Вестник МГТУ. 2020, Т. 23, № 1.

with the previously adopted general value for the lakes in the south of Karelia (Slukovskii et al., 2019). In addition, similar sedimentation rates are observed in the southern regions of Finland and Sweden (Karlsson et al., 2006; Verta et al., 1989). Fig. 2. Vertical distribution of Pb concentrations in the sediments core samples from small lakes in the south of Russian Karelia Рис. 2. Вертикальное распределение концентраций Pb в образцах колонок донных отложений малых озер юга Карелии Fig. 3. The distribution of Pb-210, Pb, Cd, and Tl by depth in the sediments of Lake Ukonlampi (southwest of Karelia) Рис. 3. Распределение Pb-210, Pb, Cd и Tl по глубине в современных отложениях озера Юконлампи (юго-запад Карелии) However, each lake is unique, and the sedimentation rate can vary greatly even within the same region or part of the region. Therefore, to estimate the background concentrations of chemical elements in the sediments in the small lakes of Karelia, only the deepest layers of all column samples were used, where the coefficient of variation of Pb concentrations does not rise above 50-60 %. These are layers between 14 and 48 cm, depending on the particular lake. In addition, concentrations of chemical elements found in the samples collected using a hand-held drill from depths of 1 meter or deeper were included in the dataset. The age of such sediments, which formed in the interval between the deglaciation of the modern Republic of Karelia and the onset of industrialization in the countries of Europe and North America, is estimated to be thousands of years (Синькевич и др., 1995). Consequently, any variations in the chemical composition of such sediments can be attributed to natural factors, which is acceptable when estimating the background concentrations of chemical elements. The resulting datasets for the 42 elements ranged from 73 to 76 samples. The concentrations of the majority of chemical elements in the samples do not follow the normal distribution, which is often the case in geochemistry; therefore, sample median values (xMe), which, unlike the arithmetic mean, are less affected by any extremely high outliers in the samples, were adopted as average background concentrations. Other indicators for each of the elements are shown in Table 2.