Abstract
Massive developments of potentially toxic cyanobacteria in Lake Stechlin, an oligo-mesotrophic lake in the Baltic Lake District of Germany raised concerns about toxic contamination of these important ecosystems. Field samples in the phase of mass developments of cyanobacteria were used for genetic and toxicological analyses. Microcystins and microcystin genes were detected in field samples of the lake for the first time. However, the toxins were not produced by the dominant taxa (Dolichospermum circinale and Aphanizomenon flos-aquae) but by taxa, which were present only in low biomass in the samples (Microcystis cf. aeruginosa and Planktothrix rubescens). The phytoplankton successions during the study period revealed an increase of cyanobacterial populations. The findings contribute to the changes that have been investigated in Lake Stechlin since the mid-1990s. The possible reasons behind these developments may be climate change, special weather conditions and an increased nutrient pool.
Highlights
The Baltic Lake District in northeastern Germany hosts a multitude of lakes formed during the last glacial period (~12,000 years before) [1]
Lake Stechlin is a glacial originated, deep, oligo-mesotrophic lake located in the Baltic Lake District
The molecular biological analysis of the mcyE gene fragments did show that Microcystis aeruginosa and Planktothrix rubescens, both minor members of the community, were the microcystin producers in Lake Stechlin
Summary
The Baltic Lake District in northeastern Germany hosts a multitude of lakes formed during the last glacial period (~12,000 years before) [1]. Some of the lakes are pristine and belong to the highest classes of water quality according to the European Water Framework Directive (WFD). The lake belongs to the type 13 of WFD that collects stratified lowland lakes with small catchment area with high content of calcite [2]. The investigation of phytoplankton started in 1959, the year the Limnological Laboratory Stechlin was founded. A number of investigations in relation to the different aspects of phytoplankton were performed: species composition, temporal and spatial distribution of the dominant species, seasonal periodicity, cell number and biomass calculation. These studies were conducted using different sampling frequencies.
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