Comparison of ice‐on and ice‐off abiotic and biotic parameters in three eutrophic lakes

Abstract The structure and abundance of winter planktonic communities are limited by environmental conditions that are unfavorable to life, but do not stop biological processes. The aim of the study was to test the hypothesis that the abundance of planktonic groups of organisms in temperate lakes can be higher during winter under ice cover than during the ice‐free seasons. Physical (ice/snow cover, temperature), chemical (organic carbon, chlorophyll a , phosphorus, nitrogen) and biological parameters (phytoplankton, protozooplankton, zooplankton) were investigated in three eutrophic lakes during two consecutive years in winter, spring, summer and autumn. The results of this study showed that in all lakes chlorophyll a concentrations were usually lower in winter than in other seasons, while total nitrogen concentrations were higher in winter than in autumn. All groups of planktonic organisms were able to reach similar or even higher abundances in winter under‐ice than in other ice‐free periods, depending on the lake morphometry and the year of the study. Winter taxonomic structure of phytoplankton was similar to the spring (medium‐sized Lake Dgał Wielki with the dominance of cryptophytes), summer (small‐sized Lake Dgał Mały with cyanobacteria as a dominant group) or autumn (the shallow lake with the dominance of diatoms) structure, depending on the lake. In all lakes, the structure of the ciliate community was the most similar to that of the spring with the clear dominance of Oligotrichida. Our results show that some species among all the studied groups of organisms can lead an active and dynamic life under the ice cover.