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| Titel |
Artificially induced migration of redox layers in a coastal sediment from the Northern Adriatic |
| VerfasserIn |
E. Metzger, D. Langlet, E. Viollier, N. Koron, B. Riedel, M. Stachowitsch, J. Faganeli, M. Tharaud, E. Geslin, F. Jorissen |
| 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 ; 11, no. 8 ; Nr. 11, no. 8 (2014-04-22), S.2211-2224 |
| Datensatznummer |
250117370
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| Publikation (Nr.) |
 copernicus.org/bg-11-2211-2014.pdf |
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| Zusammenfassung |
Long-term experimental studies suggest that, under transient anoxic
conditions, redox fronts within the sediment shift upwards, causing
sequential rise and fall of benthic fluxes of reduced species (Mn(II), Fe(II)
and S(-II)). Infaunal benthic organisms are associated with different redox
fronts as micro-habitats and must be affected by such changes during natural
hypoxia events. In order to document the geochemical evolution of the
sediment during prolonged anoxia in the framework of an in situ experiment
designed to mimic natural conditions, benthic chambers were deployed on the
seafloor of the Northern Adriatic and sampled after 9, 30 and 315 days of
incubation. Oxygen and sulfide were measured continuously in the early stages
(9 days) of the experiment. High-resolution pore water profiles were sampled
by DET probes and redox-sensitive species (S(VI), Mn(II) and Fe(II)) and
alkalinity were measured.
Starting oxygen saturation was about 80% within the chamber. After 7
days, anoxia was established in the bottom waters within the chambers. Mn(II)
and Fe(II) started diffusing towards the anoxic water column until they
reached the surficial sediment. Being reoxidized there, Mn and Fe
reprecipitated, giving a rusty coloration to the seafloor. Infaunal species
appeared at the sediment surface. After 20 days, all macro-organisms were
dead. Decomposition of macro-organisms at the sediment–water interface
generated S(-II) within the entire height of the chamber, leading to a
downward flux of sulfides into the sediment, where they were quickly oxidized
by metallic oxides or precipitated as FeS. S(-II) was below detection in the
water column and pore waters at the end of the experiment. Our results
suggest that S(-II) enrichment in the water column of coastal systems, which
are episodically anoxic, is strongly controlled by the biomass of benthic
macrofauna and its decay during anoxia, whereas its residence time in the
water column is controlled by iron availability (as solid oxides or as
dissolved reduced cations) within the sediment, even without water
circulation. |
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