Modeling the inhibition of dissolved H₂ on propionate fermentation and methanogenesis in wetland sediments

The complex interactions between hydrogen (H₂) and methane (CH₄) dynamics in wetland sediments are studied here with laboratory measurements supported by a methanogenesis model that includes interactions with H₂. Results from a series of 24-day incubation experiments producing CH₄ from wetland sediment slurries with different carbon-compound amendments and under different H₂ headspace partial pressures are presented. A simple model was formulated and calibrated to these experimental data, accounting for the interactions between propionate fermenters and H₂. This methanogenesis model is based on Michaelis-Menten and Monod kinetics with propionate as the only root exudate. While the biological interactions of CH₄ production of the model were based on and calibrated with the results of the batch experiments, the model was expanded to simulate the effects of other well-studied processes than control methanogenesis in wetlands and rice paddies: sulfate reduction, plant-mediated gas volatilization, and the presence or absence of a gas phase in sediments into which H₂ can partition. These common physical and microbial processes generally reduce the negative effects of the H₂ inhibition of propionate degradation in many scenarios, but there may still be some important situations where the inhibition of propionate degradation by H₂ may have significant controls over CH₄ production. More important, processes that aid in reducing the H₂ inhibition of propionate degradation, like plant induced venting, will result in less CH₄ production by hydrogenotrophic methanogens, which should be taken into account in established model formulations.