CONTENTS & ABSTRACTS

In English. Summaries in Estonian

Proceedings of the Estonian Academy of Sciences.

Biology. Ecology

Volume 54 No. 1 March 2005

Special issue on large lakes of Estonia

Preface; 3–4

Juta Haberman

Water level and water temperature as factors determining phytoplankton biomass and nutrient content in Lake Peipsi; 5–17

Anu Milius, Reet Laugaste, Tõnu Möls, Marina Haldna, and Külli Kangur

Abstract. This paper investigates, using mainly data of 1985–2003, the influence of water temperature and water level on nutrients and on most important phytoplankton groups in Lake Peipsi. The water environment characteristics (water level at sampling time, in spring, in autumn, in the whole sampling year, and in the previous year, and the corresponding water temperatures) were considered as potential factors determining nutrient and phytoplankton fluctuations in the lake. To overcome problems with statistical correlation between environmental characteristics, these were linearly combined into a single Water Condition Factor (WCF). This factor was calculated with the Canonical Analysis individually for each nutrient and phytoplankton variable and used then to study how and to which extent different environmental conditions determine the corresponding water variable. It appeared that in the WCF of nutrients the most important role was played by water level characteristics while in the case of phytoplankton biomasses (particularly cyanobacteria) also the water temperature parameters had a significant effect. The water temperature had some effect also on the concentration of dissolved inorganic phosphate and dissolved inorganic nitrogen. In the shallower parts of the lake, lakes Lämmijärv and Pihkva (Pskov), the correlations between WCF and the water variables were higher than in the deepest part of the lake, L. Peipsi s.s.

Key words: water level, water temperature, nutrients, phytoplankton, Lake Peipsi.

Seasonality of zoo- and phytoplankton in Lake Peipsi (Estonia) as a function of water temperature; 18–39

Reet Laugaste and Juta Haberman

Abstract. Seasonal variability of phyto- and zooplankton and water temperature was monitored in large moderately eutrophic Lake Peipsi using monthly sampling in the vegetation periods of 1997-2003. The dynamics of the fraction of small phytoplankton, edible for zooplankton (diameter up to 40 µm), was collated with that of the grazers of algae such as copepods and cladocerans. The main conclusions from this study are the following. The years of low temperatures coincide with the low biomass of cyanobacteria and cladocerans; the years of high temperatures coincide with their high biomass. The synergistic effect of low water level and high temperature can induce heavy water blooms caused by cyanobacteria. The autumn of the previous year seems to have an effect on the phytoplankton composition and biomass. Diatoms and, to a smaller extent, also cryptophytes and chlorophytes tend to ignore temperature. Cladocerans are more influenced by temperature than copepods and rotifers. The biomass of copepods and, to a smaller extent, of cladocerans changes commonly in parallel with the biomass of small algae in spring and late autumn (October–November) and in an opposite mode in summer and early autumn. The suppressing impact of cyanobacteria is only obvious in the case of very heavy water blooms. Water temperature has a stronger effect on zooplankton (particularly on cladocerans) in spring than in autumn. Water temperature is largely responsible for the variability of zoo- and phytoplankton.

Key words: phytoplankton and zooplankton seasonal dynamics, water temperature, large shallow lake.

Hepatotoxic cyanobacterial peptides in Estonian freshwater bodies and inshore marine water; 40–52

Risto Tanner, Külli Kangur, Lisa Spoof, and Jussi Meriluoto

Abstract. Mass growths of cyanobacteria (blue-green algae), leading to the production of scums and mats, occur sometimes in nutrient-enriched waterbodies throughout the world, including Estonia. This paper shortly summarizes information about cyanobacterial toxins available in scientific literature, reports first results of liquid chromatographic–mass spectrometric analyses of cyanobacterial toxins in some waterbodies in Estonia, and attempts to assess possible risk of associated local health problems by drawing some parallels with the situation in neighbouring Finland. The risk of drinking carcinogenic toxin-containing water by the population of Narva in connection with some toxic cyanobacterial bloom in Northern northern Lake Peipsi is outlined. The need for regular monitoring of toxicity of cyanobacterial blooms as well as deeper research of ecological consequences of massive blooms of toxic cyanobacteria is emphasized in this connection.

Key words: Lake Peipsi, Lake Pühajärv, Narva water supply, cyanobacteria, toxins.

Annotated list of rotifers of Lake Võrtsjärv; 53–66

Taavi Virro and Juta Haberman

Abstract. The present review makes an inventory of published information on the taxonomic composition of rotifers in L. Võrtsjärv, Estonia, since 1920, and provides a revised list of rotifers recorded from the lake, with up-to-date taxonomy. The list of synonyms used in earlier literature is also given. A total of 173 rotifer taxa (138 species) belonging to 22 families and 46 genera have so far been recorded from L. Võrtsjärv. The most taxon-rich family is Brachionidae with 41 taxa listed, followed by Synchaetidae with 19 and Trichocercidae with 18 taxa. The most diverse genera are Trichocerca (17 taxa) and Lecane (14). Most (75%) of the rotifer taxa found have cosmopolitan or wide distribution, approximately 11% have Holarctic and 2% Palaearctic occurrence. The rotifer fauna of L. Võrtsjärv includes four rare species: Cephalodella compacta, Eosphora thoides, Monommata grandis, and Resticula gelida.

Key words: Rotifera, taxonomic composition, shallow eutrophic lake.

Fish kill in Lake Peipsi in summer 2002 as a synergistic effect of a cyanobacterial bloom, high temperature, and low water level; 67–80

Külli Kangur, Andu Kangur, Peeter Kangur, and Reet Laugaste

Abstract. In Lake Peipsi (3550 km², mean depth 7.1 m) sporadic fish kills have been registered repeatedly since 1959 during cyanobacterial blooms in warm summers. At the time of the excessive fish kill in August 2002 comprehensive investigations of phytoplankton abundance, key physical and chemical parameters of lake water (including diurnal fluctuations of the dissolved oxygen and ammonium ion concentrations and pH) as well as species composition and number of dead fish were carried out along the Estonian shore. The aim of the study was to assess how many fish were killed and to determine ecological conditions in the lake that led to the fish kill. The results suggest that the fish kill was induced by the synergistic effect of several unfavourable conditions, which appeared in the lake during the strong bloom of the cyanobacterium Gloeotrichia echinulata accompanied with continuous hot weather and decreasing water level. A combination of factors such as high water temperature (up to 26 °C), low water level (70 cm below the long-term average), great spatial and diurnal variations in the dissolved oxygen (saturation 25–165%) and ammonium ion (up to 0.33 mg N L^–1) concentrations as well as in the pH (7.7–9.5) were responsible for the mass mortality of fish. The influence of cyanotoxins on the condition of fish cannot be neglected either. Ruffe, a bottom dwelling fish, suffered the most severely.

Key words: bloom of cyanobacteria, fish kill, water level, Lake Peipsi.