The Impact Of Global Change On Peatlands Carbon Pool In Northern Great Khingan Mountains In Recent Hundred Years

Peatlands are a type of wetlands that have accumulated peat layers composed of incompletely decomposed plant residues.The northern peatlands store 540 Pg of organic carbon,accounting for nearly one-third of the total global soil carbon pool.The response mechanism of peatland soil carbon pool to global change is one of the important points for global carbon cycling.The Great Khingan Mountains is one of the main distribution areas of mountain peatland in China,and it is also acts as the southern edge of the northern peatland and permafrost regions in the world.In recent hundred years,the annual average temperature increase,the high frequency of wildfires,and the intensification of human activities in the Great Khingan Mountains area cause serious effects on the peatland soil carbon pool in the area.In order to detail analyze and reveal the impact of climate change and human activities on the accumulation process and stability of peatland soil carbon in the Great Khingan Mountains in the past 100 years,this thesis reconstructs historical variation of the stability of peatland soil carbon pool in the Great Khingan Mountains in the past 100 years.Combined with regional climate changes and human activities history,this thesis analyze the impacts of climate change and human activities on the stability of peatland soil carbon pools in mid-and highlatitude regions comprehensively.The results shown that although the thermal stability and chemical stability of peat soil organic matter are important factors to evaluate the stability of soil carbon pool.However,the increasing of high energy density polymers in peat soil,the thermal stability of peat soil are increases.However,due to high energy density polymers are more easily used by microorganisms,the increase in high energy density polymers also accelerate the decomposition rate of microorganisms,and the chemical stability of soil organic matter is reduced.Therefore,the chemical stability and thermal stability of the organic matter in peat soils show opposite trends,with the chemical stability increasing and the thermal stability decreasing,and vice versa.Because the chemical compositions of soil organic matter responds more directly to the process of microbial decomposition,the chemical stability reflected by the chemical composition of peat soil organic matter is widely used in the study of soil carbon pool stability.Temperature is the most important climatic factor that affecting the stability of peatland soil carbon pool.With the average July temperature increasing,the aromatic content in peat soils increases,while the polysaccharide content decreases,and therefore the carbon stability of the peatland soil carbon pool enhances markedly.Compared to the polysaccharides,aromatic compounds are more sensitive to climate factors change such as the precipitation and solar radiation.The effect of latitude gradient changes on the content of aromatic compounds in the soil is also more significant than that of polysaccharide compounds.In addition to climatic factors,wildfire is also acts as another major factor that affecting the stability of the peatland soil carbon pools.With the increasing of wildfire frequency,more low-polysaccharide/ high-aromatic compounds accumulate in the surface of peatland,which promote peatland carbon pools more stable.At the meantime,the pyrolysis carbon produced by wildfires deposited in the peat soil carbon pool,which also increase the contents of aromatic compounds and reduce the contents of polysaccharides,thereby increasing the stability of the peatland soil carbon pool.In the recent 100 years,the increase of human activities in the Greater Khingan Mountains not only led to an increase in the frequency of wildfires in this area,but also led to the deposition of a large number of polluting elements in peatland.Since the end of the 19 th century,the mining of the Yanzhigou placer gold mine has been one of the major human activities factors that influence the local peatland,and led to significant differences effects on the peatlands in different regions of the Greater Khingan Mountains.For example,when placer gold mining began to produce gold in the early of the 20th century,the pollutant elements fluxes in the western peatlands increased significantly.Pb isotopes also shown that the sources of Pb in the western region were mainly came from the local placer gold mining.The human effects on western peatlands which located closed to placer gold mining is significantly higher than the peatlands which located at far from the placer gold mine.With the implementation of environmentally friendly policies and the improvement of the gold mining process after1980,the pollutants produced by local anthropogenic sources were reduced,and Pb produced from China and South Asia/East Asia has gradually become the main Pb source in studied area,and has decrease the difference of the deposition fluxes of pollutant elements in the peatlands in different regions of the northern Great Khingan Mountains,and the deposition fluxes of these elements are also decreased significantly.Based on the integration of historical information on historical carbon pool recorded in multiple peat cores in the study area,it is clear shown that the climate change,wildfire frequency and regional human activities are act as important factors that affecting the accumulation process and stability of peatland carbon pool.Wildfires occurred more frequently at 1900-1980 than other periods,and high frequency of wildfire not only increased the carbon accumulation rate of peatlands in this area,but also increased the contents of aromatic compounds and reduced the contents of polysaccharides compounds in the soil carbon pool,and thereby increase the stability of the soil carbon pool of peatland in studied region.After 1980,with the implementation of forest fire prevention and other environmental friendly policies,the frequency of wildfire decreased,and cause the carbon accumulation rate of peatlands in this area decreased gradually.After 2000,the carbon accumulation rates in peatlands decreased gradually and closed to those before 1920 when the local human activities were weakly.During this period,the increase in temperature and the decrease in precipitation caused by climate change promoted the accumulation of more aromatic compounds in the peat soils in this area,and also led to a significant increase the contents of recalcitrant organic matter(Q2)and T50 in the organic matter after 1980.Therefore,the temperature increasing and precipitation decreasing in recent years led to a significant increase in the thermal and chemical stability of the soil carbon pool in peatlands in studied region.