Summer phytoplankton 24-hours dynamics in the lake Svetloyar (Nizhny Novgorod region)

In this research the information of structural parameters of algocenoses (species richness, proportions of leading groups, abundance, biomass) in the photosynthetic zone of a unique karst lake Svetloyar (Nizhny Novgorod region) is provided according to the data for the summer of 2012. During the studied 24-hours period the main components of plankton were coccoid green and diatom algae, colonial and filamentous cyanobacteria, whose daily vertical migration was poorly expressed. The maximum of abundance and biomass of these species were noted at the afternoon (the period from 13:30 to 16:30) and in the most heated layer (0–4 m). Motile algae (mainly from phylum Dinophyta) were characterized with more noticeable daily activity. They were present in the algocenoses only in the daytime and evening hours and moved at night and in the morning below the photosynthetic zone. The daily dynamics of the species richness of algae demonstrated was similar with the indicators of quantitative development, while the number of dominant species remained stable during the day (amounting to 1–4 taxa in the sample).