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| Titel |
Tall tower landscape scale N2O flux measurements in a Danish agricultural and urban, coastal area |
| VerfasserIn |
Andreas Ibrom, Émeline Lequy, Benjamin Loubet, Kim Pilegaard, Per Ambus |
| Konferenz |
EGU General Assembly 2015
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| Medientyp |
Artikel
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| Sprache |
Englisch
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| Digitales Dokument |
PDF |
| Erschienen |
In: GRA - Volume 17 (2015) |
| Datensatznummer |
250110830
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| Publikation (Nr.) |
 EGU/EGU2015-10870.pdf |
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| Zusammenfassung |
| Both technical and natural processes emit the greenhouse gas nitrous oxide (N2O) into the
atmosphere. The abundant use of nitrogen (N) as fertiliser increases the concentration of
reactive nitrogen (Nr) in the atmosphere, the hydrosphere and in the biosphere, i.e. in
terrestrial and aquatic ecosystems. Surplus Nr is distributed across linkages to other
spheres until most of it is emitted to the atmosphere as NO, N2O or N2. A complete
estimate of the effects from human activities on N2O emissions must therefore
include all emissions, the direct emissions and the indirect emissions that happen in
interlinked spheres. For this it is necessary to assess the fluxes at least at the landscape
scale.
The episodic nature and the large spatial variability make it difficult to estimate
the direct and indirect emissions in a landscape. Modelling requires not only to
include the highly variable microbial processes in the ecosystems that produce N2O
but as well the accurate simulation of lateral Nr fluxes and their effects on N2O
fluxes in places remote from the primary Nr sources. In this context tall tower N2O
flux measurements are particularly useful as they integrate over larger areas and
can be run, continuously without disturbing the fluxes. On the other hand these
measurements can be difficult to interpret due to difficulties to measure the small
concentration fluctuations in the atmosphere at small flux rates and to accurately attribute
the measured flux at the tower to the area that generates the flux, i.e. the source
area.
The Technical University of Denmark (DTU) has established eddy covariance N2O flux
measurements on a 125 m tall tower at its Risø Campus as part of the EU research
infrastructure project the ’Integrated non-CO2 Greenhouse gas Observing System’ (InGOS).
The eddy covariance system consisted of a N2O/CO quantum cascade laser, Los Gatos,
Mountain View, CA, USA and a 3D sonic anemometer (USA-1), Metek, Elmshorn,
Germany.
The Risø peninsula lies at the eastern coastline of the Roskilde fjord on the Danish island
Zealand. The tower is surrounded by the fjord, by agricultural area, forests and, in the South
by the urban area of the City of Roskilde. The City of Roskilde operates a waste
incinerator and a waste water treatment plant, which drains treated waste water into the
fjord.
The level of the measured flux values was generally relatively low. Based on the clear
definition of the lag time between N2O concentrations and the vertical wind speed, fluxes
were measureable over larger periods. The fluxes showed clear directional relationships
indicating their large spatial and temporal variability in the landscape. Footprint calculations
were performed to attribute source areas to the measured fluxes ...(Kormann and Meixner,
2001; Neftel et al., 2008). The footprint of the flux measurement included areas between 200
m and several kilometres distance from the tower. A preliminary approach was
developed to generate monthly maps of N2O fluxes around the tower. Here we
present the results from the first seven months of flux measurements. Based on these
results we discuss the potential and the limitations of tall tower eddy covariance
measurements to estimate maps of N2O fluxes and the integral value of the landscape N2O
flux.
Acknowledgements: This work was funded by the EU-FP7 InGOS project. We thank
Ebba Dellwik (Technical University of Denmark) for providing sonic anemometer
data.
References:
Kormann, R. and Meixner, F.X., 2001. An Analytical Footprint Model For Non-Neutral
Stratification. Boundary-Layer Meteorology, 99(2): 207-224.
Neftel, A., Spirig, C. and Ammann, C., 2008. Application and test of a simple tool
for operational footprint evaluations. Environmental Pollution, 152(3): 644-652. |
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