Influence of flow velocity, river size, a dam, and an urbanized area on biodiversity of lowland rivers

Abstract

Biodiversity of aquatic organisms is formed under the influence of not only natural, but also anthropogenic factors. In this work, the influence of the flow velocity, river size, flow regulation and urbanization on various groups of aquatic organisms was studied in several lowland rivers. The study was conducted in 2013 on six tributaries of the Upper Sukhona River. Five sampling sites were in different parts of the Vologda River and five sites on small rivers, Losta, Lukhta, Komya, Chernyj Shingar, and Belyj Shingar (one site per river). Phytoplankton, zooplankton and zoobenthos were sampled six times, from April to October, and macrophytes were studied in August. In total, 469 species of aquatic organisms were found in the tributaries of the Upper Sukhona River, belonging to the following phyla: Cyanophyta (5 species), Chrysophyta (8), Bacillariophyta (62), Xanthophyta (1), Cryptophyta (10), Dinophyta (4), Euglenophyta (12), Chlorophyta (17), Streptophyta (1), Bryophyta (2), Marchantiophyta (3), Equisetophyta (1), Magnoliophyta (63), Rotifera (22), Cnidaria (1), Platyhelmintes (1), Annelida (29), Mollusca (33), Arthropoda (194). The maximum number of species was found in the Vologda River, the largest of all the tributaries. The number of zoobenthos species was similar at different sites in the Vologda River and in the small rivers. The number of species of other groups of aquatic organisms in the small rivers was lower than those registered in the Vologda River. The greatest number of macrophyte and zoobenthos species was recorded in the Upper Vologda River and Belyj Shingar River, where the flow is strong all the year round. The greatest number of phyto- and zooplankton species was found at the extra-city sites where current is almost absent. In the dam backwater, species richness was higher than that registered downstream of the dam. At the same time, the species richness of macrophytes and zoobenthos in the dam backwater was lower. The smallest number of species was found in the Vologda River, downstream of the city of Vologda. Decreases in the species richness and Shannon’s biodiversity index were witnessed in the Vologda River city site and in the small rivers, as they get closer to the city. Cluster analyses performed for the studied groups of aquatic organisms showed dissimilar results; however, the studied sites on the Vologda River having the highest anthropogenic load formed a cluster. Aquatic organisms of the Upper Sukhona tributaries experience both natural (flow velocity and size of the watercourse) and anthropogenic factors (proximity to the city and flow regulation).