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| Titel |
Quantifying gross fluxes of nitrous oxide and dinitrogen gas using a novel isotope pool dilution technique |
| VerfasserIn |
Yit Arn Teh, Wendy Yang, Whendee L. Silver |
| Konferenz |
EGU General Assembly 2010
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| Medientyp |
Artikel
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| Sprache |
Englisch
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| Digitales Dokument |
PDF |
| Erschienen |
In: GRA - Volume 12 (2010) |
| Datensatznummer |
250039267
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| Zusammenfassung |
| One of the existing challenges in trace gas biogeochemistry lies in understanding the
environmental controls on the net and gross fluxes of soil-derived compounds. This is
because gross production and consumption fluxes of these gases often occur simultaneously
or in close spatial proximity, making it difficult to make inferences about the effects of
environmental variables (e.g. temperature, soil water content, porosity, redox, etc.) on gross
fluxes based on bulk concentration measurements alone. One novel approach for quantifying
gross fluxes of N2O and N2 is “stable isotope pool dilution;” a technique that has been
successfully applied to study bidirectional fluxes of other biogenic compounds, such as CH4
and halocarbons. To evaluate the efficacy of this method for quantifying gross N2O and N2
fluxes, we conducted a combined field and laboratory test of the pool dilution technique along
side conventional measures of nitrification and denitrification. Experiments were
conducted in a N-rich managed peatland pasture in the Sacramento-San Joaquin
Delta, California, USA. Field and laboratory measurements were performed in a
broad range of microforms and microtopes spanning a range of hydrologic and
environmental conditions. Field experiments focussed on gross fluxes of N2O and N2 in
upper soil horizons; the soil layers that exchange most rapidly with the atmosphere.
Laboratory experiments indicated that 15N pool dilution compares favourably with more
conventional measures of N2O and N2 flux, such as acetylene inhibition or the
15NO3- pulse-trace approach. Gross N2O fluxes greatly exceeded N2 fluxes by
as much as an order of magnitude or more, and averaged 6.1 ± 2.2 mg N m-2
d-1, with a range from 0.06 to 63.13 mg N m-2 d-1. N2O:N2 emissions ratios
generally exceeded 1 except along slopes, with an overall range of 0.2 to 30.9.
NH4+ concentrations and denitrifying enzyme activity were the best predictors
of gross N2O fluxes in the field (r2 = 0.65). Net N2O production rates explained
53 percent of the variability in gross N2 fluxes, whereas N2O:N2 ratios were best
predicted by the combination of water-filled pore space and mineral N concentration (r2
= 0.44). This research highlights the potential of the pool dilution approach for
quantifying gross fluxes of N2O and N2 from surface soils under both field and
laboratory conditions. Future experiments will couple these measures of soil surface
fluxes with push-pull methods for determining gross N2O and N2 fluxes at depth,
and natural abundance isotopomer measurements to determine sources of N2O. |
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