Influence Of Surface Cracks On Soil Quality In Coal Mining Subsidence Area

Soil is an important part of mining ecosystem,which plays an important role in the stability and development of mining ecosystem.It is an irreplaceable natural element.Coal energy mining will cause serious damage to the surface of the mining area.After coal mining to a certain extent,the surface will move and deform,resulting in soil cracks.To explore the impact of coal mining subsidence cracks on the local soil quality is the basic research work of vegetation succession and ecological reclamation in the mining area.In order to clearly understand the impact of coal mining subsidence on the soil in the mining area,so as to achieve the dual purposes of coal resources development and utilization and ecological environment protection in the mining area.This paper takes the 0-60 cm soil in the subsidence area of Shandong xinjulong coal mine as the research object,divides the mining subsidence cracks into wasteland cracks and farmland cracks.Combined with the actual situation,the sampling range is set up in the wasteland crack area,farmland crack area and no crack area Taking the depth of soil layer and the horizontal distance from the crack as variables,samples of different types of soil were taken.The changes of soil physical and chemical properties,soil heavy metals and soil microbial community under different variables were analyzed to reveal the impact of coal mining subsidence cracks on soil quality.The results show that: the closer to the fissure,the worse the soil quality.The soil quality of wasteland is greatly affected by the surface cracks,and the land quality decreases obviously.However,the farmland crack soil is less affected by the surface cracks due to other factors such as artificial cultivation,fertilization,vegetation buffer and so on.The main conclusions are as follows:(1)In the physical properties,the change trend of crack water content in farmland and wasteland is consistent,and the influence of crack on farmland water content is not obvious.The closer the wasteland is to the crack,the faster the water loss.The change of field water capacity of farmland and wasteland has no obvious rule.The variation trend of saturated hydraulic conductivity of farmland and wasteland is basically similar,and cracks strengthen the soil water permeability to a certain extent.The variation characteristics of bulk density of farmland and wasteland are similar.In the vertical direction,it shows a downward trend with the increase of fracture depth,and in the horizontal direction,it shows an upward trend with the increase of distance.The variation characteristics of porosity are opposite to bulk density.The electric conductivity of farmland increases with the increase of depth,but the electric conductivity of wasteland has no obvious change.In the chemical properties,the change regularity of ammonium nitrogen content in the horizontal and vertical directions is poor,which does not reflect the impact of collapse fractures.The contents of available P and total P in the surface soil(0-20cm)of farmland were higher,and the variation regularity of P and K in the horizontal direction was weak.Tillage and fertilization methods weakened the influence of collapse cracks on the contents of P and K in farmland soil to a certain extent.In the wasteland,the content of available P and total P was lower at 0 m away from the crack,but the content of available K and total K was higher at 0 m away from the crack.According to the comprehensive evaluation of soil physical and chemical properties,the impact of collapse cracks on soil physical and chemical properties generally decreases with the increase of horizontal distance.(2)The sources of heavy metals in wasteland are single and natural.As,Cu,Pb and Zn in farmland are homologous heavy metals,while Cr and Ni come from other sources.In the horizontal direction,the variation degree of heavy metal content in wasteland is not high,and the content of heavy metals at 0m is the highest.The results showed that the vegetation had a certain buffer effect on the diffusion of pollutants,and the variation of heavy metals in farmland was low and there was no significant difference.In the vertical direction,the accumulation of heavy metals in wasteland was consistent with the distribution of soil water,and the content of heavy metals increased with the depth.The heavy metals in farmland are at the depth of 20-30 cm,because the soil around the crack is mostly silt,which has a certain effect on the retardation of pollutants,and the content of various heavy metals is relatively high.Soil cracks in wasteland have a certain impact on the migration of heavy metals,which makes heavy metals migrate horizontally to cracks and vertically downward.Cracks in farmland have little effect on the migration of heavy metals.The soil quality of wasteland and farmland is safety grade,the soil quality is good,and there is no heavy metal pollution.The Nemero pollution index of farmland samples was basically the same(0.19-0.20),and heavy metals in collapse cracks had little effect on soil quality.The Nemero pollution index(0.265)in the wasteland area was higher than that in the farmland area(0.197).The closer to the crack,the higher the pollution index,and the risk of soil quality deterioration.(3)Most of the OTUs are bacteria,otu9 and otu11 are archaea.In the control group without cracks,the proportion of acidobacteria and thaumarchaeota is closed,and they are the main microorganisms in the soil.After cracks formed,the proportion of thaumarchaeota decreased and the proportion of acidobacteria increased in the farmland;the proportion of acidobacteria and thaumarchaeota decreased in the wasteland,and the proportion of chloroflexi and proteobacteria increased.According to the bate diversity analysis results,the total samples can be divided into two categories,the farmland crack samples and the control group samples are one category,and the wasteland crack samples are a separate category,which indicates that the composition of microbial community in the farmland crack group and the control group is relatively similar,but the wasteland crack microbial community is greatly affected by the crack,which leads to great changes in the microbial community.In terms of microbial richness,the lowest is in the crack group of wasteland,and the richness decreases with the increase of horizontal distance,which destroys the balance of local microbial community and leads to the decrease of microbial richness in wasteland;there is no obvious change rule in the horizontal distance of farmland crack group,so it is less affected.In terms of microbial balance,the control group had the best balance.The Simpson index of wasteland crack group and farmland crack group were both 0.00663,with the same balance.The farther away from the crack,the better the microbial balance.The soil environment of wasteland and farmland is unstable because of cracks,and the closer the cracks are,the more unstable the soil environment is.