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<p>The flowing into the White Sea Northern Dvina River is the largest river in the European Arctic, and in contrast to other Arctic rivers, it runs through the populated regions with developed industry. Observations on seasonal variability of microplastics were organized in the Northern Dvina River mouth. The samples were collected every month from September to November 2019 and from May to October 2020 with a Neuston net that was togged 3 nautical miles in the Korbel’nyy Branch of the River delta. Surface plastic with dimensions ranging from 0.5 to 5 mm was analyzed. Chemical composition of the plastic particles was determined using an FT-IR spectrometery in Norway (Oslo) and Russia (Arkhangelsk). The majority of the microplastics were identified as polyethylene (PE) 52.63%, followed by polypropylene (PP) 36.84% and Ethylene Ethyl Acrylate Copolymer (EEA) 10.53%.  It was found that the average concentration of microplastics was 0.0054 items/m<sup>3</sup>, that is close to the average concentration of surface microplastics observed in the in the open Barents Sea, 0.005 items/m<sup>3</sup> (Yakushev et al. 2021). No detectable seasonal variability of the microplastics content in the waters of the Northern Dvina was found. With an assumption that the concentration of microplastics is the same in all the depths, we can assess how the amount of delivering to the sea microplastics changes throughout the year. The microplastics input rate during the spring flood period in May turned out to be maximum, 37.76 items/second. The minimum input rate can be in September with a value of to 5.28 items/second. The data obtained allow us to conclude that the Northern Dvina River is be one of the main sources of microplastic pollution of the White and Barents Seas. This work was partly funded by the Norwegian Ministry of Climate and Environment project RUS-19/0001 “Establish regional capacity to measure and model the distribution and input of microplastics to the Barents Sea from rivers and currents (ESCIMO)” and the Russian Foundation for Basic Research, research projects 19-55-80004.</p>

A volumetric model of accidental oil spills on the land surface was developed, based on numerical methods for solving hydrodynamic equations, and taking into account the processes of oil spreading over the surface, its filtration into the soil and evaporation into the atmosphere. Based on the results of calculations using the hydrodynamic model for the most probable scenarios of oil spills, it is possible to obtain an estimate of the spatial-temporal scale of the spill, which, together with data on the terrain and the presence of water bodies, is the input data for the expert model. Based on the joint use of the hydrodynamic model of the oil spill and expert technologies, the territory of the Nenets Autonomous Okrug and the South Khylchuyu-Varandey oil pipeline were zoned in more detail. It makes it possible to predict the scale and areas most susceptible to negative impact in the event of an accidental oil spill, and to make the necessary decisions for the location of the spill response facilities, as well as the facilities themselves, already at the stage of selection and design of the pipeline route.