Influences of various calculation options on heat, water and carbon fluxes determined by open- and closed-path eddy covariance methods

Synthesis studies using multiple-site datasets for eddy covariance potentially contain uncertainties originating from the use of different flux calculation options, because the choice of the process for calculating half-hourly fluxes from raw time series data is left to individual researchers. In this study, we quantified the uncertainties associated with different flux calculation methods at seven sites. The differences in the half-hourly fluxes were small, generally of the order less than a few percentiles, but they were substantial for the annual fluxes. After the standardisation under current recommendations in the FLUXNET communities, we estimated the uncertainties in the annual fluxes associated with the flux calculations to be 2.6±2.7 W m⁻² (the mean 90% ± confidence interval) for the sensible heat flux, 72±37 g C m⁻² yr⁻¹ for net ecosystem exchange (NEE), 12±6% for evapotranspiration, 12±6% for gross primary productivity and 16±10% for ecosystem respiration. The self-heating correction strongly influenced the annual carbon balance (143±93 g C m⁻² yr⁻¹), not only for cold sites but also for warm sites, but did not fully account for differences between the open- and closed-path systems (413±189 g C m⁻² yr⁻¹).