Vol 11, No 3 (2018)

The total biomass of the biotic component of the ecosystem has been determined and the contribution of the main ecological groups—autotrophic and heterotrophic organisms from different habitats—to its formation has been estimated in a large plain meso-eutrophic reservoir (Rybinsk Reservoir, Upper Volga). Particular attention is paid to the role of heterotrophic bacteria in the structure and functioning of the biota in the reservoir. The total biomass of the biotic component of the ecosystem is 71536 t C, which is 5.2% of the total organic carbon in the reservoir. Higher aquatic plants make the largest contribution to the formation of the biomass in the reservoir. Their biomass, including epiphyton, was 6.0 and 1.9 times larger than the biomass of plankton and benthos, respectively. Heterotrophic bacteria, most of which inhabit bottom sediments, rank second in respect to their contribution to the total biomass. The comparison of the total primary production of all phototrophic organisms and the carbon demand of heterotrophic bacteria indicates the importance of allochthonous organic matter in the functioning of the reservoir ecosystem.

One hundred and eight species and forms of planktonic organisms have been revealed in three small reservoirs in the Komi Republic (the northeast of European Russia). Species that were not previously known for the water bodies of the Vychegda River Basin (Limnosida frontosa) and the Republic of Komi (Lecane mira, Macrochaetus subquadratus, Filinia longiseta limnetica, and Rhynchotalona falcata) have been found. It has been established that the richness of the planktonic fauna depends on the age of the water body: the maximum number of species is found in the oldest reservoir, namely, the Kazhim Reservoir. The planktonic communities of artificial reservoirs are distinguished by a low level of similarity of faunas both with each other and in comparison with the natural lakes of the region. The fauna distribution in the old reservoirs is uneven. The relatively large fauna richness of planktonic communities in the littoral zones is due to the water-level regime in the reservoirs.

The micromorphology of Hydrocharis dubia (Blume) Backer (Hydrocharitaceae) from the Far East of Russia has been studied. A detailed description of anatomical structure diversity is given for the vegetative organs, and species-specific and adaptive traits of the plant are assessed. The elongated submerged vegetative shoot of the plant is shown to have a metamorphosed anatomical structure.

The abundance and biomass of bacterioplankton, phototrophic picoplankton, and heterotrophic nanoflagellates has been determined in lakes, rivers, and reservoirs located in the Valley of the Lakes and Great Lakes Depression (Mongolia). The species richness of the heterotrophic flagellates and their consumption of bacteria are estimated. Pico- and nanoplankton are the most abundant in shallow mineral lakes Orog and Tatsyn and in the freshwater Durgun Reservoir. Heterotrophic nanoflagellates consume 26–92% (on average 66%) of the daily bacterioplankton production. Thus, flagellates are important in the transfer of bacterial carbon to the higher levels of planktonic trophic webs. A total of 30 species and their forms of heterotrophic flagellates from 14 large taxa are identified. The highest species diversity of these protists are found in the Durgun and Taishyr reservoirs.

Data on the content of plant pigments in the bottom sediments (BSs) of the water bodies of Central and South Vietnam are given for the first time. The average concentration of chlorophyll a and phaeopigments (Chl + Ph) in total reaches up to 3.9 μg/g dry matter in rivers, 5.6 in ponds, 13.8 in sand quarries, 56.8 in reservoirs, and 245 in lakes. Most frequently, the concentrations of Chl + Ph in the coastal zones of watercourses and water bodies fall in the oligotrophic category, and those in the central areas are in the hypertrophic category. Relationships between concentrations of Chl + Ph and water depth, content of oxygen near the bottom, moisture content, volumetric mass, and concentrations of organic matter (OM) in the BSs are found. The content of sedimentary pigments in tropical waters of Vietnam is similar to that in freshwater ecosystems of temperate latitudes, despite the substantial differences of climatic zones in temperature and light regimes.

Aquatic and semiaquatic vegetation in Yaroslavl oblast has a long history of study and is described in detail for different types of waterbodies. The present summary report includes 65 formations. There are 36 formations in the hydrophilic vegetation of lakes, 39 in reservoirs, 39 in ponds, and 42 in rivers. More than half of the total list is made up of formations with the dominance of helophytes. Unique data have been obtained which make possible to trace changes in the structure of the lake vegetation in the course of natural succession and the formation of the reservoir vegetation since its filling as a result of long-term observations conducted by researchers in the waterbodies of the region. The penetration of alien species into the territory of the region can change the structure of hydrophilic vegetation.

The Mediterranean copepod Calanipeda aquaedulcis Kritschagin, 1873 was first recorded in the Kuibyshev Reservoir in August 2015. It has been detected at all surveyed stations from the Volga-Kama reach to the dam of the Zhiguli hydroelectric power plant; the most northern finding of the copepod has been recorded in the mouth of the Kama River (55°24′ N). C. aquaedulcis (0.3–7.3 thous. ind./m³) is in the group of dominant species and forms, on average, 13% of the total abundance and biomass of zooplankton. Comparatively large (1.0–1.4 mm) copepods reproduce intensively; females carry up to 18 eggs (on average 10 ± 0.6). The main part of the population (>90%) are represented by nauplii. The species has been found in smaller quantities (0.04–1.1 thous. ind./m³) throughout the Saratov Reservoir, which is located downstream the cascade. The ecology of the species and its potential importance in the zooplankton of the Volga reservoirs is discussed.

