Observation And Simulation Of Greenhouse Gas Exchange Between The Atmosphere And The Permafrost Peatland Of The Great Hing'an Mountains,Northeast China

The IPCC climate change report pointed out that the northern area is sensitive to climate change.Climate change has significantly influenced the thermal and hydrological conditions.In the last few decades,the increasing of global temperature resulted in the continuous degradation of permafrost in the northern area.Northern peatland stored 1/3 of global soil carbon.Under cliamte change,northern peatland is very likely to transform from carbon sink to carbon source and thus has positive feedbacks on global climate change.For now,the research concerning influence of global climate change on carbon balance of northern peatland is rare.Under this condition,the eddy covariance method was applied to observe the growing season net ecosystem exchange of CO₂ and CH₄ between a typical permafrost peatland in the Great Hing'an Mountains and the atmosphere during year 2014 2016,relative environmental factors were also collected simultaneously.Theories and methods of the observation were discussed and then promoted to achieve a goal of exploring and revealling patterns of greenhouse exchange.Taking observed dataset as referenc,statistic models and processe oriented were used seperately to simulate the CO₂ and CH₄ exchanges.Statistic models were promoted and validated based on localized condition,the estabilished models with localized dynamic parameters were applicable to simulate the CO₂ and CH₄ exchanges.The main recognitions and innovations of this study are as follows.1 More strict quantily control creteria were applied in order to fit the need of model research.When the purposes come to explore and reveal greenhouse exchane patterns,the regular filtering and gapfilling procedures used to manipulate calculated fluxes are no longer appropriate.Strictly filtering creteria of footprint analysis and turbulence stationarity test were applied to promote the qualinty and reduce the uncertainty of calculated fluxes.Most influencing factors were observed to have a unimodal distribution on different temporal scale.Under these conditions,CO₂ exchange displays clear daily variations.Besides,CH₄ also shows a significant diurnal variation when emission rates are relatively high.2 CH₄ exchange patterns and controlling facors of permafrost peatlands were revealed.Methane fluxes during 2014 and 2015 growing season were within the range of 1.8 40.2 mg CH₄ m-2 d-1 and-3.9 15.0 mg CH₄ m-2 d-1,respectively.CH₄ fluxes during the growing seasons were significantly correlated with thawing depth and soil temperatures below 15 cm depth.The CH₄ emission after Jul 25 th accounted for 77.9% of total growing season emission in 2014 and 85.9% in 2015.A standardlized thawing depth was added to classic exponential temperature response CH₄ emission equation as a controlling factor,which could promote the precision of the equation.CH₄ emission exihibited great inter-annual variations,which was probably controlled by permafrost seasonal thawing and precipitation volume.3 CO₂ exchange patterns and controlling facors of permafrost peatlands were revealed.The classic Michaelis-Menten equation was proved to be suitable to interprete light response of photosynthesis rate in study area.Besides,intense light caused photoinhibition could lead to reduce of photosynthesis rate.Parameters in the Michaelis-Menten equation exihibited unimodal distribution on seasonal scale.Combined with Lloyd-Taylor respiration equation and Michaelis-Menten equation,with validated parameters,modelled CO₂ fluxes were within the range of-4.42 2.90 g C m-2 d-1.The ecosystem scale maxmiun apparent quantum yield of photosynthesis was around 0.049 mol CO₂ mol photon-1.The theoretical maxmiun photosynthesis rate was determided to be around 24.77 ?mol CO₂ m-2 s-1.The observed maxmiun net ecosystem CO₂ exchange was around-15 ?mol CO₂ m-2 s-1.In late August of every modelled growing season,the permafrost peatland turned from a CO₂ sink to a source.4 CO₂ exchange between atmosphere and permafrost peatland under warming scenarios were predicted.A passive experimental warming device set up in study area could help to predict how environmental factors change under climate change.According to the recorded data,the open top chamber could warm air temperature and 5 cm depth soil temperature by about 0.81 °C and 2.42 °C,respectively.Under this condition,a series of experimental warming scenarios was set and the simulations indicated that when air temperatue increase about 0.67 °C and 5 cm depth soil temperature increase about 2.0 °C,the study area turned into CO₂ source on yearly scale;when air temperatue increase about 1.0 °C and 5 cm depth soil temperature increase about 3.0 °C,the study area turned into CO₂ source on growing season scale.