Chlorophyll Content and Photosynthetic Activity of Phytoplankton in Reservoirs of the Volga River (Russia)

Abstract

Using the fluorescent method in the modification of Krasnoyarsk State University, we studied the development (as chlorophyll content, ∑CHL) and photosynthetic activity of phytoplankton in seven large flat reservoirs of the Volga River cascade (Russia) in August 2015–2017. In the period of the maximal warming of water, average ∑CHL varied in limits of 19.4–33.7 μg L−1 in the Upper Volga, 8.5–27.8 μg L−1 in the Middle Volga, and 5.2–11.3 μg L−1 in the Lower Volga. The photosynthetic activity coefficient (PhAC) varied mostly in limits of 0.12–0.59, with an average of 0.22–0.38 and only in 2017 decreased to minimal < 0.10 and average < 0.20. The average PhAC values show the normal physiological state of the phytoplankton of the Upper Volga during all periods of observation, with an occasional decrease in PhAC in the Middle Volga and low photosynthetic activity in the Lower Volga. A decrease in the average ∑Chl and PhAC in 2017 was under cyclonic windy weather with a large amount of precipitation, low solar radiation, and large volume of flow. A trend towards a decrease in ∑CHL, like a decrease in PhAC from the Upper Volga to the Lower Volga, is explained by an increase in the flow rate and volume of runoff downstream of the Volga River.