Carbon Sequestration Of Reclaimed Ecological System In Typical Open Pit Coal Mine:Mechanism And Effect

Climate change caused by greenhouse gas emissions has attracted much attention globally.Capturing the carbon from the air into terrestrial ecosystems by vegetation restoration was considered efficient to mitigate climate change.The open pit coal mining triggered intensive disturbance of the ecological environment.Consequently,the carbon storage capacity in mine area declined and even lost.Fortunately,the mining area ecosystem gradually changed from "carbon source" to "carbon pool" with land reclamation,such as landform remolding,soil reconstruction and vegetation restoration.However,the understanding of the mechanism of carbon sequestration in the reclamation ecosystem is paucity.Pingshuo open pit coal mine,the land reclamation base of the Ministry of Land and Resources,provids us an opportunity to detect the mechanism and effect of carbon sequestration.Thus,the Southern and Western dump in Pingshuo mine was taken as examples and the theory and methods of soil science,biology and other disciplines were employed to analyzed the spatial and temporal changes of soil and vegetation carbon pool.The main results are as follows:(1)The reclamation pattern or the vegetation configuration determined the carbon sequestration rate.The Robinia pseudoacacia and Pinus tabulaeformis forest had the highest fraction of carbon sequestration rates among reclamation patterns.The storage of soil organic carbon(SOC)in the cultivated land decreased and then increased with the duration of reclamation.Soil microbial biomass carbon(MBC),readily oxidized carbon(EOC)and water soluble carbon(DOC)increased over time.R.pseudoacacia monoculture forest had obvious advantages of SOC and EOC storage.P.tabulaeformis monoculture forest,however,was more conducive to MBC accumulation.The carbon storage in Ulmus pumila pure forest could not match that under R pseudoacacia and P.tabulaeformis forest in the initial stage of reclamation,but after 10 years of reclamation,it was superior to that under the 2 later forest.The labile fraction of SOC showed a S trend with the depth of the soil layer,and the carbon in the 0?20 cm soil layer were higher than that in the deep layer.The accumulation of SOC and labile fractions in soil was governed by other physical and chemical properties of soil,above all,the N may play an important role in the accumulation of SOC and its labile fractions.(2)The forest ecosystem in R.pseudoacacia was in forward succession.10 years or so,soil and vegetation could be restored.Trees index(tree height,DBH,crown width,vegetation carbon storage,vegetation carbon density)increases with reclamation ages;pH,soil bulk density(BD)and decreased with time.Nutrients(SOC,TN,TK,AN,AK)increased with time as well.It could be deduced that vegetation development is mainly determined by SOC and N.Vegetation carbon sequestrated in R.pseudoacacia and P.tabulaeformis mixed forest was 26.55 Mg/ha.The distribution of tree carbon was heterogeneity.The survived R.pseudoacacia and P.tabulaeformis were found to have fiercely competition that inhibited the accumulation of tree carbon at the distance of 0?4.5 m and 0?1.2 m,respectively.The U.pumila however was observed competed with each other at any distance.(3)The two dumps reserved 8853.88 Mg soil carbon with the density of 21.96 Mg/ha.The storage and density of soil carbon were higher in the Southern dump than that in the Western dump.The middle and east of the Southern dump sequestrated more soil carbon,while the middle and south of the Western dump had more soil carbon.The vegetation carbon reserved in the two dumps was 10361.71 Mg,with the density is 25.70 Mg/ha.The vegetation carbon storages and density were higher in the Western dump than that in the Southern dump.In terms of the distribution within dumps,the carbon storage was higher in the middle and east than the west.The total carbon storage(soil + vegetation)was 19215.59 Mg with the density of 47.66Mg/ha.The carbon storages and density of the total carbon pool was higher in the Western dump than that in the Southern dump.(4)Reclamation has significantly improved the function of the ecological system in the mining area,and the multi-function of the reclaimed land ecosystem has exceeded the original geomorphology.The 35 index values of S I and S IV were were higher,among which 9 index were the highest among plots.The ecosystem function under R pseudoacacia and P.tabulaeformis mixed forest was the best in all reclamation patterns,which promoted the recovery of productivity and biodiversity of reclaimed land ecosystem,and improved the function of carbon sequestration and nutrient cycling in reclaimed land ecosystem.The recovery of ecosystem function was based on the interaction of various factors.Despite the ecosystem function was likely to be similar among plots after long-term succession,reclamation pattern was still the decisive factor of ecosystem's multi-function.Carbon sequestration was recommended as the proxy for ecosystem multifunctionality values(reclamation quality).Overall,land reclamation has significantly improved the multi-function and carbon storage ability in mining area.The carbon sequestration could well revealed the dynamics of various ecosystem elements(soil,vegetation,etc.)in different reclamation stages.