This review summarizes information on the main negative factors affecting the state of floodplain water bodies ecosystems, describes the most common consequences for abiotic and biotic processes, and suggests possible ways to conserve these ecosystems. Evidence of the negative impact of hydraulic construction, embanking of floodplains, channelizing of rivers, agriculture, and other anthropogenic impacts is presented. A special role is played by climate change, which leads to a decrease in flood inundation, drying and overgrowing of water bodies, and their eutrophication. The authors suggest criteria to choose correct indicators that can testify not only to special stages of water body succession (e.g., vegetation) or its trophic status (zooplankton), but also to the long-term effects of anthropogenic and climatic changes. As a recommendation, it is proposed not to consider water bodies separately, but to assess the whole waterscapes and use the change in β-diversity as an indicator. Further conservation strategies can be based on the approaches of the Red List of Ecosystems of the International Union for Conservation of Nature and Natural Resources (IUCN), which will help to draw attention to the problem. The key role for the conservation of floodplain water bodies should be played by territorial protection measures, up to the development of a separate category for small water bodies.

In the Russian Federation, the protection category “Zapovednik” represents a strictly protected area, where the access is restricted and the aim is to keep the area “ forever wild ”. We provide an overview about the organization of these nature reserves and highlight their contribution to fundamental research. Aquatic ecosystems in zapovedniks provide pristine sites of great importance for long-term monitoring and research, which fosters process understanding regarding interannual variability and development of aquatic coenosis. We present a long term monitoring and research project about abiotic and biotic parameters in the Central Forest State Nature Biosphere Reserve. Examples from the Privolzhskaya Lesostep Nature Reserve include monitoring of invasive fish as well as analyses about the influence of beavers on fish. The Astrakhan Biosphere Nature Reserve in the Volga delta is a hotspot for fish biodiversity; thus, there the state nature reserve security service plays an important role to avoid poaching. Our case studies from the Volga Basin exemplify the structure and function of nature reserves and highlight their contribution to research, protection and management of aquatic ecosystems. Long-term datasets from the zapovedniks can (i) improve process understanding, (ii) ensure protection of aquatic systems and sustainable water management and (iii) support knowledge-based decisions.

Trematode infection of the second intermediate hosts can lead to changes in their fitness and, as a result, a change in the invasion rate of animal communities. It is especially pronounced during the invasion of parasite species that reduce activity due to the manipulation of hosts through the changes of their morphology and physiology. One of these cases is an anomaly P syndrome hotspot found in some populations of water frogs and toads in Europe caused by the trematode Strigea robusta metacercariae. The occurrence of pathogen and their participation in ecosystems are intrigues questions in the anomaly P phenomenon, as well as the role of planorbid snails that serve as the first intermediate hosts for many trematode species. Herein, we focused on trematodes spectra from planorbid snails and amphibians from the anomaly P hosts with the aim to undetected interactions between the pathways of parasites. Emerging cercariae of 6802 planorbid snails of dominant species (Planorbarius corneus, Planorbis planorbis, and Anisus spp.) were detected by both morphological and molecular methods in seven waterbodies in Privolzhskaya Lesostep Nature Reserve (Russia). A total of 95 sequences of 18 species were received, and 48 sequences were unique and did not present in any genetic databases. The 18 species of trematodes from snails and 14 species of trematodes from amphibian hosts (Pelophylax ridibundus; Ranidae; Anura) were detected. Three species (Echinostoma nasincovae, Tylodelphys circibuteonis and Australapatemon burti) was new for the trematode fauna of the Middle Volga River region and Russia as a whole. Eleven species of parasitic flatworms have amphibians in their life cycles and nine species used amphibians as metacercariae hosts: Echinostoma nasincovae, E. miyagawai, Echinoparyphium recurvatum, Tylodelphys circibuteonis, Neodiplostomum spathula, Paralepoderma cloacicola, Macrodera longicollis, Strigea robusta, and Strigea strigis. The occurrence of trematode species from planorbid mollusks and frogs were compared.

