Modelling the Diurnal Variations of Methane Emissions from the Cyperus malaccensis Tidal Marsh in the Minjiang River Estuary

Abstract

Tidal marshes are important sources of atmospheric methane; however, the processes and mechanisms of diurnal methane flux variations in tidal marshes remain unclear. In this study, we modified the Walter model to simulate diurnal variations of methane fluxes in the Cyperus malaccensis tidal marsh in the Minjiang River Estuary. The sediment environmental variables, relative humidity (RH), and the tide level were considered in the modified model; the explicit difference scheme was applied for model calculation. Our simulated and observed results indicate that the methane fluxes are higher in non-inundation periods and lower in inundation periods, higher during the day and lower at night. Moreover, our simulation suggests that plant-mediated transport and ebullition are dominant pathways for methane emissions, and the diurnal variation patterns of methane fluxes are directly regulated by the tide level, sediment temperature, and RH. The model sensitivity tests suggest that methane fluxes are significantly influenced by the maximum potential methane production rate and various environmental variables. The model comparison indicates that our modifications have significantly improved the performance of the model in simulating diurnal variations of methane emissions in the C. malaccensis tidal marsh.