HR: 15:35h
AN: B43C-08    [Abstracts]
TI: Constraining Night Time Ecosystem Respiration by Inverse Approaches
AU: * Juang, J
EM: jj19@duke.edu
AF: Nicholas School of the Environment and Earth Sciences, Duke University, Box 90328, Durham, NC 27708 United States
AU: Stoy, P C
EM: pcs3@duke.edu
AF: Nicholas School of the Environment and Earth Sciences, Duke University, Box 90328, Durham, NC 27708 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: 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: Estimating nighttime ecosystem respiration remains a key challenge in quantifying ecosystem carbon budgets. Currently, nighttime eddy-covariance (EC) flux measurements are plagued by uncertainties often attributed to poor mixing within the canopy volume, non-turbulent transport of CO$_{2}$ into and out of the canopy, and non-stationarity and intermittency. Here, we explore the use of second-order closure models to estimate nighttime ecosystem respiration by mathematically linking sources of CO$_{2}$ to mean concentration profiles via the continuity and the CO$_{2}$ flux budget equation modified to include thermal stratification. By forcing this model to match, in a root-mean squared sense, the nighttime measured mean CO$_{2}$ concentration profiles within the canopy the above ground CO$_{2}$ production and forest floor respiration can be estimated via multi-dimensional optimization techniques. We show that in a maturing pine and a mature hardwood forest, these optimized CO$_{2}$ sources are (1) consistently larger than the eddy covariance flux measurements above the canopy, and (2) agree well with chamber-based measurements. We also show that by linking the optimized nighttime ecosystem respiration to temperature measurements, the estimated annual ecosystem respiration from this approach agrees well with biometric estimates, at least when compared to eddy-covariance methods conditioned on a friction velocity threshold. The difference between the annual ecosystem respiration obtained by this optimization method and the friction-velocity thresholded night-time EC fluxes can be as large as 700 g C m$^{-2}$ (in 2003) for the maturing pine forest, which is about 40% of the ecosystem respiration. For 2001 and 2002, the annual ecosystem respiration differences between the EC-based and the proposed approach were on the order of 300 to 400 g C m$^{-2}$.
DE: 1615 Biogeochemical processes (4805)
DE: 0315 Biosphere/atmosphere interactions
DE: 0400 Biogeosciences
SC: Biogeosciences [B]
MN: 2004 AGU Fall Meeting