Abstract
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 language | English |
|---|---|
| Pages (from-to) | 3027-3050 |
| Number of pages | 36 |
| Journal | Biogeosciences |
| Volume | 14 |
| DOIs | |
| Publication status | Published - 2017 |
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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 journal › Article
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
VL - 14
SP - 3027
EP - 3050
JO - Biogeosciences
JF - Biogeosciences
SN - 1726-4170
ER -