## 4 Conclusions  
On example of a peat section collected in the territory of the Arkhangelsk Region within the Ilassky peat massif, which is typical of the European Subarctic of Russia we studied the activity levels and features of the vertical distribution of several atmospheric fallout radionuclides and physicochemical parameters of the peat bog. Among the radionuclides of atmospheric fallout, the following isotopes were studied: \({}^{137}\)Cs, \({}^{210}\)Pb, \({}^{234}\)U and \({}^{238}\)U. Among the physicochemical parameters of peat, the following components were studied: contents of CO\({}_{3}\)\({}^{2-}\), ash, organics, water-soluble salts, pH values of water and salt extracts, the degree of oxidation of organic matter, moisture saturation, and contents of N, C, H and O. In total, more than 400 determinations of various physicochemical parameters and radionuclides were performed in samples of peat core. The following conclusions can be drawn from the results of the conducted research. The investigated part of the profile of the peat deposit is composed mainly of sphagnum peat. The physicochemical parameters of the studied peat deposit are in the ranges typical for undisturbed high-moor peatlands of the Subarctic region of European Russia. Variations in physicochemical parameters with the depth of the deposit are apparently associated with the occurrence of multidirectional redox processes, the vertical transfer of organic matter in the deposit, and the dynamics of swamp water level fluctuations. It has been established that the horizon is distinguished in the section at a depth of 20 cm, characterized by significant fluctuations in the parameters of the degree of oxidation, ash content, the content and composition of organic matter. The formation of this horizon can be due to both the washing out of the mineral part from the overlying horizons and the anthropogenic dust content of the atmosphere during the formation of the peat deposit. The depth distribution of \({}^{137}\)Cs reveals two prominent activity maxima, in the upper part of the profile and at a depth of 20 cm, due to the peculiarities of vertical migration and the dynamics of caesium supply with atmospheric fallout. For the distribution of lead-210, a non-exponential decrease in activity with depth was revealed with the formation of an activity peak at a depth of 20 cm, in which the activity of \({}^{210}\)Pb is close to the values on the surface of the deposit and coincides with the maximum activity of caesium and the content of ash elements. In this regard, this horizon can be considered a complex geochemical barrier of the redox, sulphide and sorption type, the conditions of which contribute to the retention of technogenic \({}^{137}\)Cs and the accumulation of \({}^{210}\)Pb washed out from the overlying horizons. The distribution of uranium with depth, most likely, is mainly due to the dynamics of historical inputs with atmospheric fallout to the surface of the deposit and with extremely low mobility of uranium along the profile. Factor analysis showed that the distribution of \({}^{137}\)Cs and \({}^{210}\)Pb was associated with the content of water-soluble salts, water saturation of the deposit and the value of Eh (rH) because \({}^{137}\)Cs is found in peat mainly in the ionic form, and \({}^{210}\)Pb in the form of complexes with humic acids. The results of dating the peat profile with the CF model showed that the 19-21 cm horizon, identified by the peak of \({}^{137}\)Cs activity and several other physicochemical parameters (in particular, ash content), corresponds to the age of 1965 years; with the additional use of the Monte Carlo method, the age was 1962, which confirms the correctness and adequacy of the chosen peat core dating model. The use of the CF dating model together with the Monte Carlo method provides the best congruency with the reference horizon for \({}^{137}\)Cs (taking into account the error).