Nadezhda Y. Stepanova

Relevance. Freshwater ecosystems, including reservoirs, contribute significantly to the global emissions of the greenhouse gas methane (CH4). Shallow-water reservoir zones are considered emission “hotspots”; however, their contribution to the carbon budget of large reservoirs, such as the Kuibyshev Reservoir, has not been sufficiently quantified. Methods. A quantitative assessment of specific CH4 fluxes in the shallow-water zone of the Kuibyshev Reservoir was performed during the summer–autumn period of 2024 using the floating chamber method. CH4 concentrations were determined using a Nexis GC-2030 gas chromatograph. Measurements were conducted at two contrasting stations: an open shallow-water area (Station 1) and a semi-enclosed channel with slow water exchange (Station 2). Hydrophysical and physicochemical parameters were recorded concurrently, and sediment samples were collected for particle size and organic matter analysis. Results. High spatial variability of CH4 fluxes was revealed. The average emission at the open shallow-water station was 22.9 ± 3.5 mg CH4·m−2·day−1, while in the semi-enclosed channel, it was an order of magnitude higher (231.8 ± 50.3 mg CH4·m−2·day−1). The maximum values (up to 623.5 mg CH4·m−2·day−1) were recorded in July and are associated with ebullition against the background of near-bottom hypoxia (< 0.5 mg O2 ·dm−3). Shallow isolated bays, despite their small area, contribute disproportionately to the total CH4 emissions from the reservoir surface. This phenomenon is driven by a combination of factors: specific morphometry promoting thermal and oxygen stratification, as well as accumulation of silty sediments enriched with organic matter. Accurate assessment of the carbon footprint of large reservoirs requires targeted monitoring of such “hotspots”, which should be taken into account when developing regional and national carbon budgets.

—The anthropogenic impact on various components of aquatic ecosystems and, in particular, on the structure of river zooplankton communities requires comprehensive study in modern conditions of intensive environmental natural resource management. The aim of our study is to assess the impact of urban wastewaters on the chemical composition of water and structural parameters of river zooplankton of the River Stepnoy Zay, a small river from the industrial zone of the Middle Volga region and left tributary of the Kama River. Sampling was carried out from 2008 to 2019 upstream and downstream of municipal wastewater discharges of the four cities located in the upper, middle, and lower reaches of the river. Our results have shown that the main chemical compounds that significantly differed in their concentrations in the areas above and below urban discharges are ammonium, nitrates, phosphates, and organic substances (BOD₅). These pollutants are also the most significant variables explaining variations in the species composition and quantitative indicators of zooplankton. In relation to the leading environmental factors, three groups of species are distinguished: indicators of organic pollution, species tolerating increased mineralization, and species sensitive to oxygen content. A total of 114 zooplankton taxa have been identified in the river. The abundance and biomass of zooplankton varied significantly at stations above and below cities. Zooplankton communities below cities in the upper and middle reaches of the river (Bugulma, Leninogorsk, and Almetyevsk) are influenced by the influx of planktonic organisms from biological treatment facilities with wastewaters. The stations in the lower reaches of the river belong to the mouth section, and zooplankton communities here are formed under the influence of the Kama River. Observations of the development of zooplankton communities will continue.

The study of microplastic content in water, sediments, gills and gastrointestinal tract of bream (Abramis brama) at the mouth of the Mesha River, the right tributary of the Kama River, was conducted. The content of microplastics in water was found at the level of 20.5 ± 22.3 units/m3, in bottom sediments 44.7 ± 41.8 units/kg, in fish gills 12.3 ± 8.4 units/example, in the gastrointestinal tract 14.5 ± 11.5 units/example. Fibers dominated in water samples, in the gills and gastrointestinal tract of fish, fragments dominated in the sediment. Correlation analysis showed the presence of a negative relationship between the content of microplastics in the gills, gastrointestinal tract and biologic indicators of studied fish. In terms of the frequency of occurrence and content of microplastics in the gills and gastrointestinal tract, the contamination of the studied fish is at a high level compared to literature data, which is associated with the feeding behavior of bream.

A study of the microplastic (MP) content in water, sediments, and gills and gastrointestinal tract (GIT) of bream (Abramis brama L., 1758) at the mouth of the Mesha River (right tributary of the Kama River) has been conducted. The content of MPs in water is found at the level of 20.5 ± 22.3 items/m³, in bottom sediments (BSs) 44.7 ± 41.8 items/kg, in fish gills 12.3 ± 8.4 items/individual, and in the GIT 14.5 ± 11.5 items/individual. Fibers dominate in water samples and in the gills and GIT of fish; fragments dominate in the sediments. Correlation analysis has shown the presence of a negative relationship between the content of MPs in the gills, GIT, and biological parameters of the fish. In terms of the frequency of occurrence and content of MPs in the gills and GIT, the contamination of the studied fish is at a high level when compared to literature data, which is due to the feeding behavior of bream.

