Phytoplankton Change Along the Length of the Ural River under Conditions of Eutrophication

Abstract

The change in phytoplankton along the length of the Ural River from Verkhneuralsk to Orenburg (on a site of more than 1000 km) has been studied for the first time. The powerful eutrophying effect of Magnitogorsk on the river for more than 150 km has been revealed. It manifests itself in the fact that the phytoplankton biomass in this area increases greatly, averaging about 15 mg/L (with the dominance of cyanobacteria Microcystis aeruginosa), whereas the species diversity index (Shannon index), on the contrary, reaches extremely low values of 0.25. This indicates a significant oppression of the plankton community and deterioration of water quality. In the Ural River above this site (from Verkhneuralsk to Magnitogorsk reservoir), as well as below it (from Orsk to Orenburg), phytoplankton indicators correspond to the usual values of 1.6–1.7 mg/L of biomass, with a Shannon index of 3.3–3.5 (on average for each site). This suggests that the conditions for the existence of plankton in the upper and lower areas are favorable. At the same time, the sites differ in the composition of algae: the first is dominated by diatoms and the second is mainly dominated by green algae. This may be due to geographical factors: in the north, the Ural River flows in the forest-steppe zone, and in the south it flows in the steppe.