Spatial Characteristics Of Reclaimed Soil Organic Carbon In A Coal Mine Area With The High Groundwater Level

The problem of mining subsidence in mining area with high groundwater level has become a hot issue in society.Land subsidence will cause serious reconstruction and variation of soil nutrients and soil levels,which will lead to crop reduction or even crop loss,and pose serious potential risks to China’s food security strategy.At present,domestic and foreign experts have done a lot of research on the governance measures of land subsidence and made great social,economic and ecological achievements,making significant contributions to maintaining China’s economic and social stability.Land reclamation is the general name of all engineering measures to control land collapse.However,due to the lack of experience in early reclamation work,the reclamation soil used large machinery for repeated compaction because of the excessive pursuit of land leveling,resulting in a high degree of soil compactness,and at the same time,the implementation of surface soil stripping is not in place.Therefore,land reclamation has the defects of immature reclamation theory,high cost of filling materials and slow recovery of reclaimed soil quality.In addition,soil organic carbon is an important index to measure land quality and soil fertility,and also an important index to measure the effect of land reclamation in mining areas.In summary,it is found that under the dual influence of land subsidence（natural factors）and land reclamation（human factors）,how to change the spatial characteristics of soil organic carbon in the mining area needs to be studied urgently.The experimental area is located in jining mining area of high groundwater level mining area.The spatial characteristics of reclaimed soil organic carbon in high groundwater level mining area are studied through field sampling and experimental analysis.In this study,the reclaimed soil of different filling materials（yellow river sand,lake mud and foreign soil）,different utilization modes（garden land,cultivated land and woodland）and different reclamation modes（filling reclamation,non-filling reclamation and pre-reclamation）were selected as the research objects.Soil organic carbon（SOC）,soil organic carbon components（WDOC,POC,MOC,LFOC,HFOC and MBC）and soil organic carbon levels（based on the 13C isotope ratio）were taken as the study indexes.Meanwhile,the surrounding normal farmland was taken as the control.The soil samples were analyzed by the national engineering laboratory for the efficient utilization of soil and fertilizer resources in shandong agricultural university.The purpose of this paper is to analyze the spatial characteristics of soil organic carbon from different reclamation perspectives,explore the best reclamation methods applied under different external conditions,and provide data support and basis for scientific management of coal subsidence areas in the mining area with high groundwater level.The research results show that:（1）The spatial characteristics of SOC of reclaimed soil in different filling materialsIn terms of total organic carbon content,the best recovery effect of SOC in reclaimed soil is M2,followed by M3,and the worst is M1.The SOC of reclaimed soil has the property of surface agglomeration and its content decreases gradually with soil depth.The proportion of SOC in the surface of reclaimed soil is higher than that in the deep layer,and the proportion of SOC in the deep layer of M1 and M3 is significantly lower.The damage to the total amount of organic carbon is from large to small:M1>M3>M2;In terms of organic carbon component,the surface organic carbon component of the reclaimed soil is better than the deep layer（except MBC）,the mean value and stratification value of MOC and HFOC are significantly lower than the control,and both show great negative sensitivity and high proportion（both proportion of>65%）.In addition,we found that the proportion of the larger component of the reclamation decreased significantly,and the proportion of the smaller component increased significantly.Organic carbon composition varies from large to small:M2>M3>M1.The positive sensitivity to organic carbon components ranges from large to small:M2>M1>M3.The degree of negative sensitivity ranges from big to small:M1>M2>M3;In terms of the organic carbon level,the¹³C value of reclaimed soil is generally low,and the variation between 0 and 60 cm is relatively small.In conclusion,it was found that the organic carbon content could not be restored to the normal cultivated land in a short time no matter the filling and reclamation method was adopted.Comparatively speaking,the restitution effect of lake mud is the best,and the foreign soil is the second,and the yellow river is poor.