Interactions between nocturnal turbulent flux, storage and advection at an ‘ideal’ eucalypt woodland site

Ian McHugh, Jason Beringer, Shaun Cunningham, Patrick Baker, Timothy Cavagnaro, Ralph MAC NALLY, Ross THOMPSON

    Research output: Contribution to journalArticlepeer-review

    16 Citations (Scopus)
    11 Downloads (Pure)


    While the eddy covariance technique has become
    an important technique for estimating long-term ecosystem
    carbon balance, under certain conditions the measured turbulent
    flux of CO2 at a given height above an ecosystem does
    not represent the true surface flux. Profile systems have been
    deployed to measure periodic storage of CO2 below the measurement
    height, but have not been widely adopted. This is
    most likely due to the additional expense and complexity and
    possibly also the perception, given that net storage over intervals
    exceeding 24 h is generally negligible, that these measurements
    are not particularly important. In this study, we
    used a 3-year record of net ecosystem exchange of CO2 and
    simultaneous measurements of CO2 storage to ascertain the
    relative contributions of turbulent CO2 flux, storage, and advection
    (calculated as a residual quantity) to the nocturnal
    CO2 balance and to quantify the effect of neglecting storage.
    The conditions at the site are in relative terms highly
    favourable for eddy covariance measurements, yet we found
    a substantial contribution (40 %) of advection to nocturnal
    turbulent flux underestimation. The most likely mechanism
    for advection is cooling-induced drainage flows, the effects
    of which were observed in the storage measurements. The
    remaining 60% of flux underestimation was due to storage
    of CO2.We also showed that substantial underestimation
    of carbon uptake (approximately 80 gCm􀀀2 a􀀀1, or 25% of
    annual carbon uptake) arose when standard methods (u filtering)
    of nocturnal flux correction were implemented in the
    absence of storage estimates. These biases were reduced to
    approximately 40–45 gCm􀀀2 a􀀀1 when the filter was applied
    over the entire diel period, but they were nonetheless large
    relative to quantifiable uncertainties in the data. Neglect of
    storage also distorted the relationships between the CO2 exchange
    processes (respiration and photosynthesis) and their
    key controls (light and temperature respectively). We conclude
    that the addition of storage measurements to eddy covariance
    sites with all but the lowest measurement heights
    should be a high priority for the flux measurement community.
    Original languageEnglish
    Pages (from-to)3027-3050
    Number of pages36
    Publication statusPublished - 2017

    Fingerprint Dive into the research topics of 'Interactions between nocturnal turbulent flux, storage and advection at an ‘ideal’ eucalypt woodland site'. Together they form a unique fingerprint.

    Cite this