Phytoplankton composition and biomass structure in relation to trophic gradient in some temperate and subarctic lakes of north-western Russia and the Prebaltic

Abstract

A comparative analysis of the phytoplankton of 27 lakes of three Lake Districts (Karelian Isthmus, Latgalian Elevation and Bolshezemelskaja Tundra), all situated at high temperate (60 and 56 ° N) and subarctic (67–68 °N) latitudes with a wide range of the trophy, is presented. A direct correlation between TP content and phytoplankton biomass was observed in all three regions. As the mean annual TP concentrations range from 10 to 137 mg m^-3, the variation of average biomass for a growing season was 0.4–20 g m⁻³. The total number of phytoplankton species found in individual lakes varied from 25 to 160, increasing along the trophic gradient. The largest number of phytoplankton species was found in lakes supporting mean biomass in the range 10–20 g m⁻³. Taxonomic diversity decreased in some hypertrophic polluted lakes and in acidic lakes. In lakes of all regions, the number of species of chlorophyte, blue-green and euglenophyte algae increased with lake trophy. Analyses of distribution and ecology of mass species shows that in spite of the influence of latitudinal factors, such as the mineral content of lake waters the succession of dominant phytoplankton species show consistent trends: more cosmopolitan species with wide ecological amplitudes accompany the trophic gradient. Step-wise regression analyses showed that trophic factor had the greatest influence on the total phytoplankton biomass and biomass of blue-greens, chlorophytes and euglenophytes. Biomass of dinoflagellates and chrysophytes was influenced considerably more by total ionic concentration than by the trophic factor. The most important factor for diatoms was lake morphometry. Biomass of nanoplankton algae was influenced by trophic factors but also by lake depth.