The transfer of biomass and polyunsaturated fatty acids by the spadefoot P. vespertinus (previously subspecies of P. fuscus) from aquatic to terrestrial ecosystems was studied for five years in small floodplain water bodies of a forest-steppe zone. Average emergence of metamorphs from unit of water area, wet mass was 6.7 g m-2 year-1. A ratio of the emergence to biomass was calculated and represented as E/B coefficient (an analog of P/B production/ biomass coefficient). The average E/B was found to be 0.038 year-1. The introduced coefficient can be used for a coarse estimation of the emergence on the basis of tadpole biomass measurements. A considerable partitioning of tad-poles and metamorphs in the composition of fatty acids in their biomass was revealed. Tadpoles had significantly higher mean levels (percent of total fatty acids) of 16:0, 16:1n-9, 18:0, 20:5n-3 and 22:5n-3, while metamorphs had significantly higher levels of 14:0, 15:0, 17:0, 17:1n-8, 18:2n-6, 20:2n-6, 20:4n-6 and 22:5n-6, likely due to the shifting to terrestrial food. Metamorphs had significantly higher content of total fatty acids, mg g-1 of wet weight, and, in spite of lower level, they had significantly higher content of eicosapentaenoic acid (20:5n-3, EPA) than tadpoles. Metamorphs also had significantly higher content of docosahexaenoic acid (22:6n-3, DHA) and sum of EPA + DHA than tadpoles. Average flux of EPA + DHA from unit of water area with metamorphs was 3.27 mg m-2 year-1. The metamorphs appeared to be qualitatively and quantitatively prominent prey for a number of terrestrial consumers.

The aim of the study is to assess concentrations of compounds of biogenic elements (nitrates, nitrites, ammonium, and phosphates) and to analyze their distribution in water bodies and watercourses of the forest-steppe, where beavers were reintroduced recently. The study was carried out in the State Nature Reserve Privolzhskaya Lesostep' (Penza oblast). We studied beaver ponds, oxbows inhabited by beavers, and also uninhabited streams. The concentrations of biogenic compounds in water were measured twice a year at the beginning and the end of summer. The results showed that, in general, all water bodies were characterized by an excess of threshold limit value (TLV) of concentrations for ammonium (TLV 2 mg/L, an excess in 76% samples) and phosphates (TLV 3.5 mg/L, 64%). Excesses were less common for nitrites (TLV 3.3 mg/L, 28%) and quite occasional for nitrates (TLV 45 mg/L, 2%). Moreover, the differences between the concentrations of biogenic compounds in the water bodies inhabited by beavers and uninhabited waters did not have statistical significance. Significant differences were observed only for different types of water bodies, which was associated with their water regime. The presence or absence of beavers, as well as their density and abundance, did not lead to significant changes in the concentrations of nutrients. The studied water bodies were surrounded by territories with a high level of agricultural impact, and under these conditions, the effect of beavers on the concentration of nutrients was not observed.

BackgroundCases of polydactyly in natural populations of amphibians have attracted great interest from biologists. At the end of the 1940s, the French biologist Jean Rostand discovered a polymorphic syndrome in some water frog (Anura: Pelophylax) populations that included polydactyly and some severe morphological anomalies (he called it 'anomaly P'). The cause of this anomaly remains unknown for 70 years. In a previous study, we obtained anomaly P in the laboratory in tadpoles of water frogs that developed together with molluscs Planorbarius corneus (Mollusca: Gastropoda) collected in the field. We thus proposed the 'trematode hypothesis', according to which the infectious agent responsible for anomaly P is a trematode species.MethodsMetacercariae from tadpoles with anomaly P were identified using ITS2 gene sequencing as Strigea robusta (Trematoda: Strigeidae). To verify teratogenic features of the species, cercariae of S. robusta were tested for the possibility to cause anomalies. Identification of cercariae species was made using morphological and molecular methods (sequencing of ITS2 and 28S rRNA). The tadpoles were exposed to parasites at four doses of cercariae (control, low, medium and high) and divided into two groups: "early" (at 25-27 Gosner stages) and "late" (at 29-34 Gosner stages) exposure.ResultsA total of 58 (72.5%) tadpoles survived until metamorphosis under the dose-dependent experiment with the trematode S. robusta. Differences in the survival rates were observed between the exposed and unexposed tadpoles both in the group of "early" tadpoles and "late" tadpoles. The exposure of tadpoles to the cercariae of S. robusta induced anomaly P in 82% of surviving tadpoles. The severe forms developed only in "early" stages under all doses of cercariae exposure. Polydactyly predominantly developed in the "late" stages; under a light exposure dose, polydactyly also developed in "early" tadpoles. Laboratory-hatched tadpoles reared together with infected snails had different rates of survival and complexity of deformations associated with the period of coexistence.ConclusionsThe experiments with direct cercariae exposure provide compelling evidence that S. robusta leads to anomaly P in tadpoles of water frogs. The manifestation of anomaly P turned out to be dependent on the stage of development, cercariae dose, and the location of the cysts.

