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The bloom of nitrogen-fixing cyanobacteria in the northern Baltic Proper stimulates summer production
Stockholm University, Faculty of Science, Department of Ecology, Environment and Plant Sciences.
Stockholm University, Faculty of Science, Department of Ecology, Environment and Plant Sciences.
Stockholm University, Faculty of Science, Department of Ecology, Environment and Plant Sciences.
Stockholm University, Faculty of Science, Department of Ecology, Environment and Plant Sciences.
2016 (English)In: Journal of Marine Systems, ISSN 0924-7963, E-ISSN 1879-1573, Vol. 163, 102-112 p.Article in journal (Refereed) Published
Abstract [en]

In the northern Baltic Sea Proper, total nitrogen (TN) increases during the summer bloom of filamentous heterocystous cyanobacteria. To follow the fate of the nitrogen they fix, we studied several N fractions during the bloom. We measured cyanobacterial biomass, TN, particulate organic N (PON, two size fractions), dissolved organic N (DON), and PON sedimentation in two areas in 2011. TN increased mainly due to increasing PON, but also to DON. Cyanobacteria contributed about 20% of the PON increase and ~ 10% of the TN increase. About half the PON changes (increase, then decrease) could be explained by the sum of cyanobacteria, other autotrophs (> 2 μm) and zooplankton, indicating that the bloom stimulates primary and secondary production. TN decreased after the bloom mainly due to declining PON > 10 μm, but sedimentation rates did not increase and could explain little of the post-bloom N-loss. There was little settling of undecomposed cyanobacteria.

The seasonal development of Aphanizomenon sp. and N pools was similar among stations and areas. For Nodularia spumigena between-station variability increased once patchy surface accumulations developed. A brief Dolichospermum spp. bloom indicated that sampling frequency may be more important than spatial resolution for capturing dynamics of this bloom.

Place, publisher, year, edition, pages
2016. Vol. 163, 102-112 p.
Keyword [en]
Cyanobacteria, Nitrogen fixation, Nitrogen pools, Particulate and dissolved organic nitrogen, Secondary production, Sedimentation
National Category
Ecology
Research subject
Marine Ecology
Identifiers
URN: urn:nbn:se:su:diva-132744DOI: 10.1016/j.jmarsys.2016.07.003OAI: oai:DiVA.org:su-132744DiVA: diva2:954299
Funder
Swedish Research Council for Environment, Agricultural Sciences and Spatial Planning, 215-2009-813
Available from: 2016-08-22 Created: 2016-08-22 Last updated: 2016-08-30Bibliographically approved
In thesis
1. Cyanobacterial Nitrogen Fixation in the Baltic Sea: With focus on Aphanizomenon sp.
Open this publication in new window or tab >>Cyanobacterial Nitrogen Fixation in the Baltic Sea: With focus on Aphanizomenon sp.
2016 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

Cyanobacteria are widely distributed in marine, freshwater and terrestrial habitats. Some cyanobacterial genera can convert di-nitrogen gas (N2) to bioavailable ammonium, i.e. perform nitrogen (N) fixation, and are therefore of profound significance for N cycling. N fixation by summer blooms of cyanobacteria is one of the largest sources of new N for the Baltic Sea. This thesis investigated N fixation by cyanobacteria in the Baltic Sea and explored the fate of fixed N at different spatial and temporal scales. In Paper I, we measured cell-specific N fixation by Aphanizomenon sp. at 10 ºC, early in the season. Fixation rates were high and comparable to those in late summer, indicating that Aphanizomenon sp. is an important contributor to N fixation already in its early growth season. In Paper II, we studied fixation and release of N by Aphanizomenon sp. and found that about half of the fixed N was rapidly released and transferred to other species, including autotrophic and heterotrophic bacteria, diatoms and copepods. In Paper III, we followed the development of a cyanobacterial bloom and related changes in dissolved and particulate N pools in the upper mixed surface layer. The bloom-associated total N (TN) increase was mainly due to higher particulate organic N (PON) concentrations, but also to increases in dissolved organic nitrogen (DON). About half the PON-increase could be explained by the sum of N-fixing cyanobacteria, other phytoplankton (>2µm) and zooplankton, indicating that production was stimulated by the N fixation. In Paper IV, we used a growth model based on measured photosynthesis–irradiance relationships to explore the production potential of Aphanizomenon sp. The model included data on irradiance, biomass, temperature and light attenuation (1999–2013). Until the bloom peak, the modelled production matched the measured biomass, indicating low production losses. Over the whole season, the modelled production could explain a substantial part of the summer TN increase, assuming that plausible losses (such as grazing or cell lysis) are retained within the upper mixed layer. Complementing the other data, we also investigated the nutrient content (Paper I) and varying cell width (Paper IV) of Aphanizomenon sp. By a combination of approaches, this thesis has contributed new information on cyanobacterial N fixation rates, the transfer of fixed N to other organisms in the food web and shown the potential for fixed N to stimulate summer primary and secondary production in the Baltic Sea.

Place, publisher, year, edition, pages
Stockholm: Department of Ecology, Environment and Plant Sciences, Stockholm University, 2016. 43 p.
Keyword
cyanobacteria, Baltic Sea, nitrogen fixation, Aphanizomenon sp., dissolved nitrogen, particulate nitrogen, sedimentation
National Category
Ecology
Research subject
Marine Ecology
Identifiers
urn:nbn:se:su:diva-132773 (URN)978-91-7649-481-3 (ISBN)
External cooperation:
Public defence
2016-10-14, Vivi Täckholmsalen (Q-salen), NPQ-huset, Svante Arrhenius väg 20, Stockholm, 09:00 (English)
Opponent
Supervisors
Funder
Swedish Research Council for Environment, Agricultural Sciences and Spatial Planning, 215-2009-813Swedish Research Council for Environment, Agricultural Sciences and Spatial Planning, 215-2010-779Max Planck SocietyBaltic Ecosystem Adaptive Management (BEAM)Swedish Research Council, 621-2011-4406Knut and Alice Wallenberg Foundation
Note

At the time of the doctoral defense, the following paper was unpublished and had a status as follows: Paper 4: Manuscript.

Available from: 2016-09-21 Created: 2016-08-23 Last updated: 2016-09-12Bibliographically approved

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Svedén, Jennie B.Walve, JakobElmgren, RagnarLarsson, Ulf
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