Poster (Scientific congresses and symposiums)
Unexpected sensitivity of the annual net ecosystem exchange to the high frequency loss corrections in a grazed grassland site in Belgium
Mamadou, Ossénatou; Gourlez de la Motte, Louis; De Ligne, Anne et al.
2016European Geoscience Union genral assembly 2016
 

Files


Full Text
pp_OM_EGU2016.pdf
Author postprint (614.43 kB)
Download

All documents in ORBi are protected by a user license.

Send to



Details



Keywords :
Eddy covariance; cosprectral correction; Carbon dioxide; Net Ecosystem Exchange
Abstract :
[en] The eddy covariance technique is widely used to measure CO2 and other gas fluxes. However, eddy covariance fluxes are affected by systematic errors that must be corrected. Among them, high frequency loss corrections are particularly important in this regard, especially when using a closed-path infrared gas analyzer. In this study, we compared three approaches to do these corrections for CO2 fluxes and evaluated their impact on the carbon balance an intensively grazed grassland site in Belgium . In the first approach, the computation of correction factors was based on the measured sensible heat cospectra (‘local’ cospectra), whereas the other two were based on theoretical models (Kaimal et al., 1972). The correction approaches were validated by comparing the nighttime eddy covariance CO2 fluxes corrected with each approach and in situ soil respiration measurements. We found that the local cospectra differed from the Kaimal theoretical shape, although the site could not be considered ‘difficult’ (i.e., fairly flat, homogeneous, low vegetation, sufficient measurement height), appearing less peaked in the inertial subrange. This difference greatly affected the correction factor, especially for night fluxes. Night fluxes measured by eddy covariance were found to be in good accord with in situ soil respiration measurements when corrected with local cospectra and to be overestimated when corrected with Kaimal cospectra. As the difference between correction factors was larger in stable than unstable conditions, this acts as a selective systematic error and has an important impact on annual fluxes. On the basis of a 4-year average, at DTO the errors reach 71-150 g C m-2 y-1 for net ecosystem exchange (NEE), 280-562 g C m-2 y-1 for total ecosystem respiration (TER) and 209-412 g C m-2 y-1 for gross primary productivity (GPP), depending on the approach used. We finally encourage site PIs to check the cospectrum shape at their sites and, if necessary, compute frequency correction factors on the basis of local cospectra rather than on Kaimal cospectra.
Disciplines :
Environmental sciences & ecology
Author, co-author :
Mamadou, Ossénatou ;  Université de Liège > Ingénierie des biosystèmes (Biose) > Echanges Ecosystèmes - Atmosphère
Gourlez de la Motte, Louis ;  Université de Liège > Ingénierie des biosystèmes (Biose) > Echanges Ecosystèmes - Atmosphère
De Ligne, Anne ;  Université de Liège > Ingénierie des biosystèmes (Biose) > Echanges Ecosystèmes - Atmosphère
Heinesch, Bernard  ;  Université de Liège > Ingénierie des biosystèmes (Biose) > Echanges Ecosystèmes - Atmosphère
Aubinet, Marc ;  Université de Liège > Ingénierie des biosystèmes (Biose) > Echanges Ecosystèmes - Atmosphère
Language :
English
Title :
Unexpected sensitivity of the annual net ecosystem exchange to the high frequency loss corrections in a grazed grassland site in Belgium
Publication date :
2016
Event name :
European Geoscience Union genral assembly 2016
Event date :
du 18 Avril 2016 au 22 Avril 2016
Name of the research project :
Bilan carboné d’une exploitation agricole wallonne pratiquant le système allaitant.
Funders :
SPW DG03-DGARNE - Service Public de Wallonie. Direction Générale Opérationnelle Agriculture, Ressources naturelles et Environnement [BE]
Available on ORBi :
since 26 May 2016

Statistics


Number of views
74 (12 by ULiège)
Number of downloads
43 (5 by ULiège)

Bibliography


Similar publications



Contact ORBi