Overgrowth dynamics of the Tsimlyanskoe reservoir

The Tsimlyanskoe reservoir is characterized by large near-shore shallows with a depth up to 5 m covering about 30 % of the reservoir and providing favorable environments for the development of aquatic vascular vegetation. Vegetation overgrowing influences negatively the water body ecosystem and natural reproduction of commercial fishery species. In this paper the preliminary results on the spatiotemporal dynamics of aquatic vascular vegetation overgrowth of the shallow water zones in the Tsimlyanskoe Reservoir from 1987 to 2017 are presented. The processing of Landsat images and GIS-based analysis supported by field research data provided insight in the features and dynamics of aquatic vascular vegetation overgrowth in the reservoir as a whole, and in case-study sites in particular. The analysis of the general long-term trend shows the successive change of two distinctive phases of near-shore zones overgrowth. In phase I (1987–1998), overgrowing processes were moderate, and annually the total area of overgrown shallows barely reached 1.3 % of the total reservoir area. Subsequent phase II (1998–2017) is characterized by an explosive overgrowth, when the total area of overgrowth increased up to 5.5-5.8 %. At that the overgrowth dynamics is largely related to reservoir water level regime, morphological conditions of shallows and reservoir bank transformation processes. The types of near-shore shallows the most prone to overgrowth were identified as: sheltered “pocket-type” shallows on locations of inundated the Don River floodplain lakes and distributaries, typically overgrown up to 40–70 %, seldom up to 90 %; and large bays of flooded estuaries of lateral tributaries with extended sand bars and alluvial fans, overgrown by 45–60 % in average and almost completely overgrown in river mouth areas.