Study On The Greenhouse Gas Emission Patterns And Influencing Mechanisms Of Subtropical And Temperate River

River floodplain,transition zone between aquatic and terrestrial ecosystem,is playing a vital role in carbon cycling and its processes.The range and frequency of temperature change and water level fluctuation are two important factors impacting carbon turnover and greenhouse gas emissions（especially CO₂and CH₄）.Thus,it is crucial to understand the carbon cycle of freshwater ecosystems under climate change to elucidate the characteristics and influencing mechanism of carbon emissions from river floodplain under changing temperature and water level conditions.This study analyzed the CO₂and CH₄emission from the air-water interface of typical rivers in Jiangsu Province（Nanjing）and Jilin Province（Changbai Mountain）,and then analyzed meteorological factors and water quality parameters to investigate the spatio-temporal variability and key influencing factors impacting potential of GHG emissions.Besides,benthic sediments from the Yangtze River floodplain and the river sediments from Changbai Mountain were selected for in-situ-laboratory incubation to explore the effects of temperature,and wet and dry treatment on the GHG emissions,hoping to provide reference for the study and estimation of carbon emissions from subtropical and temperate rivers.The main conclusions of the study are as follows:（1）From the perspective of GHG fluxes from the air-water interface of subtropical and temperate rivers,the CO₂and CH₄fluxes in Nanjing are larger in wet season（July and August）and smaller in normal season（September and October）,while those in Changbai Mountain are larger in normal season and smaller in the wet season.Temperature is the key meteorological factor,and pH and dissolved oxygen（DO）are the important water quality parameters affecting GHG emissions.（2）From the perspective of GHG emissions from sediments under different temperature,and wet and dry treatments,warming and drying and rewetting significantly increased the rate of GHG emissions in the studied rivers falling under subtropical and temperate climatic zone.Although,warming had a greater impact on temperate rivers,and drying and rewetting had a greater impact on subtropical rivers.The combination of warming and drying and rewetting had a greater impact on temperate rivers,which increased the equivalent of GHG emissions by 29.67 times.（3）According to the temperature sensitivity coefficient(Q₁₀),Q₁₀of subtropical and temperate soil respiration decreases with the increase in temperature and is more sensitive under low water levels.Subsequently,temperate soils are more sensitive to temperature,suggesting that temperate rivers have a higher GHG risk compared to subtropical.In conclusion,temperature and water level are important factors affecting CO₂and CH₄fluxes from the air-water interface.Both warming and drying and rewetting significantly increased GHG emissions from subtropical and temperate river sediments,and the combined effects of warming and drying and rewetting had a greater impact for temperate river sediments.Rapid increase in global warming and frequent change in extreme weather events,the response of carbon emissions from temperate rivers is more pronounced to climate change point of view,and the associated GHG risk cannot be ignored.