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External Growth Control of Baltic Sea Cyanobacteria
Stockholm University, Faculty of Science, Department of Ecology, Environment and Plant Sciences. (Marin ekologi)ORCID iD: 0000-0003-0187-4415
2015 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

The overall aim of the study was to provide better insights to the ecological role and impact of cyanobacteria in Baltic Sea (BS) bay, coastal and open sea areas. Biomass and heterocyst development of diazotrophic, heterocystous cyanobacteria were monitored over several years simultaneously as physical parameters such as nutrients and temperature. Nitrogen fixation was estimated as well as its transfer in the BS food web. Even after decades of debate there is still controversy whether eutrophication of lakes and estuaries/coastal areas should be managed by reducing phosphorus only or also nitrogen. Central to this debate is whether nitrogen fixation by cyanobacteria can replace shortages of combined nitrogen quickly enough to make phosphorus the limiting nutrient and nitrogen removal pointless or even harmful. Also, it is not clear if available combined nitrogen inhibits heterocystous cyanobacterial nitrogen fixation and if it is used for their growth in situ. A large ecosystem-wide experiment started in Himmerfjärden bay in year 1997, where the N-loadings and release depth from a modern sewage treatment plant (STP), located in the inner part of the bay, were modulated. The STP creates a steep gradient of nutrients and stable nitrogen isotopes, which can be used to study uptake of combined nitrogen, as well as biomass development and primary productivity. A 35-year long data series was used to achieve good insights into phytoplankton development and primary productivity in the Baltic Sea over the last couple of decades. These in vivo long time series, based on monitoring data, in combination with shorter series (2-3 seasons, including measurements of colony stoichiometry and stable isotopes), have resulted in a unique meta-dataset, allowing for high-resolution observations into the role of the cyanobacteria in the Baltic Sea ecosystem.

Place, publisher, year, edition, pages
Stockholm: Department of Ecology, Environment and Plant Sciences, Stockholm University , 2015. , 47 p.
Keyword [en]
Cyanobacteria, Baltic Sea, diazotrophs, diazotrophy, heterocysts, primary productivity, stable isotopes, sewage treatment
National Category
Ecology
Research subject
Marine Ecology
Identifiers
URN: urn:nbn:se:su:diva-112753ISBN: 978-91-7649-086-0 (print)OAI: oai:DiVA.org:su-112753DiVA: diva2:782894
Public defence
2015-03-20, The Lecure Hall, Department of Ecology, Environment and Plant Sciences, Lilla Frescativägen 5, Stockholm, 10:00 (English)
Opponent
Supervisors
Funder
Swedish Research Council Formas
Note

At the time of the doctoral defense, the following papers were unpublished and had a status as follows: Paper 3: Manuscript. Paper 4: Manuscript.

Available from: 2015-02-26 Created: 2015-01-14 Last updated: 2015-06-30Bibliographically approved
List of papers
1. Do Baltic Sea diazotrophic cyanobacteria take up combined nitrogen in situ?
Open this publication in new window or tab >>Do Baltic Sea diazotrophic cyanobacteria take up combined nitrogen in situ?
2014 (English)In: Journal of Plankton Research, ISSN 0142-7873, E-ISSN 1464-3774, Vol. 36, no 5, 1368-1380 p.Article in journal (Refereed) Published
Abstract [en]

We used nitrogen stable isotopes to study the regulation of nitrogen fixation by filamentous cyanobacteria. Nitrogen fixation was found to be almost insensitive to combined nitrogen, along a gradient from the Himmerfjarden sewage treatment plant discharge to the open sea. We found similarly low cyanobacterial (mostly Aphanizomenon sp.) delta N-15-values at all stations, despite significant differences along the bay in both total nitrogen concentrations in water and delta N-15 in seston (particles <10 mu m), the latter used as a proxy for algae growing on combined nitrogen alone. Only late in the productive season, when cyanobacterial biomass was declining or already low, did elevated delta N-15 suggest uptake of combined nitrogen. However, this coincided with an increase in the contribution of Dolichospermum spp. to overall diazotrophic biomass and may indicate uptake of combined nitrogen by this species. These results indicate that almost all nitrogen used for growth by nitrogen-fixing cyanobacteria in the study area comes from nitrogen fixation, and very little from uptake of dissolved combined nitrogen. This study was part of a whole ecosystem experiment analyzing the effects of nitrogen removal in a sewage treatment plant discharging to the Himmerfjarden Bay, northern Baltic Sea Proper.

