| Underground mining is the main method of coal mining and the land subsidence caused by underground mining is becoming an increasingly prominent problem in China.It is an urgent task that land reclamation and ecological reconstruction in the high groundwater level mining area.As key indicators of soil quality and ecological characteristics,the evolution of soil aggregates and organic carbon has great significance in evaluating the quality change and ecological effect of reclaimed soil,and guiding the improvement of reclaimed soil.Reclaimed soil filled with coal gangue in Dongtan coal mine was selected as research object.This study analyzed the characteristics of soil basic physico-chemical properties,water-stable aggregate,soil organic carbon and aggregate-associated organic carbon under different reclamation years and land-use patterns.In addition,three organic carbon fractions were separated within the small macroaggregates and microaggregates,using a density fractionation method: free light fraction(free LF),intra-aggregate particulate organic matter(iPOM),and mineral associated organic carbon(Mineral-C).Meanwhile,the dynamics of three organic carbon fractions were analyzed.The main results and conclusions are as follows:(1)The proportion of small macroaggregate was the biggest(50.05%~59.37%)in reclaimed soil water-stable aggregates.Macroaggregate content and aggregate stability increased with reclamation years.The mass proportions of surface soil small macroaggregate were farmland(54.26%),woodland(52.75%)and wasteland(52.18%).This result indicated that the soil aggregate improve effect of farmland was better than woodland and wasteland.(2)Soil organic carbon content and density increased with reclamation years and had a higher level in 13 and 15 years of reclamation than control farmland.This result indicated that the carbon sequestration ability of reclaimed soil was higher than control soil under appropriate environment and management measures.The carbon sequestration rate of reclaimed surface soil rised and then decreased during 5~15 years of reclamation and had the biggest value(0.186 kg m-2 yr-1)in 13 years of reclamation.Correlation analysis showed that the increase of reclaimed soil organic carbon and the formation of water-stable macroaggregate had a close relationship.(3)Reclaimed soil organic carbon content decreased with the decrease of aggregate particle size.The main contribution of reclaimed soil organic carbon came from small macroaggregate(56.94%~62.17%)because of its high mass proportion.Aggregate-associated organic carbon contents of all particle size increased with reclamation years.The contribution of macroaggregate organic carbon increased in 5~13 years of reclamation and then decreased in 13~15 years of reclamation.In addition,the reclaimed surface soil organic carbon and aggregate-associated organic carbon contents were higher than subsurface soil and had great significance in analyzing soil organic carbon translation and accumulation.(4)The free LF and iPOM contents of small macroaggregate and microaggregate were significantly increased with reclamation years.The free LF content of small macroaggregate was higher than microaggregate and indicated the fresh plant residues combined into large aggregate firstly.The fine particulate organic carbon of microaggregate plays a key role in the improvement of soil organic carbon content.Small macroaggregate turnover of reclaimed soil decreased and then rised during 5~15 years of reclamation.Mineral-C was an important part of soil organic carbon sequestration and increased with reclamation years.The reclaimed soil total free LF content of woodland was significantly higher than farmland and wasteland in 7 years of reclamation.Microbial activity may be more conducive to the accumulation of free LF in woodland compared with plant residues of surface soil in farmland.However,the total iPOM and total Mineral-C contents of farmland were the highest and were very significant positive correlation with R0.25 and SOC(p < 0.01).The results showed that the contents of iPOM and Mineral-C in 7 year of reclamation were mainly affected by the content of macroaggregate and soil organic carbon.(5)The proportion of total free LF content in soil organic carbon was 4.38%~10.72%.Although the free LF is very sensitive to tillage and land use,it is little relationship with agglomeration process due to the effects of plant and animal residues input,soil microclimate and soil surface conditions.Mineral-C accounted for the highest proportion(40.68%~49.18%)of soil organic carbon.The free LF growth rate was quick and then slow but the Mineral-C growth rate was slow and then quick with reclamation years.The results showed that organic carbon was first stored in free LF,and then transformed into iPOM and Mineral-C.The process of transformation and accumulation of organic carbon was closely related to the formation of soil aggregates and conform to "aggregate turnover" conceptual model. |
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