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| Titel |
First on-line isotopic characterization of N2O above intensively managed grassland |
| VerfasserIn |
B. Wolf, L. Merbold, C. Decock, B. Tuzson, E. Harris, J. Six, L. Emmenegger, J. Mohn |
| Medientyp |
Artikel
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| Sprache |
Englisch
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| ISSN |
1726-4170
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| Digitales Dokument |
URL |
| Erschienen |
In: Biogeosciences ; 12, no. 8 ; Nr. 12, no. 8 (2015-04-29), S.2517-2531 |
| Datensatznummer |
250117916
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| Publikation (Nr.) |
 copernicus.org/bg-12-2517-2015.pdf |
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| Zusammenfassung |
The analysis of the four main isotopic N2O species
(14N14N16O, 14N15N16O,
15N14N16O, 14N14N18O) and especially the
intramolecular distribution of 15N ("site preference", SP) has been
suggested as a tool to distinguish source processes and to help constrain the
global N2O budget. However, current studies suffer from limited spatial
and temporal resolution capabilities due to the combination of discrete flask
sampling with subsequent laboratory-based mass-spectrometric analysis.
Quantum cascade laser absorption spectroscopy (QCLAS) allows the selective
high-precision analysis of N2O isotopic species at trace levels and is
suitable for in situ measurements.
Here, we present results from the first field campaign, conducted on an
intensively managed grassland site in central Switzerland. N2O mole fractions
and isotopic composition were determined in the atmospheric surface layer
(at 2.2 m height) at a high temporal resolution with a modified state-of-the-art
laser spectrometer connected to an automated N2O preconcentration unit.
The analytical performance was determined from repeated measurements of a
compressed air tank and resulted in measurement repeatability of 0.20, 0.12
and 0.11‰ for δ15Nα, δ15Nβ
and δ18O, respectively. Simultaneous eddy-covariance N2O flux
measurements were used to determine the flux-averaged isotopic signature of
soil-emitted N2O.
Our measurements indicate that, in general, nitrifier-denitrification and
denitrification were the prevalent sources of N2O during the campaign
and that variations in isotopic composition were due to alterations in
the extent to which N2O was reduced to N2 rather than to other pathways, such
as hydroxylamine oxidation. Management and rewetting events were
characterized by low values of the intramolecular 15N site preference
(SP), δ15Nbulk and δ18O, suggesting that nitrifier-denitrification and incomplete heterotrophic bacterial denitrification
responded most strongly to the induced disturbances. The flux-averaged isotopic
composition of N2O from intensively managed grassland was
6.9 ± 4.3, −17.4 ± 6.2 and 27.4 ± 3.6‰ for SP,
δ15Nbulk and δ18O, respectively. The approach
presented here is capable of providing long-term data sets also for other
N2O-emitting ecosystems, which can be used to further constrain global
N2O inventories. |
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