N2O from the Swiss midlands: regional sources and hot spots
Final Report Abstract
The Lead-Agency project between EMPA and KIT on “N2O from the Swiss midlands: regional sources and hot spots” focused on three main objectives: 1. Real-time analysis of N2O isotopic species (mainly EMPA); 2. Regionalization of N2O emissions (mainly KIT); 3. Atmospheric transport and inversion modelling (mainly EMPA). The underlying hypotheses of this project was that the isotopic composition of N2O can be used to identify source processes and that models can be developed which allow to simulate isotopic discrimination during N2O formation and consumption. In this project KIT was mainly responsible for developing the isotope modeling approach for N2O. For this we developed the first N2O isotope tracing model worldwide that considers site specific N2O isotopic composition, the so-called SIMONE model (Stable Isotope MOdel for Nutrient cyclEs). SIMONE allows to calculate isotopic fractionation of nitrogen compounds during the cycling of N in the plant-soil system. It calculates explicitly the N2O isotopic signal, thereby also considering the positioning of the heavy N in the linear N2O molecule (i.e. isotopomer formation). For the development of the SIMONE model, a thorough literature review was carried. For scaling isotopic fractionation to the ecosystem scale, SIMONE can be linked to biogeochemical models, i.e. models which simulate plantsoil and ecosystem N cycling and soil N gas emissions on basis of the underlying physico-chemical and plant-microbial physiological processes. SIMONE can be operated with daily or subdaily outputs of biogeochemical models, in our case the KIT model LandscapeDNDC, and produces predictions of the isotopic signal of the emitted N2O. To test that this complex model approach indeed produces reliable results, we applied the linked LandscapeDNDC – SIMONE model to sites at which measurements of the N2O isotopic composition were performed (Chamau and Beromünster sites, Switzerland, TERENO Fendt site, Germany; in the course of these measurements we developed an innovative approach how to directly measure the isotopic composition of emitted N2O by using automated chamber systems). These model applications showed, that the developed approach indeed allows to explain the observed variations in the isotopic signal of emitted N2O. Analyzing deviations between simulations and measurements allowed us to find weaknesses in process parameterizations of LandscapeDNDC, e.g. with regard to the representation of the microbial process of nitrification in the model. Thus, SIMONE and measurements of N2O isotopic composition opens up new ways to constrain process descriptions and to further narrow parametric uncertainties in complex biogeochemical models. While at first the coupled SIMONE-LandscapeDNDC model was only used and tested at site scale, we finally succeeded to run first regional scale simulations. With these regional simulations we will produce soil N2O emission fields at national scale (within this project for Switzerland), which do not only indicate the spatio-temporal variability of soil N2O emissions, but also its isotopic signature. Together with the N2O emission inventory produced by EMPA using measurements of atmospheric N2O mixing rations at the tall tower Beromünster and inverse transport modelling, the Swiss national N2O emission inventory will be refined. Overall, the realized approach within this project resulted in major progress in N2O isotopic measurements and modeling. The realized progress will allow to better constrain and trace sources of N2O. It, thus, also allows to be used to test mitigation options for N2O from agricultural sources, i.e. the dominating atmospheric N2O source.
Publications
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The nitrogen cycle: A review of isotope effects and isotope modeling approaches, Soil Biol. Biochem., 105, 121–137, 2017
Denk, T. R. A., Mohn, J., Decock, C., Lewicka-Szczebak, D., Harris, E., Butterbach-Bahl, K., Kiese, R. and Wolf, B.
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Tracking nitrous oxide emission processes at a suburban site with semicontinuous, in situmeasurements of isotopic composition, J. Geophys. Res., 122(3), 1850–1870, 2017
Harris, E., Henne, S., Hüglin, C., Zellweger, C., Tuzson, B., Ibraim, E., Emmenegger, L. and Mohn, J.
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Attribution of N2O sources in a grassland soil with laser spectroscopy based isotopocule analysis, Biogeosciences, 16, 3247–3266, 2018
Ibraim, E., Wolf, B., Harris, E., Gasche, R., Wei, J., Yu, L., Kiese, R., Eggleston, S., Butterbach- Bahl, K., Zeeman, M., Tuzson, B., Emmenegger, L., Six, J., Henne, S. and Mohn, J.
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Development of a field-deployable method for simultaneous, real-time measurements of the four most abundant N2O isotopocules, Isotopes Environ. Health Stud., 54(1), 1–15, 2018
Ibraim, E., Harris, E., Eyer, S., Tuzson, B., Emmenegger, L., Six, J. and Mohn, J.
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Constraining N cycling in the ecosystem model LandscapeDNDC with the stable isotope model SIMONE, Ecology, e02675, 2019
Denk, T. R. A., Kraus, D., Kiese, R., Butterbach-Bahl, K. and Wolf, B.
