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B41A-12
Estimating Nocturnal Respiration from Profile Measurements in a Subalpine Forest

* Anderson, D E
deander@usgs.gov
U.S. Geological Survey, M.S. 413, Federal Center, Denver, CO 80225-0046 United States

Turnipseed, A A
aturnip@stripe.colorado.edu
E.P.O. Biology, University of Colorado, Boulder, CO 80236 United States

Estimates of nocturnal respiration of forest ecosystems derived from vertical profile measurements of carbon dioxide (CO$_{2}$) concentration and wind velocity offer an effective means of supplementing, or at times, replacing eddy covariance and chamber measurements. For example, under near calm conditions, stable atmospheric stratification leads to situations in which application of eddy covariance methodology is ill-suited. An alternative approach under these conditions is to sum changes in subcanopy airspace storage and advection of CO$_{2}$ to estimate ecosystem respiration. Profile measurements of wind velocity and CO$_{2}$ concentration were conducted in a subalpine forest (mostly lodgepole pine, ingleman spruce, and aspen) on sloping (6-7\%) terrain, about 8 km east of the continental divide, northwest of Boulder, Colorado. The profiles were measured from three locations at multiple levels, ranging from 1m above ground to 33m (more than twice canopy height). All measurements were averaged over half-hour intervals. A single infrared gas analyzer, located 73m from either profile location, measured concentrations from which change in storage and advection were calculated. Under typical nocturnal conditions during the growing season (May-Sept.), katabatic winds develop near sunset and strengthen during the night reaching 0.5-0.9 m/s. Due to considerable temporal variability in wind speed and in CO$_{2}$ concentration, advective and storage fluxes were highly variable. Mid-summer concentration differences with downslope distance typically averaged about 0.1 ppm/m between heights of 1-6m. Advective flux was typically several times larger than storage flux, ranging from about 5-15 micromole/m$^{2}$/s shortly after drainage (katabatic) flow began, then decreasing through the night with temperature. On nearly calm nights during the May-August 2001 growing season, advective flux often reached about one-third the daytime uptake by the forest.


0315 Biosphere/atmosphere interactions
1615 Biogeochemical processes (4805) 3307 Boundary layer processes
3322 Land/atmosphere interactions
2001 AGU Fall Meeting