## 3 Results and Discussion
### Variations in the Radioisotopes Content in the ISO-1 Peat Profile
From the horizons 22-24 and down to the lowest layer, the activity of \({}^{210}\)Pb ceases to change and varies slightly from 19 to 23 Bq/kg, indicating no excess atmospheric lead in the lower layers. The vertical distribution of \({}^{210}\)Pb in the ISO-1 profile also shows significant differences from the site with a natural hydrological regime of ISNO-1 [29]. Therefore, the natural deposit of ISNO-1 is characterised by the active leaching of \({}^{210}\)Pb from the overlying horizons and concentrating on the geochemical barrier at the range of 19 to 21 cm. At the same time, the concentration of \({}^{210}\)Pb at the range of 19 to 21 cm is close to the values of the upper horizon (310.8 Bq/kg in the 0-3 cm horizon and 243.9 Bq/kg in the 19-21 cm horizon, respectively), indicating the intensive downward migration of \({}^{210}\)Pb under conditions of the natural hydrological regime. The differences in \({}^{210}\)Pb activities between the top horizons of cores from the dried ISO-1 and natural ISO-1 sites (567.9 Bq/kg vs. 310.8 Bq/kg) with comparable reserves are probably associated with this process; that is, redistribution of \({}^{210}\)Pb across the section is observed. What is also significant is the difference in the depths in which the presence of excess lead is recorded. In the natural deposit of ISNO-1, excessive lead was fixed at a depth of 35-37 cm, while in the drained area atmospheric lead was not detected below the horizon 22-24. This indicates significantly lower rates of peat mass accumulation within the dried section of ISO-1, associated with compaction of the peat. The accumulation of the ISO-1 peat column will be discussed in more detail in the section \"\({}^{210}\)Pb dating\". The U concentration in the dried ISO-1 peat core fluctuates between 0.20 and 2.37 mg/kg, for a mean concentration of 0.75 mg/kg, which is the norm for peatlands of the damp areas of the European North (subarctic zone) of Russia [61]. The range of variation and mean value of uranium concentration in the ISO-1 profile is comparable to the natural site of ISNO-1 (0.10-3.06 mg/kg, average 0.83 mg/kg). In a vertical distribution of uranium in the ISO-1 profile, an interval of 6-18 cm with a maximum concentration of U is clearly distinguished, which is probably due to the behaviour of past U deposits with atmospheric deposition to the top of the peatland. The uranium isotope ratio of \({}^{234}\)U/\({}^{238}\)U varies between 0.88 and 1.82, which is generally the typical range for surface waters, whose main source of nutrition is atmospheric precipitation [62]. Figure 4: Variation in the radioisotopes in the ISO-1 peat core by depth. In addition to the man-made isotope \({}^{137}\)Cs, the trans-uranic radionuclide \({}^{241}\)Am was found in the dried peat deposit of ISO-1. Significantly, \({}^{241}\)Am was detected only in the depth interval of 8-20 cm with an activity variation from 1.0 to 2.1 Bq/kg. In other horizons, the activity of \({}^{241}\)Am was below the detection limit. At the same time, ISNO-1 was not reliably detected on any horizon at the natural site. Given the proximity of the ISO-1 and ISNO-1 sites and the apparently uniform atmospheric flux of \({}^{241}\)Am, we can assume that the possibility of detecting \({}^{241}\)Am in the dried section of ISO-1 is related to the compaction of the deposit and the \"concentration effect\". An evaluation of the influence of changes in the physical and chemical parameters of the dried peat column and radionuclide activity is presented in the \"The statistical analysis\" section. Thus, variations in the hydrological regime of a peat deposit resulting from drainage contribute to important variations in both the physicochemical parameters and the vertical distribution of a selected number of radioisotopes.