PHYTOPLANKTON AS A NATURAL INDICATOR FOR ECOLOGICAL STATE, RISK ZONE AND RESILIENCE OF LAKE ZADOVZHE (THE NOBEL NATIONAL NATURE PARK)

Abstract

The study presents changes in phytoplankton indicators (taxonomic composition, abundance, biomass, dominants) of Lake Zadovzhe, and also analyzes hydroecosystem ecological state, risk zones and resilience in accordance with the development of indicator species. It has been found that during 2022–2025 (August) phytoplankton of Lake Zadovzhe was represented by 74 (76 intraspecific taxa) species), from 57 genera, 40 families, 29 orders and 12 classes, 5–8 divisions. The main taxonomic richness of phytoplankton is formed by the divisions Bacillariophyta, Chlorophyta and Cyanobacteria. It has been shown that Cyanobacteria species reach high abundance. However, active water blooms were not recorded, since Ceratium hirundinella (O.F. Müller) Dujardin (35.7%–77.4%) dominates in biomass. During 2022–2025, the total biomass is 0.0305–0.6872 mg/dm3, and the number is 127–5614 thousand cells/dm3. The ecological state of Lake Zadobzhe in terms of phytoplankton biomass mainly meets the criterion of “excellent”, and in terms of number it is “good”. In the phytoplankton of Lake Zadovzhe, planktonic, planktonic and benthic forms, indifferents (by pH, halophyte, water oxygen saturation and rheophilicity), eurysaprobes (by organic water pollution according to the Watanabe system) prevail. In terms of trophicity, mesoeutrophic (2022–2023), mesotrophic (2024) species are most represented, as well as oligo-mesotrophic, mesotrophic and meso-eutrophic (2025). In terms of type of nutrition and ratio to the amount of nitrogen-containing organic compounds, autotrophs that withstand elevated concentrations of NСС prevail. Among the saprobity indicators according to the Pantle – Buk system in the Sladechek modification, the most numerous group is β-mesosaprobionts (2022–2023), oligo-α-mesosaprobionts (2024) and oligosaprobionts and β-mesosaprobionts (2025). It has been highlighted that within the level of organic pollution according to the Pantle – Buk system (in the Sladechek modification), in 2022–2024, the water quality of Lake Zadovzhe mainly corresponds to class III (moderately polluted), and in 2025 it corresponds to class II and III (clean, moderately polluted). During the research the risk zone for Lake Zadovzhe changes in the direction of naturally clean ↔ self-purification to natural background ↔ threat. According to phytoplankton indicators, Lake Zadovzhe is assessed as a resilient ecosystem.