Comprehensive Evaluation On Effects Of Coal Gangue Filling And Reclamation On Soil Characteristics In Coal Mining Subsidence Area

Coal mining causes the land subsidence of mining area in large area,aggravating the vulnerability of local ecosystem.The coal gangue filling and reclamation is considered to be a common method to restore the subsidence land in the mining area.However,the soil productivity level is limited and has a negative impact on the soil characteristics due to corresponding poor reclamation efficiency.Physical and chemical properties of the soil are normally used to characterize the changes in the fertility,carbon cycle and environmental quality of the soil.The soil fertility quality is eligible to measure the capacity of soil to promote the carbon cycle,supply nutrients required for activities of animals,plants and microbial and promote production,and the environmental quality of the oil can reflect the capacities of the soil to absorb,accommodate and transform heavy metals and other pollutants.Conclusively,the explorations on changes in physical and chemical properties,organic carbon and its components,bacterial community,heavy metals and other characteristics of soil undergoing coal gangue filling and reclamation,studies on relations among the characteristics as well as comprehensive evaluation on the level of soil quality after filling deliver important significance on the restoration level of the soil quality in current mining subsidence area.The soil(G)undergoing coal gangue filling and reclamation in the high underground water,coal mining subsidence area of Zoucheng,Jining,Shandong Province was used as the research subject in the present study.The soil sampling and indoor test analysis were implemented.Normal cultivated land soil(CK)around the studied area in the study was selected as the control group to investigate the differences in the content distributions of bulk density(BD),soil moisture content(SWC),electrical conductivity(EC),available nitrogen(AN),available potassium(AK),available phosphorus(AP),soil organic matter(SOM),p H and other soil physical and chemical properties under different soil depths(0-20 cm,20-40 cm and 40-60 cm).The distributional differences and characteristics of soil organic carbon(SOC)and its components dissolved organic carbon(DOC),microbial biomass carbon(MBC),readily oxidized orgainic carbon(ROC)and particulate organic carbon(POC)were analyzed.The diversity,abundance and structure of soil bacterial communities under different soil depths were studied by 16 S r RNA gene high-throughput sequencing technology.The vertical distribution characteristics of heavy metals under different soil depths in the studied area were technically tested and analyzed by ICP-MS and ICP-OES.The effects of coal gangue filling and reclamation on soil characteristics of G and CK by multiple perspectives and hierarchical comparison,and the interaction and relations between four soil characteristics were further explained by(pearson correlation coefficient,Pearson)and(redundancy analysis,RDA),and the level of soil quality in the studied area was evaluated by principal component analysis.The results are show as follows:(1)Changes in Characteristics of Soil Undergoing Coal Gangue Filling and ReclamationThe physical and chemical properties of the soil undergoing coal gangue filling and reclamation as well as soil organic carbon and its components,bacterial community and heavy metal of the soil changed significantly.The specific performance is as follows:Compared with CK,G had a higher p H and BD,and the performance of soil fertility was improved and maintained a gap with that of CK.The properties of SOM,AN,AP,AK,SWC and p H were negatively correlated with the soil layer(P<0.05),while EC and BD were found to be positively correlated with the soil layer(P<0.05).The average content of soil organic carbon and its components of G was lower than such index of CK,the average content of SOC,MBC,ROC and POC layers decreased with the increase of soil layer,and DOC decreased firstly and then increased with the increase in the soil layer.Both the diversity and abundance of bacterial community of the soil of G were lower than such indexes of CK,and were negatively correlated with the soil layer(P<0.05).The change in the bacterial community of the soil structure was mainly reflected in the proportion of dominant bacteria community under different soil depths.Besides,Proteobacteria,Actinomycetes and Acidobacteria were found to be the dominant species in all treatments.The difference in the composition of bacterial community was great in the layer sized in 40-60 cm.The average content of elements of satisfied Cd < As < Pb < Cu < Cr < Zn,the average content of elements was higher than that such index of CK in the soil layer sized in 40-60 cm,and the average content of Cu and Zn in the soil layer sized in 40-60 cm was higher than the value of soil background in Shandong Province,and a certain degree of enrichment was found.(2)Correlation between Characteristics of Soils Undergoing Coal Gangue Filling and ReclamationThe correlation between characteristics of the soil receiving gangue filling and reclamation was significant.The correlation between soil characteristics of G was significantly higher than such index of CK when compared.Physical and chemical properties of the soil were significantly correlated with the soil organic carbon and its components as well as Zn and Cr elements in heavy metals except EC(P<0.05).SOM,p H,BD and SWC were main factors influencing the bacterial community of the soil,and the dominant bacteria groups including Proteobacteria,Actinobcteria and Acidobacteria were significantly related with most physical and chemical properties(P<0.05).The soil organic carbon and its components were significantly correlated with the dominant bacteria(P<0.05).SOC,MBC,ROC,POC were significantly correlated with Zn and Cr(P<0.05).Additionally,Zn,Cr and Cu were main heavy metal elements influencing the structure of soil bacteria community,and were correlated with Proteobacteria,Actinobcteria,Acidobacteria and other dominant bacteria to varying degrees.(3)Comprehensive Evaluation on Quality of Soil Undergoing Coal Gangue Filling and ReclamationThe quality level of the soil undergoing coal gangue filling and reclamation changed.The soil quality of the studied area was evaluated by principal component analysis,and the soil quality evaluation system for G and CK was constructed.The soil quality of G and CK under different soil depths were compared by using soil integrated quality index(SQI).The results showed that the level of soil quality of G was lower than that of CK under different soil depths,and the quality of reclaimed soil decreases with the increase of soil layer.The soil quality level of G in 40-60 cm was far lower than that of other soil layers.The above results show that the characteristics and quality of reclaimed soil are greatly influenced by gangue filling,especially the soil layer sized in 40-60 cm is the focus of prospective remediation in this area.The research results may provide the basis for land reclamation and ecological restoration of coal mining subsidence in China.