,process and mechanism of soil damage in subsidence land after mining.However,comparative studies on the characteristics and extent of soil damage under different land use types in the damaged area are relatively weak,which limits the accuracy of the evaluation of the degree of ecological damage to the subsidence of the mining area and he formulation of targeted ecological restoration measures for different land use types.Therefore,on the basis of clarifying the damage characteristics of soil physical and chemical properties of different land use types in the loess subsidence area of Yushenfu mining area,this paper uses the soil quality index method to comprehensively evaluate soil quality under different land use types.The main conclusions are as follows:(1)After the surface subsidence,the four types of land use,grassland,woodland,garden land and cultivated land,showed different changes in soil physical properties.Among them,the pH value and bulk density of woodland and garden land are reduced after the surface subsidence.The bulk density of grassland decreased by 19%,and the soil pH value increased from 8.41 to 8.48,However,the impact of the subsidence on the soil bulk density and pH value of the cultivated land was not significant.The mechanical composition of soil particles after subsidence is generally expressed by the increase in sand content,decrease in silt content and insignificant change in clay content in the four land use types,and the composition of soil particles in the garden has the most significant changes.After the subsidenc,the soil water content of the cultivated land dropped from 8.98%before the subsidence to 5.96%after the collapse,the largest decrease of 34%.In terms of different soil depths,comparing subsidence area and unsubsidence area,the soil pH value of woodland and grassland increased with soil depth,and cultivated land decreased with depth,but the soil pH value of garden land increased with soil depth after subsidence,which was different from that of unsubsidence area.After the subsidence,the silt and clay particles of the cultivated land decrease with the soil depth,and the sand content increases with the depth,the clay and sand content of garden land increases with soil depth,and the silt decreases with depth,and the change trend of the mechanical composition of the two in depth is opposite to that of unsubsidence area.The soil mechanical composition of woodland in unsubsidence area has no significant change in depth,while the content of clay and sand after subsidence decreases with soil depth,and the silt increases with depth.The change trend of the mechanical composition of grassland soil with soil depth is the same before and after the subsidence.The soil moisture content of woodland,garden plot and grassland increases with soil depth before and after the subsidence,but the soil water content of the cultivated land after the subsidence first decreased and then increased with the soil depth,which was different from the change trend of the unsubsidence area.(2)According to the characteristics of soil nutrient damage in different land use types,after the subsidence,the content of soil organic matter and available nitrogen,phosphorus and potassium of wood land decreased;although the content of nitrogen,phosphorus and potassium of grassland decreased,the content of soil organic matter increased by 20%;and the soil organic matter and nitrogen content of garden and cultivated land decreased,but the available potassium and phosphorus content increased.In terms of different depths,the organic matter content of wood land,cultivated land and grassland after the subsidence has no significant change with depth compared with the unsubsidence area,and the soil organic matter of garden land does not change significantly with the depth after the subsidence,which is different from the trend of decreasing with the depth when it is not subsidence.The content of nitrogen,phosphorus and potassium in the soil of the study area decreased with the soil depth before and after subsidence.(3)After the surface subsidence,soil sucrase activity of cultivated land and garden increased by 35%and 73%respectively,while that of woodland and grassland decreased by 22%and 36%respectively;After the subsidenc,the activities of soil phosphatase and urease in woodland and cultivated land decreased,while those in garden and grassland increased;The activity of soil catalase in different land use types increased significantly after subsidence compared with that in unsubsidence area,and garden land increased by 64%with the largest amplitude.In terms of different depths,after the surface subsidence,the activities of soil invertase,urease,and phosphatase of different land use types all decrease significantly with the depth,which is similar to the change trend of unsubsidence area;The soil catalase activity of woodland,cultivated land and grassland did not change significantly with the change of depth before and after the collapse;The activity of catalase in the unsubsidence area of garden land decreased with the depth,while the catalase activity of the subsidence soil increased with the depth of the soil.(4)From the perspective of the number and composition of microorganisms,the number of soil bacteria in cultivated land after the surface subsidenced decreased by 48%,while the number of fungi,actinomycetes,and archaea increased by 207%,238%,and 56%respectively;The number of bacteria in gardens and grassland decreased,and the number of other bacteria increased,while the change trend of woodland was opposite.The diversity indexes of soil bacteria and fungi under different land use types in the study area have relatively small differences,and both show a decreasing trend of diversity indexes after the subsidence.The bacterial communities of different land use types before and after the subsidence were mainly actinomycetes.After the subsidence,the relative abundance of actinomycota in wood land,cultivated land,and garden land decreased,and there was no significant change in grassland;the fungal community is dominated by Ascomycota.After the subsidenc,the relative abundance of Ascomycota in woodland increased by 21%,garden land decreased by 26%,and there was no significant change in cultivated land and grassland.After the ground surface subsidence,the number of grassland microorganisms decreases with depth,and its change trend is similar to that of unsubsidence area.The number of microorganisms in woodland and garden plots changes with depth differently from that of unsubsidence area.The number of fungi except bacteria in cultivated land decreased with depth,and the changing trend was similar to that of unsubsidence area.(5)By comparing the correlation of soil physical,chemical and biological properties under different land use types in subsidence area,the soil nutrients,enzyme activity and microbial quantity of woodland,garden land and grassland are all related to soil moisture content,while the above-mentioned soil indicators of cultivated land have a small relationship with soil moisture content;The mechanical composition of cultivated land has a greater impact on soil moisture content.Under different land use types,soil moisture and nutrients are the main relevant indicators that affect soil enzyme activity and the number of microorganisms.There was significant correlation between bacterial diversity and soil bulk density in cultivated land and garden land,but no significant correlation between fungal diversity and soil physical,nutrient and enzyme activity indexes.However,fungal diversity in woodland and grassland was mainly affected by enzyme activity,while bacterial diversity had weak correlation with other indexes.Comprehensive analysis of soil physical,chemical and biological characteristics,subsidence reduces soil quality under different land use types.Subsidence mainly interferes with the physical properties and available nutrient characteristics of woodland and grassland,while cultivated land and garden lands mainly affect soil organic matter,enzyme activity and microbial characteristics after the subsidence.The soil quality index of the unsubsidence area of different land use types is lower than that of the unsubsidence area.Compared with unsubsidence area,the soil quality of woodland decreased by 21%,followed by grassland and cultivated land(reduced by 17%and 14%,respectively),and the impact of subsidence on the soil quality of garden land was smaller.