Variation Characteristics And Its Influencing Factors Of Soil Organic Carbon Storage In Opencast Coal Mine Dump Under Vegetation Reconstruction

ObjectiveVegetation reconstruction is an effective solution to improve ecology of the opencastcoal mine dump. Studying the effects of the vegetation reconstruction patterns on soil organiccarbon (SOC) storage is essential for selecting measures for vegetation restoration. We aimedat the disturbed soil of opencast coal mine in Shanxi-Shaanxi-Inner Mongolia mine areas, toexplore the variations characteristics of SOC and total nitrogen (TN) and its influencingfactors under different vegetation reconstruction patterns, and evaluate the contributions ofthe vegetation reconstruction patterns on SOC and TN content, so as to provide certainguidance to reclaim land and vegetation reconstruction, meanwhile, significant to evaluate thesoil organic carbon storage and carbon sequestration potential.Experimental DesignIn the study, we chosen Heidaigou opencast coal mine in Inner Mongolia in Loess hillyregion, focused on dump platform and slope, collected1,276soil samples,502soil bulkdensity samples,102litter samples and392root samples, analyzed the samples in laboratory,combined with such classical statistics methods as analysis of variance, regression analysis, tostudy the variations of SOC and TN content, density and storage under the four vegetationreconstruction patterns: natural recovery land, grassland, shrub land, woodland.Main ResultsFirstly, vegetation reconstruction noticeably influenced the content and distribution ofSOC and TN in the dump platform soil profile (p<0.05). Under different vegetationreconstruction patterns, the SOC and TN content were distributed as follows: grassland>shrub land> woodland> natural recovery land. Under the optimal vegetation configurationtypes, the content of SOC and TN in Medicago sativa surface layer soil was the highest,which were166.7%and171.3%higher than those of the natural recovery land respectively,and were about twice of the other three patterns. Under the same vegetation reconstructionpattern, the SOC density and storage were as follows: original landform area> reclaimeddump> new dump. After15years of vegetation reconstruction, the SOC storage of grassland,shrub land and woodland were increased by15.47t·hm-2,6.93t·hm-2and6.95t·hm-2respectively, only equaling2/3,1/2and1/2of the original landform area. From the perspective of land reclamation and carbon sequestration, the vegetation reconstructionpatterns in dump platform was suggested to focus on grassland, while the vegetation wassuggested to focus on pasture such as Medicago sativa.Secondly, under vegetation reconstruction patterns in dump slope, the content of SOCand TN on grassland was the highest, followed by shrub land and woodland, while that of thenatural recovery land was the lowest. After15years of vegetation reconstruction, SOCstorage in grassland and woodland only equaled59%and53%of that of the natural recoveryland, increasing by11.85t·hm-2and5.38t·hm-2respectively compared with the new dump.Carbon sequestration rates of grassland and woodland were79.01g C·m-2yr-1and35.87gC·m-2yr-1respectively. Vegetation reconstruction on dump had huge potential on carbonsequestration and soil carbon storage increasement. From the perspective of soil nutrientsquality and slope erosion control, the vegetation reconstruction patterns in dump should befocused on grassland, with shrub land following.Thirdly, under the natural soil, for the same watershed, the SOC density on sloping field,woodland and grassland in surface soil (0~10cm) and subsurface soil (10~20cm) weredistributed as follows: had significantly higher SOC density than sloping field (p<0.05);among the three watersheds, SOC density on sloping field and woodland increased from northto south, while it increased first, and then decreased on grassland. SOC density from the northto the south was gradually increased under the conversion from sloping field to woodland,which increased nearly four-fold from18.8%to72.7%; on the contrary, SOC density wasreduced from32.1%to20.1%from north to south under the conversion from sloping field tograssland.Fourthly, in a similar topography and vegetation conditions, the carbon (nitrogen) storagein small watershed was significantly higher than that in the dump, and grassland was higherthan woodland (p<0.05). To reach the carbon storage of the small watershed,1hm2dumpslope in1m depth woodland and grassland need to increase13.64t and11.15t SOCrespectively.And fifthly, biomass of litter and fine roots under vegetation patterns significantlyaffected the SOC density and its distribution (p<0.05). Relationship between litter, fine rootbiomass and SOC storage in line with the logarithmic equation (y=alnx+y0,R2=0.4294~0.8332, p<0.05); Relationship between the carbon content of litter, fine root andSOC storage in line with the linear equation (y=ax+y0, R2=0.4163~0.7228, p<0.05).