Hydrological processes govern methane flux fluctuations in a subtropical floodplain

Abstract

Floodplain methane (CH₄) emissions represent a significant component of the global CH₄ budget. However, their response to escalating extreme drought events remains poorly understood, mainly due to high temporal variability under alternating wet-dry conditions. To address this gap, we conducted two years of in-situ CH₄ flux measurements using the chamber technique across alternating hydrological cycles (2022–2023) in the Poyang Lake floodplain, during which the region experienced a prolonged drought. Our results showed that CH₄ emissions during non-flooding periods (1.82 ± 1.36 mg CH₄ m^–2 h^–1) (mean ± standard deviation) were significantly higher than those during flooding periods (1.26 ± 0.96 mg CH₄ m^–2 h^–1). Notably, CH₄ fluxes in the autumn growing period (2.04 ± 1.43 mg CH₄ m^–2 h^–1) were 35 % higher than in the spring (1.51 ± 1.21 mg CH₄ m^–2 h^–1) under drought conditions. Further analysis revealed that, apart from air temperature, CH₄ fluxes were primarily regulated by vegetation during non-flooding periods and by fluctuating water levels and flooding duration that influence biogeochemical processes during flooding periods. The enhanced temperature sensitivity of CH₄ emissions emerged as a key factor for the higher autumn emissions compared to spring, which is directly linked to the shortened flooding period in the Poyang Lake floodplain. These findings underscore the critical role of extreme drought in reshaping hydrological conditions and CH₄ emissions in floodplain wetlands, with important implications for predicting wetland responses under future climate change scenarios.