The modern state of the species structure and spatial distribution of zooplankton cenoses in the upper part of the river hydraulics zone in the Cheboksary Reservoir, where the construction of a low-head dam is planned, and in the mouth part of the Oka River has been studied based on the data of 2016 and 2017. Two zooplankton communities have been identified in these areas; differences in their species structure are determined by several ecological factors: total mineralization, water transparency, temperature, pH, etc.

The swash-ice zone of the Curonian Lagoon comprises the depths from a lower margin of the supralittoral to a lower margin of the swash subzone (0.7 m). This zone extends from a few meters to 250 m. This zone is the area of expatriation of Dreissena polymorpha because of its complete freezing in winter. However, this species prevails in the swash-ice zone in terms of the frequency of occurrence and the ratio in the total abundance and biomass of macrozoobenthos. Zebra mussels form large beds; their abundance and biomass reach 1420 ind./m² and 74.334 g/m², respectively. Population replenishment in this zone occurs sporadically due to adult individuals brought here from the consortium communities, where zebra mussel + Unionidae and zebra mussel + Viviparidae are the determining centers, as well as due to the settling of the mollusks of the veliconch stage.

Changes in the total content and composition of lipids in yearlings of the Lake Krugloye Amur sleeper depending on their body length during the active feeding period have been analyzed. It is found that fatness of the juvenile Amur sleeper does not change with an increasing body length. The seasonal dynamics of fatness is expressed to a greater degree in fish of the same size. The lipid composition of juvenile specimens of the Amur sleeper varies considerably depending on the length of the body of the fry and the time of observation. The character of the fractional composition of lipids in yearlings of the Amur sleeper with body lengths >25–29 mm in September and October indicates a decline in food supply of the largest specimens of the generation by the end of the active feeding period and their lower readiness for wintering.

Amphibians are one of the most poorly studied groups of vertebrates in ecotoxicology and radioecology. The level of cytogenetic damage in the blood cells of tadpoles Rana arvalis Nilsson living on the territory of the Ukhta district of the village of Vodnyi in the Komi Republic, which is contaminated with technogenic radionuclides and heavy metals, is evaluated by “Comet assay”. It is shown that, in animals that develop in water bodies with high concentrations of radionuclides and heavy metals, the frequency of alkalilabile sites and single-strand break of DNA is higher than in the control area. No significant differences have been found when estimating the level of double-strand break of DNA. AFLP analysis indicates a weak genetic differentiation of the studied populations of amphibians.

The density of some species and total density of fishes have been estimated in river channel parts of the Ivankovo Reservoir in 2012–2015. The significant differences in the total abundance of fishes in 2012–2013 and 2014–2015 have been revealed. The increase in the number of tyulka (Clupeonella cultriventris (Nordmann, 1840)) in the Black and Azov seas in 2014–2015 was determined by their periodic fluctuations typical for any species with a short life cycle. Changes in the abundance of bream and silver bream in the reservoir pelagial relate to their vertical redistribution under the effect of environment factors.

Data on the chlorophyll a (Chl a) content in water of the Volga River reservoirs sampled at 64–73 sampling stations in the summer period of 2015 and 2016, analyzed using the standard spectrophotometric method, are presented. Chl a content varied from a minimum of 0.9–3.0 to a maximum of 7.6–32.1 μg/L in June 2016, from 2.1–15.5 to 9.4–86 μg/L in August 2015, and from 1.1–6.7 to 15.1–62.7 μg/L in August 2016. A local increase in Chl a occurred in the near-dam areas of the reservoirs, as well as downstream of the confluence with tributaries. The highest Chl a concentrations were constantly recorded in the highly eutrophic Shoshinskii Reach in the Ivankovo Reservoir and at the Oka River mouth in the Cheboksary Reservoir. The average values of Chl a concentrations make it possible to classify the Ivankovo, Uglich, Rybinsk, and Cheboksary reservoirs as eutrophic; the Gorky and Kuibyshev reservoirs as moderately eutrophic; and the Saratov and Volgograd reservoirs as mesotrophic.

This article analyzes the indices of oxidative stress activity in freshwater bivalve Dreissena polymorpha (Pallas) from areas of the Rybinsk Reservoir with different levels of anthropogenic load. The following indices are studied: activity of catalase (CAT), glutathione reductase (GST), glutathione S-transferase (GST) and content of reduced glutathione (GSH), malondialdehyde (MDA), and carbonyl groups of oxidized proteins (CG). During the study period (July), the indices of oxidative stress of zebra mussel D. Polymorpha did not differ between sexes. Mussels that were collected in the most polluted part of the reservoir, the Sheksna stretch near the industrial complex of the city of Cherepovets, had a higher activity of catalase, glutathione S-transferase, and glutathione reductase and a higher content of malondialdehyde than zebra mussels taken from the relatively clean Volga stretch.