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Introduction. The Shchuchiy Bay is located in the western part of the skerry area of Lake Ladoga near the town of Priozersk. For almost 20 years, the bay has experienced an anthropogenic impact from the ingress of untreated wastewater from the Priozersk Pulp and Paper Mill (PPM). Systematic microbiological studies of the Shchuchiy Bay ecosystem were started in the middle of the 1970s by the Institute of Limnology of the Russian Academy of Sciences and continued after the PPM closure in 1986. Materials and methods. The ecosystem of the bay was studied in detail during the growing season of 2013–2014; periodic studies were carried out in 2015–2018. Retrospective data were also used for the analysis. Water samples were taken at four stations from the surface horizon. The following microbiological indicators were determined: the abundance of bacterioplankton and the percentages of various morphological types of bacterial cells. Results and discussion. A comparison of the quantitative level of development of the bacterial community in the bay in different periods showed a gradual decrease in the abundance of bacterioplankton as the anthropogenic impact weakened after the closure of the Priozersky PPM from 12.40 million cells ml–1 in 1987 to an average value of 2.62±1.03 million cells ml–1 in 2013–2018. A positive correlation was found between the concentration of bacteria and water temperature. The percentage of rod-shaped microorganisms in the water of the bay also decreased as the anthropogenic impact weakened from 73.4 % in 1987 to 53.1±7.6 % in 2013–2018, which indicated an improvement in water quality. Conclusion. A stable decrease in the abundance of bacteria from the level characteristic of highly polluted and eutrophic water bodies to the level characteristic of mesotrophic and mesotrophic-eutrophic water bodies is a reliable criterion for the restoration of the ecosystem of the Shchuchiy Bay to the state characteristic of similar bays of Lake Ladoga.

The modern distribution of invasive amphipods of Baikal (Gmelinoides fasciatus (Stebbing, 1899), Micruropus possolskii Sowinsky, 1915) and Ponto-Caspian origin (Pontogammarus robustoides Sars, 1894, Chelicorophium curvispinum (Sars, 1895)) in Lake Ladoga is described. The heterogeneity of the distribution of quantitative indicators of amphipods in different parts of the lake was established. The most widespread species in the littoral zone was G. fasciatus. A decrease in the contribution of G. fasciatus in the bottom communities of macrozoobenthos was noted. The dominant role of G. fasciatus was observed only in those parts of the lake where other species of invasive amphipods were not established yet. The range of Ponto-Caspian amphipods is limited by the boundaries of the Volkhov Bay. A significant increase in the quantitative development of P. robustoides and active southward spread of M. possolskii along the west coast of the lake indicate the ongoing restructuring of littoral biocenoses.

The modern distribution of invasive amphipods of Baikal ( Gmelinoides fasciatus (Stebbing, 1899) , Micruropus possolskii Sowinsky, 1915) and Ponto-Caspian origin ( Pontogammarus robustoides Sars, 1894 , Chelicorophium curvispinum (Sars, 1895)) in Lake Ladoga was shown. The heterogeneity of the distribution of quantitative indicators of amphipods in different parts of the lake was established. The most widespread species in the littoral zone was G. fasciatus . A decrease in the contribution of G. fasciatus in the bottom communities of macrozoobenthos was noted. The dominant role of G. fasciatus was observed only in those parts of the lake where other species of invasive amphipods did not penetrated yet. The habitat of Ponto-Caspian amphipods is limited by the boundaries of the Volkhov Bay. A significant increase in the quantitative development of P. robustoides and active dispersal of M. possolskii to the South along the west coast of the lake indicate the ongoing structural restructuring of littoral biocenoses.

Amphipods play the leading role among alien species in Lake Ladoga. In particular, the Baikal species Micruropus possolskii Sowinsky, 1915 is becoming increasingly important here. The purpose of this paper is to present updated data on the appearance of M. possolskii in Lake Ladoga and on the temporal and spatial dynamics of its development and expansion in this water body. The species was initially recorded in the Shchuchiy Bay of Lake Ladoga in 2003. Its spread to the south to the Petrokrepost Bay (where it was recorded in 2017) is shown. The further expansion of the species in Lake Ladoga and its significant quantitative development in the colonized biotopes and possible expansion to Lake Onega and the Neva Bay of the Gulf of Finland are expected.

