Pyrogenic alterations of Podzols at the North-east European part of Russia: Morphology, carbon pools, PAH content

- Changes in soil morphology of pyrogenic origin are within the depth of 20-30 cm down soil profile.
- There are no significant fire-caused changes in carbon and nitrogen stocks in the soils.
- The PyС reflected an increase of SOCtot at the upper mineral horizons at fire-sites.
- Fires are one of the main factors responsible for an increase in the PAH content in studied soils.

Fires are a natural factor for taiga ecosystems of the North-European part of Russia. Pine forests on sandy soils often suffer from fires. The paper surveys in what extent fires in lichen pine forests (burnt 2, 10 and 16 years ago) affect soils and soil organic matter (SOM). Ground fires in lichen pine forests fully disturb soil litters. Changes in soil morphology of pyrogenic origin are observed in the topsoil down to depth of 20-30 cm. The greatest changes were found in soil 2-year fire affected site. The physicochemical soil properties of the sites affected by fire 10 and 16 years ago were similar to those at the reference sites. There are no great after-fire changes in nitrogen and carbon stocks in the soils. The concentration (and stocks) of total carbon and nitrogen in soil litter decreases at the first after-fire years. Mineral soil horizons, particularly the upper mineral layer, become enriched with combustion products, i.e. pyrogenic carbon and nitrogen of free and occluded fractions. There is a Ctot. increase in the upper mineral soil horizons possibly due to black carbon or to OM absorbed at the charcoal particles. Fires increase content of Polycyclic Aromatic Hydrocarbons (PAHs) in the soils, their concentration in the upper subhorizon of forest litter exceeds that of the background by 2-9 times. This increase is due to the presence of di- and trinuclear polyarenes.