The aim of our study was to identify the main abiotic factors that influence the biodiversity of forest-steppe oxbows in limnophase. Experiments were performed in 2016–2017 in Penza oblast, Central Russia. In addition to disturbed water exchange, isolated oxbows experienced such human influence as logging and plowing on watersides, and the construction of roads and mounds. Under those conditions, some water bodies became unstable and temporal, while others remained stable and were relatively unaffected. Higher light intensity in unstable oxbows led to higher plant diversity because of the mass occurrence of helophytes. However, the diversity of hydrophytes in stable oxbows remained higher, which contributed to higher vegetation coverage. This resulted in increased zooplankton diversity, which was also influenced by lower fluctuations in water level and oxygen level. Disturbed water regimes impacted organisms with a full aquatic life cycle (phyto- and zooplankton, fish). The diversity of unstable oxbows decreased due to their isolation from the river and from drying. The absence of fish may positively affect the abundance and biomass of benthos; however, we found no influence on zooplankton. Instability and high fluctuations in water level may lead to the high diversity of organisms that spawn in water. The higher diversity of benthos may also be influenced by the abundance of amphibian larvae which are a necessary food resource. In addition to predation, amphibians are at risk of mass larval mortality because of drying. Although the degradation of oxbows in limnophase is an undesirable consequence of anthropogenic impact, the coexistence of all types of oxbows is necessary to conserve the freshwater biodiversity of forest-steppes.

The "anomaly P" was described in Palearctic water frogs of the genus Pelophylax by Jean Rostand as complex morphological anomalies of water frogs, including polydactyly, brachymely, hind limb oedema, bone outgrowths, spikes, flexions and additional limbs in the inguinal region. In 2016, the anomaly P syndrome was rediscovered in central Russia, confirming the hypothesis concerning its wider distribution. Here, three new records of this syndrome in two species of western Palearctic water frog from Russia are described.

An estimation of sedimentation rate of suspended matter was done in beaver (Castor fiber) ponds and oxbows of the River Khoper valley (State Nature Reserve "Privolzhskaya Lesostep'", Penza region. Russia). In beaver ponds the sedimentation rate varied from 7.33 g/m(2) per day to 71.81 g/m(2) per day, in oxbows - from 7.83 g/m(2) per day to 10.69 g/m(2) per day. The share of the mineral part was different in different water bodies. In beaver ponds organic matter formed 39.93-56.12%, in oxbows - 77.11-81.29%. The organic percentage showed that long existence and stability of oxbows lead to a higher biodiversity and biomass of flora and fauna. The rate values could depend on some factors that beavers influence on. We used six parameters for the estimations of the beaver impact: location of water body, abundance of animals, building activities, area of flooded valley, digging activities, input of woody material. Mainly, their building activities and area of flooded valleys increased sedimentations and decreased the share of organic matter. Also, we suggest that amounts of suspended matter could depend on vegetation (woody or grasslands), age of beaver settlements, and other zoogenic activities. Beaver ponds could accumulate less volume of sediments, because they are situated on small rivers and have less size and watershed area than oxbows, and existed not so long as natural water bodies. The chemical composition of sediment was studied with the X-ray fluorescence spectroscopy. The chemical compound of suspended matter was connected with the composition of watershed. So, maximum concentrations were observed for iron, silicon and calcium. Some concentrations indicated anthropogenic fertilisation (phosphorus, chlorine, potassium) and technogenic pollution (zinc, copper, lead, arsenic). Our results suggest a possible beaver impact on concentrations of phosphorus (inflow from burrows) and zinc (input with branches and twigs). The study confirms the importance of beaver ponds for accumulation of pollutants and ecosystem purification.

In summer 2016, we investigated Ostrovtsovskaya Lesostep' (Penza region, Russia) and caught more than 130 specimens belonging to 4 species of anuran amphibians. We found a symmetric case of "hyperxanthism" of the eyes (a new type of anomaly among amphibians) in one Rana arvalis specimen, one asymmetric amely in Bombina bombina, and 21 specimens of Pelophylax ridibundus (19% of total sample) with deformed fore and hind limbs. We define some anomalies as "Rostand's anomaly P" (in its extreme manifestations). The potential reasons of the morphological anomalies were discussed.

