A critical review of wetland greenhouse gas measurement techniques and scaling considerations

The role of wetlands in terrestrial greenhouse gas fluxes is disproportionately large compared to the relatively small terrestrial area they encompass. There is an established and growing interest in accurately measuring these fluxes, and extrapolating inferences to larger spatial scales. However, a lack of uniformity in measurement approaches impedes progress because it is a challenge to synthesize data, parameterize models, and develop generalizable concepts from disparate data. Furthermore, pairing different methods can result in double-accounting and other aggregation errors. Our objective is to review gas flux measurement techniques and synthesize concepts, factors, and constraints associated with measuring and scaling greenhouse gas fluxes. This work will contribute to a conceptual framework designed to aid in the collection and use of gas flux data obtained by different methods. This review focuses specifically on wetlands which have both distinct transport processes and a unique biogeochemical environment, causing gas fluxes that are not prominent in other terrestrial or aquatic systems. We review techniques and implications of measuring at different steps along the soil-plant-atmosphere continuum; an emphasis of this work is identifying pathways and transit times for different fluxes in different wetland hydrogeomorphic settings. Measurement location along the path from source to atmosphere connotes the spatial and temporal scales at which a technique is applied, the spatiotemporal representation, and the factors that constrain extrapolation.