The species composition of algae differs significantly in areas of reservoirs.

The species composition of algae differs significantly in areas of reservoirs.

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Dnieper cascade: reconstruction of the river biota after its transformation into a reservoir. Abstract

Reservoir dams create an obstacle for passable fish; in addition, those fish that penetrate fish pass structures usually do not find favorable conditions in reservoirs for reproduction due to poor flow and siltation of spawning grounds.

Phytoplankton. Regulation of runoff, creation of reservoirs and their cascades leads to significant changes in the biology of the river and changes the qualitative composition of phytoplankton. This is primarily manifested in a significant increase in the number of green and blue-green algae.

The formation of the phytoplankton species composition is influenced by the position of the reservoir in the cascade. In the middle and lower reservoirs of the cascade, the species composition is significantly poorer, and even if water exchange is significant, there is a « bloom » of water.

The species composition of algae differs significantly in areas of reservoirs. The richest in species is the phytoplankton of the upper and river basins, in the lower and middle parts, usually less species (although more biomass).

Creation of reservoirs, use of their water and biological resources cause intensification of « flowering » of water. The most common and well-known is the « bloom » of blue-green algae (although, of course, « bloom » and diatoms and greens).

Due to the presence of gas vacuoles, in calm weather, blue-green algae float to the surface of the water, forming spots of « bloom » of a specific bluish-green color.

In the spots of « flowering » develop the phenomena of biological pollution and self-pollution. In this case, the decomposition products of algae – ammonia, phenols, cyanides; the content of dissolved organic substances exceeds the norm for carbon by 20-40 times, for nitrogen – in 30-150, for phosphorus – in 20-25 times. The total number of bacteria increases by 25-100 times, and heterotrophic – up to 400 times.

The dominance of blue-green algae and the intensification of their reproduction are facilitated by many factors:

reduction of flow and water exchange, slowing down the flow rate (blue-green – stagnophiles), increasing the transparency of water during settling, accumulation of nutrients and organic compounds during the creation of the reservoir and its subsequent natural and anthropogenic eutrophication; lowering the level of oxygen saturation of water and increasing the recovery of the environment in the bottom layers due to siltation, as well as a high rate of reproduction of algae (offspring of one cell during the growing season is 10 individuals); their resistance to the absence of light, temperature fluctuations; high resting inhibitory activity of metabolites of blue-green algae in relation to other representatives of algae; toxicity and low rate of their use in food chains; lack of active consumers of this species among aquatic organisms of reservoirs, which would regulate its number.


After the regulation of runoff in the species and quantitative composition of ichthyofauna there are noticeable changes. Due to the sharp decrease in water exchange and flow velocities, increasing the depth and width of the waters, the number of rheophilic fish species is declining, while the number of limnophilous species, on the contrary, is increasing.

Reservoir dams create an obstacle for passable fish; in addition, those fish that penetrate fish pass usually do not find favorable conditions in reservoirs for reproduction due to poor flow and siltation of spawning grounds. Therefore, if some species of passage fish continue to exist, their numbers are rapidly declining, and they are concentrated mainly in the upper reaches, where sandy-pebble soils are found and increased flow is observed.

The process of ichthyofauna formation in reservoirs is accompanied by the loss of some of its species and significant intrapopulation differentiation. After the creation of reservoirs, especially in the first years of their existence, the species composition of the fauna is depleted. With the age of the reservoir, the number of fish species in them can increase due to both directed and spontaneous universe.

Fish populations in reservoirs are formed mainly due to the reproduction of local (native) species that lived in the river or located near water bodies and streams.

The largest number is observed in the generations of fish born in the first years of filling the reservoir, when the most favorable conditions are created for their spawning, development, survival of eggs and young. This is a gradual increase in water level, flooding of large areas of floodplain covered with meadow vegetation, which is the best substrate for the deposition and development of eggs. In freshly flooded areas, flow is maintained and zooplankton and zoobenthos develop, which also promotes the development of fish; and in the reservoir there are still few caviar-eating predators and young predators.

In the future, the breeding conditions of fish, especially phytophilous species, deteriorate due to the reduction of spawning area and feeding grounds for young. Meadow vegetation disappears on spawning grounds, and air-water plants begin to develop abundantly on protected ones.

As a rule, the number of young fish in high-water and medium-water years is higher than in low-water, but the growth rate and fertility are higher in low-water.

In the first years of the formation of ichthyofauna of reservoirs in populations the number of young individuals prevails, but later the ratio of age groups equalizes.

With the age of reservoirs there is a tendency to increase the number of a small group of species with a constant species composition. Perch breed especially intensively, because the conditions for it are quite favorable. However, the increase in the number of perch leads to a decrease in the number of valuable commercial fish, as the perch eats their eggs, and the natural regulator of the number of this species – pike – in the reservoir does not have normal conditions for existence.


Radiological pollution of nature: phytoindication. Abstract

The role of forests in the primary retention of radioactive releases. Formation of radiation syndrome in plants. Lethal outpouring of ionizing radiation on the plant. Influence of ionizing radiation on meristems, stem, leaves, needles. Influence of ionizing radiation on the reproductive sphere. Influence of ionizing radiation on seeds

The role of forests in the primary retention of radioactive releases

At the stage of primary release of radionuclides from the atmosphere, the field of radioactive contamination is formed under the influence of meteorological and landscape factors. The most significant of the landscape factors are: the relief of the earth’s surface, the type of vegetation, the hydrographic network, united by the term – the underlying surface. All physical processes occurring in the lower atmosphere are formed under the influence of the underlying surface.

The deposition of aerosol particles on the earth’s surface is determined depending on their size by the influence of gravitational forces and turbulent mixing of air. The particle sizes vary considerably – from 0.001 to 800 microns. The behavior of light particles of small size (up to 200 μm) near the boundary between atmosphere and earth is largely determined by turbulent diffusion, so the rate of their subsidence varies depending on the nature of the underlying surface.

Of all the elements of the underlying surface, forest plantations change the turbulent wind structure the most. The transformation of the flow structure is to reduce the vertical ripples of wind speed and the formation of smaller vortices under the influence of the forest.

Thus, through the transformation of air currents on the deposition of aerosol particles, forest stands play an important role in the formation of fields of radioactive contamination. They perform the function of a kind of filters – radionuclide accumulators.

After the Chernobyl accident, the highest density of radioactive contamination of forests with long-lived radionuclides is observed on the edges of the windward side. The opposite situation was revealed from the leeward. In general, forests have accumulated about 30% more activity than the surrounding fields. During the period of the most intensive emissions, when there was a large number of short-lived radioactive elements in the environment, the role of the forest in the redistribution of radionuclides was especially significant. This is evidenced by measurements of the exposure dose rate of gamma radiation in the middle of the summer of 1986.

The results of recent studies show that with high pollution, there is significant variability in the density of soil contamination in forest stands, even within one quarter and allocation. This diversity of pollution can be explained by the heterogeneity of forests and their local impact on the rate of air transport of radionuclides and the intensity of rainfall.

Terrestrial vegetation is the first screen that traps radioactive substances in the air.

Retention of solid aerosols deposited on plants and their subsequent losses depend on many factors:

phytomass per unit surface area; shape, size and orientation of leaves and other aboveground organs of plants; characteristics of their surface; wind speed during and after the fall of particles; the size of aerosol particles and the number of precipitation; relative humidity during precipitation, etc.

The retention of radioactive particles depends on the surface area capable of collecting particles.