1. Introduction

Small rivers and their tributaries are the most important element of natural and economic systems. The special role of small rivers lies in the fact that, being in the upper and peripheral parts of large river basins, they largely determine the ecological situation in them. Bottom sediments are a complex multicomponent system and are characterized by a variety of forms. They play an extremely important role in the formation of the hydro-chemical regime of water masses and the functioning of the ecosystem of water bodies and watercourses as a whole. Since bottom sediments can be considered as one of the main sources of secondary pollution in the aquatic environment, they must be investigated to determine the pathways of potential geochemical migration of pollutants. Under the influence of changes in hydrological conditions, the likelihood of water pollution due to compounds accumulated in bottom sediments may increase (Kramer, 2015).

In 1980, a diamond deposit was named after M. V. Lomonosov. The deposit included six contiguous kimberlite pipes (Arkhangelskaya, named after Karpinsky 1, named after Karpinsky 2, Pionerskaya, Pomorskaya, and named after M. V. Lomonosov), stretching in a chain for 9. 5 km². Within this chain, the distance between ore deposits ranges from 130 m to 2 km. The total area of the deposit is 28 km². The field named after M. V. Lomonosov is the largest in Europe among the primary diamond deposits. The reserves of the Arkhangelsk diamondiferous province account for 20% of the total Russian reserves. In 2002, the project mining and processing plant at the diamond deposit. For the field named after M. V. Lomonosov, it was found expedient to use the traditional combined method of mining reserves with the primary stage of open pit mining. In total, the mining and processing plant at the diamond deposit named after M. V. Lomonosov will operate in the field for at least 50 years. Another problem that arose during the development of the field is the water pollution by suspended particles. Due to a decrease in the level of groundwater, forests within a 3 km radius from the deposit began to dry out. The turbidity of the water affects the number of fish in the Zolotitsa river, and during floods, suspended matter reaches the villages of Nizhnyaya and Verkhnyaya Zolotitsa. Several years after the open joint stock company “Severalmaz” began actively working at the M. V. Lomonosov deposit, the salmon disappeared from this river (Lithosphere and Hydrosphere..., 2001; Gofarov et al., 2006).

The study of radioactivity is of the utmost importance for assessing the ecological state of the given territory. This is due to the fact that the studied territories since the beginning of the atomic era have been significantly affected by technogenic radioactivity, which had global and local sources. According to Table 2, the activity values of natural radionuclides are below the world average (UNSCEAR, 2000).

The main sources of technogenic radioactivity for this territory were a) global (stratospheric) fallout as a result of atmospheric nuclear tests, b) local (tropospheric) fallout as a result of tests carried out at the only nuclear test site in the Arctic on Novaya Zemlya from 1955 to 1990, c) the entry into the Arctic seas of technogenic radionuclides from Western European radiochemical plants in Great Britain and France, and d) the consequences of the 1986 Chernobyl disaster (Aybulatov, 2000; Crane et al., 2000; Smith et al., 2000; Strand et al., 2002; Dowdall et al., 2005; Kiselev et al., 2005; Khalturin et al., 2005; Mikhailov, 2006; Masque et al., 2007; Kershaw et al., 2009; Camara-Mor et al., 2010; Johannessen et al., 2010; Ł okas et al., 2013; Povinec et al., 2013; Thakur et al., 2013; Matishov et al., 2014; AMAP, 2015; Miroshnikov et al., 2017; Chen et al., 2017; Matishov et al., 2019; Cwanek et al., 2020; Saniewski et al., 2020). Additional sources of technogenic radionuclides entering North European were direct emissions from radiochemical plants located in the Urals and Siberia (Vorobiova et al., 1999; Waters et al., 1999; Vakulovsky et al., 2005). Some other local sources also contribute to the technogenic radiation pollution of the territory(Tracy et al., 1984; Eriksson et al., 2005; Matiyashchuk and Lazareva, 2010). A potential contribution to the radioactive contamination of this region can be made by nuclear shipbuilding and ship repair enterprises, bases on nuclear ships and submarines of the Northern Fleet of the Russian Navy, plants for the processing and storage of radioactive waste, and dumping of radioactive waste into the Kara and Barents Seas (Ilin et al., 2017; Sarkisov et al., 2011; Sarkisov et al., 2015).

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