The negative consequences of global climate change are widely known, in particular leading to a decrease in soil fertility and a decrease in the efficiency of crop production. In connection with the above, approaches to greening agriculture are constantly being developed, which should lead to improved soil quality, preservation and increase in the amount of nutrients in it, as well as a reduction in greenhouse gas emissions. One of these approaches may be the use of peas as ground cover plants to reduce CO2 emissions from bulk soil, due to the fixation of C in phytomass, which will later be plowed into the soil. To evaluate the effectiveness of this approach, a vegetation experiment was conducted in a greenhouse under different temperature conditions (20°C, 25°C, 30°C) with soil on which pea plants (Pisumsativum) were grown and soil without plants (imitation of open arable land) . In the dynamics of the experiment, indicators characterizing the process of carbon accumulation in phytomass were assessed, namely the rate of increase in plant phytomass and chlorophyll content in leaves, as well as the process characterizing CO2 emission from the soil - an increase in the intensity of soil basal respiratory activity under peas over that of bulk soil. Next, the carbon balance was calculated for each temperature regime. It was shown that with an increase in temperature from 20°C to 30°C, there is a decrease in C fixation in plant phytomass and a decrease in CO2 emission due to the respiratory activity of the soil microbial community. The maximum fixation of C when growing peas (Pisumsativum) was established for a temperature regime of 20°C and amounted to 585 kg C/ha.

The negative consequences of global climate change are widely known, in particular leading to a decrease in soil fertility and a decrease in the efficiency of crop production. In connection with the above, approaches to greening agriculture are constantly being developed, which should lead to improved soil quality, preservation and increase in the amount of nutrients in it, as well as a reduction in greenhouse gas emissions. One of these approaches may be the use of peas as ground cover plants to reduce CO2 emissions from bulk soil, due to the fixation of C in phytomass, which will later be plowed into the soil. To evaluate the effectiveness of this approach, a vegetation experiment was conducted in a greenhouse under different temperature conditions (20°C, 25°C, 30°C) with soil on which pea plants (Pisumsativum) were grown and soil without plants (imitation of open arable land) . In the dynamics of the experiment, indicators characterizing the process of carbon accumulation in phytomass were assessed, namely the rate of increase in plant phytomass and chlorophyll content in leaves, as well as the process characterizing CO2 emission from the soil - an increase in the intensity of soil basal respiratory activity under peas over that of bulk soil. Next, the carbon balance was calculated for each temperature regime. It was shown that with an increase in temperature from 20°C to 30°C, there is a decrease in C fixation in plant phytomass and a decrease in CO2 emission due to the respiratory activity of the soil microbial community. The maximum fixation of C when growing peas (Pisumsativum) was established for a temperature regime of 20°C and amounted to 585 kg C/ha.

The method of ecological modifications was used to determine the invariant state of aquatic ecosystems in the Middle Volga basin. Based on the analysis of long-term regime hydrochemical and hydrobiological information using the methods of mathematical statistics (cluster, hierarchical cluster analysis, ordination methods), the studied water bodies were grouped according to the chemical composition of water, highlighting the main indicators of natural and anthropogenic genesis. We highlighted the general indicators of the chemical composition of water (temperature, salinity, hardness, content of oil products, chromium ions) that affect the change in the qualitative and quantitative characteristics of hydrobiocenoses, as well as specific indicators (nitrogen-containing compounds, phosphates, chlorides, sulfates, copper and iron ions), negatively affecting the quantitative and qualitative characteristics of hydrobiocenoses. A group of ciliates – cilioplankton (qualitative and quantitative characteristics) was used to assess the invariant state. Cilioplankton in the ecosystem of the Kuibyshev reservoir is characterized by high species diversity, which indicates anthropogenic stress. The quantitative characteristics of cilioplankton in rivers are low, and the community changes are ecological modulations. The share of rotifers development in zooplankton indicates the elements of ecological regress in water bodies, as well as anthropogenic eutrophication with elements of ecological regress (in most of the Kuibyshev reservoir). The level of zoobenthos development and its size, as well as the oligochaetes relative proportion indicate anthropogenic stress in the ecosystem of most parts of the Kuibyshev reservoir. The elements of ecological regress are traced only in the area of Chistopol. The water ecosystem in Tetyusha area is characterized as a transition from background to anthropogenic stress. The Vyatka and Mesha rivers are characterized as background rivers with the transition to anthropogenic stress. Anthropogenic eutrophication with elements of ecological regress can be traced in the Kazanka River. The Stepnoy Zai, Noksa and Ilet rivers has elements of ecological regress. Hydrobiocenoses indicators statistically depend on hydrochemical composition.