Modeling nighttime ecosystem respiration from measured CO₂ concentration and air temperature profiles using inverse methods

Abstract

[1] A major challenge for quantifying ecosystem carbon budgets from micrometeorological methods remains nighttime ecosystem respiration. An earlier study utilized a constrained source optimization (CSO) method using inverse Lagrangian dispersion theory to infer the two components of ecosystem respiration (aboveground and forest floor) from measured mean CO 2 concentration profiles within the canopy. This method required measurements of within-canopy mean velocity statistics and did not consider local thermal stratification. We propose a Eulerian version of the CSO method (CSO E ) to account for local thermal stratification within the canopy for momentum and scalars using higher-order closure principles. This method uses simultaneous mean CO 2 concentration and air temperature profiles within the canopy and velocity statistics above the canopy as inputs. The CSO E was tested at a maturing loblolly pine plantation over a 3-year period with a mild drought (2001) The modeled ecosystem respiration exceeded estimates from eddy covariance measurements (uncorrected for storage fluxes) by at least 25%, even at high friction velocities. Finally, we showed that the CSO E annual nighttime respiration values agree well with independent estimates derived from the intercept of the ecosystem light-response curve from daytime eddy covariance CO 2 flux measurements.

Estimation of In-Canopy Ammonia Sources and Sinks in a Fertilized Zea mays Field

“…As described in SI sections S1 and S2, the measured NH 3 concentration gradients are always much larger than the corresponding temperature gradients. While the agreement between measured and modeled heat fluxes presented here is comparable to and in some cases exceeds the performance of other Eulerian and LNF techniques (22)(23)(24)(25)(26)(27)(28)(29)(30) in different canopies, it may not be truly indicative of the skill of the proposed method. Comparison to the flux of a nonreactive compound such as N 2 O, which is emitted only from the soil and at similar rates to NH 3 , would be more appropriate.…”

Scalar Concentration Profiles in the Canopy and Roughness Sublayer

“…Similar consideration of the source/sink distribution should also be applied for any other scalar including trace gases. For studies, such as estimating net ecosystem exchange, that require detailed knowledge of the scalar concentration profiles within the canopies alternative approaches such as multiply constrained optimization (Lai et al 2002) or second-order turbulence closures are more appropriate (Juang et al 2006). However if an alternative within-canopy scalar concentration model is available then it is relatively easily to substitute this for the within-canopy component of the model presented here.…”

“…Recognising this, Raupach (1989a,b) developed Localized Near Field theory (LNF) as the appropriate alternative to K -theory although other approaches have been proposed (e.g. constrained optimization (Lai et al 2002) or coupled second-order closure models (Juang et al 2006). LNF theory recognises that the scalar concentration at any point is the result of advection from near-field 1 sources and diffusion from sources further away.…”

On the Anomalous Behaviour of Scalar Flux–Variance Similarity Functions Within the Canopy Sub-layer of a Dense Alpine Forest

“…While much attention has thus far centered on the TKE budget and FV similarity functions for T and q (Hogstrom et al 1989;Leclerc et al 1990;Lamaud and Irvine 2006), there is growing interest in exploring FV similarity relationships for carbon dioxide concentration (C), in addition to T and q. Contemporary applications utilizing FV similarity functions for C include, (1) evaluating components of the turbulent CO 2 flux budget near the canopy top for testing higher-order turbulent closure models (Juang et al 2006), (2) developing alternative gap-filling methods for estimating annual carbon budgets (Choi et al 2004), (3) comparing turbulent transport efficiencies between CO 2 and other scalars such as T and q to inspect similarities in the transfer pathways near the ground.…”