Filling the Gaps: How Much Gap Filling Is Needed in the Ameriflux Network

Quality control methods are used on eddy covariance flux tower measurements in order to guarantee the highest quality data possible. According to Falge et al. 2001, eddy covariance measurements result in 65% resulting data gaps. These gaps can be filtered out due to low turbulent flow, precipitation impact to open-path gas analyzers, spikes due to instrument error, lack stationarity, electronic noise, sensor malfunctions, or loss of power (Mauder et al. 2013). The AmeriFlux network is a long-term flux measurement network that requires significant quality control. The gaps created by these quality control procedures can cause issues with long-term questions pertaining to specific ecosystems to researchers, and cause uncertainty when gap-filling methods are employed. To assess the quality of individual sites, statistical tests were used to determine the percentage of observations that require gap filling methodologies in the AmeriFlux network. Missing data statistics were stratified by land cover, land management, and climate zone to assess reliability of the observational network as a function of ecosystem characteristics. The results provide researchers with an estimate of overall data quality due to gaps in flux measurements, which is necessary prior to analysis of fluxes across sites and years.