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Effect of reoxygenation and Marenzelleria spp. bioturbation on Baltic Sea sediment metabolism
Stockholm University, Faculty of Science, Department of Geological Sciences.
Stockholm University, Faculty of Science, Department of Systems Ecology.
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2013 (English)In: Marine Ecology Progress Series, ISSN 0171-8630, E-ISSN 1616-1599, Vol. 482, 43-55 p.Article in journal (Refereed) Published
Abstract [en]

Nutrient reduction and the improvement of bottom water oxygen concentrations are thought to be key factors in the recovery of eutrophic aquatic ecosystems. The effects of reoxygenation and bioturbation of natural hypoxic sediments in the Baltic Sea were studied using a mesocosm experiment. Anoxic sediment box cores were collected from 100 m depth in Kanholmsfjärden (Stockholm Archipelago) and maintained in flow-through mesocosms with 3 treatments: (1) hypoxic: supplied with hypoxic water; (2) normoxic: supplied with oxic water; and (3) Marenzelleria: supplied with oxic water and the polychaete Marenzelleria spp. (2000 ind. m–2). After a 7 wk long conditioning period, net fluxes of dissolved O2, CH4, Fe2+, Mn2+, NH4+, NO2-, NO3-, PO43- and H4SiO4, and rates of nitrate ammonification (DNRA), denitrification and anammox were determined. Phosphate was taken up by the sediment in all treatments, and the uptake was highest in the normoxic treatment with Marenzelleria. Normoxic conditions stimulated the denitrification rate by a factor of 5. Denitrification efficiency was highest under normoxia (50%), intermediate in bioturbated sediments (16%), and very low in hypoxic sediments (4%). The shift from hypoxic to normoxic conditions resulted in a significantly higher retention of NH4+, H4SiO4 and Mn2+ in the sediment, but the bioturbation by Marenzelleria reversed this effect. Results from our study suggest that bioturbation by Marenzelleria stimulates the exchange of solutes between sediment and bottom water through irrigation and enhances bacterial sulfate reduction in the burrow walls. The latter may have a toxic effect on nitrifying bacteria, which, in turn, suppresses denitrification rates.

Place, publisher, year, edition, pages
2013. Vol. 482, 43-55 p.
Keyword [en]
Hypoxia, Macrofauna, Mesocosm, Denitrification, Dissimilatory nitrate reduction to ammonium, DNRA, Benthic Flux, Baltic Sea
National Category
Earth and Related Environmental Sciences
Research subject
URN: urn:nbn:se:su:diva-90105DOI: 10.3354/meps10232ISI: 000319337100004OAI: diva2:622664

AuthorCount: 8;

Available from: 2013-05-22 Created: 2013-05-22 Last updated: 2015-03-19Bibliographically approved
In thesis
1. Control factors of the marine nitrogen cycle: The role of meiofauna, macrofauna, oxygen and aggregates
Open this publication in new window or tab >>Control factors of the marine nitrogen cycle: The role of meiofauna, macrofauna, oxygen and aggregates
2015 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

The ocean is the most extended biome present on our planet. Recent decades have seen a dramatic increase in the number and gravity of threats impacting the ocean, including discharge of pollutants, cultural eutrophication and spread of alien species. It is essential therefore to understand how different impacts may affect the marine realm, its life forms and biogeochemical cycles. The marine nitrogen cycle is of particular importance because nitrogen is the limiting factor in the ocean and a better understanding of its reaction mechanisms and regulation is indispensable. Furthermore, new nitrogen pathways have continuously been described. The scope of this project was to better constrain cause-effect mechanisms of microbially mediated nitrogen pathways, and how these can be affected by biotic and abiotic factors.

This thesis demonstrates that meiofauna, the most abundant animal group inhabiting the world’s seafloors, considerably alters nitrogen cycling by enhancing nitrogen loss from the system. In contrast, larger fauna such as the polychaete Marenzelleria spp. enhance nitrogen retention, when they invade eutrophic Baltic Sea sediments. Sediment anoxia, caused by nutrient excess, has negative consequences for ecosystem processes such as nitrogen removal because it stops nitrification, which in turn limits both denitrification and anammox. This was the case of Himmerfjärden and Byfjord, two estuarine systems affected by anthropogenic activities, such as treated sewage discharges. When Byfjord was artificially oxygenated, nitrate reduction mechanisms started just one month after pumping. However, the balance between denitrification and nitrate ammonification did not favor either nitrogen removal or its retention.

Anoxia is also present in aggregates of the filamentous cyanobacteria Nodularia spumigena. This thesis shows that even in fully oxic waters, millimetric aggregates can host anaerobic nitrogen processes, with clear implications for the pelagic compartment. While the thesis contributed to our knowledge on marine nitrogen cycling, more data need to be collected and experiments performed in order to understand key processes and regulation mechanisms of element cycles in the ocean. In this way, stakeholders may follow and take decisions in order to limit the continuous flow of human metabolites and impacts on the marine environment.

Place, publisher, year, edition, pages
Stockholm: Department of Geological Sciences, Stockholm University, 2015. 35 p.
Meddelanden från Stockholms universitets institution för geologiska vetenskaper, 357
Nitrogen cycle, denitrification, DNRA, anammox, anoxia, hypoxia, eutrophication, meiofauna, macrofauna, aggregates, cyanobacteria, Baltic Sea
National Category
Research subject
urn:nbn:se:su:diva-115036 (URN)978-91-7649-129-4 (ISBN)
Public defence
2015-04-29, Nordenskiöldsalen, Geovetenskapens hus, Svante Arrhenius väg 12, Stockholm, 13:00 (English)
Baltic Ecosystem Adaptive Management (BEAM)Swedish Research Council Formas

At the time of the doctoral defense, the following paper was unpublished and had a status as follows: Paper 2: Manuscript.

Available from: 2015-04-07 Created: 2015-03-16 Last updated: 2015-07-01Bibliographically approved

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Bonaglia, StefanoGunnarsson, Jonas S.Raymond, CarolineSvensson, OlaBrüchert, Volker
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