We estimated additional soil respiration carbon losses during year 1 using a
combination of chamber, eddy covariance, and modeling approaches. Chamber
measurements of soil respiration were made at six sites within the eddy covariance tower
footprint four times a day, for a total of eight days between the 5th and 26th of July 1999.
A LI-COR 6200 portable photosynthesis system was used in conjunction with a 20 cm
diameter (8 L Plexiglas) chamber within which the air was circulated using a pair of slow
moving 50 mm fans (6). The chamber was allowed to equilibrate to ambient pressure via
a 20 cm length of 1 mm inner diameter copper tubing mounted through the top of the
chamber. Each measurement consisted of ten CO2 concentration observations at eightsecond
intervals. A regression of CO2 with time was then performed from which
respiration estimates were made based on chamber temperature, humidity, and ambient
pressure. For each measurement the chamber was clamped to pre-installed PVC collars
that were each left in position for the duration of the measurement period.