Keyword
cyanobacteria, diazotrophs, Baltic Sea, nitrogen fixation, stable isotopes
National Category
Biological Sciences
Identifiers
urn:nbn:se:su:diva-108380 (URN)10.1093/plankt/fbu053 (DOI)000342235000017 ()
Note

AuthorCount:3;

Available from: 2014-10-24 Created: 2014-10-22 Last updated: 2017-12-05Bibliographically approved
2. Regulation of heterocyst frequency in Baltic Sea Aphanizomenon sp.
Open this publication in new window or tab >>Regulation of heterocyst frequency in Baltic Sea Aphanizomenon sp.
2014 (English)In: Journal of Plankton Research, ISSN 0142-7873, E-ISSN 1464-3774, Vol. 36, no 5, 1357-1367 p.Article in journal (Refereed) Published
Abstract [en]

Heterocyst frequencies in Baltic Sea Aphanizomenon sp. were similar along a strong nutrient gradient from the discharge point of a sewage treatment plant at the head of the Himmerfjarden bay to the open sea. Filaments lacked heterocysts in winter and for over a month after the spring bloom had depleted combined nitrogen in the surface layer. Heterocyst-free filaments in spring contained granulate structures that decreased in abundance simultaneously as colony nitrogen content decreased, but delta N-15 remained unchanged, indicative of storage of fixed nitrogen in over-wintering Aphanizomenon sp. filaments. Heterocyst formation was initiated when water temperature was sufficient to form a shallow seasonal pycnocline that allowed filaments to be exposed to enough light to initiate growth and a subsequent intracellular shortage of nitrogen. During the growth season, heterocyst frequency varied significantly with maximum values in early summer (May), lower values in mid-August that coincided with maximum temperatures and an increase in late summer. Heterocyst frequencies decreased with increased temperatures, suggesting a more efficiently functioning nitrogenase enzyme. Based on data from three seasons, filament C: P ratios did not correlate with heterocyst frequencies, neither did reduced heterocyst frequencies coincide with high dissolved inorganic nitrogen concentrations. Increased heterocyst frequencies, however, resulted in decreased C:N ratios, probably as more heterocysts likely increase nitrogen fixation.

Keyword
Aphanizomenon sp., heterocysts, cyanobacteria, diazotrophs, Baltic Sea proper
National Category
Biological Sciences
Identifiers
urn:nbn:se:su:diva-108379 (URN)10.1093/plankt/fbu055 (DOI)000342235000016 ()
Note

AuthorCount:2;

Available from: 2014-10-24 Created: 2014-10-22 Last updated: 2017-12-05Bibliographically approved
3. Turnover of Fixed Nitrogen in a Baltic Sea Coastal Area
Open this publication in new window or tab >>Turnover of Fixed Nitrogen in a Baltic Sea Coastal Area
(English)Manuscript (preprint) (Other academic)
Keyword
diazotrophs, nitrogen fixation, Aphanizomenon, Nodularia spumigena, Baltic Sea, trophic interactions
National Category
Ecology
Research subject
Marine Ecology
Identifiers
urn:nbn:se:su:diva-113186 (URN)
Funder
Mistra - The Swedish Foundation for Strategic Environmental ResearchSwedish Environmental Protection Agency
Available from: 2015-01-26 Created: 2015-01-26 Last updated: 2016-01-29Bibliographically approved
4. Baltic Sea phytoplankton: Long-term variability of major groups and primary production in spring and summer related to nutrients and temperature
Open this publication in new window or tab >>Baltic Sea phytoplankton: Long-term variability of major groups and primary production in spring and summer related to nutrients and temperature
Show others...
(English)Manuscript (preprint) (Other academic)
Keyword
Primary productivity, Baltic Sea, spring bloom, diatoms, dinoflagellates, sewage, nutrient stochiometry, diazotrophs
National Category
Ecology
Research subject
Marine Ecology
Identifiers
urn:nbn:se:su:diva-113188 (URN)
Available from: 2015-01-26 Created: 2015-01-26 Last updated: 2016-01-29Bibliographically approved

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