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| Titel |
Nitrite: the key to understanding nitrogen cycling in ammonium-rich systems? |
| VerfasserIn |
Naomi Wells, Kay Knöller, Vivien Hakoun, Serge Brouyère |
| Konferenz |
EGU General Assembly 2015
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| Medientyp |
Artikel
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| Sprache |
Englisch
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| Digitales Dokument |
PDF |
| Erschienen |
In: GRA - Volume 17 (2015) |
| Datensatznummer |
250113691
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| Publikation (Nr.) |
 EGU/EGU2015-13909.pdf |
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| Zusammenfassung |
| Mounting evidence for the importance of biological nitrogen (N) transformation pathways
that do not use or produce nitrate (NO3-) (e.g., anaerobic ammonium oxidation,
co-denitrification, and nitrifier-denitrification) necessitates the development of new
approaches for determining a system’s N balance. Efforts to parameterize groundwater N
cycling are typically based on measurements of only the dominant ions (ammonium (NH4+)
and NO3-), while isotope-based approaches rely on NO3- isotopes (δ15N and δ18O).
Looking beyond these two species, highly reactive nitrite (NO2-) is unlikely to account for
an appreciable proportion of the inorganic N pool (and thus generally assumed to be
insignificant). However, its role as a reactive intermediate makes it a potentially useful
indicator of all microbial N transformations.
The isotopic composition of NO2- (δ15N and δ18O) therefore could be useful for identifying
the N removal hotspots that would be missed by measuring only NO3- isotopes (i.e.
those not driven by denitrification). We explored this possibility by measuring the
variations in NO2- concentrations and isotopic composition from across NH4+ plumes
in two aquifers, one in eastern Germany (L: 40 wells, sampled thrice) and one in
western Belgium (C: 56 wells, sampled once). Nitrite concentrations were tightly
coupled with NH4+ concentrations in both locations, which had maximum values
of 100 mg NH4+-N and 0.3 mg NO2--N in L and 900 mg NH4+-N and 1 mg
NO2--N in C. The importance of NO2- reduction processes was determined by
comparing δ18O-NO2- data to the calculated range possible for in-situ nitrification
(ammonia oxidation and/or NO2- oxidation) based on the measured δ18O-H2O range.
Discontinuities between NO3- reduction zones and NO2- reduction zones were then used to
identify where N removal was driven by non-denitrification processes. Overall
NO2- isotopic values spanned a range of values two- to three-times greater than
that of either NO3- or NH4+. For instance, δ15N-NO2- ranged from -30oÂto
+80oÂin L and from -20oÂto +40oÂin C). While denitrification at the plume
fringe was the dominant N removal pathway in both systems, this NO2- data from
within the plumes reveals an unexpectedly dynamic N cycling that necessitates a
re-evaluation of our understanding of how biology handles N within NH4+ contaminated
groundwater. |
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