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 journalArticle

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    Abstract

    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
    JournalBiogeosciences
    Volume14
    DOIs
    Publication statusPublished - 2017

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    woodlands
    woodland
    advection
    eddy covariance
    uptake mechanisms
    net ecosystem exchange
    diel activity
    carbon
    flux measurement
    surface flux
    eddy
    photosynthesis
    drainage
    respiration
    uncertainty
    cooling
    methodology
    filter
    ecosystems
    ecosystem

    Cite this

    McHugh, Ian ; Beringer, Jason ; Cunningham, Shaun ; Baker, Patrick ; Cavagnaro, Timothy ; MAC NALLY, Ralph ; THOMPSON, Ross. / Interactions between nocturnal turbulent flux, storage and advection at an ‘ideal’ eucalypt woodland site. In: Biogeosciences. 2017 ; Vol. 14. pp. 3027-3050.
    @article{4d16989d2bda4c0c8a49a8f3accb4544,
    title = "Interactions between nocturnal turbulent flux, storage and advection at an ‘ideal’ eucalypt woodland site",
    abstract = "While the eddy covariance technique has becomean important technique for estimating long-term ecosystemcarbon balance, under certain conditions the measured turbulentflux of CO2 at a given height above an ecosystem doesnot represent the true surface flux. Profile systems have beendeployed to measure periodic storage of CO2 below the measurementheight, but have not been widely adopted. This ismost likely due to the additional expense and complexity andpossibly also the perception, given that net storage over intervalsexceeding 24 h is generally negligible, that these measurementsare not particularly important. In this study, weused a 3-year record of net ecosystem exchange of CO2 andsimultaneous measurements of CO2 storage to ascertain therelative contributions of turbulent CO2 flux, storage, and advection(calculated as a residual quantity) to the nocturnalCO2 balance and to quantify the effect of neglecting storage.The conditions at the site are in relative terms highlyfavourable for eddy covariance measurements, yet we founda substantial contribution (40 {\%}) of advection to nocturnalturbulent flux underestimation. The most likely mechanismfor advection is cooling-induced drainage flows, the effectsof which were observed in the storage measurements. Theremaining 60{\%} of flux underestimation was due to storageof CO2.We also showed that substantial underestimationof carbon uptake (approximately 80 gCm􀀀2 a􀀀1, or 25{\%} ofannual carbon uptake) arose when standard methods (u filtering)of nocturnal flux correction were implemented in theabsence of storage estimates. These biases were reduced toapproximately 40–45 gCm􀀀2 a􀀀1 when the filter was appliedover the entire diel period, but they were nonetheless largerelative to quantifiable uncertainties in the data. Neglect ofstorage also distorted the relationships between the CO2 exchangeprocesses (respiration and photosynthesis) and theirkey controls (light and temperature respectively). We concludethat the addition of storage measurements to eddy covariancesites with all but the lowest measurement heightsshould be a high priority for the flux measurement community.",
    author = "Ian McHugh and Jason Beringer and Shaun Cunningham and Patrick Baker and Timothy Cavagnaro and {MAC NALLY}, Ralph and Ross THOMPSON",
    year = "2017",
    doi = "10.5194/bg-2016-184",
    language = "English",
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    Interactions between nocturnal turbulent flux, storage and advection at an ‘ideal’ eucalypt woodland site. / McHugh, Ian; Beringer, Jason; Cunningham, Shaun; Baker, Patrick; Cavagnaro, Timothy; MAC NALLY, Ralph; THOMPSON, Ross.

    In: Biogeosciences, Vol. 14, 2017, p. 3027-3050.

