Contrasting distribution patterns of subfossil testate amoebae and cladocerans in a stratified freshwater lake and their significance for bioindication and palaeoreconstructions

The aim of this study was to investigate and compare the distribution patterns of subfossil testate amoebae and cladocerans in the surface bottom sediments of a stratified freshwater Glubokoe lake (East European plain, the Smolensk-Moscow upland) and assess environmental variables correlated with these patterns. Samples were collected with a depth range of 0–32 m and intervals of 3 m along two transects, resulting in a total of 69 samples from 33 sites. We distinguished three testate amoeba assemblages and four Cladocera taphocenoses. The distribution patterns of testate amoebae were determined by the local hydrological conditions in bottom sediments: temperature, productivity of habitats, BGA-PC and oxygen content, while the distribution patterns of cladocerans were driven by the presence of waterplants and postmortem transition of littoral species remains. Clear shifts observed in species structure of testate amoebae assemblages corresponding boundaries between hydrologically different bottom zones and reflect changes in the environmental conditions within a single waterbody. Changes in cladoceran taphocenoses were gradual and reflect the presence of waterplants in lakes but did not reflect changes in the hydrochemical characteristics within a single modern waterbody. When interpreting changes in the species structure of the studied groups of organisms in the past, one should consider the observed features that can improve the quality of palaeoreconstruction