Preliminary data on the impact of the activity of the Eurasian beaver on the ecosystem biodiversity of small rivers in three steppe areas within the Privolzhskaya Lesostep' State Nature Reserve in the Khoper River basin were obtained. With zooplankton, amphibians, and fish as examples, it was shown that after beaver-made ponds had appeared, the abundance of all these groups increased. In old ponds, the fish abundance decreased while that of amphibians continued to increase. In drained ponds, the zooplankton and amphibian abundance decreased while fish became more numerous, due to the appearance of better flowage.

The work presents the first results of annual monitoring of a beaver population on the territory of Ostrovtsovskaya Lesostep' (State Nature Reserve Privolzhskaya Lesostep', Penza region). In 2014-2017 all water-courses and water-bodies, including the River Khoper, River Selimutka, River Yuzhnaya and several oxbows of the Khoper were investigated twice a year for assessing the beaver abundance using the method of settlements capacity. The mean density of dams was 7.7 dams/km of watercourse, the maximum was on the River Yuzhnaya - 10.8 dams/km, and the minimum was on the River Selimutka - 5.5 dams/km. During the study period 10 to 13 beaver settlements were observed, the total abundance of beavers tends to decrease (from 42 to 30 animals). The present density of beavers and a lack of food resources limit a further increase of the species abundance.

The study of the composition of fatty acid markers of tadpoles of cohabiting amphibian species for the first time revealed differences in their diets: the moor frog Rana arvalis prefers bacteria not associated with plant detritus, whereas the diet of the common spadefoot Pelobates fuscus is based on cyanobacteria, green algae, diatoms, and possibly higher plants. Major differences in the fatty acid composition are determined by the difference in the percentage of eicosapentaenoic and myristic acids.

We present results of analytical and numerical investigation of explosive evaporation and burning scenarios of hydrogen droplets in hydrogen/oxygen aerosols. The following two scenarios have been elucidated. The first scenario, corresponding to sufficiently large droplets, is characterized by three stages: (i) an essentially homogeneous heating of a droplet to a near-critical temperature by IR radiation from the hot gas; (ii) explosive evaporation; and (iii) burning of hydrogen cloud formed by evaporation. The second scenario, corresponding to small droplets, differs in that a droplet is heated mainly by thermal conduction from the hot gas. The heating is accompanied by evaporation which can become explosive at the final stage of evaporation. The crossover droplet size separating the two scenarios is calculated. Conservative finite-difference numerical analysis is used to explore the predicted scenarios and verify analytical estimates.

The study of beaver’s (Castor fiber) impact on steppe rivers’ ecosystems was held within the Privolzhskaya Lesostep’ State Nature Reserve (Penza Province, Russia). We investigated how pond age and permanence of beaver ponds influenced the abundance and diversity of fishes and amphibians. The majority of beaver ponds in our study area were small and dams were easily destroyed by spring floods. The formation of stable long-term ponds was evident in rivers with low discharge. The most favorable parts of rivers for beavers were anthropogenic reservoirs, where swamping and high biomass of reeds were common. The rivers were inhabited by one species of lamprey (Eudontomyzon mariae), six fish species (Esox lucius, Leucaspius delineatus, Sabanejewia baltica, Misgurnus fossilis, Barbatula barbatula, Carassius carassius), and five amphibian species (Lissotriton vulgaris, Pelobates fuscus, Bufo viridis, Rana arvalis, Pelophylax lessonae). As a result of the damming, abundance, biomass of fishes, species diversity and abundance of amphibians increased. During long-term persistence of beaver ponds fish abundance declined (the oxygen level reduced), but the number of amphibians continued to appear (more shallow water bodies appeared). Also beaver dams led to isolation of fishes in different parts of valleys and served as barriers to spawning migrations (e.g. for pike and lamprey). When beavers abandoned ponds, amphibian abundance declined, and fish abundance increased — due to increased water flow. Thus, despite some positive effects, beaver ponds were not the key habitats for fishes and amphibians.

The size and age composition of the population of Black and Caspian Sea sprat Clupeonella cultriventris, as well as the variation of the growth of fish in the reservoirs of the upper reaches of the Volga, are reported and a comparative analysis of group and individual variability of fish growth within the native (Caspian, Azov, and Black seas) and contemporary (formed due to invasion) ranges is presented. The degree of variability and the asymmetry of sprat body length distribution have been shown to increase under the conditions of large population sizes, deficit of food, and slow growth. Variability was also elevated near the borders of the range of the species, notwithstanding the abundance of food. It is shown that invasion of sea walnut comb jelly Mnemiopsis leydi into the Azov and Caspian Seas had so undermined feed base of sprat, that it is not only decreased its abundance and fecundity but also slowed growth of the fish.