Summer phytoplankton species composition and abundance in the southern basin of Lake Baikal and Irkutsk Reservoir

Abstract

Phytoplankton has higher species richness in summer, when water temperatures are higher than in other seasons in aquatic ecosystems. Here, we characterized phytoplankton communities using microscopy and environmental parameters (temperature, pH, transparency) in the southern basin of Lake Baikal and Irkutsk Reservoir, which is directly connected with the lake as it is the upper part of Angara River, the Lake Baikal outlet. Surface water temperature was 10.1-18.4 °С in the southern basin of Lake Baikal and 14.9-20.0 °С was in Irkutsk Reservoir, pH values were similar both in the lake and the reservoir (8.09-8.44 and 7.96-8.28, respectively), and Secchi disc water transparency was 4.5-9.0 m in the lake and 2.5-4.5 m in the reservoir. The phytoplankton community included 104 species from 7 high-rank taxa such as Chrysophyta (36), Chlorophyta (30), Bacillariophyta (22), Cyanobacteria (11), Cryptophyta (2), Dinophyta (2), and Haptophyta (1). Species composition of summer phytoplankton communities of the Irkutsk Reservoir and the southern basin of Lake Baikal were different, however the community composition in terms of high-level phylotypes was very similar. At the same time, a large number of small-cell cyanobacteria were identified in the lake. A high species richness of Chrysophyta, genus Dinobryon (11 species) and silica-scaled chrysophytes (22) was founded. The composition of dominant species of the southern basin of Lake Baikal and Irkutsk Reservoir became wider compared to data published earlier, and included Cyanodictyon planctonicum, Cyanodictyon sp., Microcystis sp., Dinobryon sociale, Dinobryon sociale var. americanum, Chlorella vulgaris and Mychonastes homosphaera.