Floristic diversity in the small rivers with different morphology in the zone affected by backwater of a lowland reservoir
A comparative study of the floristic diversity of small rivers is of great importance in the assessment of their environmental state, which allows assessing the degree of pollution of the environment. The floristic diversity of the estuaries of the small rivers Korozhechna, Latka, Il'd', and Chesnava, has been studied with special attention to the ecological groups and biological peculiarities of certain species. All the studied rivers flow into the Rybinsk Reservoir and have different morphology of the studied estuaries. The largest number of species has been recorded for the Chesnava River, the lowest, for the Il'd' River. The representatives of families Poaceae, Cyperaceae, and Juncaceae evidence on the active overgrowing of shallow waters and periodically flooded coasts. Most of the species can grow on various soils, they are typical for water bodies with an oscillating water level and weak flow. The species-to-genus ratio, which is inversely proportional to the diversity of ecological conditions, is the highest in the Korozhechna River and the smallest in the Chesnava and Latka rivers. On the rivers Hydrophytes and hygrophytes dominated in the Korozhechna and Latka rivers; hygrophytes, hydrophytes, and hydrogelophytes, in the Il'd' River; hygrophytes, mesophytes and hydrophytes, in the Korozhechna River. Such differences are explained by the peculiarities of environmental conditions. The highest similarity, by the absolute number of common species and by Jaccard coefficient, is found between the Chesnava River and the Latka River and between the Il'd' River and the Latka River. According to hydrophytic cover index (HCI), near-water species dominated in the Chesnava River, a slight advantage in the proportion of the aquatic component of the flora was observed in the other rivers.