Biogeosciences
www.biogeosciences.net
1726-4170
1726-4189
4
5
2007
10.5194/bg-4-927-2007
http://www.biogeosciences.net/4/927/2007/
http://www.biogeosciences.net/4/927/2007/bg-4-927-2007.html
http://www.biogeosciences.net/4/927/2007/bg-4-927-2007.pdf
927
939
2007-10-26
Methodical study of nitrous oxide eddy covariance measurements using quantum cascade laser spectrometery over a Swiss forest
W. Eugster
werner.eugster@ipw.agrl.ethz.ch
K. Zeyer
M. Zeeman
P. Michna
A. Zingg
N. Buchmann
L. Emmenegger
Institute of Plant Sciences, ETH Zürich, 8092 Zürich, Switzerland
Empa, Swiss Federal Laboratories for Materials Testing and Research, Überlandstrasse 129, 8600 Dübendorf, Switzerland
Institute of Geography, University of Bern, 3012 Bern, Switzerland
WSL, Swiss Federal Institute for Forest, Snow, and Landscape Research, 8903 Birmensdorf, Switzerland
Nitrous oxide fluxes were measured at the Lägeren CarboEurope IP flux
site over the multi-species mixed forest dominated by European beech and
Norway spruce. Measurements were carried out during a four-week period in
October–November 2005 during leaf senescence. Fluxes were measured with a
standard ultrasonic anemometer in combination with a quantum cascade laser
absorption spectrometer that measured N<sub>2</sub>O, CO<sub>2</sub>, and H<sub>2</sub>O mixing
ratios simultaneously at 5 Hz time resolution. To distinguish insignificant
fluxes from significant ones it is proposed to use a new approach based on
the significance of the correlation coefficient between vertical wind speed
and mixing ratio fluctuations. This procedure eliminated roughly 56% of our
half-hourly fluxes. Based on the remaining, quality checked N<sub>2</sub>O
fluxes we quantified the mean efflux at 0.8±0.4 μmol m<sup>−2</sup> h<sup>−1</sup> (mean ± standard error). Most of the contribution to
the N<sub>2</sub>O flux occurred during a 6.5-h period starting 4.5 h
before each precipitation event. No relation with precipitation amount could
be found. Visibility data representing fog density and duration at the site
indicate that wetting of the canopy may have as strong an effect on
N<sub>2</sub>O effluxes as does below-ground microbial activity. It is
speculated that above-ground N<sub>2</sub>O production from the senescing leaves
at high moisture (fog, drizzle, onset of precipitation event) may be
responsible for part of the measured flux.
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