Eddy covariance measurements of carbon exchange and latent and sensible heat fluxes over a boreal lake for a full open‐water period

TLDR: In this paper, the authors applied the statistical criteria for CO2 concentration and vertical wind speed, averaging over a 5min period and selecting only the wind direction with longest fetch, to obtain lake-representative CO2 fluxes.

Abstract: was >0 W/m 2 at night and <0 W/m 2 in daytime. The latent heat flux dominated clearly over H in spring and summer; that is, the Bowen ratio was less than 1. Highermoment turbulence statistics proved to be efficient in detection of frequent nonstationary situations. Applying the statistical criteria for CO2 concentration and vertical wind speed, averaging over a 5-min period and selecting only the wind direction with longest fetch, we could obtain lake-representative CO2 fluxes. Footprint analysis based on a closure model revealed that the source areas were relatively short because of the presence of turbulence generated by the surrounding forest, compared to a larger lake with an extended smooth surface. We observed a net CO2 source of 0.2–0.4 mmol m � 2 s � 1 excluding July, when the flux was closer to zero. The results are consistent with the gradient method, based on more infrequent sampling, and both methods gave the same average flux, 0.2 mmol m � 2 s � 1 , over the whole open-water period.