Contributions of diffusion and ebullition processes to total methane fluxes from a subtropical rice paddy field in southeastern China

Abstract

Diffusion and ebullition are two important processes regulating methane (CH₄) emission from rice fields. Studies on diffusion and ebullition CH₄ fluxes can provide the scientific foundation for better investigating the impact of climate change on CH₄ emission. In this study, we measured CH₄ fluxes using the static chamber (CC) and eddy covariation (EC) methods over a subtropical rice paddy field in southeastern China in 2021 and 2022. In addition, the diffusive and ebullition fluxes of CH₄ were quantified according to CC measurements and estimations from EC data using the wavelet analysis (WW) method. The total and diffusive fluxes obtained by CC and WW methods were both significantly correlated at the hourly and daily scales. However, the correlation between ebullition fluxes obtained by CC and WW methods was insignificant. The CC measurements indicated that the dominant role of the diffusive process in contributing to CH₄ fluxes, accounting for 89 % and 91 % of the total CH₄ flux in rice paddy in 2021 and 2022, respectively. The total, diffusive, and ebullition CH₄ fluxes all peaked at 13:00. Air temperature and water table depth acted as the most important factors regulating the seasonal variations of total and diffusive CH₄ fluxes at this rice field. Overall, the study provided valuable insights into the CH₄ flux dynamics in rice paddies, which can inform the development of process-based models for simulating CH₄ emission in rice paddies.