Expert survey shows needs for standardized data processing and process-level understanding of chamber flux data

Quantifying spatial heterogeneity is important for the accurate measurement of broader scale greenhouse gas fluxes and can be done with relatively low construction costs using manual chambers. Existing guidelines on chamber measurements promote more standardized measurement and processing techniques but the extent to which they are implemented within the flux community is unknown. We aimed to identify major differences between the approaches for chamber methane fluxes used by different researchers. We conducted an expert survey to collect information on chamber-based methane flux measurements, including field sites, research questions, measurement setups and routines as well as data processing and quality control of data. We received 36 responses from researchers in North America, Europe, and Asia which indicated that most, but not all, of the respondents use recommended chamber designs, such as airtight sealing, fans, and a pressure vent. In addition, we asked about data processing and quality control of chamber flux data, presented a standardized set of methane concentrations from observed flux measurements and used this information for flux calculations. The responses showed broad disagreement among the experts on the processes resulting in nonlinear methane concentration increases and how to treat many non-linear and low fluxes. Based on the expert responses, we estimated an uncertainty of 17 to 28% across flux measurements due to researcher-based differences: different researchers deciding differently on discarding vs. accepting a measurement and choosing different time periods within the same measurement for flux calculation. This highlights the need to understand drivers of the concentration patterns visible from high-resolution analyzers and to develop standardized procedures and guidelines for future chamber methane flux measurements.