Vertical Distribution of Chlorophyll in the Upper Volga Reservoirs

Abstract

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).