The impact of an extreme flood in spring/summer 2010 on phytoplankton communities in oxbow lakes of the lower Vistula River, central Poland

Abstract

In 2010, central Europe was hit by a massive flood. The main objective of this study was to assess the impact of this natural disaster on phytoplankton communities in four oxbow lakes of the lower Vistula River. In order to explain changes caused by the flood, the data from the year 2010 were compared with the data from the previous year. In summer 2009, the abundance and biomass of phytoplankton as well as chlorophyll a content in small isolated oxbow lakes were relatively low. Small nanoplankton flagellates prevailed. Much higher abundance and biomass of phytoplankton and chlorophyll a content were recorded in a large oxbow lake, characterized by the predominance of filamentous cyanobacteria. After the flood wave, the abundance and biomass of phytoplankton in the small oxbow lakes increased dramatically (18 and 7 times, respectively), but the number of species decreased. Filamentous cyanobacteria (Dolichospermum), euglenophyta and dinoflagellates were identified. In the large oxbow lake, the number of species increased but the abundance and biomass of phytoplankton decreased (by approximately 60 and 75%). There was a shift in dominant algal species. Cyanobacteria were replaced mainly by cryptophyta, small chlorophyta (Chlamydomonas) and xanthophyta (Heterothrix). The least significant changes were recorded in the Vistula River. Here, before and after the flood, the abundance and biomass of phytoplankton as well as chlorophyll a content and the dominant algal species remained unchanged. The massive flood caused severe environmental stress, which disturbed phytoplankton development and led to shifts between clear water and turbid states in the lakes.