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| Titel |
First real-time measurements of N2O isotopic signatures above intensively managed grassland: analytical performance, validation and illustrative examples |
| VerfasserIn |
Benjamin Wolf, Béla Tuzson, Lutz Merbold, Charlotte Decock, Lukas Emmenegger, Joachim Mohn |
| 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 |
250091873
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| Publikation (Nr.) |
 EGU/EGU2014-6188.pdf |
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| Zusammenfassung |
| Measurement of the four main N2O isotopic species (14N15N16O / 15N14N16O / 14N14N18O
/ 14N14N16O) has been suggested as a powerful tool to trace the biogeochemical cycle of
N2O and to allocate its emission sources. Studies carried out with microbial pure cultures
and mixed population systems (Wunderlin et al. 2012) allowed the determination
of characteristic isotopic signatures for the most important production processes.
These characteristic signatures have been applied to identify relevant sources at
different scales (Park et al. 2012). However, current studies suffer from limited
spatial and temporal resolution due to the combination of discrete flask sampling
in conjunction with laboratory-based mass spectrometric analysis. We recently
demonstrated that a quantum cascade laser (QCL) based absorption spectrometer
is capable of simultaneously measuring the three main N2O isotopomers at trace
levels (Waechter et al. 2008). Furthermore, its potential for in-situ measurements in
conjunction with a liquid nitrogen-free preconcentration unit has been proven (Mohn et al.
2012).
Here we present results from the first long-term field measurement campaign conducted
on intensively managed grassland in central Switzerland during three months. A modified
state-of-the-art laser spectrometer (Aerodyne Research, Inc.) employing a mid-infrared
cw-QCL (4.54 μm) and a novel astigmatic multipass cell with 204 m optical path-length was
connected to a N2O preconcentration unit. High analytical performance in combination with
the applied calibration strategy resulted in excellent long-term precision of 0.20, 0.12 and
0.11ofor δ15Nα, δ15Nβ and δ18O which was determined from repeated preconcentration
and measurement of target gas from a compressed air tank. This instrumental setup
allowed investigating responses of isotopic composition in soil-emitted N2O to
management events and weather influences. The accompanying measurements of soil
temperature, soil water content, ammonia, and nitrate concentrations made the
identification of controls on N2O isotopic composition possible. Furthermore, simultaneous
eddy-covariance N2O flux measurements (Merbold et al. 2014) were used to derive a
flux-averaged isotopic signature of soil-emitted N2O of intensively managed grassland. In
this context, the potential of the derived N2O isotopic signatures for partitioning
of microbial source processes will be discussed in relation to available literature
data.
Merbold, L, W Eugster, J Stieger, M Zahniser, D Nelson and N Buchmann. 2014.
“Greenhouse gas budget (CO2, CH4 and N2O) of intensively managed grassland following
restoration” Global Change Biology doi:10.1111/gcb.12518
Mohn, J, B Tuzson, A Manninen, N Yoshida, S Toyoda, W A Brand, and L
Emmenegger. 2012. “Site selective real-time measurements of atmospheric N2O
isotopomers by laser spectroscopy.” Atmospheric Measurement Techniques 5(7):
1601–1609
Park, S, P Croteau, K A Boering, D M Etheridge, D Ferretti, P J Fraser, K-R Kim, P B
Krummel, R L Langenfelds, T D van Ommen, L P Steele, and C M Trudinger. 2012. “Trends
and seasonal cycles in the isotopic composition of nitrous oxide since 1940.” Nature
Geoscience 5(4): 261–265.
Waechter, H, J Mohn, B Tuzson, L Emmenegger, and M W Sigrist. 2008. “Determination
of N2O isotopomers with quantum cascade laser based absorption spectroscopy.” Optics
Express 16(12): 9239–44.
Wunderlin, P, M Lehmann, H Siegrist, B Tuzson, A Joss, L Emmenegger, and J Mohn.
2013. “Isotope signatures of N2O in a mixed microbial population system: Constraints on
N2O producing pathways in wastewater treatment.” Environmental Science and Technology
47: 1339-48. |
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