**3. Results**

#### *3.1. Species Composition of Algae during 100-Year Investigated Period*

The taxonomic structure of the algal composition of the Nesamovyte Lake is a summary of the available data on the species composition of algae for 100 years of investigations during the following study periods: 1910–1920, 1967–1978 to 2013–2021 [2,4,61,63,65,67,106,121]. It is represented by 234 species (245 infraspecific taxa (inft) composing eight divisions, 15 classes, 33 orders, 55 families, 100 genera of Cyanobacteria and algae (Table 2, Figure 2).


**Table 2.** Systematical composition of algae of the Nesamovyte Lake (1910–2021).

The basis of this taxonomic and species diversity for the lake is formed by Bacillariophyta and Charophyta, uniting together giving about 57% generic diversity and over 83% species and infraspecific composition of algae in different habitats of the Nesamovyte Lake. Less diverse, but indicative for presenting the dynamics of changes in taxonomic structure over time, presented the divisions of Chlorophyta (6.0%) and Euglenozoa (5.1%). A slight variety of species is inherent for the divisions' Cyanobacteria and Ochrophyta (Chrysophyceae) (2.1–1.7%), as for Cryptophyta and Miozoa (Dinophyta)—they are noted as having a few representatives (>1.0%).

**Figure 2.** Species composition of algae and cyanobacteria in the Nesamovyte Lake (split by taxonomic groups and three stages of research in 1910–2021).

At the same time, the leading set of orders of these taxonomic groups is formed by representatives of Desmidiales (15 genera—66 species—75 inft), Naviculales (10 genera— 50 species), Cymbellales (5–25), Achnanthales (5–11), Eunotiales (1–11), Sphaeropleales (6–7), Fragillariales (4–9), Zygnematales (6–6) and Euglenidida (2–5). These orders account for around 56% of the generic and species composition of algae in the Nesamovyte Lake. Leading genera of the algal composition are *Staurastrum* Meyen ex Ralfs (21–22 inft), *Pinnularia* Ehrenberg (14–16), *Euastrum* Ehrenberg ex Ralfs (12–15), *Navicula* Bory (12), *Cosmarium* Corda ex Ralfs (12), *Eunotia* Ehrenberg (11), *Gomphonema* Ehrenberg (10), *Encyonema* Kützing (5), *Planothidium* Round & L. Bukhtiyarova (5) and *Closterium* Nitzsch ex Ralfs (4). The named 10 genera cover about half (45.5%) of the whole diversity of species composition of this waterbody. However, almost 60% of genera are represented only by one species, which could serve as a characteristic feature of the studied lake flora.
