Change search
CiteExportLink to record
Permanent link

Direct link
Cite
Citation style
  • apa
  • ieee
  • modern-language-association-8th-edition
  • vancouver
  • Other style
More styles
Language
  • de-DE
  • en-GB
  • en-US
  • fi-FI
  • nn-NO
  • nn-NB
  • sv-SE
  • Other locale
More languages
Output format
  • html
  • text
  • asciidoc
  • rtf
Nutrient limitation and elemental ratios in Baltic Sea plankton
Stockholm University, Faculty of Science, Department of Systems Ecology.
2002 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

Phytoplankton growth is frequently limited by the supply of nitrogen (N), phosphorus (P), or sometimes other elements. N2-fixing cyanobacteria are favoured by N limitation, which they may alleviate by adding new N to the ecosystem. Focussing on the Baltic Sea, this thesis deals with the regulating mechanisms for such cyanobacteria, the magnitude of the N2 fixation, and the effect of the newNon the pelagic ecosystem. This is done mainly through fieldstudies of the seasonal variation in nutrient elemental composition of the plankton.

The C:N:P stoichiometry of zooplankton was found to differ only slightly from that of seston, implying that zooplankton recycle a relatively balanced N:P ratio compared to general phytoplankton demand. Thus, from this aspect, zooplankton should have a small effect on the development of cyanobacterial blooms in the Baltic Sea.

In the Baltic proper, there was a recurrent summer increase in upper mixed layer total N, which coincided with the biomass build-up of heterocystous cyanobacteria. N2 fixation in the Baltic proper estimated from this increase ranged between 180-430 thousand tons N yr-1, several times higher than commonly assumed. The upper end estimate is almost as large as the entire riverine load and twice the atmospheric load of N. The N2 fixation is sufficient to sustain 30-90% of the summer pelagic net community production, and thus important for the nourishment of pelagic zooplankton and fish.

Seston element ratios were generally close to Redfield values (C106N16P1) in the upper 0-20 m. Consistent withNlimitation of the spring bloom, the C:N ratio increased (to ~9) when nitrate, but not phosphate, was depleted. From June, surface (5 m) seston C:P and N:P ratios increased through summer and peaked at the biomass maximum of N2-fixing cyanobacteria. This suggests that new nitrogen from N2 fixation and competition for P resulted in P deficiency, albeit weak, also in non-N2-fixers.

The P content of was very high in spring and early summer (~3% of dwt, C:P=30-40, N:P=6-7) and decreased as the biomass increased in summer. The storage of P in biomass in early summer was potentially important for the later bloom formation. The culmination of the C:P and N:P ratios at the biomass peak (C:P=380-480, N:P=60-80, P=0.25-0.3% of dwt) strongly indicate biomass P limitation. The iron (Fe) content of was relatively low compared to reported values for other N2-fixing cyanobacteria but did not decrease in summer, thus not indicating Fe limitation. Also had low P content in summer and higher Fe content, indicating P-deficiency. In , the specific C uptake rate, measured in short-term (3 hrs) incubations, was mainly correlated to temperature and not to P content. This is however compatible with the large total-N-increase, which suggests substantial N-leakage from growing cyanobacteria.

In conclusion, this thesis shows the importance of N2-fixing cyanobacteria in the Baltic Sea and indicates that P has a critical role as controlling factor. Despite the large annual N2 fixation, biogeochemical nutrient cycling favour N limitation in the Baltic proper. This thesis demonstrates how the stoichiometric approach can be used for reconciling element cycles with population dynamics of plankton in aquatic ecosystems.

Place, publisher, year, edition, pages
Stockholm: Department of Systems Ecology, Stockholm University , 2002. , 42 p.
Keyword [sv]
Plankton, Östersjön, Ekosystem i vatten
National Category
Ecology
Research subject
Systems Ecology
Identifiers
URN: urn:nbn:se:su:diva-142868ISBN: 91-7265-450-3 (print)OAI: oai:DiVA.org:su-142868DiVA: diva2:1094611
Public defence
2002-05-03, 10:00 (English)
Opponent
Note

Härtill 4 uppsatser

Available from: 2017-05-10 Created: 2017-05-10 Last updated: 2017-09-27Bibliographically approved

Open Access in DiVA

No full text

Other links

PDF (Not accessible to users outside Sweden)
By organisation
Department of Systems Ecology
Ecology

Search outside of DiVA

GoogleGoogle Scholar

Total: 18 hits
CiteExportLink to record
Permanent link

Direct link
Cite
Citation style
  • apa
  • ieee
  • modern-language-association-8th-edition
  • vancouver
  • Other style
More styles
Language
  • de-DE
  • en-GB
  • en-US
  • fi-FI
  • nn-NO
  • nn-NB
  • sv-SE
  • Other locale
More languages
Output format
  • html
  • text
  • asciidoc
  • rtf