Mercury is one of the most dangerous environmental pollutants due to its high toxicity to animals and humans. The aim of the study was to determine the presence or absence of seasonal changes in the mercury level in small mammals in forest ecosystems near the Cherepovets town. The fur, organs and tissues of the common shrew (Sorex araneus Linnaeus, 1758) and Ural field mouse (Apodemus uralensis Pallas, 1811) were examinied during September 2020–August 2021. The content of total mercury (THg) in dried samples (n = 319) was determined on a PA-915+ mercury analyzer with a PYRO console by cold vapor atomic absorption. The content of THg in the Ural field mouse varies from <0.001 (sensitivity limit of the device) in the kidneys, spleen, brain, muscles, and liver up to 0.560 mg/kg dry weight in the spleen; the average maximum THg value was found in the spleen (0.179±0.072 mg/kg) and the minimum was in the muscles (0.023±0.011 mg/kg). The content of THg in the common shrew varies from <0.001 (sensitivity limit of the device) in the brain up to 4.570 mg/kg dry weight in the fur, the average maximum THg value was found in the fur (0.754±0.152 mg/kg), and the average minimum was in the liver (0.112±0.013 mg/kg). It was established that the level of THg in common shrews was higher in winter than in summer, statistically significant differences were found for the fur, muscles, and liver (p = 0.008, 0.001, 0.033, respectively, at p < 0.05). An interspecies comparison showed differences in seasonal changes in the THg content, namely: in autumn it was higher in the common shrew than in the Ural field mouse; statistically significant differences were found for the fur, kidneys, and muscles (p = 0.005, 0.046, 0.001, respectively, at p < 0.05).

The authors’ and literary data on the geographical distribution of few Sicista sibling species of the caucasica group (S. caucasica, S. kluchorica, S. kazbegica, and S. armenica) are summarized. For the first time, based on an analysis of our own collections obtained in the period from 1979 to 1990 and in 2010, environmental features (biotopic correspondence, abundance, reproduction strategy, and food specializations) are compared for several geographically replacing Sicista sibling species of the caucasica group (S. caucasica, S. kluchorica, S. kazbegica, and S. armenica), inhabiting different sectors of the middle mountains and highlands of the Caucasus, considered in a comparative aspect in connection with the differentiation of the group.

The results of the study of the ecological status of the Kurdyum river within the municipal formation “Saratov city” are presented. The hydrochemical regime, hydrophilic flora and vegetation of the watercourse were studied in the 2022–2023 field seasons. The ecological status of the river by structural parameters of macrophytes was assessed. The species composition of aquatic plants in the river Kurdyum was represented by 41 macrophyte species belonging to 32 genera, 23 families and three divisions (Charophyta, Polypodiophyta, and Magnoliophyta). The families Potamogetonaceae, Asteraceae, Poaceae, Typhaceae and Ranunculaceae predominated by the number of species. The genus Potamogeton contained the greatest number of species (four) while other genera were represented by one – two species. Hydrophytes were a numerous ecological group, accounting for 51% of the total number of species. New locations of species rare for the Saratov region (Myriophyllum verticillatum and Zannichellia palustris) were revealed. The vegetation cover of the Kurdyum river is characterized by the greatest phytocenotic diversity of true aquatic vegetation. The impoverishment of the phytocenotic composition of helophytic and hygrophytic vegetation is explained by the lack of favorable conditions for the development of their phytocenoses (the watercourse has abrasion banks along a significant length) or trampling and eating by grazing animals. The studied river is characterized by species diversity in comparison with previously studied urban watercourses. Index comparison has revealed an inverse relationship between species diversity and the level of anthropogenic load. Cluster analysis has revealed that the structure of flora and vegetation from the source to the mouth of the river is not homogeneous and is formed under the influence of a combination of hydrological, chemical and anthropogenic factors. The results of our chemical analysis of the water showed that the maximum permissible concentrations of Fe, Zn, Cu, surfactants, NO₂ and NH₃ were exceeded throughout the river. However, the environmental indicators assessed based on the structural parameters of macrophytes allow us to consider the ecological status of the watercourse satisfactory. Thus, the Kurdyum river is moderately polluted with a high trophic status.

