• • Diurnal CH4 amplitude in Deqing is smaller than in Huzhou due to wetland influence; winter concentrations peak while autumn are lowest, with background seasonal order winter > spring > autumn > summer.
• • PSCF analysis reveals high CH4 potential sources in eastern Zhejiang, with seasonal shifts: spring in Yangtze River Delta and southeast coast, summer in southeastern Zhejiang, autumn minimal regional transport, winter in eastern Jiangxi.
• • Winter high CH4 values are attributed to weakened oxidation and stable atmospheric stratification; summer lows result from strong photochemical processes and vertical diffusion dilution.
• • Artificial aquaculture ponds and wetlands in Deqing emit higher CH4 concentrations and fluxes than Huzhou station area, leading to smaller diurnal amplitude and overall higher CH4 levels, especially during plum rain season.