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Titel:
Uncertainty in CH4 and N2O emission estimates from a managed fen meadow using EC measurements
 
Auteur(s):
Kroon, P.S.; Hensen, A.; Jonker, H.; Veen, W.H. van 't; Vermeulen, A.T.; Ouwersloot, H.G.; Bosveld, F.C.
 
Gepubliceerd door: Publicatie datum:
ECN Biomassa, Kolen en Milieuonderzoek 4-2-2009
 
ECN publicatienummer: Publicatie type:
ECN-L--09-016 Presentatie
 
Aantal pagina's: Volledige tekst:
16 Download PDF  (953kB)

Gepresenteerd op: NitroEurope meeting, Gothenburg, Sweden, January 26-29th, 2009.

Samenvatting:
The overall uncertainty in annual flux estimates derived from chamber measurements may be as high as 50% due to the temporal and spatial variability in the fluxes (Flechard et al., 2005). As even a large number of chamber plots still cover typically less than 1% of the total field area, the field-scale integrated emission necessarily remains a matter of speculation (Flechard et al., 2005). High frequency micrometeorological methods are a good option for obtaining integrated estimates on a hectare scale with a continuous coverage in time. Instrumentation is now becoming available that meets the requirements for CH4 and N2O eddy covariance (EC) measurements. A system consisting of a quantum cascade laser (QCL) spectrometer and a sonic anemometer has recently been proven to be suitable for performing EC measurements (Kroon et al., 2007). This study analyses the EC flux measurements of CH4 and N2O and its corrections, like calibration, Webb-correction, and corrections for high and low frequency losses, and assesses the magnitude of the uncertainties associated with the precision of the measurement instruments, measurement set-up and the methodology. The uncertainty of one single EC flux measurement, a daily, monthly and 3-monthly average EC flux is estimated. In addition, the cumulative emission of C-CH4 and N-N2O and their uncertainties are determined over several fertilizing events at a dairy farm site in the Netherlands. These fertilizing events are selected from the continuously EC flux measurements from August 2006 to September 2008. The EC flux uncertainties are compared by the overall uncertainty in annual flux estimates derived from chamber measurements. It will be shown that EC flux measurements can decrease the overall uncertainty in annual flux estimates. Flechard et al., (2005), Bi-directional soil/atmosphere N2O exchange over two mown grassland system with contrasting management practices, Global Change Biology, 11, 2114-2127. Kroon et al., (2007), Suitability of quantum cascade laser spectroscopy for CH4 and N2O eddy covariance flux measurements, Biogeosciences, 4, 715-728.


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