Rare earth elements in surface lake sediments of Russian arctic: Natural and potential anthropogenic impact to their accumulation

Investigations of the rare earth elements (REEs) concentrations in surface sediments of small lakes in the Arctic zone of the Russian Federation are presented. The territories of Murmansk Region and the Republic of Karelia were used as key study areas. The sampling of 9 lake sediments was carried out. Inductively coupled plasma mass spectrometry (ICP-MS) method was used as a main approach to estimate total concentrations of REEs and heavy metals and content of their elements in different fractions, using sequential extraction method. The role of the natural landscapes factor (tundra, forest-tundra, taiga) in the process of REEs accumulation in lake sediments was evaluated in the course of the work. It was revealed that the highest median accumulation of REEs occurred in the sediments of lakes in the tundra zone, and the lowest median accumulation of REEs occurred in the lakes in the forest zone (taiga). The dynamics of the REEs accumulation in the lakes of the background (pristine) regions of the Arctic, as well as in the lakes of urbanized territories, is shown on the example of the cities of Murmansk Region. The analysis of the vertical distribution of REEs and heavy metals in the cores of sediments of the studied lakes showed that the anthropogenic factor plays an important role in the accumulation of REEs in urban water bodies. First of all, this is due to dust from construction, wear and tear of houses and road structures, and weathering of soils and quaternary deposits in urban areas. All urban lakes showed similarity between distribution of REEs and heavy metals in the sediments. The main fractions of REEs in the sediments of the lakes of the Arctic zone of Russia were determined. It was revealed that the residual phase of sediments and organic matter plays a significant role in the accumulation of REEs in surface sediments of the North of Russia. At the same time, mobile forms and phases of REEs associated with Fe and Mn oxides also did not play a large role in the accumulation of REEs in the sediments of lakes in Northwest Russia.