Composition and Genesis of Polyarenes in Soils of Burnt Areas of Different Ages in the Baikal Nature Reserve

Data on the contents of eleven polycyclic aromatic hydrocarbons (PAHs) in soils of single-time and repeatedly burnt areas of different ages in taiga landscapes of the Khamar-Daban Ridge (southern Baikal region, Buryatia) are presented. Morphological soil features inherited from the fires are identified: charcoal layer (pyr), ash layer (Cpyr), charred forest litter, (Opyr) and pyrogenic humus horizon (Apyr). The post-fire variability of the soil cover within burnt areas is related to the presence of areas with six degrees of burning of litter material. The content of PAHs in soils decreases with increasing fire intensity, as well as in the case of repeated fires on the already burnt area. Background soils of forests not disturbed by fire have a higher content of PAHs compared to that in soils of 42-year-old burnt area and one-year-old intensely burnt area. Four groups of PAHs differing in their origin have been identified using factor analysis: polyarenes of pyrogenic autochthonous origin formed in situ (naphthalene, tetraphene, pyrene, chrysene, anthracene, naphthalene, to a lesser extent benzo(a)pyrene and benzo(ghi)perylene); polyarenes of pyrogenic allochthonous origin that accumulated in soils due to atmospheric transport of ash material (benzo(a)pyrene and benzo(ghi)perylene); polyarenes of biochemical origin (fluorene and biphenyl); and polyarenes of biochemical and petrogenic origin accumulating in the deep soil horizons (phenanthrene).