Zooplankton of the Bol'shoi Tsivil River (Middle Volga Region) under a Changing Hydrological Mode and an Increasing Anthropogenic Load

摘要

The zooplankton composition and structure in the Bol'shoi Tsivil River have been studied. The results were compared to A.S. Morozov's study of this river in 1913-1914, when it was a water-mill dam regulated stream. The fauna still features a significant number of eutrophic water indicators, and Rotifera prevails as before. The zooplankter average weight has decreased, and saprogenicity has increased. Surface food secondary filtrators and grazers gained a higher profile in the trophic structure. Such transformations can be evidence of increasing pollution of the Bol'shoi Tsivil River by biogenic and organic matter. The listed characteristics are the most sensitive and can be used for further monitoring of the Bol'shoi Tsivil River and for estimation of the state of other minor rivers of this region.