Geochemical background of oligotrophic peatlands in the northern taiga (European Northeast): Assessing the contribution of endogenous processes and wildfires to potentially toxic elements accumulation.

The present study is devoted to the vertical distribution of potentially toxic elements (PTEs) in the peat profiles of the northern taiga, which depend on endogenous processes, external inputs, geochemical barriers, and are also influenced by fires. Based on the obtained results, elements were distributed within the soil profile into two distinct groups. The first group predominantly concentrates in the lower horizons and includes zinc (Zn), nickel (Ni), cobalt (Co), manganese (Mn), iron (Fe), chromium (Cr), vanadium (V), titanium (Ti), and magnesium (Mg). The second group is primarily found in the peat layer and comprises mercury (Hg), copper (Cu), lead (Pb), cadmium (Cd), Zn, Ni, Mn, aluminum (Al), V, barium (Ba), strontium (Sr), calcium (Ca), and arsenic (As). The plant biomass, in particular that of pine and birch wood, plays a significant role in the deposition of PTEs. The key geochemical barriers that immobilize PTEs include humic acids, sulfur-containing compounds, and iron oxides and hydroxides, which form stable associations with these elements under reducing conditions. Special attention is paid to the fire events: ash resulting from fires is a source of alkaline and alkaline earth elements (potassium (K), Ca), as well as Mn, V, Ni, Cd, Pb, and Cu. Statistically significant spatial differences in PTE content were observed between the studied soil pits, likely attributable to meteorological factors influencing the atmospheric transport of elements from fires. Manganese exhibits high mobility and a downward distribution pattern, while Cu and Pb remain associated with and immobilized by organic matter. Overall, the study highlights the complex, multifactorial nature of the formation of the geochemical structure of peat ecosystems.