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The significance of methane production by lakes to the global production of greenhouse gas is well acknowledged while underlying processes sustaining the lacustrine methane budget remain largely unknown. We coupled biogeochemical data to functional and phylogenetic analyses to understand how sedimentary parameters characterize the methane cycle vertically and horizontally in the icecovered bay of the second largest lake in Europe, Lake Onego, Russia. Our results support a heterogeneous winter methane cycle, with higher production and oxidation closest to riverine inputs. Close to the river mouth, the largest numbers of copies of methane-related functional genes pmoA and mcrA were associated with a specific functional community, and methane production potential exceeded oxidation, resulting in 6-10 times higher methane fluxes than in the rest of the bay. The elevated fluxes arise from the spatial differences in quantity and type (lacustrine versus riverine sources) of organic matter. More homogeneity is found toward the open lake, where the sediment is vertically structured into 3 zones: a shallow zone of methane oxidation; a transitional zone (5-10 cm) where anaerobic methane oxidation is dominant; and a methane production zone below. This vertical pattern is structured by the redox gradient and human-induced changes in sedimentary inputs to the bay. Retrieved 16S rRNA gene sequences from Candidatus Methanoperedens and Cand. Methylomirabilis suggest that anaerobic oxidation of methane occurs in these freshwater lake sediments.

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The morphology and mineralogical and geochemical compositions of the freshwater ferromanganese formations (FMF) of Lake Onego (NW Russia) and small lakes located in its catchment area were studied. The lake waters, bottom sediments and FMF were analyzed by a set of modern methods of geochemistry, mineralogy, and crystal chemistry (powder X-ray diffraction, IR spectroscopy, electron microscopy, ICP–MS analysis, atomic absorption, etc.). A detailed description of the microscopic structure in comparison with the geochemical characteristics of the FMF provides new information on the role of biota in the formation and behavior of individual elements at various stages in the nodule formation process. This study shows the homogeneous composition of microconcretions—only manganese or only ferruginous—in bottom sediments throughout the entire water area of Lake Onego and the rhythmic structures of the nodules, formed by macro- and microlayers with mineralized microbiota. The layers are composed of either crystalline Mn mineral phases (pyrolusite, rhodochrosite) or crystalline Fe mineral phases (siderite, goethite). The separation of Mn and Fe mineral phases in the nodules proceeded during their formation and diagenesis. The examined chemical and mineral compositions, textures, and structures of the nodules are a testament to the hydrogenic source of their ore substance and the formation of FMF is controlled primarily by redox environments at the water–sediment interface.

Once oil has been spilled, urgent decisions need to be made concerning response options, so that environmental impacts are kept to the minimum. Options for protection of shorelines include containment and recovery, in-situ burning, use of dispersants or just leaving the oil to dissipate and degrade naturally. All response options have both limitations and benefits which need to be compared with each other. This process is known as Net Environmental Benefit Analysis (NEBA). A NEBA for protection of coastal areas in the Russian part of the Barents Sea and the White Sea was performed by Ramboll in the framework of the UNEP/GEF project "Improvement of the emergency oil spill response system under the Arctic conditions for protection of sensitive coastal areas (case study: the Barents and the White seas)". The analysis was based on the results from modeling of spills of oil and oil products which are transported through the Barents and the White seas, oil spill sensitivity mapping as well as assessment of available oil spill response (OSR) resources in the region. The analysis shows that coastline protection methods such as using dispersants or in-situ burning lack methodological and regulatory framework and at the moment they cannot be used in the Russian part of the Barents Sea and the White Sea. The optimal available technique in case of a spill of fuel oil or crude oil will be mechanical containment and recovery (use of booms and skimmers). However, mechanical methods will be both inefficient and extremely hazardous to combat spills of gas condensate or naphtha due to high explosion and fire risk until full evaporation of the volatile fractions has taken place. In such a case it is recommended to observe the slicks and await natural dissipation. Challenging logistics in the region and harsh climatic conditions can significantly impede timely response to offshore oil spills and use of traditional mechanical recovery that creates need for adapting alternative tactics such as in-situ burning and dispersants.

Here, we present new results from seismic, geological, and geochemical studies conducted in 2015–2019 in the Petrozavodsk Bay of Lake Onego, NW Russia. The aims of these investigations were to (i) to characterize the structure of Quaternary deposits and (ii) provide new evidence of modern geodynamic movements and gas-seepage in Holocene sediments. The structure of the recovered deposits was composed of lacustrine mud, silt and sands from the Holocene, limno-glacial clays (varved clays) from the Late Glacial–Interglacial Transition, and glacial deposits (till) from the Late Pleistocene. The thickness of these deposits varied in different parts of the bay. Many pockmarks created by gases escaping and reaching sediment-water interface were observed in these deposits. Such pockmarks can play a significant role in the geochemical and biological processes in the bottom sediment surface, and gases that escape might modify the physicochemical characteristics of the environment.

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