, Volume 599, Issue 1, pp 77–86 | Cite as

Critical N:P ratio for cyanobacteria and N2-fixing species in the large shallow temperate lakes Peipsi and Võrtsjärv, North-East Europe

  • Tiina Nõges
  • Reet Laugaste
  • Peeter Nõges
  • Ilmar Tõnno
ELLS 2007


In the 1990s a sharp decrease in nitrogen loading occurred in Estonian rivers, bringing about a reduction of the nitrogen-to-phosphorus ratio (N:P ratio) in the large shallow lakes, Peipsi (3,555 km2, mean depth 7.1 m) and Võrtsjärv (270 km2, 2.8 m). The average mass ratio of total nitrogen (TN) and total phosphorus (TP) in Võrtsjärv (45) was about twice as high as that in Peipsi (22). In Peipsi, the N2-fixing Gloeotrichia echinulata, Aphanizomenon flos-aquae and Anabaena species prevailed in the summer phytoplankton, while in Võrtsjärv the dominant cyanobacteria were Limnothrix planktonica, L. redekei and Planktolyngbya limnetica, which cannot fix N2; the main N2-fixing taxa Aphanizomenon skujae and Anabaena sp. seldom gained dominance. In May–October the critical TN:TP mass ratio, below which N2-fixing cyanobacteria (Nfix) achieved high biomasses, was ∼40 in Võrtsjärv and ∼30 in Peipsi. The percentages of both total cyanobacteria (CY) and Nfix (CY% and Nfix%) in Peipsi achieved their maximum values at an N:P mass ratio at or below 20 for both TN:TP and Nmin:SRP. In Võrtsjärv, the TN:TP supporting a high Nfix% was between 30 and 40 and the Nmin:SRP supporting this high percentage was in the same range as that in Peipsi (<20), though the maximum Nfix% values in Võrtsjärv (69%) were much lower than in Peipsi (96%). The Nmin:SRP ratio explained 77% of the variability in Nfix% in May–October. The temperature dependence of Nfix% approximated to the maximum function type, with an upper limiting value at a certain water temperature, and this was most distinct in May–October. The critical TN:TP ratios obtained from our study (roughly 30 for Peipsi and 40 for Võrtsjärv) are much higher than the Redfield N:P mass ratio routinely considered (7). Our results represent valuable guidelines for creating effective management strategies for large shallow lakes. They provide a basis for stressing the urgent need to decrease phosphorus loading and to keep the in-lake P concentration low, and not to implement nitrogen reduction measures without a simultaneous decrease of phosphorus concentration.


Large and shallow lake Nitrogen–phosphorus ratio Cyanobacteria N2-fixing cyanobacteria 



Funding for this research was provided by target funding project 03962480s03 by the Estonian Ministry of Education and by Estonian Science Foundation grant 5738. We used data obtained from frames of the State Monitoring Program of the Estonian Ministry of Environment. The authors are grateful to the guest editor Heikki Simola and to two anonymous reviewers for valuable advice and comments for improving the manuscript.


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Copyright information

© Springer Science+Business Media B.V. 2007

Authors and Affiliations

  • Tiina Nõges
    • 1
  • Reet Laugaste
    • 1
  • Peeter Nõges
    • 1
    • 2
  • Ilmar Tõnno
    • 1
  1. 1.Institute of Environmental and Agricultural Sciences, Centre for LimnologyEstonian University of Life SciencesTartu CountyEstonia
  2. 2.Institute of Environment and SustainabilityEuropean Commission – Joint Research CentreIspraItaly

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