The Relationship Between Peatland Water Table And The Degree Of Peat Decomposition From The Paleoecological Perspective

In recent years,global climate change marked by“global warming”has gradually attracted the general attention of scientists and all sectors of society.Carbon dioxide（CO2）is the main driving factor of climate change.Some studies have shown that the peat swamp ecosystem can not only significantly balance the global atmospheric carbon dioxide concentration,but also sensitively respond to changes in the climate system.This thesis selects four typical peatlands in Changbai Mountains,including Luo Tuo Li Zi,Tou Xi,Lao Fang Zi Shan and Heng Shan.The age-depth models are established by the 210Pb/137Cs dating technique and the water table depth is rebuild by testate amoebae and the established water table depth transfer function models,which can reveal the characteristics of modern water level changes of peatlands in Changbai Mountains.Using humification and elements analysis（H/C、C/N）to test the degree of peat decomposition,analyze the dynamic changing characteristics of modern peat decomposition and reveal the influence of water table depth on peat decomposition.The main conclusions are as follows:（1）The age-depth models of Luo Tuo Li Zi（LTLZ）,Tou Xi（TX）,Lao Fang Zi Shan（LFZ）,and Heng Shan（HS2021）are separately established by the ²¹⁰Pb/¹³⁷Cs dating technique.The peat profiles of them are 37 cm,38 cm,48 cm and 26 cm;the deposition histories are 269,215,186 and 216 years respectively;the rate of peat deposition are 0.14 cm year^-1,0.21 cm year^-1,0.40 cm year^-1,0.27.Among them,LTLZ and TX are herbal peat profiles while LFZ and HS2021 are peat moss profile.The peat moss profile has a relatively high deposition rate.（2）Compared with the herbal peat profile,the testate amoebae in peat moss profile have more species and abundance.The water table depth is rebuilt by testate amoebae and the established water table depth transfer function models.The results shows that the water table depth of the four peat profiles is consistent.The results indicate a shift to dry environment from 1750 to 1850;from 1851 to 1930,it briefly shifts to a humid environment;the dryness continues from 1931 to 2021.On the whole,the environment of Changbai Mountains is gradually drying.（3）The results of meteorological data and water table depth reconstruction show that precipitation and temperature have certain impact on water table depth.But due to the high altitude and overall low temperature in the Changbai Mountain area,the warming effect results in relatively weak evaporation.Therefore,precipitation has a relatively greater impact on water table depth.Moreover,data analysis suggests that meteorological factors may have a certain lag effect on the water table depth of peatland.（4）The degree of peat decomposition is influenced by decomposition time,water table depth and meteorological factors（precipitation and temperature）.The deeper the profile depth,the longer the decomposition time of peat,and the higher the degree of decomposition.Moreover,the degree of decomposition tends to stabilize after the profile reaches 22-23 cm.The higher the water table depth（i.e.the lower the water level）,the relatively higher the degree of peat decomposition.The impact of meteorological factors on decomposition degree is complicated.Due to the high altitude of the Changbai Mountain area,the temperature is relatively low and there is not much variation.And it is located in the East Asian monsoon region and the variation of precipitation is relatively large.Therefore,precipitation has a greater impact on the decomposition degree of peatlands.（5）In this thesis,three surrogate indicators,including C/N,H/C,and humification degree,are applied to indicate the degree of peat decomposition.Among them,C/N is greatly influenced by plant species and has little significance in indicating the degree of peat decomposition,especially in herbaceous peat profiles.Humification degree is easily interfered by decomposition time factors at the bottom（below about 23 cm）and surface（approximately the aerobic layer）of the profile,and its relationship with water table depth is not particularly close,but it is still a good indicator of peat decomposition degree.H/C has a more significant indication of the degree of peat decomposition,and its response to water table depth is also relatively close,especially when the humification degree of surface peat is disturbed by a short decomposition time,H/C shows a significant response to changes in water table depth.