（2）The spatial characteristics of SOC of reclaimed soil with different utilization modesIn terms of total organic carbon,the best recovery effect of SOC is M4,followed by M6,and the worst is M5.The ratio of surface organic carbon of M4 and M5 is larger,while that of deep organic carbon of M6 is obviously larger.No matter how it is used,The ash reclamation will result in the loss of SOC content.M4 has low negative sensitivity in topsoil,M6 has low negative sensitivity in subsoil,and M5 has high negative sensitivity.In terms of organic carbon component,the organic carbon component of M4 has a tabular property in the 0-60 cm soil layer,the organic carbon component of M5 is stable in the 20-60 cm soil layer,and the content of deep organic carbon component（MOC and HFOC）increases in M6.The mean values of MOC and HFOC of the three utilization modes were all significantly smaller than those of the control cultivated land,and all of them had the problem of great negative sensitivity（accounting for 60%of>）.Before and after reclamation,the change range of component proportion was obvious（except MBC）.In addition,The organic carbon composition varies from large to small:M4>M6>M5.The positive sensitivity to organic carbon components ranges from large to small:M4>M6>M5.Component negative sensitivity ranges from large to small:M5>M4>M6;In terms of organic carbon level,the ¹³C value of three types of reclaimed soil is significantly lower than that of the respective control in 0-60cm soil layer,and the difference of reclamation soil with different utilization modes mainly exists in 40-60 cm soil layer.Through the analysis of soil fluctuation,it is found that different utilization modes of ash filling reclamation have a certain protective effect on soil level,but there is still a problem of poor consistency of soil source.In conclusion,it is found that for the same filling and reclamation modes（this paper is fly ash reclamation）,although no one use modes can completely restore to the level of normal cultivated land in a short time,the characteristics of different use modes are more obvious.Relatively speaking,the M5 is the best,followed by M6,and the M4 is the worst.（3）The spatial characteristics of SOC under different reclamation modesIn terms of the total amount of organic carbon,the recovery degree of SOC of the reclaimed soil is from high to low:M8>M9>M7.The SOC content of the reclaimed soil is all tabular,and its content gradually decreases with the soil depth.The proportion of M7 and M8 in the depth of each soil layer was not significant,while the proportion of M9 in the surface layer was significantly larger.The negative sensitivity of SOC to M7 is strong,while the negative sensitivity to M8 and M9 is weak or even positive;In terms of organic carbon components,most of the organic carbon components have a tabular property,and their contents gradually decrease with the soil depth.The content of MOC and HFOC in reclaimed soil was significantly lower than that in control,while WDOC and MBC were significantly higher than that in control.According to the specific gravity analysis,MOC and HFOC account for a large proportion（60%of>）,while MBC accounts for a very small proportion（less than0.5%）.The proportion of POC and LFOC（except M9）in the reclaimed soil increased,the proportion of WDOC and MBC did not change significantly,and the proportion of MOC and HFOC decreased.It was also found that both MOC and HFOC showed negative sensitivity between 0-60 cm soil layers,in which the negative sensitivity of M8 was significantly less than that of M7 and M9.The variation range of different filling reclamation methods is from large to small:M7>M9>M8.In addition,organic carbon abundance:M8>M9>M7.Positive sensitivity of soil organic carbon component:M8>M7>M9,negative sensitivity:M7=M9>M8;In terms of organic carbon level,the¹³C value of M7 is significantly different from CK7 in both numerical value and variation trend.Besides,the ¹³C value of M8 is similar to CK8 in both numerical value and variation trend,while that of M9 is consistent with that of CK9.There are slight parallel differences in numerical value.According to the analysis of soil fluctuation,the soil level of M7 is not obvious,and the soil source consistency is not good.M8 and M9 have good consistency of soil level and soil source.In conclusion,non-filling reclamation can make soil organic carbon return to the level of normal cultivated land in a short time,and the consistency between soil level and soil source is better.As an"upgraded version"of filling reclamation,pre-reclamation can accelerate the recovery of soil organic carbon under the premise of maintaining soil layer as much as possible.While M7 has the common defects of filling reclamation.