Journal cover Journal topic
Biogeosciences An interactive open-access journal of the European Geosciences Union
Biogeosciences, 11, 2211-2224, 2014
© Author(s) 2014. This work is distributed under
the Creative Commons Attribution 3.0 License.
Research article
22 Apr 2014
Artificially induced migration of redox layers in a coastal sediment from the Northern Adriatic
E. Metzger1, D. Langlet1, E. Viollier2, N. Koron3, B. Riedel4, M. Stachowitsch4, J. Faganeli3, M. Tharaud2, E. Geslin1, and F. Jorissen1 1Laboratoire des Bio-Indicateurs Actuels et Fossiles, UMR6112 CNRS LPG-BIAF, Université d'Angers, 2 Boulevard Lavoisier, 49045 Angers Cedex, France
2Laboratoire de Géochimie des Eaux, UMR7154 CNRS, Université Paris Diderot, Sorbonne Paris Cité, Institut de Physique du Globe de Paris, 75013 Paris, France
3Marine Biology Station, National Institute of Biology, Fornace 41, 6330 Piran, Slovenia
4Department of Limnology and Oceanography, University of Vienna, Althanstrasse 14, Vienna 1090, Austria
Abstract. 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.

Citation: Metzger, E., Langlet, D., Viollier, E., Koron, N., Riedel, B., Stachowitsch, M., Faganeli, J., Tharaud, M., Geslin, E., and Jorissen, F.: Artificially induced migration of redox layers in a coastal sediment from the Northern Adriatic, Biogeosciences, 11, 2211-2224,, 2014.
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