Seasonal variation in phytoplankton and aquatic plants in floodplain lakes (lower Vistula River, Poland)

Abstract

The study focused on three oxbow lakes which have been isolated from the water of the Vistula River for several years. The diversity of phytoplankton communities was observed biweekly in the growing season (April–October), both in the three floodplain lakes along the lower Vistula River (northern Poland) and in the main current of the river. The water level in the Vistula River remained low, so the lakes were not filled with the surface water of the river. Different phytoplankton communities occurred in the studied lakes compared to the Vistula River. The phytoplankton in the oxbow lakes consisted mainly of small unicellular and colonial flagellates: Cryptomonas, Chlamydomonas, Trachelomonas, and Dinobryon. During the limnophase, only 2–3 species co-dominated, and the reservoirs were in a stable water conditions. The river phytoplankton had both higher diversity and higher abundance compared to the floodplain lakes. In total, 4–8 species co-dominated in the river, usually Chlorococcales and diatoms. The floodplain lakes were characterized by unexpected differences in the quality, quantity, and dynamics of planktonic algae. The differences were strictly associated with the occurrence of macrophytes. During the limnophase, the investigated oxbow lakes were also diversified in terms of colonizing plant communities. Different types of vegetation—free floating plants (W-1 lake), communities of submerged macrophytes, free floating plants and algal mats detached from the bottom (W-2 lake), and submerged macrophytes (Ma lake), affected the development of the microflora to a varying extent.