Comparative Characteristics of Phytoplankton and Epiphyton Productivity in the Upper Volga Reservoirs

Abstract

Comparative data from field observations in August 2005 and 2013 on phytoplankton and epiphyton productivity in the Ivankovo and Uglich reservoirs (Upper Volga) are presented. The average chlorophyll content (Chl a) varies from 7.6 ± 1.6 to 39.1 ± 0.7 μg/L in plankton and from 6.6 ± 2.8 to 28.4 ± 4.2 mg/m² of the substrate in epiphyton; the daily primary production values are 0.55–1.64 mg C/L and 0.10–0.68 g C/m² of substrate, respectively. Interannual different-direction changes in the development of the two communities have been identified. In the conditions of more intensive heating in 2013, Chl a content in plankton increased by factors of 1.5–2.5 when compared to 2005, while in epiphyton it decreased by factors of 2–3.5 times. In the Ivankovo Reservoir, abounding in large shallow areas, phytoplankton of the pelagic zone accounted for a lower proportion of algae biomass and primary production (66.6–78.6%) than in the Uglich Reservoir (86.5–97.0%), while, on the contrary, the share of epiphyton in the former reservoir (22.2 and 14.2% in 2005; 8.2 and 4.6% in 2013) was 1.8–5.1 times higher than in the latter.