Influence of Water-Level Regime on the Overgrowing of Shallow Waters of the Rybinsk Reservoir

Abstract

The long-term and seasonal dynamics of the water level in the Rybinsk Reservoir has been studied for the period of 1947–2015. The dependence of the area of overgrowing of shallow waters (S) on the water-level fluctuations (Z) has been obtained: S = 30^‒45e^1.054Z. The overgrowing of open shallow waters is restrained by the hydrodynamic influence on the littoral zone, while, in the case of protected shallow waters, the limiting factor is the drying up of habitats of aquatic plants, which takes place at the end of the vegetation season. For different ecological groups, the calculated maximum and optimum areas of overgrowing vary from 10 to 100% of the total available shallow water area. Reserve areas suitable for the possible future distribution of plants vary from 40 to >90%. Results of the study show that, due to sharp long-term and annual fluctuations in water level, actual areas occupied by a higher aquatic vegetation are always significantly less than the calculated optimum and maximum areas. Under the current regime of reservoir regulation, its overgrowing will be maintained at a current level for a long time.