The issue of the formation of the compound composition of low-molecular-weight organic compounds in aquatic macrophytes, which make up their low-molecular-weight metabolism, has hardly been studied when introducing them into new habitats. The study aims to compare the component composition of the low-molecular-weight metabolome of sago pondweed (Potamogeton pectinatus L.) on the low-molecular-weight organic compounds contained in the essential oil from the invasive population in the Lake Ladoga and the populations from the native range in Astrakhan Region, Russia. Gas chromatography–mass spectrometry was the major research method. Upon the invasion of P. pectinatus into Lake Ladoga, there was a change in the content of various groups of low-molecular-weight organic compounds in the essential oil and a change in the complex of major components. Fatty acids (29.3–40.0%) and ketones (14.5–18.5%) prevailed in the low-molecular-weight metabolome of sago pondweed in the lakes of the native range. Ketones (27.4%) and aldehydes (18.1%) were the main groups in this species inhabiting Lake Ladoga. About a third of the compounds in the composition of the low-molecular-weight metabolome were specific both to the invasive population of the sago pondweed in the Lake Ladoga and to the population from the lakes of the native range. The plasticity of the metabolism of P. pectinatus allows it to adapt to a wide spectrum of abiotic conditions and different biological environments and to settle in new habitats, primarily those under anthropogenic impact.

Alkylphenols (APs)—nonylphenol (NP) and octylphenol (OP)—are well-known environmental contaminants due to their widespread application and have been identified as endocrine-disrupting chemicals. A novel APs-tolerant fungus designated F6 was isolated from the bottom sediments of the coastal part of the Eastern Gulf of Finland (Neva Bay) and was identified as Aspergillus tubingensis F6 based on ITS sequencing and morphological analysis. The APs presence caused morphological and ultrastructural changes in fungal cells. Major differences were detected in mitochondria, vacuoles, and cell walls. Nonenzymatic antioxidants—pigments, reduced glutathione, exopolysaccharides—played important roles in A. tubingensis F6 resistance to APs toxicity. A low level of lipid peroxidation showed that the protective effects of the antioxidant system were sufficient despite the fact that antioxidant enzymes activity levels were low. Another defense response employed by A. tubingensis F6 against the tNP- and 4-tert-OP-induced stress was based on the ability of the strain to efficiently utilize xenobiotics. After 120 h of cultivation

The aim of the research was to study a removal of polycyclic aromatic hydrocarbons (PAHs) and phytoextraction of bromine (Br) from contaminated soils. The experiments using pea and wheat seedlings as potential candidates for soil remediation were performed. The soil for the experiments was collected from a site slightly contaminated by some PAHs. Before planting, the soil was exposed to 20 mg of Br/kg of soil. In the soil taken from rhizosphere of pea and wheat, the concentrations of many PAHs decreased up to 7 times compared to the concentrations of the compounds in the initial soil. Pea was capable of more effectively influencing the soil PAHs than wheat. The growth of pea and wheat in the soil spiked with Br resulted in a significant increase of Br concentration in a plant. Concentration of Br in roots of pea and wheat increased 21 and 3 times, respectively. Bromine content in leaves of wheat and pea increased 10 and 4.5 times. This accumulation of Br in the plants led to a decrease of its concentration in the rhizosphere soil. The experimental results demonstrated a good ability of the plants to cleanup the soils contaminated with organic and inorganic compounds.

The regularities that shape the composition of low molecular weight organic compounds (LMWOCs) in aquatic macrophytes in response to aquatic environment alterations remain poorly characterized. The aim of the present study consists of a comparative interannual investigation into LMWOC composition in rigid hornwort (Ceratophyllum demersum L.) from a Volga-Akhtuba floodplain lake with a variable trophic state. A high variability of LMWOC composition and individual compound levels in hornwort is detected as different trophic states of the water body are analyzed. Active allelochemicals are the predominant LMWOCs in the case of a “macrophytic” mesotrophic state of the lake, with fatty acids (the free fatty acid fraction) apparently being the most important in this group. Hornwort LMWOC composition in the case of a “cyanobacterial” eutrophic type of lake development is characterized by the predomination of compounds that enhance the protective reactions (manool being the most important) under the conditions of suppression by cyanobacteria, which is also manifested as an almost twofold decrease in the overall intensity of organiccompound biosynthesis.

