Lake waters often act as important methane sources for global greenhouse gas emission,but it would be more complex as lakes are regulated by rivers.In this study,seasonal variations of dissolved and emitted methane in the Poyang Lake,the largest freshwater lake in China,are investigated based on a specially designed monitoring.As a typical subtropical linking-to-river lake,the Poyang shows characteristics of the“lake”in wet season and the“river”in dry season alternatively over a year.Consequently,CH4 flux from the Poyang Lake to the Yangtze River closes to the highest in January due to concentrated dissolved CH4 and“river”effects in dry season,while CH4 flux to the atmosphere falls to the lowest in July because of intensified CH4 oxidization and diluted dissolved CH4 as well as“lake”effects in wet season.Overall,CH4 fluxes from Poyang Lake to the atmosphere and to the Yangtze River were 19 and 0.35 Gg CH4 yr-1,respectively.The Three Gorges Dam,the world's largest dam in the Yangtze River,would further intensify this pattern,enhancing the transformation between“lake phase”and“river phase”.This study also provides the paradigm for CH4 budget from other large lakes in similar situations around the world.