Patterns of seasonal phytoplankton dynamics as the element of ecological successional changes proceeding in a lake (Lake Kortowskie, northern Poland)

The aim of the research was to determine the successional changes proceeding in the phytoplankton of a lake. The basis of the study was the analysis of long-term seasonal changes in the taxonomic structure and the estimation of the intensity of algal community development in phytoplankton of Lake Kortowskie. Seasonal changes in the phytoplankton taxonomic structure manifested themselves as a decreasing share of Bacillariophyceae in spring and autumn and Chlorophyta in summer phytoplankton. The retreating chlorophytes and the diatoms were replaced by blue-green algae, the increasing share of which caused a reduction in the stability of the remaining phytoplankton taxonomic groups, and consequently, taxonomic shifts and progressive development of the overall phytoplankton community in all phenological seasons. Intensive algal growth was observed in spring and lasted until late autumn. The highest phytoplankton biomass was always recorded in summer. Summer phytoplankton development was related to increased bluegreen algae domination, the massive growth of which was observed from spring to autumn. The development of the Cyanoprokaryota community had a negative impact on the diatoms, since the latter earlier disappeared from the biocenosis in spring and re-developed to a lesser degree in autumn.