Dynamics of algae communities in an oxbow lake (Vistula River, Poland)

This paper presents the results of research on phytoplankton in an oxbow lake on the Vistula River. Originally, the reservoir was natural; however, at the beginning of the twentieth century, the basin of the oxbow lake was dredged and broadened. In 1934, the harbor basin became a protected spawning ground for pikeperch, and as such is a unique site in Poland. The research presented herein was conducted during the growing season of 2008, when 249 taxa of algae were identified in the phytoplankton, mainly Chlorophyta and Bacillariophyceae. The average biomass of the oxbow lake during the entire research period was 33 mg dm^-3. The largest biomass was recorded in August at more than 90 mg dm^-3. During the entire growing season, the dinoflagellates Peridinium willei (Huitfeld-Kaas) played a significant role in the phytoplankton. In the summer, a mass bloom of blue-green algae occurred in the phytoplankton, with the following dominant species: Aphanizomenon flos-aquae (L.) Ralfs ex Born. et Flah.; Dolichospermum planctonicum (Brunnthaler) comb.n.; Synechocystis aquatilis (Sauvageau). Port Drewny was classified as hypertrophic based on the results of the phytoplankton research and the physicochemical conditions. The dominance of blue-green algae, including potentially toxic species, could be dangerous for Port Drzewny as a protected spawning ground for pikeperch.