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Seasonal oxygen, nitrogen and phosphorus benthic cycling along an impacted Baltic Sea estuary: regulation and spatial patterns
Stockholm University, Faculty of Science, Department of Geological Sciences.
Stockholm University, Faculty of Science, Department of Applied Environmental Science (ITM).
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Number of Authors: 5
2014 (English)In: Biogeochemistry, ISSN 0168-2563, E-ISSN 1573-515X, Vol. 119, no 1-3, 139-160 p.Article in journal (Refereed) Published
Abstract [en]

The regulatory roles of temperature, eutrophication and oxygen availability on benthic nitrogen (N) cycling and the stoichiometry of regenerated nitrogen and phosphorus (P) were explored along a Baltic Sea estuary affected by treated sewage discharge. Rates of sediment denitrification, anammox, dissimilatory nitrate reduction to ammonium (DNRA), nutrient exchange, oxygen (O2) uptake and penetration were measured seasonally. Sediments not affected by the nutrient plume released by the sewage treatment plant (STP) showed a strong seasonality in rates of O2 uptake and coupled nitrification-denitrification, with anammox never accounting for more than 20% of the total dinitrogen (N2) production. N cycling in sediments close to the STP was highly dependent on oxygen availability, which masked temperature-related effects. These sediments switched from low N loss and high ammonium (NH4+) efflux under hypoxic conditions in the fall, to a major N loss system in the winter when the sediment surface was oxidized. In the fall DNRA outcompeted denitrification as the main nitrate (NO3-) reduction pathway, resulting in N recycling and potential spreading of eutrophication. A comparison with historical records of nutrient discharge and denitrification indicated that the total N loss in the estuary has been tightly coupled to the total amount of nutrient discharge from the STP. Changes in dissolved inorganic nitrogen (DIN) released from the STP agreed well with variations in sedimentary N2 removal. This indicates that denitrification and anammox efficiently counterbalance N loading in the estuary across the range of historical and present-day anthropogenic nutrient discharge. Overall low N/P ratios of the regenerated nutrient fluxes impose strong N limitation for the pelagic system and generate a high potential for nuisance cyanobacterial blooms.

Place, publisher, year, edition, pages
2014. Vol. 119, no 1-3, 139-160 p.
Keyword [en]
Sediment, Benthic flux, Denitrification, Anammox, DNRA, Eutrophication
National Category
Earth and Related Environmental Sciences
Research subject
Geochemistry
Identifiers
URN: urn:nbn:se:su:diva-97297DOI: 10.1007/s10533-014-9953-6ISI: 000336028400010OAI: oai:DiVA.org:su-97297DiVA: diva2:676596
Projects
Baltic NutrientsBaltic Ecosystem Adaptive Management - BEAMStockholm University Marine research Centre
Funder
Ecosystem Approach to the Baltic Sea (Upphört/Closed 2010)Swedish Research Council Formas
Available from: 2013-12-06 Created: 2013-12-06 Last updated: 2017-12-06Bibliographically 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.
Series
Meddelanden från Stockholms universitets institution för geologiska vetenskaper, 357
Keyword
Nitrogen cycle, denitrification, DNRA, anammox, anoxia, hypoxia, eutrophication, meiofauna, macrofauna, aggregates, cyanobacteria, Baltic Sea
National Category
Geochemistry
Research subject
Geochemistry
Identifiers
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)
Opponent
Supervisors
Funder
Baltic Ecosystem Adaptive Management (BEAM)Swedish Research Council Formas
Note

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, StefanoDeutsch, BarbaraBruchert, Volker
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