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| Titel |
Measurements of CO2 exchange with an automated chamber system throughout the year: challenges in measuring night-time respiration on porous peat soil |
| VerfasserIn |
M. Koskinen, K. Minkkinen, P. Ojanen, M. Kämäräinen, T. Laurila, A. Lohila |
| 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 ; 11, no. 2 ; Nr. 11, no. 2 (2014-01-28), S.347-363 |
| Datensatznummer |
250117147
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| Publikation (Nr.) |
 copernicus.org/bg-11-347-2014.pdf |
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| Zusammenfassung |
We built an automatic chamber system to measure greenhouse gas (GHG)
exchange in forested peatland ecosystems. We aimed to build a system
robust enough which would work throughout the year and could measure
through a changing snowpack in addition to producing annual GHG fluxes
by integrating the measurements without the need of using models. The
system worked rather well throughout the year, but it was not service
free. Gap filling of data was still necessary.
We observed problems in carbon dioxide (CO2) respiration flux estimation
during calm summer nights, when a CO2 concentration gradient
from soil/moss system to atmosphere builds up. Chambers greatly
overestimated the night-time respiration. This was due to the
disturbance caused by the chamber to the soil-moss CO2
gradient and consequent initial pulse of CO2 to the chamber
headspace. We tested different flux calculation and measurement
methods to solve this problem. The estimated flux was strongly
dependent on (1) the starting point of the fit after closing the chamber, (2)
the length of the fit, (3) the type of the fit (linear and polynomial), (4)
the speed of the fan mixing the air inside the chamber, and (5) atmospheric
turbulence (friction velocity, u*). The best fitting method (the most robust, least random variation) for respiration measurements on our sites was
linear fitting with the period of 120–240 s after chamber
closure. Furthermore, the fan should be adjusted to spin at minimum
speed to avoid the pulse-effect, but it should be kept on to ensure
mixing. If night-time problems cannot be solved, emissions can be
estimated using daytime data from opaque chambers. |
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