Toxic cyanobacteria in the lakes located in R- lga (the capital of Latvia) and its surroundings: present state of knowledge

  • M Balode
  • I Purina
  • S Strake
  • S Purvina
  • M Pfeifere
  • I Barda
  • K Povidisa
Keywords: cyanobacteria, lakes, microcystins

Abstract

The intensity and toxicity of cyanobacterial blooms in lakes located near R-
lga (the capital of Latvia) were investigated between 1998 and 2004. These lakes are shallow eutrophic water bodies with a high surface to
depth ratio and are widely used for recreational and fishing activities. Intense cyanobacterial blooms were associated with calm weather, high water temperatures (>20°C), and low oxygen saturation in surface (40–70%) and bottom (1–30%) waters. The maximum biomass of harmful cyanobacteria occurred during August–September. Cyanobacterial blooms were dominated by Anabaena spp., Aphanizomenon flos-aquae and Microcystis spp. A significant decrease of the Shannon-Wiener species diversity index was observed during bloom periods. Hepatotoxins (microcystins) were detected in 50% of the surveyed lakes. High-performance liquid chromatography analysis of algal biomass indicated the presence of microcystins MC-LR, MC-YR, MCRR
and MC-LA. The most abundant was MC-LR, contributing on average 43% of the total microcystins. Microcystin concentrations showed a significant interannual variation. The highest concentration of microcystins was observed in Lake Lielais Baltezers
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Articles

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eISSN: 1814-2338
print ISSN: 1814-232X