AmeriFlux: Its Impact on our understanding of the ‘breathing of the biosphere’, after 25 years

Baldocchi, Dennis; Novick, Kim; Keenan, Trevor; Torn, Margaret

doi:10.1016/j.agrformet.2024.109929

Cited by 8 publications

(1 citation statement)

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“…In this context, vegetated canopies play an important role in both cycles through their contributions to evapotranspiration (ET ) and net CO 2 exchange (F c ). Facilitated by an extensive network of eddy-covariance (EC) towers setup across the globe, we are currently able to quantify the long-term budgets for both quantities over many land use types (Baldocchi, 2003;Baldocchi et al, 2001Baldocchi et al, , 2024Fisher et al, 2008;Hollinger et al, 2004;Novick et al, 2018). Nonetheless, long-term quantification of their individual soil (evaporation and respiration) and plant canopy (transpiration and photosynthesis) components is an equally important but much more challenging research goal.…”

Section: Introductionmentioning

confidence: 99%

Numerical Investigation of Observational Flux Partitioning Methods for Water Vapor and Carbon Dioxide

Zahn,

Ghannam,

Chamecki

et al. 2024

JGR Biogeosciences

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While yearly budgets of CO2 flux (Fc) and evapotranspiration (ET) above vegetation can be readily obtained from eddy‐covariance measurements, the separate quantification of their soil (respiration and evaporation) and canopy (photosynthesis and transpiration) components remains an elusive yet critical research objective. In this work, we investigate four methods to partition observed total fluxes into soil and plant sources: two new and two existing approaches that are based solely on analysis of conventional high frequency eddy‐covariance (EC) data. The physical validity of the assumptions of all four methods, as well as their performance under different scenarios, are tested with the aid of large‐eddy simulations, which are used to replicate eddy‐covariance field experiments. Our results indicate that canopies with large, exposed soil patches increase the mixing and correlation of scalars; this negatively impacts the performance of the partitioning methods, all of which require some degree of uncorrelatedness between CO2 and water vapor. In addition, best performances for all partitioning methods were found when all four flux components are non‐negligible, and measurements are collected close to the canopy top. Methods relying on the water‐use efficiency (W) perform better when W is known a priori, but are shown to be very sensitive to uncertainties in this input variable especially when canopy fluxes dominate. We conclude by showing how the correlation coefficient between CO2 and water vapor can be used to infer the reliability of different W parameterizations.

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