Analysis of the seasonal dynamics of river phytoplankton based on succession rate indices for key event identification

The seasonal dynamics of river phytoplankton was analyzed using succession rate indices based on data collected from year-round observations of two small plain rivers in the Upper Ob Basin (Western Siberia). The study revealed a generally clear seasonal pattern of structural changes in the phytoplankton of the lower reaches of the studied rivers. The dynamics of succession rate indices reflects the key events in the life of phytoplankton in the Bolshaya Losikha and Barnaulka Rivers, showing mainly changes in the dominant species during the main phases of the hydrological cycle. The most significant changes in phytoplankton structure tend to occur in the period between the spring flood decline and the beginning of summer–autumn low water. These changes coincide with the most drastic changes in both environmental conditions and phytoplankton successional stages. Use of succession rate indices to analyze the seasonal dynamics of phytoplankton allowed us to distinguish between periods of abrupt change and periods of comparatively low-intensity changes in plankton composition in small lowland temperate rivers.