Estimation of methane diffusion and ebullition flux and water environmental controls during flooding period in Lake Dongting wetlands

水体甲烷（CH4）主要通过气泡和扩散传输排放到大气，这两种途径在CH4总排放中的相对贡献及环境影响因子目前关注较少.本文以洞庭湖湿地3种生境类型（光滩、苔草、芦苇）为研究对象，通过静态箱法和扩散模型法估算洪水期CH4总排放通量、扩散排放通量和气泡排放通量，并分析其水体环境因子影响.结果表明：苔草地CH4总排放量最高，为6.49±3.12 mg（C）/（m2·h）.在3个生境中，CH4扩散排放占总排放通量的1.34%~3.91%，气泡排放占96.09%~98.66%.扩散排放通量受水体pH、电导率和水温的影响，而CH4的总排放和气泡排放主要受水温的影响.当水温低于11.7℃时，水体CH4以扩散排放为主，但当水温高于11.7℃时，水体CH4主要通过气泡排放.但这一温度阈值是否同样适用于其他类型湿地还需要更多实验验证.本研究对于揭示中低纬度内陆湖泊水体CH4排放过程有重要意义.;The main pathways of CH4 exchange between air and water are molecular diffusion and ebullition. However, the relative contribution of these two pathways to total methane emissions and their environmental controls are far from clear. In this paper, by using float static chamber and diffusion model, we measured the CH4 total emission flux (Ftotal), diffusion flux (Fdiff) and ebullitive flux (Febul) in three types of habitats (mudflat, Carex meadow and reed land) in Lake Dongting wetlands during flooding period. Further, the environmental controls on CH4 flux were analyzed through stepwise regression and linear regression model. The results showed that total CH4 emission flux was the highest in Carex meadow (6.49±3.12 mg (C)/(m2·h)) among three habitat types. The CH4 diffusion fluxes accounts for 1.34% to 3.91% to total CH4 emissions in the three sites, while the ebullitive flux contributed 96.09% to 98.66% to total CH4 emissions. The stepwise regression analysis between CH4 emission and environmental factors showed that CH4 diffusion flux was affected by water pH, conductivity and water temperature, while the total CH4 emission flux and CH4 ebullitive flux were mainly affected by water temperature. Furthermore, we found that water temperature determines the dominant emission pathway:when the water temperature was below 11.7℃, diffusion was the main way for CH4 emission otherwise ebullition pathway dominant the CH4 emission. However, whether this temperature threshold is equally applicable to other types of wetlands still requires more experimental verification. This study is important for revealing the mechanism of CH4 emissions in tropical and subtropical lakes.