Expedition to the Angara Cascade reservoirs in June 2024

Written on 24 June 2024.

Within the RSF project “Microeukaryote Communities in Reservoirs of the Angara Cascade” (led by Ye.V. Likhoshway), a research expedition to the Bratskoye, Ust-Ilimskoye, and Boguchanskyoe reservoirs was conducted from June 1 to 14, 2024. The expedition consisted of researchers Cand. Sc. (Biology) A.M. Marchenkov (head of the team), Cand. Sc. (Biology) Yu.P. Galachyants, Cand. Sc. (Biology) A.I. Tanichev, and drivers D.V. Nikonov and F.A. Zamkovoy. Ship captains K.V. Stolyarov (in the Bratskoye reservoir), V.T. Shalimov (in Ust-Ilimskoye reservoir) and P.P. Shipunov (in the Boguchanskoye reservoir) assisted in water sampling in the reservoirs.

Water samples were taken with a Niskin bathometer from depths of up to 10 m. Nine samples were taken from the Bratskoye reservoir, including tributaries of the Oka and Iya rivers; nine samples from the Ust-Ilimskoye reservoir; and eight samples from the Boguchanskoye reservoir. The total number of samples amounted to 26. Water clarity was determined with a Secchi disk, water temperature and pH with a field instrument at the time of sampling. Water samples were concentrated onto filters for further examination of samples by scanning electron microscopy (SEM), filtered and fixed for quantitative analysis of phytoplankton composition by light microscopy (LM), and deposited onto filters for further DNA extraction and metabarcoding of microeukaryotes, and frozen for hydrochemical analysis of biogen composition.

Preliminary studies of phytoplankton composition were carried out by A.D. Firsova in the laboratory using SM and SEM. The phytoplankton of the studied reservoirs was represented by diatoms, golden greens, cryptophytes, and dinophytes had both similarities and differences between samples. A common component for all sites studied was the development of small centric diatoms Stephanodiscus minutulus (Kützing) Cleve & Möller. КBesides, all reservoirs were dominated by diatom algae such as Aulacoseira islandica (O.Müller) Simonsen, Asterionella formosa Hassall, Fragilaria radians (Kützing) D.M. Williams & Round – these species were present to a greater or lesser extent at all stations studied. Green algae were mainly represented by two species Monoraphidium contortum (Thuret) Komárková-Legnerová и Koliella longiseta (Vischer) Hindák. Dinophytes and cryptophytes were present in small amounts, the most prominent of which were Glenodinium sp. and Rhodomonas pusilla (Bachmann) Javornický respectively. According to SEM data, the scaly chrysophyte Mallomonas alpina Pascher & Ruttner and Mallomonas crassisquama (Asmund) Fottwere present at many stations of the reservoirs. According to preliminary data, no development of blue-green algae was observed in the reservoirs.

Surface water temperature in the Bratskoye reservoir varied from 4.4 to 13.6 °С, pH 7.64-8.29, and transparency from 2 to 6.5 m. At the station Naratai Nitzschia graciliformis Lange-Bertalot & Simonsen were dominant, from the greens – Monoraphidium contortum and Koliella longiseta. In another part of the Bratskoye reservoir, at Artuma station, the dominant composition changed to larger celled species Aulacoseira islandica, Asterionella formosa and Fragilaria radians.

The surface water temperature of the Ust-Ilimskoye reservoir was 4.9-10.2 °C, pH 7.3-8.0, transparency 5.5-6.5 m. It was noted that phytoplankton of the reservoir was not rich, at the Gluboky station, Stephanodiscus minutulus, Monoraphidium contortum and Glenodinium sp. predominated among all species encountered. In another part of the reservoir, at the station Ershovo, phytoplankton was more diverse, Stephanodiscus minutulus, Asterionella formosa, Fragilaria radians, Aulacoseira islandica, and Monoraphidium contortum predominated.

The surface water temperature in the Boguchanskoye reservoir was 4.1-11.8 °C, pH 7.24-8.1, and transparency 3-6 m. At the station Nedokura, phytoplankton was the most abundant and rich, dominated by centric diatoms Stephanodiscus minutulus and Aulacoseira islandica; Stephanodiscus alpinus Hustedt was common, as were Asterionella formosa and Fragilaria radians pennate ones. Fragilaria crotonensis Kitton and Fragilaria sublanceolata-baikali (Flower & D.M. Williams) Novais, C. Delgado & S. Blanco were also found. Among the greens, Monoraphidium contortum was most frequently observed. At the Rozhkovskaya station, small centric diatoms came to the fore, and among representatives of Aulacoseira, except for Aulacoseira islandica and Aulacoseira subarctica (O. Müller) E.Y. Haworth и Aulacoseira valida (Grunow) Krammer were also observed; Rhodomonas pusilla. was more frequently observed among cryptophytes.