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| Titel |
Eddy covariance N2O flux measurements at low flux rates: results from the InGOS campaign in a Danish willow field. |
| VerfasserIn |
Andreas Ibrom, Christian Brümmer, Arjan Hensen, Hella van Asperen, Mette S. Carter, Rainer Gasche, Daniela Famulari, Werner Kutsch, Kim Pilegaard, Per Ambus |
| Konferenz |
EGU General Assembly 2014
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| Medientyp |
Artikel
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| Sprache |
Englisch
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| Digitales Dokument |
PDF |
| Erschienen |
In: GRA - Volume 16 (2014) |
| Datensatznummer |
250096464
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| Publikation (Nr.) |
 EGU/EGU2014-11972.pdf |
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| Zusammenfassung |
| Nitrous oxide (N2O) fluxes from soils are characterised by their high spatial and temporal
variability. The fluxes depend on the availability of the substrates for nitrification and
denitrification and soil physical and chemical conditions that control the metabolic microbial
activity. The sporadic nature of the fluxes and their high sensitivity to alterations of the soil
climate put very high demands on measurement approaches. Laser spectroscopy enables
accurate and fast response detection of atmospheric N2O concentrations and is used for eddy
covariance (EC) flux measurements. Alternatively N2O fluxes can be measured with
chambers together with high precision analysers. Differences in the measurement
approaches and system designs are expected to have a considerable influence on the
accuracy of the flux estimation. This study investigates how three different eddy
covariance systems perform in a situation of low N2O fluxes from a flat surface.
Chamber flux measurements with differing chamber and analyser designs are used for
comparison.
In April 2013, the EU research infrastructure project InGOS (http://www.ingos-infrastructure.eu/)
organised a campaign of N2O flux measurements in a willow plantation close to the Risø
Campus of the Technical University of Denmark. The willow field was harvested in February
2013 and received mineral fertiliser equivalent to 120 kg N ha-1 before the campaign
started. Three different eddy covariance systems took part in the campaign: two
Aerodyne quantum cascade laser (QCL) based systems and one Los Gatos Research
off-axis integrated-cavity-output spectroscopy (ICOS) system for N2O and CO. The
sonic anemometers were all installed at 2 m height above the bare ground. Gill R3
type sonic anemometers were used with QCL systems and a Gil HS-50 with the
ICOS system. The 10 Hz raw data were analysed with group specific softwares and
procedures.
The local conditions in the exceptionally cold and dry spring 2013 did not lead to large
N2O flux rates. All three EC systems showed 30 min. flux values varying around zero nmol
m-2 s-1. This noise was considerably lower in the EC systems that used QCL
analysers. The maximum daily averages of the uncorrected fluxes from two of the EC
systems reached 0.26 (ICOS/HS50) and 0.28 (QCL/R3) nmol m-2 s-1.Spectral
correction increased the flux estimates up to, e.g., 180% equivalent to 0.54 nmol m-2
s-1.
The flux estimates from the soil chambers were with one exception higher than the flux
estimates obtained from the EC systems with highest daily averages ranging from 0.1 up to 2
nmol m-2 s-1. These large differences were unexpected, because at least two of the EC
systems were shown to accurately measure fluxes at such higher levels at another InGOS
campaign in a fertilised Scottish grazed meadow. We use spectral analysis to examine the
raw data for the effects of sensor noise on the flux estimates and discuss strategies
on how to correct or account for it. Furthermore possible causes for the observed
differences between the observed EC and chamber flux estimates will be discussed. |
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