Diel Greenhouse Gas Emissions Demonstrate a Strong Response to Vegetation Patch Types in a Freshwater Wetland

Wetland methane (CH₄) fluxes are highly variable over spatial and temporal scales due to variations in CH₄ production, oxidation, and transport. While some aspects of temporal variability in CH₄ fluxes are well documented, diel variability is poorly constrained, and studies report conflicting findings, making it difficult to generalize. Topographic, geochemical, hydroclimatic, and vegetative variability can result in characteristically different “patches” that likely influence differences in diel patterns. We investigated diel patterns of CH₄ fluxes from a large seasonal-mineral soil wetland in Maryland (USA) across three functionally unique patches: two with vegetation (emergent and submerged aquatic vegetation) and one without (open water) during the summer of 2021. To explore the relationships between vegetation, environmental conditions, and flux patterns, we also measured physiochemical variables (air and water temperature, pH, relative humidity, PAR, dissolved oxygen, and water depth). To our knowledge, this is the first study comparing diel variability using chambers across such distinct vegetation patch types. We found that diel patterns were strongly linked to patch types: CH₄ fluxes from the emergent vegetation did not display a consistent diel pattern, while fluxes from the submerged vegetation and no vegetation patches frequently peaked at 13:00 and 05:00, respectively. These differences could be a direct result of vegetation impact on production, oxidation, and/or transport of CH₄ or on conditions covarying with patch type. This study contributes to the growing understanding of how CH₄ fluxes vary spatially over diel cycles and emphasizes the importance of considering spatially varying diel patterns when estimating fluxes.