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| Titel |
Isotopomer mapping approach to determine N2O production pathways and N2O reduction |
| VerfasserIn |
Dominika Lewicka-Szczebak, Reinhard Well, Laura Cardenas, Roland Bol |
| Konferenz |
EGU General Assembly 2016
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| Medientyp |
Artikel
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| Sprache |
en
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| Digitales Dokument |
PDF |
| Erschienen |
In: GRA - Volume 18 (2016) |
| Datensatznummer |
250137176
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| Publikation (Nr.) |
 EGU/EGU2016-18379.pdf |
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| Zusammenfassung |
| Stable isotopomer analyses of soil-emitted N2O (δ15N, δ18Oand SP = 15N site preference
within the linear N2O molecule) may help to distinguish N2O production pathways and to
quantify N2O reduction to N2. Different N2O forming processes are characterised by distinct
isotopic characteristics. Bacterial denitrification shows significantly lower SP and
δ18Ovalues when compared to fungal denitrification and nitrification processes.
But SP and δ18Ovalues are also altered during N2O reduction to N2, when the
residual N2O is enriched in 18Oand centrally located 15N, resulting in increased
δ18Oand SP values. Hence, the interpretation of these isotope characteristics is not
straightforward, because higher δ18Oand SP values may be due to admixture of N2O
from fungal denitrification or nitrification, or due to N2O reduction to N2. One of
these processes, either admixture or reduction, can be quite well quantified if the
other one is determined with independent methods. But usually both processes are
unknown and the ability to estimate both of them simultaneously would be very
beneficial.
Here we present an attempt to determine both the admixture and the reduction
simultaneously using the isotopomer mapping, i.e. the relation between δ18Oand SP. The
measured sample points are typically situated between the two lines: reduction line with a
typical slope of about 0.35 and mixing line with a higher slope of about 0.8. Combining the
reduction and the mixing vector allows for the determination of both processes based on the
location of the sample point between the lines.
We tested this new approach for laboratory incubation studies, where a reference method
for N2O reduction quantification was applied, i.e. 15N gas flux method or incubations in He
atmosphere. This allowed us to check how well the calculated amounts for N2O reduction
agree with the results provided by the reference method. The general trend was quite well
reflected in our calculated results, however, quite often we deal with significant
underestimation of N2O reduction. This may be due to numerous sources of uncertainties,
especially for the assumed slopes for mixing and reduction lines. The slope of the
mixing line depends on the endmembers isotopic signatures which are represented by
quite wide ranges of values. The slope of the reduction line depends on the isotope
effects associated with N2O reduction which also represent possible ranges of values. |
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