Peculiarities of under-ice phytoplankton development in deep, cold-water lakes: Lake Teletskoye (Altai, Russia) case study

Abstract

The under-ice phytoplankton was studied in the latitudinal part of Lake Teletskoye in 1997, 2006, 2018, 2023, and 2024 under different ice conditions–partial and complete freeze-up. During the under-ice period, the total diversity and abundance of phytoplankton decreased compared to the period of open water during the spring-summer-autumn growing season. With thick ice cover and a thick snow layer, diatoms and flagellates develop predominantly in numbers–a group of small-celled centric Pantocsekiella teletskoyensis, Stephanodiscus minutulus, S. binatus, and Stephanocostis chantaicus and the cryptophyte algae, Komma caudata. These species dominate in numbers even during the period of open water. Large algae, for example, Mallomonas alpina from golden algae, periodically make a significant contribution to the biomass of phytoplankton. The diversity and abundance of phytoplankton in the pelagic zone are typically lower than in littoral areas. With stable freeze-up, but with thin ice and a thick snow layer, cyanobacteria develop predominantly in the under-ice phytoplankton of Lake Teletskoye; in all other cases, diatoms and cryptophyte algae develop. In littoral areas (with depths down to 30 m), benthic forms and periphyton inhabitants, mainly diatoms, make a significant contribution to the diversity and abundance of winter under-ice phytoplankton, especially to its biomass. Overall, the development of phytoplankton under the ice of Lake Teletskoye in different ice conditions ranged from extremely low to average levels for this water body. Between 1989 and 1997, phytoplankton biomass varied from 0.5 to 1207.5 mg/m³ with a seasonal average of ~150 mg/m³ (Mitrofanova, 2000). In winter phytoplankton, the average biomass over the four studied years was 94.3 ± 21.3 mg/m³ (for the entire dataset) or 175.3 ± 28.7 mg/m³ (for the 0–10 m layer), so according to the trophic scale of lakes by I.S. Trifonova (1990), Lake Teletskoye can be classified as an ultra-oligotrophic water body (0–500 mg/m³). High values of the Shannon-Weaver diversity index may indicate the formation of an under-ice algal community.