, Volume 646, Issue 1, pp 33–48 | Cite as

Analysis of changes over 44 years in the phytoplankton of Lake Võrtsjärv (Estonia): the effect of nutrients, climate and the investigator on phytoplankton-based water quality indices

  • Peeter Nõges
  • Ute Mischke
  • Reet Laugaste
  • Angelo G. Solimini


We analysed long-term changes in phytoplankton composition in relation to hydrological, meteorological and nutrient loading data in the large (270 km2) shallow (mean depth 2.8 m) Lake Võrtsjärv. Nutrient loads to the lake were heavy in the 1970s and 1980s and decreased considerably thereafter. The average nutrient concentrations for 1985–2004 (1.6 mg l−1 of total nitrogen and 53 μg l−1 of total phosphorus) characterize the lake as a eutrophic water body. All four calculated taxonomic indices showed a unidirectional deterioration of the lake’s ecological status, despite reduced concentrations of nutrients. We focused our analysis on the PTSI index, which revealed a stepwise change between the years 1977 and 1979 that coincided with a large increase in water level, but also with a change of investigator. After correcting input data for possible investigator-induced differences, the step change remained because it was caused by major changes in the whole phytoplankton community. The previous dominant Planktolyngbya limnetica was replaced by two species of seasonally altering Limnothrix. Among phytoplankton functional groups, there was a decrease in all groups comprising small-sized phytoplankton species, such as X1, E, F, J, N and an increase in S1 and H1, both represented by filamentous cyanobacteria. Our results suggest a non-linear response of phytoplankton to changing nutrient loadings, and that the change observed between 1977 and 1979 was a regime shift triggered by water level change. High shade tolerance of the new dominants, and their ability to create shade, obviously stabilized the new status making it resistant to restoration efforts.


Regime shift Lake water level Nutrient loading Trophic index Phytoplankton functional groups 



The study was supported by SF 0170011508 from Estonian Ministry of Education and Research, by grant 7600 from Estonian Science Foundation and by EC FP7 project WISER. Data collection in frames of the state monitoring programme was supported by the Estonian Ministry of Environment. We acknowledge hydrological and meteorological data contributed by the Estonian Institute of Hydrology and Meteorology.


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Copyright information

© Springer Science+Business Media B.V. 2010

Authors and Affiliations

  • Peeter Nõges
    • 1
    • 2
  • Ute Mischke
    • 3
  • Reet Laugaste
    • 1
  • Angelo G. Solimini
    • 2
    • 4
  1. 1.Centre for Limnology, Institute of Agricultural and Environmental SciencesEstonian University of Life SciencesTartumaaEstonia
  2. 2.European Commission, Joint Research CentreInstitute for Environment and SustainabilityIspraItaly
  3. 3.Department of Shallow Lakes and Lowland RiversLeibniz-Institute for Freshwater Ecology and Inland FisheriesBerlinGermany
  4. 4.Department of Experimental MedicineSapienza University of RomeRomeItaly

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