Diversity and dynamics of phytoplankton in Lake Sakadaš (Kopački Rit Nature Park): results of the long-term studies

This report aimed at presenting the almost half century long investigations on phytoplankton species richness and dynamics of the most important taxa in the floodplain Lake Sakadaš, a part of the Kopački Rit Nature Park. According to the revised and updated data on taxonomic composition, a complete list of phytoplankton taxa in the lake summarized a total of 685 taxa belonging to 233 genera, among which, chlorophytes and diatoms were the most diversified groups. The appearance of the most abundant taxa shows certain regularity, indicating the seasonal periodicity of phytoplankton communities. Chlorophytes occur during all seasons, with higher abundance in late spring and summer communities. Beside regular seasonal development in colder water periods, overdomination of diatoms is connected with strong mixing events during the floodings. Cyanobacterial blooms, formed by different filamentous species regularly appear in summer, depending on the timing and magnitude of flooding. Anthropogenically derived pollution in the past, eutrophication as well as the extreme hydrological events which became more frequent in this part of the Danube Basin showed significant influence on lake phytoplankton community structure. Long-term studies have also resulted in several findings of alien and potentially invasive phytoplankton species, whose occurrence and spreading is continuously monitored. Investigating the diversity and ecological dynamics of phytoplankton in a long time period is very important as it provides a framework for the evaluation and monitoring of ecological status of riverine floodplains according to requirements of the European Water Framework Directive and is crucial in designing measures for floodplain conservation.