Diel greenhouse gas emissions demonstrate a strong response to vegetation patch types in a freshwater wetland

Abstract

Wetland methane (CH4) fluxes are highly variable over spatial and temporal scales due tovariations in the functional controls of CH4 production, oxidation, and transport. While some aspects of temporal variability in CH4 fluxes are well documented (like seasonal patterns), diurnal variability is still poorly constrained. Existing studies report conflicting evidence of diurnal patterns so we cannot make broad generalizations about diurnal patterns of CH4 flux. This is further confounded by the within-wetland spatial heterogeneity that characterizes many wetland systems: variations in topography, soil chemistry, hydrologic regime, and vegetation type can result in characteristically different “patches” that could likely influence existing diurnal patterns. Limited availability of nighttime data due to current methodological constraints also limits our ability to make broad generalizations about CH4 flux patterns. I investigated the diurnal patterns of CH4 fluxes in a seasonal-mineral soil wetland on the Delmarva Peninsula (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 potential relationship between physicochemical variables and flux patterns, we also measured a series of physicochemical variables including temperature (air and water), relative humidity, PAR, DO, etc. To my knowledge, this is the first study to compare diel variability across these three patch types. We found that diel patterns in wetland systems are strongly linked to the dominant vegetation cover of a patch, but whether these differences in patterns are a direct result of vegetation impact on production, oxidation and/or transport of CH4 or on patch-specific conditions that covary with patch type will require extended study. Ultimately, this study contributes to the growing understanding of how CH4 flux vary spatially over diel cycles.