HR: 1340h
AN: B33E-1665    [Abstracts]
TI: New Approach to Estimate Daytime Ecosystem Respiration From Conventional Eddy Covariance Data Using Conditional Sampling Methods
AU: * Thomas, C K
EM: christoph.thomas@oregonstate.edu
AF: Department of Forest Science, Oregon State University, 321 Richardson Hall, Corvallis, OR 97330, United States
AU: Martin, J G
EM: jonathan.martin@oregonstate.edu
AF: Department of Forest Science, Oregon State University, 321 Richardson Hall, Corvallis, OR 97330, United States
AU: Siqueira, M B
EM: mbs4@duke.edu
AF: Nicholas School of the Environment and Earth Sciences, Duke University, Box 90328, Durham, NC 27708, United States
AU: Foken, T
EM: thomas.foken@uni-bayreuth.de
AF: Department of Micrometerology, University of Bayreuth, Universitaetsstr. 30, Bayreuth, 95440, Germany
AU: Law, B E
EM: bev.law@oregonstate.edu
AF: Department of Forest Science, Oregon State University, 321 Richardson Hall, Corvallis, OR 97330, United States
AU: Loescher, H W
EM: hank.loescher@oregonstate.edu
AF: Department of Forest Science, Oregon State University, 321 Richardson Hall, Corvallis, OR 97330, United States
AU: Katul, G G
EM: gaby@duke.edu
AF: Nicholas School of the Environment and Earth Sciences, Duke University, Box 90328, Durham, NC 27708, United States
AB: Daytime respiration from tall-forested ecosystems remains among the least understood components in the total carbon balance. These forests pose unique challenges to respiration measurements because of the large number of respiring organs, their complex vertical distribution and their high spatial variability in forest floor carbon dioxide efflux. The definition of the net vertical flux (F_N) as covariance between fluctuations of vertical velocity and perturbations in carbon dioxide density using the Eddy covariance (EC) technique does not lend itself to a formal decomposition into its 'ecologically desirable' component fluxes photosynthesis (F_A) and respiration (R_e) at daytime. Here, a new approach based on conditional sampling methods, quadrant analysis, and Relaxed Eddy Accumulation formulation is explored on carbon dioxide, water vapor, and vertical velocity time series to arrive at independent estimates of daytime R_e directly from conventional EC measurements. The conceptual framework is based on the assumption that organized updrafts carry an unambiguous imprint of different scalar sinks and sources within the canopy volume. The new method is tested against datasets from 4 coniferous and 1 deciduous sites in North America and Europe (4 AMERIFLUX, 1 FLUXNET) most of them providing multi-level EC measurements. Results from comparisons of i) daytime R_e against R_e = F_N at night, ii) temperature sensitivity coefficients (Q₁₀) and base respiration rates (R₁₀) derived from soil carbon dioxide efflux chambers and the new method, and iii) intercepts of light-response curves (F_N versus shortwave down-welling radiation) to bulk respiration at daytime showed the effectiveness of the proposed method at 3 out of the 5 sites. Limitations were posed by the dense canopy of the deciduous site, and possibly by a summer drought reducing the coherence of scalar exchange in the carbon dioxide and water vapor signals at one coniferous site. A predictive skill indicator based on simple metrics of the canopy (i.e. drag coefficient, leaf area density, and canopy height) was explored to identify success or failure. The new method has the potential to become a powerful tool for flux network data analysis and syntheses, as it can be applied to both existing and current high-frequency EC measurements to independently constrain ecosystem daytime respiration in addition to other methods.
DE: 0426 Biosphere/atmosphere interactions (0315)
DE: 0428 Carbon cycling (4806)
DE: 3307 Boundary layer processes
DE: 3379 Turbulence (4490)
SC: Biogeosciences [B]
MN: 2007 Fall Meeting