Eddy Covariance Measurements
Water (H2O), carbon dioxide (CO2) and momentum fluxes were measured at the site with an Eddy Covariance (EC) system deployed at the meteorological tower from 7 June to 10 September. The EC system consisted of a 3D sonic anemometer (CSAT3; Campbell Scientific Inc., Logan, Utah, USA) and an open-path infrared CO2/H2O gas analyzer (IRGA) (LI-7500, LI-COR Inc., Lincoln, Nebraska, USA) mounted 3 m above the surface. Raw fluxes were sampled at a frequency of 10 Hz on a CR1000 datalogger (Campbell Scientific, Logan, Utah, USA) and averaged over a half-hour. All fluxes were corrected for density, sensor separation, time lag and coordinate rotation (double coordinate rotation was used) following common Fluxnet protocols (Webb, Pearman, & Leuning, 1980; Kaimal and Finnigan, 1994; Leuning and Judd, 1996; Foken and Leclerc, 2004; Aubinet et al., 2012; Burba et al., 2012). The resulting half-hour fluxes were then processed in a custom R-Software script, which filtered each half-hour to ensure that it had at least 80% of the high-frequency records and that there was no potential for dew formation on the IRGA lenses by either precipitation or by comparing the dew point temperature to Ta. Additional filtering removed values that were greater than ±3 standard deviations of a moving average, which consisted of 10 half-hour neighbouring values; further filtering was completed to check for physically improbable values. The Kljun, Calanca, Rotach, & Schmid (2015) footprint analysis was used to constrain the measured fluxes to be within 80% of the desired site boundaries, using their FFP R-functions. Thereafter, fluxes with a corresponding friction velocity (u*) of u* < 0.15ms-1 were removed from the dataset. Following this, the filtered net ecosystem exchange (NEE) data was gap-filled using the MDS method outlined in Reichstein et al. (2005); and then partitioned into respiration (R) and gross primary productivity (GPP) using the relationship between night-time respiration and Ta (Reichstein et al., 2005). The filtered energy fluxes were forced closed, with the additional energy partitioned based on the Bowen ratio (ß) (Wilson et al., 2002). ß is the ratio of sensible heat (Qh) to latent heat (Qe). For each available half-hour, Qe was gap-filled by scaling potential evapotranspiration, PET (Priestley and Taylor, 1972) to ET. The scaler (α) was calculated from the ratio between ET and PET. For periods where no α was available, the ratio was gap-filled using the MDS method outlined in Reichstein et al. (2005), where Q*, VPD, and u* were used as the gap-filling conditions; however, when this was not possible, the seasonal mean α was used. Qh was then gap-filled by solving the energy balance equation using the measured and gap-filled Q*, Qe and Qg.