Dynamics of Yenisei zoobenthos evolution in the downstream of Krasnoyarsk Hydroelectric Power Station

The Yenisei River is the main Siberian River, it is one of seven largest rivers in the world and it is the most high-water river in our country. The construction of Krasnoyarsk hydroelectric power station caused global changes in hydrological, hydrochemical and hydrobiological regimes in the Yenisei River. Zoobenthos plays a very big role in the food chain throughout the whole Yenisei River due to the fact that the evolution of plankton is limited by a large flow rate and a large water turbidity which accompanies it. In this work there are the main results of researches of the zoobenthos community of the Yenisei River from the dam of Krasnoyarsk hydroelectric power station to the estuary of the Podkamennaya Tunguska River. The modern population of Yenisei zoobenthos basically consists of chironomids, oligochaetes and amphipods. There are 164 species of invertebrates in the composition of benthic fauna in the examined area. There is a great variety of larvae of Diptera - 91 species. For the Upper Yenisei River the litoreofilny biocenosis with predominance of chironomids, oligochaetes and amphipods is typical. Near Krasnoyarsk the mass evolution of oligochaetes is registered. The average abundance of benthic fauna from the dam of Krasnoyarsk HPS to the estuary of the Podkamennaya Tunguska River is 3500 spec./ m, biomass - 10,8 g/m. After confluence with the Angara River, the areas, which are covered by sand deposits, grow. Chyronomids are still the most major, but the percentage of amphipods and oligochaetes significantly decreases, they are replaced by clams, mayflies and caddisflies. Amphipods and members of the group "others " make a very big contribution in biomass. The average bottom productivity in the area from the Angara River to the Podkamennaya Tunguska River is 1200 spec./m and 2,8 g/m. Regulation of the Yenisei River has caused global changes in the river's zoobenthos; first ofall, it is the dissemination of Baikal's amphipods above the estuary of the Angara River. Quantitative characteristics of zoobenthos greatly increase after regulation, especially in the area from the dam to the Angara's estuary: the quantity - by more than 2 times and the biomass - by 5 times. The percentage of amphipods in zoobenthos' biomass has increased in 10 times, the percentage of chironomids - in 9 times and of oligochaetes - in 40 times as compared with the materials of V.N. Greze. At the same time, stoneflies and midges have almost disappeared from benthic fauna, a number of species and a quantity of caddisflies and mayflies have greatly decreased. The analysis of the temporary dynamics indicates the continuing rise of biomass of zoobenthos in the Yenisei River, especially in the area from the dam of Krasnoyarsk HPS to the estuary of the Angara River. The reason for the increase in the biological productivity of the Yenisei River is the strengthening of an anthropogenic pressure on the Yenisei ecosystem which has caused magnification of the river trophicity and the enrichment of the water column with biogenic elements.

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