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| Titel |
Isotope investigations of nitrification dynamics in the Elbe River and in pure cultures of nitrifying bacteria |
| VerfasserIn |
Juliane Jacob, Tina Sanders, Kirstin Dähnke |
| Konferenz |
EGU General Assembly 2013
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| Medientyp |
Artikel
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| Sprache |
Englisch
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| Digitales Dokument |
PDF |
| Erschienen |
In: GRA - Volume 15 (2013) |
| Datensatznummer |
250076321
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| Zusammenfassung |
| Since the onset of industrialisation, the nutrient input to aquatic systems is significally
enhanced. This leads to high nitrogen loads in rivers, which drain densely populated
catchments, and an increased eutrophication pressure on coastal water bodies. Along the river
– estuary – continuum, nitrogen processing in aquatic environments has the potential to alter
river loads significantly. Especially nitrification, the stepwise oxidation of ammonium to
nitrite and further to nitrate, is important, because it can create additional nitrate from freshly
remineralized organic matter, but also represents the link to subsequent removal via
denitrification.
Stable isotopes are a valuable tool to track overlapping source and sink processes in
natural environments: Changes in stable isotope ratios can be attributed to the corresponding
turnover processes, if the corresponding isotope effects are carefully assessed. However, the
data base on N and O isotope fractionation in natural environments and during specific
turnover processes is scarce. Thus we aimed to better understand the isotope dynamics of
nitrification, assigning specific fractionation factors to environmentally relevant bacterial
species.
Besides N and O isotope analyses of river nitrate over an annual cycle, we performed
incubation experiments with pure cultures and river water.
Biweekly water samples from the Elbe River (Northern Germany) were taken to analyse,
among other parameters, the seasonal variations of δ15N and δ18O in nitrate, corresponding
nitrification rates and isotope effects during nitrification. While changes in δ15N and δ18O
suggest phytoplankton assimilation as the main turnover process, incubations of
river water reveal the relevance of nutrient regeneration via nitrification, which
increase 15-fold with the onset of spring. In these incubations, we analysed rates
of ammonium and nitrite oxidation and the corresponding isotope fractionation
factors.
Additional experiments with newly isolated nitrospina 347 and nitrospira ecomaris 2.1
cultures confirm the suggested inverse isotope fractionation during nitrite oxidation, but also
suggest that the precise fractionation factor crucially depends on the culturing conditions. |
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