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| Titel |
The effect of atmospheric turbulence and chamber deployment period on autochamber CO2 and CH4 flux measurements in an ombrotrophic peatland |
| VerfasserIn |
D. Y. F. Lai, N. T. Roulet, E. R. Humphreys, T. R. Moore, M. Dalva |
| Medientyp |
Artikel
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| Sprache |
Englisch
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| ISSN |
1726-4170
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| Digitales Dokument |
URL |
| Erschienen |
In: Biogeosciences ; 9, no. 8 ; Nr. 9, no. 8 (2012-08-24), S.3305-3322 |
| Datensatznummer |
250007249
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| Publikation (Nr.) |
 copernicus.org/bg-9-3305-2012.pdf |
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| Zusammenfassung |
| Accurate quantification of soil-atmosphere gas exchange is essential for
understanding the magnitude and controls of greenhouse gas emissions. We
used an automatic, closed, dynamic chamber system to measure the fluxes of
CO2 and CH4 for several years at the ombrotrophic Mer Bleue
peatland near Ottawa, Canada and found that atmospheric turbulence and
chamber deployment period had a considerable influence on the observed flux
rates. With a short deployment period of 2.5 min, CH4 flux
exhibited strong diel patterns and both CH4 and nighttime CO2
effluxes were highly and negatively correlated with ambient friction
velocity as were the CO2 concentration gradients in the top 20 cm of
peat. This suggests winds were flushing the very porous and relatively dry
near-surface peat layers and reducing the belowground gas concentration
gradient, which then led to flux underestimations owing to a decrease in
turbulence inside the headspace during chamber deployment compared to the
ambient windy conditions. We found a 9 to 57% underestimate of the net
biological CH4 flux at any time of day and a 13 to 21% underestimate
of nighttime CO2 effluxes in highly turbulent conditions. Conversely,
there was evidence of an overestimation of ~ 100% of net
biological CH4 and nighttime CO2 fluxes in calm atmospheric
conditions possibly due to enhanced near-surface gas concentration gradient
by mixing of chamber headspace air by fans. These problems were resolved by
extending the deployment period to 30 min. After 13 min of chamber
closure, the flux rate of CH4 and nighttime CO2 became constant
and were not affected by turbulence thereafter, yielding a reliable estimate
of the net biological fluxes. The measurement biases we observed likely
exist to some extent in all chamber flux measurements made on porous and
aerated substrate, such as peatlands, organic soils in tundra and forests,
and snow-covered surfaces, but would be difficult to detect unless high
frequency, semi-continuous observations were made. |
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