    Research output: Contribution to journalArticle

    TY - JOUR

    T1 - Interactions between nocturnal turbulent flux, storage and advection at an ‘ideal’ eucalypt woodland site

    AU - McHugh, Ian

    AU - Beringer, Jason

    AU - Cunningham, Shaun

    AU - Baker, Patrick

    AU - Cavagnaro, Timothy

    AU - MAC NALLY, Ralph

    AU - THOMPSON, Ross

    PY - 2017

    Y1 - 2017

    N2 - While the eddy covariance technique has becomean important technique for estimating long-term ecosystemcarbon balance, under certain conditions the measured turbulentflux of CO2 at a given height above an ecosystem doesnot represent the true surface flux. Profile systems have beendeployed to measure periodic storage of CO2 below the measurementheight, but have not been widely adopted. This ismost likely due to the additional expense and complexity andpossibly also the perception, given that net storage over intervalsexceeding 24 h is generally negligible, that these measurementsare not particularly important. In this study, weused a 3-year record of net ecosystem exchange of CO2 andsimultaneous measurements of CO2 storage to ascertain therelative contributions of turbulent CO2 flux, storage, and advection(calculated as a residual quantity) to the nocturnalCO2 balance and to quantify the effect of neglecting storage.The conditions at the site are in relative terms highlyfavourable for eddy covariance measurements, yet we founda substantial contribution (40 %) of advection to nocturnalturbulent flux underestimation. The most likely mechanismfor advection is cooling-induced drainage flows, the effectsof which were observed in the storage measurements. Theremaining 60% of flux underestimation was due to storageof CO2.We also showed that substantial underestimationof carbon uptake (approximately 80 gCm􀀀2 a􀀀1, or 25% ofannual carbon uptake) arose when standard methods (u filtering)of nocturnal flux correction were implemented in theabsence of storage estimates. These biases were reduced toapproximately 40–45 gCm􀀀2 a􀀀1 when the filter was appliedover the entire diel period, but they were nonetheless largerelative to quantifiable uncertainties in the data. Neglect ofstorage also distorted the relationships between the CO2 exchangeprocesses (respiration and photosynthesis) and theirkey controls (light and temperature respectively). We concludethat the addition of storage measurements to eddy covariancesites with all but the lowest measurement heightsshould be a high priority for the flux measurement community.

    AB - While the eddy covariance technique has becomean important technique for estimating long-term ecosystemcarbon balance, under certain conditions the measured turbulentflux of CO2 at a given height above an ecosystem doesnot represent the true surface flux. Profile systems have beendeployed to measure periodic storage of CO2 below the measurementheight, but have not been widely adopted. This ismost likely due to the additional expense and complexity andpossibly also the perception, given that net storage over intervalsexceeding 24 h is generally negligible, that these measurementsare not particularly important. In this study, weused a 3-year record of net ecosystem exchange of CO2 andsimultaneous measurements of CO2 storage to ascertain therelative contributions of turbulent CO2 flux, storage, and advection(calculated as a residual quantity) to the nocturnalCO2 balance and to quantify the effect of neglecting storage.The conditions at the site are in relative terms highlyfavourable for eddy covariance measurements, yet we founda substantial contribution (40 %) of advection to nocturnalturbulent flux underestimation. The most likely mechanismfor advection is cooling-induced drainage flows, the effectsof which were observed in the storage measurements. Theremaining 60% of flux underestimation was due to storageof CO2.We also showed that substantial underestimationof carbon uptake (approximately 80 gCm􀀀2 a􀀀1, or 25% ofannual carbon uptake) arose when standard methods (u filtering)of nocturnal flux correction were implemented in theabsence of storage estimates. These biases were reduced toapproximately 40–45 gCm􀀀2 a􀀀1 when the filter was appliedover the entire diel period, but they were nonetheless largerelative to quantifiable uncertainties in the data. Neglect ofstorage also distorted the relationships between the CO2 exchangeprocesses (respiration and photosynthesis) and theirkey controls (light and temperature respectively). We concludethat the addition of storage measurements to eddy covariancesites with all but the lowest measurement heightsshould be a high priority for the flux measurement community.

    U2 - 10.5194/bg-2016-184

    DO - 10.5194/bg-2016-184

    M3 - Article

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    EP - 3050

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    JF - Biogeosciences

    SN - 1726-4170

    ER -