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 study development (as chlorophyll content, ∑CHL) and photosynthetic activity of phytoplankton in seven large flat reservoir of the Volga River cascade (Russia) in August 2915–2017. In period of 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. Photosynthetic activity coefficient (PhAC) varied mostly in limits of 0.12–0.59 with average of 0.22–0.38 and only in 2017 decreased to minimal <0.10 and average <0.20. The average PhAC values shows the normal physiological state of the phytoplankton of the Upper Volga during all periods of observation, occasional decrease of 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. Trend towards a decrease in ∑CHL, like decrease in PhAC from the Upper Volga to the Lower Volga is explained by increasing in the flow rate and volume of runoff downstream the Volga River.

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

“…The photosynthetic activity coefficient (PhAC) changed less than ∑CHL, and it looked like a more stable parameter as well as photosynthesis measured via the oxygen flask method [8]. The same PhAC range was obtained for phytoplankton of the Yangtze River [30], Lake Shira [50], and earlier in reservoirs of the Upper Volga, including Rybinsk reservoir, which also had a low PhAC variation [25,26].…”

“…Phytoplankton form the basis of the trophic pyramid in the largest river in Europe, the Volga River, which has now been transformed into a cascade of reservoirs [7,8]. Research of the pigments in the Volga River was started in the middle of the XX century [9], and these studies have been supplemented with new data [10][11][12], which are summarized in [13].…”