How long does the summer last for zooplankton in the Onego lake?

To describe the responce of aquatic ecosystems to possible climate changes, the investigation of the lake phenology is needed. Earlier, four seasons in the ice-free period of the Onego lake were determined for zooplankton, but their duration was defined very approximately, because in the lake it is unable to observe this sesonal division exactly. It is well known that the composition of zooplankton has regular seasonal changes. This fact allowed us to distinguish the structural formal features of seasonal conditions using discriminant analysis on the abundance and biomass of the main groups of zooplankton. Seasonal division was defined more exactly. Summer period continues for 40 days and consists of two seasonal phases: early and late summer. This period does not coincide with calendar summer (July-August), it begins in early July (190th day of year) and ends in mid-August (230th day of year).