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Abstract Lake Baikal is facing several environmental stressors, including climate change and nearshore eutrophication. To assess recent ecological changes in Lake Baikal and provide a baseline for future comparisons, we sampled spring plankton communities from the pelagic zone of the lake in 2016 and compared these data with unpublished and published historical information going back to 1990. In 2016, one pelagic long-term monitoring station was sampled in early spring (March) during ice cover and 21 long-term monitoring stations located throughout the lake were sampled in late spring (May-June). We measured water chemistry parameters at most stations and the abundance, taxonomic composition and biomass of bacteria, ciliates and phytoplankton at several locations in different areas of the lake. Biotic parameters from 2016 were compared with historical data, showing significant changes in the spring pelagic microbial community since the 1990s. We show increased quantities of small species, mixotrophic ciliates, and the appearance (or increasing number) of small coloured and colourless flagellates. We also show substantially decreased densities of formerly dominant heavily silicified diatoms such as Aulacoseira spp. Since 2007, Synedra acus subsp. radians, a smaller and weakly silicified diatom, has dominated the spring plankton of the lake. These results suggest that Lake Baikal's pelagic plankton community may be changing, with climate likely playing a dominant role in these changes. [ABSTRACT FROM AUTHOR]

Abstract: In two reservoirs of different trophic state, the abundance of autotrophic picoplankton was continuously assessed for 7 and 11 years, respectively. Simultaneously, other important environmental and biotic factors (nutrients, temperature, phyto- and zooplankton) were analysed. The mesotrophic Saidenbach Reservoir receives five- to sevenfold higher phosphorus imports, and exhibits twice higher phosphorus contents, and tenfold higher phytoplankton concentrations than the oligotrophic Neunzehnhain Reservoir. Despite these differences, the quantities and dynamics of autotrophic picoplankton (APP) showed remarkable similarities in both reservoirs. The APP consisted almost exclusively of Phycoerythrin-rich cyanobacteria. A notable growth of cyanobacteria never started before the onset of stratification and finished no later than the beginning of the autumnal turnover. Although the soluble reactive phosphorus (SRP) concentrations in the epilimnion were always near the limit of detection, there was no evidence for growth restriction of APP by nutrients in either of the reservoirs. However, the data reveal a strong grazing impact of all potential grazers, especially of the daphnids. This zooplankton group always showed a strict behaviour opposite of the APP during its growth periods. The grazing influence of rotifers and protozoans is less pronounced but also obvious, notable by the frequently observed inverse relationships between their quantities and those of APP. It is assumed that during the stratification period in the summer the APP dynamics is mainly top-down controlled. [Copyright &y& Elsevier]