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| Titel |
One method is not enough to determine denitrification in a Histic Gleysol following different grassland renovation techniques in Northwest Germany |
| VerfasserIn |
Reinhard Well, Caroline Buchen, Wolfram Eschenbach, Dominika Lewicka-Szczebak, Mirjam Helfrich, Andreas Gensior, Heinz Flessa |
| 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 |
250089863
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| Publikation (Nr.) |
 EGU/EGU2014-4076.pdf |
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| Zusammenfassung |
| Grassland renovation by reseeding is a common practices to improve productivity, but
knowledge on enhanced nitrate leaching and N2O emission due to disturbance during
associated soil tillage is scarce. Denitrification in hydromorphic soils under agricultural
management is potentially extremely high due to the coincidence of high nitrate
concentrations, labile organic carbon and oxygen depletion during extended periods of water
saturation close to the soil surface (Well et al. 2003; Well et al. 2005). We investigated the
impact of grassland renewal or conversion to arable land on greenhouse gas fluxes and N
losses in field plot experiments. One of the two sites is a hydromorphic soil (Histic Gleysol)
rich in organic C, with groundwater level always within the rooting zone and close to the
surface during winter. Assessment of the N budget to estimate enhanced N mineralization
following grassland renewal as well as associated N leaching is complicated by
potentially complete NO3- consumption via denitrification. Robust estimation on
denitrification losses at this site is crucial to assess the impact of grassland renewal on its N
dynamics and budget. One aim of this study is to determine denitrification in the
surface and subsoil in order to close the N budget. We apply five approaches to
investigate spatial and temporal dynamics of denitrification and will report first
results.
(1) N balance approach: The N budget is obtained by weekly measurement of N2O fluxes
and mineral N in the top soil, mineral N twice a year at 0 to 90 cm depth, N uptake, N
fertilization and modeling N leaching based on mineral N and hydrological model data.
Unaccounted N is attributed to possible denitrification.
(2) Isotopologue approach: δ18O, average δ15N and 15N site preference of N2O as well as
δ15N and δ18O of NO3- are measured at times to estimate N2O reduction to N2 in the topsoil
during periods of unsaturated conditions using the N2O isotope fractionation approach
(Lewicka-Szczebak et al., 2014).
(3) 15N gas flux method: N2 and N2O fluxes from denitrification will be measured
periodically by in situ 15N-labelling of soil mesocosms and analysing 15N enrichment of
emitted denitrification products (Lewicka-Szczebak et al., 2013). This is to validate results of
the isotope fractionation approach.
(4) Excess-N2 method for groundwater: During winter, dissolved N2 and Argon are
analysed to determine excess-N2 from denitrification (Blicher-Matthiesen et al., 1999;
Weymann et al., 2008). Loss of dissolved N2 by diffusion will be estimated by modeling
(Well et al., 2001).
(5) Emperical functions: Denitrification during phases of water-saturation is modeled
based on groundwater level data, organic C, C/N ratio, texture and pH using regression
functions for potential denitrification in hydromorphic soils (Well et al., 2003, Well et al,
2005).
All experimental approaches will be presented and first results of N2O isotopologues,
excess-N2 and modeling denitrification in the saturated zone will be reported.
References
Blicher-Mathiesen, G., McCarty, G. W. Nielsen, L. P. (1998): Denitrification and
degassing in groundwater estimated from dissolved dinitrogen and argon. Journal of
Hydrology 208(1–2): 16-24.
Lewicka-Szczebak, D., Well, R., Giesemann, A., Rohe, L., Wolf, U. (2013): An
enchanced technique for automated determination of 15N signatures of N2, (N2+N2O) and
N2O in gas samples. Rapid Commun Mass Sp 27, 1548-1558.
Lewicka-Szczebak, D., Well, R., Köster, J.R. , Senbayram, M. , Dittert, K., Fuß,R.,
Flessa, H. (2014): Experimental Determinations of Isotopic Fractionation Factors Associated
with N2O Production and Reduction during Denitrification, submitted to Geochimica and
Cosmochimica Acta.
Well R, Augustin J, Davis J, Griffith SM, Meyer K and Myrold DD (2001): Production
and transport of denitrification gases in shallow ground water. Nutrient Cycling in
Agroecosystems 60, 65 – 70.
Well R, Augustin J, Meyer K and Myrold DD (2003): Comparison of field and laboratory
measurement of denitrification and N2O production in the saturated zone of hydromorphic
soils. Soil Biology and Biochemistry 35, 783 – 799.
Well R, Höper H, Mehranfar O (2005): Denitrification in the saturated zone of
hydromorphic soils—laboratory measurement, regulating factors and stochastic modeling.
Soil Biology and Biochemistry 10, 1822-1836.
Weymann, D., R. Well, H. Flessa, C. von der Heide, M. Deurer, K. Meyer, Ch.
Konrad, and W.Walther (2008): Denitrification and Nitrous Oxide Accumulation in
Nitrate-Contaminated Aquifers estimated from dissolved Nitrate, Dinitrogen, Argon and
Nitrous Oxide. Biogeosciences 5, 1215–1226. |
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