LAUSR

The vertical distribution of phytoplankton (chlorophyll a, CHL) was investigated in August 2015 at 25 sampling stations in the Ivankovo, Uglich, and Rybinsk reservoirs (Upper Volga, Russia) using a bbe Moldaenke Fluoroprob submersible fluorimeter. Three types of CHL vertical distribution were identified under homothermy. There was a gradual CHL decline in the water column at the upper part of reservoirs; a sharp decline at a certain depth in most riverine sections; and uniform distribution opposite the mouth of a small river (the Kashinka River, Uglich Reservoir), as well as at the open lacustrine sites of the Rybinsk Reservoir under wind-driven mixing. The average CHL content in the euphotic layer at the stations of three groups were 25.0 ± 6.3, 44.1 ± 4.0, and 20.8 ± 2.9 μg/L, respectively; the CHL contributions to the PAR absorption were 47 ± 9%, 66 ± 4%, and 38 ± 6%. Under thermal stratification the vertical distribution of CHL corresponds to the course of the temperature dynamics (r = 0.85).