Investigating Spatial And Temporal Variation And Climate Influence Of Atmospheric Methane Concentration At Zoige Wetland,China Using Remote Sensing Technology

Wetlands are the largest single natural source for methane(CH₄)emissions,representing 30%to 50%of the total CH₄ emissions budget.The emission fluctuations at wetlands could explain 70%of the substantial inter-annual anomalies in atmospheric CH₄concentration.Peatlands in the middle and high latitudes of the Northern Hemisphere have been regarded as the most crucial source of worldwide wetlands CH₄ emission.The peatlands are primarily located in cold regions where permafrost exists.As a result of the global change and possible warming,the permafrost in the middle and high latitudes of the Northern Hemisphere has begun to melt,releasing a large amount of CH₄.Increased concentration of CH₄ will exacerbate climate change and the climate change that,in turn,alters the intensity and spatial distribution of CH₄ emissions from peatlands or wetlands.Therefore,the analysis of spatiotemporal characteristics and influencing factors of wetland CH₄ concentrations can provide data support and theoretical basis for predicting the impact of further climate change on wetland CH₄ concentration and its feedback mechanism.The Zoige Plateau is located at the eastern edge of the Qinghai-Tibetan Plateau,China.Elevations of the plateau range from about 2400 to 5000 m above the mean sea level.The mean is?3500 m.The wetland in the plateau,approximately 4600 km²,consists mainly of peatland that is about 40%of the peat stock in China.The peatland is a typical alpine wetland on the Qinghai-Tibet Plateau and one of the largest alpine peatlands in the world.Therefore,the analysis of CH₄ emissions in the Zoige wetland will help understand the dynamic changes of CH₄ emissions in the Qinghai-Tibet Plateau and their impact on global climate change.The primary studies of this dissertation are summarized as follows:(1)The spatial and temporal characteristics of CH₄concentration at the Zoige wetland are revealed.The analysis of the spatiotemporal features of CH₄ concentration in wetlands is mainly focused on the studies of CH₄ concentrations in different regions of wetlands.The spatial and temporal characteristics of CH₄ concentration over the Zoige wetland from 2002 to 2018 are analyzed using the AIRS(Atmospheric Infrared Sounder)satellite data.The results show that the annual mean CH₄ concentration increased from1846.024 ppb(parts per billion)in 2002 to 1909.720 ppb in 2018.The growth rate is about 5.306 ppb/year.The growth rate of CH₄ concentration increased significantly over A₁(34°?35°N,101°?102°E)and A₄(33°?34°N,101°?102°E)cells.The A₉(32°?33°N,103°?104°E)cell has the lowest growth rate.The CH₄ concentration is gradually decreased as the latitude increased and varied with the vegetation distribution change in longitude.This conclusion can provide a reference for future estimation of CH₄ emission in wetlands.(2)The emission characteristics of CH₄ in growing and non-growing seasons are revealed.The spatiotemporal characteristics of CH₄ concentration over the A₅(33°?34°N,102°?103°E)cell from November 2018 to February 2021 are analyzed based on the TROPOMI(Tropospheric Monitoring Instrument)satellite data.From 2018 to 2021,the A₅ cell is an atmospheric CH₄ source in both growing and non-growing seasons.The contribution of CH₄ emission in the non-growing season to the annual sources is greater than that in the growing season.Changes in temperature,soil freezing/thawing processes,and dynamic changes in soil moisture lead to different CH₄ concentrations in the A₅ cell between the growing and non-growing seasons.This conclusion provides the information to support the future estimation of CH₄ concentration in the non-growing season.(3)The breaks of CH₄ time series data are detected and interpreted.The monitoring of wetland CH₄ emission is essential in the context of global CH₄ emission and climate change.The remotely sensed multitemporal AIRS CH₄ data and the BFAST(Breaks for Additive and Seasonal Trend)algorithm are used to detect the atmospheric CH₄ dynamics at the Zoige wetland,China,between 2002 and 2018.After decomposing the time-series of CH₄ data using the algorithm,a total of seven breaks are detected in the trend component of four cells.Because of a significant correlation between the air and soil temperatures and a significant correlation between the air temperature and soil moisture,extreme temperature change events are primarily responsible for the abrupt change of CH₄ concentration at the Zoige wetland.(4)The CH₄ concentration at cell A₅ before and after extreme events is analyzed to understand the events'influence on the concentration,using the TROPOMI data.Extreme events,altering the spatial distribution of temperature and rainfall,affect the CH₄concentration.However,the degrees of influence from different extreme events vary.Notably,the effects of extreme rainfall events differ from those of extreme temperature events in terms of the patterns of both time and magnitude.Excessive rainfall and extremely high temperature are predicted to favor higher CH₄ concentration.The extremely low temperature decreases the concentration.The response of CH₄concentration to extreme rainfall events is nearly real-time but has a long-term effect.The answer to extreme temperature changes is delayed,and the effect is short-term.When both events coincide,the rainfall affects the CH₄ concentration and its variation more than the temperature.