The ecological and sanitary state of the littoral zone of Lake Ladoga is described according to the data from microbiological observations in 2006, 2010, 2014, and 2019. The total bacterial numbers (TBN) in different parts of the littoral zone varied from 1.10 million cells/ml (2006, Lyaskelya Village and Koionsaari Island) to 15.90 million cells/ml (2014, entrance to Impilahti Bay). It is shown that based on the average total bacterial numbers during the observation period the trophic status of most of the studied water area was typically mesotrophic. Some parts of the littoral have a mesotrophic-eutrophic status: entrance to Impilahti Bay; the area near Pitkyaranta in the channel opposite to the pulp and paper mill (northern region), and near the Voronovo Village (southern region). Correlation analysis revealed a positive relationship between TBN and water temperature. The development of bacterioplankton in the littoral zone was more intensive in the “warm years” (2010, 2014) compared to the “colder” ones (2006, 2019). The content of rod-shaped bacteria ranged from 30 % in the water area near the Lyaskelya Village and in Haukkalahti Bay in summer 2014 up to 73 % near Nazia Village in summer 2010. Based on the average quantitative ratios of saprophytic bacteria and TBN in 2019, the water masses in all the littoral areas were conventionally classified as “clean” and “very clean”. The main environmental risk spots, where a relatively high number of saprophytes and a growth of total coliform bacteria were detected (even if in small quantities), were the littoral part of the Rautalahti Peninsula; littoral zone near Pitkyaranta; water area near Priozersk, the mouth of the River Vuoksa; Shchuchiy Bay; waters at Cape Osinovets; Taipolovsky Bay; water areas near Nazia Village and the village Imeni Morozova.

A chromatographic-mass spectrometric study of the low molecular weight metabolome (LMWM) of water smartweed (Persicaria amphibia (L.) Delarbre, family Polygonaceae Juss.), growing in various biotopes of Lake Ladoga, was carried out for the first time during the flowering phase in order to reveal its qualitative and quantitative composition. Essential oil containing low molecular weight organic compounds (LMWOC) from dried plants was obtained by Clevenger hydrodistillation with steam. The composition and content of LMWOC in the essential oil were detected using a TRACE DSQ II chromato-mass spectrometric complex (Thermo Electron Corporation) in a programmed temperature mode using decafluorobenzophenone and benzophenone as internal standards. A total of 124 LMWOC were detected, of which 110 were identified. Carboxylic acids (50–60 % by content), aldehydes (9–14 %) and hydrocarbons (6-9%) prevailed among the LMWOC in the water smartweed. The LMWM of P. amphibia from the biotope exposed until recently to heavy human impact (effluents from the pulp and paper industry and woodworking enterprises) featured the smallest number of LMWOC (87 versus 107 and 114 in other biotopes), and their total content was 3–3.5 times lower than in plants growing under more favourable conditions. The presence of a number of biologically active metabolites in the LMWM of water smartweed suggests this plant has a pronounced effect on littoral aquatic organisms communities in Lake Ladoga.

The composition of detectable small organic compounds in the ethanol extract of Achillea micrantha was defined by means of gas chromatography-mass spectrometric analysis. There were 71 low molecular weight organic compounds observed, two of which remained unidentified. The antibacterial activity of the extract was studied in respect to Escherichia coli, Staphylococcus aureus, Pseudomonas aeruginosa using the agar diffusion test and serial dilutions to define minimum inhibitory concentration. In order to compare the antibacterial activity of the herb and blossom truss extract of A. micrantha, the extracts of A. millefolium and A. leptophylla was used. In relation to the microorganisms tested, a significant inhibitory effect was observed with the aqueous alcoholic extract of A. micrantha at the minimum inhibitory concentration of 0.05 µg/ml.

The paper focuses on the assessment of the spectrum of biological activities (antineoplastic, anti-inflammatory, antifungal, and antibacterial) with PASS (Prediction of Activity Spectra for Substances) for the major components of three macrophytes widespread in the Holarctic species of freshwater, emergent macrophyte with floating leaves,Nuphar lutea(L.) Sm., and two species of submergent macrophyte groups,Ceratophyllum demersumL. andPotamogeton obtusifolius(Mert. et Koch), for the discovery of their ecological and pharmacological potential. The predicted probability of anti-inflammatory or antineoplastic activities above 0.8 was observed for twenty compounds. The same compounds were also characterized by high probability of antifungal and antibacterial activity. Six metabolites, namely, hexanal, pentadecanal, tetradecanoic acid, dibutyl phthalate, hexadecanoic acid, and manool, were a part of the major components of all three studied plants, indicating their high ecological significance and a certain universalism in their use by various species of water plants for the implementation of ecological and biochemical functions. This report underlines the role of identified compounds not only as important components in regulation of biochemical and metabolic pathways and processes in aquatic ecological systems, but also as potential pharmacological agents in the fight against different diseases.