Our survey was carried out in five local populations of Pelobates vespertinus (Pallas, 1771) in the floodplain of the Medveditsa river (Russia, Saratov region, Lysogorsky district) in 2009–2018. We have found that the sexual dimorphism in body length (SDIL) and weight (SDIW) of males and females of the Pallas spadefoot toad is a widespread feature of populations of this anuran amphibian species, characteristic not only among sexually mature individuals, but also among metamorphs. In metamorph populations, sexual dimorphism averages 3% and 9% in body length and live weight, respectively. It is less pronounced in metamorphs than in sexually matured individuals (by 3 and 4.5 times, respectively). The sexual dimorphism development level may undergo a significant transformation by temperature conditions during the tadpole development period in the spawning lake. The threshold value of the average temperature for the period of development up to the stage of metamorphosis (MDT90), at which any differences between males and females in body length are lost in metamorphs, is 18.2ºС. Against the background of climate warming over the past decade (2011–2020), there has been a significant expansion of the range area of this species, which is exposed to abnormally high water temperatures. Nevertheless, size–weight sexual dimorphism, even at the stage of metamorphosis, should hardly be excluded from the list of diagnostic characters of the species.

Data of our long-term observations of the bacterioplankton development in the mouth section of the Usinsky bay (the Kuibyshev reservoir) during the summer–autumn periods are presented. The total abundance of heterotrophic bacterioplankton varied within (1.61–7.44)×10⁶ cells/mL, the biomass was 39.01–249.53 µgC/L, which corresponds to III–V water quality classes. Between 2010 and 2017 the total abundance of heterotrophic bacterioplankton was nonmonotonically decreasing, and since 2021 its significant increase is recorded. Among heterotrophic bacteria, single freefloating cells predominated, mainly cocci and coccobacilli, and the proportion of rod-shaped cells increased during cyanobacterial bloom. Picocyanobacteria and picodetritus particles were almost always present in plankton, but their average contribution to the total organic carbon of picoseston was insignificant.

DNA studies of badgers (Meles sp.) from the right-bank and left-bank areas of the Volga river in the Saratov region are described. Asian badgers (Meles leucurus Hodgson, 1847) inhabit the Left Volga Bank of the Saratov region, while European badgers (M. meles Linnaeus, 1758) inhabit the Right Volga Bank districts of the region, but Asian badgers were found in Khvalynsky district of the Saratov region, besides the European badger. Despite a sufficient number of publications devoted to the Asiatic badger distribution in the Vyatka–Kama region and the Volga region, and studies devoted to the development of systematics of the genus Meles in Russia, the question of the boundaries of the ranges of European and Asiatic badgers and the zones of their sympatry (parapatry) in the Volga–Kama region has not been fully investigated to date. Our work is devoted to the study of this question. As a result of analyzing the biological material collected by us, it was found that all five studied individuals of badgers from the Saratov Volga region phenotypically looked like Asian badgers, but our DNA analysis showed that only two of them were M. leucurus, whilst three ones were heterozygous individuals carrying genes from both species and were identified as hybrids. The remaining 29 individuals were captured in the right-bank areas of the region. Badgers were sampled from individuals from the northern to southern borders of the region in areas located along the Volga river on the Volga upland and in the Oka–Don plain. Of these, one individual from Khvalynsky district turned out to be an Asian badger, one individual from Krasnoarmeysky district was a hybrid of the two named species, and three individuals, one from Tatishchevsky, the second from Volsky and the third from Khvalynsky districts showed introgression of Asian badger genes into the genotype of the European badger. Thus, we have managed to find out that at this stage of development of the phase of the climatic cycle in the Lower Volga region, characterized by warming winters, the Volga river, with its two reservoirs within the Saratov region, is not an absolute zoogeographical boundary, and badgers, whose species are characterized by winter sleep, can in certain conditions overcome, most likely on ice, both the river itself and the lake parts of the Volgograd and Saratov reservoirs. According to the revealed introgression in some individuals from different areas on the Volga upland of the right bank of the Saratov region, it can be assumed that such traveling across the Volga river took place earlier, possibly before its flow was regulated by dams.

