A comparison of phytoplankton development in Lake Baikal, Siberia, and Rybinsk Reservoir, Volga River, European Russia, using stability indices

Abstract

Based on observations of 2009–2022, the state of phytoplankton and its main taxa was analyzed in Lake Baikal (Siberia, Russia) and Rybinsk Reservoir (European Russia), two large freshwater lake reservoirs. Data were collected during periods of phytoplankton seasonal maxima which determine the total level of their annual production. The development of phytoplankton was assessed by biomass expressed in units of wet weight for Lake Baikal and units of chlorophyll a for the Rybinsk Reservoir. To assess the sustainability of biomass, its coefficients of variation, deviation from the mean value, and population stability index were calculated. These metrics did not reveal any definite inter-annual trends in the state of phytoplankton, but showed sharp changes in the level of community resistance in years with different trophic state. In both water bodies, a decrease in stability was observed under conditions atypical for the ecosystem. In the oligotrophic Lake Baikal, the most unstable situation was noted in highly productive years with the mass development of diatoms in the spring plankton. In the moderately eutrophic Rybinsk Reservoir, its resistance decreased in low productivity years with a weak summer development of phytoplankton and cyanobacteria due to the unfavorable weather conditions. The proposed approach will be of interest for assessing the stability of other aquatic ecosystems.