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| Titel |
The N-isotope effect and fractionation of nitrification in the tidal influenced Elbe River estuary, Germany |
| VerfasserIn |
Tina Sanders, Kirstin Dähnke |
| 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 |
250088517
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| Publikation (Nr.) |
 EGU/EGU2014-2625.pdf |
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| Zusammenfassung |
| Estuaries act as a nutrient filter for coastal waters. The eutrophic Elbe River estuary is loaded
with fertilizer-derived nitrogen, but management efforts have started to reduce this load
effectively. However, an internal nitrate source in turn gained in importance and the
estuary changed from a sink to a source of reactive nitrogen. Nitrification plays a
key role in this estuarine nutrient regeneration but has to be quantified. The aim
of our study was to assess the impact of nitrification on seasonal nitrogen loads
and turnover using stable N- isotopes to identify the natural fractionation factor of
nitrification.
Therefor we measured the dissolved inorganic nitrogen (ammonium, nitrite and nitrate),
their stable isotope signatures and the in-situ nitrification rates in the tidal influenced
part of the river during 9 cruises from August 2011 to August 2013. The DIN load
was higher in winter than in summer, the main compound was nitrate. In summer
concentrations of nitrate entering the estuary were between 50 and 100 μM and
δ15N and δ18O were enriched to 15.5 to 21.5 oand 7.5 to 11.5o respectively.
Strong nitrification was found in the Hamburg port region. The nitrate concentrations
increased significantly downstream after the port of Hamburg, along with a decrease of
isotope values. Ammonium and nitrite peaked in the Hamburg port region with up to
25μM and 12 μM, respectively. In July 2013, δ15N of ammonium has shown
a mean value of 16.2±3.3oand nitrite of -9.8±4.7oṪhe N-fractionation of
nitrification in July 2013 was 15Énit -10o the sub-process ammonia oxidation
15Éamox-24o and the nitrite oxidation of 15Éniox 13o while fractionation was less
pronounced during the other cruises Our data show that N-isotope fractionation
generally confirmed culture experiments, but that it strongly depended on discharge,
availability of substrate, temperature and the coupling of ammonia and nitrite oxidation. |
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