Age shifts in fir–spruce forests and the potential influence of ongoing climate changes upon them are pressing issues. The study focuses on a stand of undisturbed fir–spruce forest located in the southern Sikhote-Alin at an altitude of 530 m a.s.l. A permanent sample plot was established there in 2001, and a revision was conducted in 2022–2023 with wood samples (cores) obtained. The research has revealed significant deviations in the stand development from the previously described pattern of age shifts in virgin fir–spruce forests. Firstly, it was established that there have been no major stand disturbances over the last 242 years, and only minor ones occurring in 1831–1850 and 1931–1950 were identified. About 50% of Jezo spruce trees survived at least 2 minor disturbances during their development. Secondly, it is shown that Jezo spruce does not form a single-age generation within the studied stand. It was also found that at the time of revision, the stand was in a situation preceding a new stand disturbance. An important result obtained is that a stable trend of decreasing growth has been observed in 75% of Jezo spruce trees since 2001. This trend might not be associated with age shifts within the stand but could be attributed to the spruce’s response to global climate changes. Such a trend could significantly impact the age shifts in fir– spruce forest stands.

In the Simferopol city, the numbers of Common hamsters began to grow since the early 1970s and reached a peak in the mid-1990s. The abundance was kept at a high level until 2014–2015 and then began to decline. In multi-storey residential development areas, steady settlements of hamsters have now virtually disappeared, and even in large green areas (the City Park and Botanical Garden), the numbers dropped almost tenfold. One of the possible causes for this decline was cutting down shrubs and hedges, which began since 2016–2017. However, the population has also severe declined in areas with no such activities. Thus, the fate of the Simferopol hamster population is worrisome. Obviously, we are dealing with a multi-factor process which requires special studying, without which no estimating of population viability or developing of conservation measures are possible.

Agriculture has a large area of coverage and places the greatest burden on land, soil, water and biological resources in many countries of the world. Agricultural lands occupy huge areas in the world (4.8 billion hectares, or 37% of the land) and in Russia (221.9 million hectares, or 13% of the Russian Federation area). The agriculture best adapted to local conditions is the most beneficial one for people and nature. The main direction of agricultural adaptation is agrolandscape-ecological zoning. In order to provide information support for regionally, landscapeand ecologically differentiated agriculture and rational environmental management, an agrolandscape– ecological zoning of natural and natural-agricultural ecosystems was developed for the first time for all 11 natural-economic regions of Russia, namely, Northern, North-Western, Volga–Vyatka, Central, Central Black Earth, Volga, North Caucasus, Ural, West Siberian, East Siberian, and Far Eastern. The zoning was carried out using comparative geographical and agrolandscape-ecological methods, ecological-landscape and agroecological approaches. The contour and information basis for zoning is the map of Soil–Ecological zoning of the Russian Federation from the Faculty of Soil Science of Lomonosov Moscow State University. Maps of other types of zoning, numerous maps and atlases, statistical data, available literary and stock sources, ground-based and remote data were also used. Our sets of zoning materials included: a map, a map legend, 3 databases (land, forage lands, and negative processes), 2 classifications (forage lands, reindeer pastures, if any), articles, monographs, recommendations, and proposals for production. The maps have been compiled on a 1:2,500,000 scale on a modern, highly informative topographic cartographic basis for the map of Russian Federation. The maps show 6 types of boundaries, including 4 types of agrolandscape-ecological ones (taken from the Soil–Ecological Zoning map): 1) zones, 2) mountainous territories, 3) provinces, 4) districts and 2 types of administrative ones (available on the cartographic basis) of: 1) constituent entities of the Russian Federation, and 2) natural-economic regions.