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| Titel |
Occurrence of benthic microbial nitrogen fixation coupled to sulfate reduction in the seasonally hypoxic Eckernförde Bay, Baltic Sea |
| VerfasserIn |
V. J. Bertics, C. R. Löscher, I. Salonen, A. W. Dale, J. Gier, R. A. Schmitz, T. Treude |
| Medientyp |
Artikel
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| Sprache |
Englisch
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| ISSN |
1726-4170
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| Digitales Dokument |
URL |
| Erschienen |
In: Biogeosciences ; 10, no. 3 ; Nr. 10, no. 3 (2013-03-01), S.1243-1258 |
| Datensatznummer |
250018120
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| Publikation (Nr.) |
 copernicus.org/bg-10-1243-2013.pdf |
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| Zusammenfassung |
| Despite the worldwide occurrence of marine hypoxic
regions, benthic nitrogen (N) cycling within these areas is poorly
understood and it is generally assumed that these areas represent zones of
intense fixed N loss from the marine system. Sulfate reduction can be an
important process for organic matter degradation in sediments beneath
hypoxic waters and many sulfate-reducing bacteria (SRB) have the genetic
potential to fix molecular N (N2). Therefore, SRB may supply fixed N to
these systems, countering some of the N lost via microbial processes, such as
denitrification and anaerobic ammonium oxidation. The objective of this
study was to evaluate if N2 fixation, possibly by SRB, plays a role in
N cycling within the seasonally hypoxic sediments from the Eckernförde Bay,
Baltic Sea. Monthly samplings were performed over the course of one year to
measure nitrogenase activity (NA) and sulfate reduction rates, to determine
the seasonal variations in bioturbation (bioirrigation) activity and
important benthic geochemical profiles, such as sulfur and N compounds, and
to monitor changes in water column temperature and oxygen concentrations.
Additionally, at several time points, the active N-fixing community was
examined via molecular tools. Integrated rates of N2 fixation
(approximated from NA) and sulfate reduction showed a similar seasonality
pattern, with highest rates occurring in August (approx. 22 and 880 nmol cm−3 d−1 of N and SO42−, respectively) and October
(approx. 22 and 1300 nmol cm−3 d−1 of N and SO42−
respectively), and lowest rates occurring in February (approx. 8 and 32 nmol cm−3 d−1 of N and SO42−, respectively). These rate
changes were positively correlated with bottom water temperatures and
previous reported plankton bloom activities, and negatively correlated with
bottom water oxygen concentrations. Other variables that also appeared to
play a role in rate determination were bioturbation, bubble irrigation and
winter storm events. Molecular analysis demonstrated the presence of nifH
sequences related to two known N2 fixing SRB, namely Desulfovibrio vulgaris and Desulfonema limicola, supporting
the hypothesis that some of the nitrogenase activity detected may be
attributed to SRB. Overall, our data show that Eckernförde Bay
represents a complex ecosystem where numerous environmental variables
combine to influence benthic microbial activities involving N and sulfur
cycling. |
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