Analysis of diatom algae from the water column and bottom sediments of Shira Lake (Khakassia, Russia)

Lake Shira as a meromictic lake is object of interest for paleolimnological studies. In May 2011 core samples were collected from the bottom of Lake Shira and the species composition of diatom algae, which serve as bioindicators of the state of the lake, were studied. In addition, in 2012, seasonal water samples and material from sediment traps were collected and the species composition of diatoms in them was analyzed. The results of the analysis showed that the lake, like in previous years of research, was dominated by Cyclotella choctawhatcheeana Prasad. Diatoms were found twice in the studied core above the white carbonate layers and were absent in other layers. The species living in the lake at present were observed down to the first white carbonate layer, including the predominant Cyclotella choctawhatcheeana . This fact presumably proves the consistency of the species composition of diatoms and the overall stable condition of the lake since 1946 (Rogozin et al., 2005). Down to the second white carbonate layer, the dominant species were Aulcosira valida (Grunow) Krammer and Aulcosira italica (Grunow) Simonsen. Nitzchia sigmodea (Nitzsch) W. Smith and Fragilaria construens var. venter (Ehrenberg) Grunow were also observed at these depths, dating approximately to 1655–1690. These are freshwater species that belong to the diatoms of arctic, alpine, and temperate latitudes, which develop in shallow waters under moderate temperature conditions. This fact suggests that Lake Shira was less salty in the middle and end of the 17th century than today.