Rainfall can significantly reduce pond methane emissions by depressing ebullition

Small freshwater bodies like ponds are recognised as hotspots of methane (CH₄) emissions. However, the impact of rainfall on pond CH₄ emissions remains largely unknown. Here we studied the impact of different rainfall events on CH₄ fluxes from an urban pond through continuous and high-frequency measurements of CH₄ ebullition and diffusion across an entire rainy season, which included 15 rainfall events with precipitation ranging from 3.5 to 66.9 mm. The mean total CH₄ emission flux (ebullition and diffusion) decreased from 7.1 ± 3.5 mg m^-2 h^-1 before rainfall to 3.9 ± 2.7 mg m^-2 h^-1 after rainfall, and recovered gradually 12 h after the end of rainfall. This significant decline was likely caused by the air temperature drop accompanied by rainfall and the dilution effect of rainwater. Cumulatively, excluding the impact of rainfall resulted in a 35.3 % overestimation of total CH₄ emissions, with CH₄ ebullition contributing 90.4 % of this overestimation. Given the expected increase in rainfall and significant CH₄ emissions in the rainy season worldwide, high-frequency and long-term measurements of CH₄ diffusion and ebullition during and shortly after rainfall should help improve the global estimates of small water CH₄ emissions.