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www.biogeosciences-discuss.net/7/503/2010/
doi:10.5194/bgd-7-503-2010
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Kinetics of N2O production and reduction in a nitrate-contaminated aquifer inferred from laboratory incubation experiments
1Soil Science of Temperate and Boreal Ecosystems, Büsgen-Institute, University of Göttingen, Büsgenweg 2, 37077 Göttingen, Germany
2Department of Soil Physics, Helmholtz Centre for Environmental Research – UFZ, Theodor-Lieser-Str. 4, 06120 Halle (Saale), Germany
3Institute of Agricultural Climate Research, Johann Heinrich von Thünen-Institute, Bundesallee 50, 38116 Braunschweig, Germany
4Institute of Soil Science, University of Hannover, Herrenhäuser Str. 2, 30419 Hannover, Germany
Abstract. Knowledge of the kinetics of N2O production and reduction in groundwater is essential for the assessment of potential indirect emissions of the greenhouse gas. In this study, we investigated this kinetics using a laboratory approach. The results were compared to field measurements in order to examine their transferability to the in situ conditions. The study site was the unconfined, predominantly sandy Fuhrberger Feld aquifer in Northern Germany. A special characteristic of the aquifer is the occurrence of the vertically separated process zones of heterotrophic denitrification in the surface groundwater and of autotrophic denitrification in the deeper groundwater, respectively. The kinetics of N2O production and reduction in both process zones was studied during long-term anaerobic laboratory incubations of aquifer slurries using the 15N tracer technique. We measured N2O, N2 and NO3− concentrations as well as parameters of the aquifer material that were related to the relevant electron donors, i.e. organic carbon and sulfur. The anaerobic incubations showed a low denitrification activity of heterotrophic denitrification with initial rates between 0.0002 and 0.0133 mg N kg−1 day−1. The process was carbon limited due to the poor availability of its electron donor. In the autotrophic denitrification zone, initial denitrification rates were considerably higher, ranging between 0.0303 and 0.1480 mg N kg−1 d−1 and NO3− as well as N2O were completely removed within 60 to 198 days. N2O accumulated during heterotrophic and autotrophic denitrification, but maximum concentrations were substantially higher during the autotrophic process. The results revealed a satisfactory transferability of the laboratory incubations to the field scale for autotrophic denitrification, whereas the heterotrophic process less reflected the field conditions due to considerably lower N2O accumulation during laboratory incubation. Finally, we applied a conventional model using first-order-kinetics to determine the reaction rates of the NO3−-to-N2O step and the N2O-to-N2 step, and evaluated the reaction rate constants for both steps. The model yielded fits to the experimental data that were of limited goodness, indicating that a more sophisticated approach is essential to describe the investigated reaction kinetics satisfactorily.
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Notice on Discussion StatusCitation: Weymann, D., Geistlinger, H., Well, R., von der Heide, C., and Flessa, H.: Kinetics of N2O production and reduction in a nitrate-contaminated aquifer inferred from laboratory incubation experiments, Biogeosciences Discuss., 7, 503-543, doi:10.5194/bgd-7-503-2010, 2010. Bibtex EndNote Reference Manager XML
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