Vertical Water Structure and Reservoir Plankton in Spring

Changes in the vertical water structure and the associated plankton succession in the Mozhaisk Reservoir in the transition period from winter to summer in 2019 are considered. It is shown that the characteristic features of these changes remain the same as they were several decades ago. However, differences have appeared. The current global warming leads to the activation of photosynthesis under the ice in the spring, the early beginning of spring homothermy, and a faster establishment of stratification in the Mozhaisk Reservoir. The annual spring cycle of cyclops (emerging from diapause) occurs much earlier; the next maximum of Daphnia is observed earlier. At the same time, the level of development of zooplankton in 2019 was less than 30–40 years ago. It is possible that the reason for this is an increase of anoxia in the hypolimnion, caused by the early onset and increase in the duration of stratification of the water masses observed in recent decades, as well as by the eutrophication of the reservoir.