Mass development of phytoplankton in the River Warta in Poznań (Poland) in the 21st century
AbstractThe first studies of phytoplankton of the River Warta in Poznań (Poland) were carried out in the 20thcentury (in 1922–23 and 1950–57). In the growing seasons the dominant groups were diatoms and green algae. Cyanobacteria were noted, but they did not have high abundance. The aim of this work is to present the phytoplankton research conducted on the River Warta in Poznań in the 21stcentury (in 2003, 2009, 2010 and 2016). In all years the dominance of diatoms and green algae in terms of biomass was noted. However, in late summer cyanobacteria biomass was high and this group became dominant or co-dominant. Spring blooms were created by unicellular centric diatoms, e.g.Stephanodiscus minutulusand colonial green algae:Coelastrum microporumorMicractinium pusillum. In summer, bloom-forming taxa were unicellular centric diatoms, colonial diatoms:Aulacoseira granulataorFragilaria crotonensisand cyanobacteria:Aphanizomenon flos-aquaeandWoronichinia naegeliana. The occurrence of taxa typical of dam reservoirs and lakes suggests the influence of the Jeziorsko Reservoir on the phytoplankton of the River Warta, but it does not exclude the impact of tributaries and oxbow lakes. The research conducted in the 20thand 21stcentury show important changes in the taxonomical structure and abundance of phytoplankton.
