Methane emissions from wetlands are temporally dynamic. Relatively few chamber-based studies have explored diurnal variation in methane flux with high replication across a range of conditions. Using an automated gas-flux sampling system, we measured methane flux every 2.5–4 hours for 205 diel cycles during three growing seasons (2013–2015) from a seasonal wetland in the Prairie Pothole Region of North America. The wetland underwent changes in hydrological states throughout growing seasons that ranged from ponded, semi-saturated and dry conditions. Covariates air and soil temperature, soil water-filled pore space and PAR were measured continuously at the automated flux system.
Results/Conclusions
During ponded conditions, fluxes were generally positive (i.e., methanogenesis dominant), with the highest fluxes occurring during late day and lowest at pre-dawn. In contrast, during dry conditions, fluxes were primarily negative (i.e., oxidation dominant), with the lowest (most negative) fluxes occurring during late day and highest at pre-dawn. During semi-saturated conditions, methane fluxes oscillated between positive and negative values (i.e., balance between methanogenesis and methane oxidation) and exhibited no diel pattern. Methane flux was correlated positively with air temperature during ponded conditions (r = 0.57) and negatively during dry conditions (r = -0.42). Multiple regression analyses showed that temperature, light and water-filled pore space explained 72% of variation in methane flux. Methane fluxes follow distinct diel patterns dependent on dominant microbial processes, which are influenced by saturation state and temperature. Despite differences in diel patterns, average flux rates generally occurred around midday.