A new Ameriflux site was established in 1997 on Vancouver Island, near Campbell River, British Columbia, Canada, to monitor the long-term carbon sequestration and water use by a 50-year old Douglas fir (Pseudotsuga menziesii) forest. This paper reports the eddy covariance fluxes of carbon dioxide, latent and sensible heat during the first year of operation. The trees are about 33 m tall and their diameter at breast height is about 33 cm. Due to its 5-10 degree slope and location about 9 km west of Georgia Strait, the site is influenced both by anabatic and katabatic winds and a land-sea circulation.
The eddy covariance sensors are mounted 43 m above the ground on a 51-cm triangular tower and consist of a 3-dimensional sonic anemometer (model R2, Gill Instruments), a krypton open-path hygrometer (model KH20, Campbell Scientific Inc.) and an infrared gas analyzer (IRGA) (model 6262, LI-COR Inc.). The IRGA is temperature-controlled and equipped with a 3-m heated sampling tube and a solenoid-valve system required for weekly calibration and zeroing. Climate instruments, including a net radiometer, quantum sensors, soil heat flux plates, soil and tree temperature sensors (thermocouples), raingauges and time domain reflectometry probes provide the supporting measurements. Power is supplied by a 3000 A-h 12-V battery system, recharged twice a week by a propane generator. Fluxes are calculated on-line by a PC, with raw data saved on magnetic tapes. Using modem/cellular phone communication, half-hour flux data are transmitted daily to the laboratory. All above operations are automated or controlled remotely, supplemented by monthly site visits.
Flux measurements have been made continuously since September 1997. Results so far indicate photosynthesis occurs throughout the year. Of particular interest are the strong diurnal variations of carbon dioxide and water vapor fluxes, even during the winter months. Maximum half-hourly averages of carbon dioxide uptake were as high as 18 micromol/(m2s) until the end of October and after the beginning of March. Daily uptake was largest in March, with an average of 1.6 g C/(m2d). So far, the only months with a net loss of carbon were December and January with values less than 0.1 and 0.2 g C/(m2d), respectively. A 6-day-period in January was the only time, when temperatures fell below freezing and photosynthetic rates were close to zero. The relationship between daytime carbon dioxide flux and photosynthetically active radiation was described best by a rectangular hyperbolic function.
During calm nights eddy fluxes of carbon dioxide were very small. These low values were likely due to mass flow resulting from cold air drainage down the slope. Low fluxes on calm nights are being corrected using respiration-temperature relationships obtained on windy nights. Average nighttime respiration rates on windy nights (wind speed > 1.9 m/s) were 2-3 micromol/(m2s) for soil temperatures of about 5 C. Preliminary results indicate that, during the daytime, energy balance closure was greater than 70% and Bowen ratios were about 1. Daily (24-h) evaporation rates during the September-March period commonly reached 2.1 mm/d, while the monthly averaged evaporation rates were 0.5-1.1 mm/d.