A. S. Tsibart

Polycyclic aromatic hydrocarbons in soils: Sources, behavior, and indication significance (a review)

The current ideas of polycyclic aromatic hydrocarbons (PAHs) in soils are reviewed. Their natural and anthropogenic sources are discussed, and the mechanisms of their arrival from other environmental components to soils are considered. The main processes typical for PAHs in soils are defined; the sorption, degradation, and translocation features of polyarenes in the soil profile are shown. Attention is paid to the geographical features of the PAH distribution in soils. The use of data on the PAHs in soils for the indication of different natural and technogenic processes is also discussed.

Pyrogenic Polycyclic Aromatic Hydrocarbons in Soils of Reserved and Anthropogenically Modified Areas: Factors and Features of Accumulation

The accumulation features of pyrogenic polycyclic aromatic hydrocarbons (PAHs) in soils were analyzed depending on the type of burning material and the combustion conditions (the temperature, oxygen access, and dispersion of the combustion products). The PAH accumulation features in the soils of three reserved areas of forest, steppe, and peat fires were revealed. The distribution features of the PAHs resulting from the anthropogenic pyrogenic processes (the household combustion of wood and the inflammation of coal dumps) in soils were established. The differences in the qualitative composition of the PAHs arriving to the soils from the different pyrogenic sources were shown.

The influence of fires on the properties of forest soils in the Amur River basin (the Norskii Reserve)

The influence of forest fires on the properties of taiga brown, gley taiga brown, and alluvial bog soils widespread in the area of the Norskii Reserve (the Amur River basin) was studied. During several years after the fire, the humus content increased, especially in the soils subjected to fires of high intensity. In the soils of steep slopes, the humus content decreased due to damage to the forest vegetation and activation of lateral runoff after the fire. As a rule, in the soils subjected to fire, the C ha-to-C fa ratio increased and correlated with the fire intensity. Some relationships between the forest fires and the acid-base properties of the soils were revealed. After the fires, the pH values often became higher. The stronger the fire, the higher the pH values. The stony soils differed from the other ones, since the reaction of their upper horizons turned out to be more acid after the fires. The analysis of the authors’ and literature data showed that the pyrogenic changes of some soil properties have been poorly studied and need further investigation, including their geographical aspects.

Hydrocarbons in Soils: Origin, Composition, and Behavior (Review)

It has been shown that a large body of evidence on the sources, transformation, and migration of hydrocarbons in soils has been acquired by different researchers. Available data about the origin and behavior of hydrocarbon gases, total petroleum hydrocarbons, polycyclic aromatic hydrocarbons, alkanes, and other compounds have been considered successively. A wide range of natural and anthropogenic factors affecting the transformation and migration of hydrocarbons in soils have been analyzed. The indicative value of these compounds has been explained. At the same time, many problems related to hydrocarbons in soils are still insufficiently understood. Sparse and fragmentary data are available in the literature on the interaction of different hydrocarbon groups in the soil. Few data refer to the features of hydrocarbons in background zonal soils; there are almost no interzonal comparisons. The behavior of hydrocarbons in soils of different landscape-geographical positions is characterized in isolated publications. The hydrocarbon status of soils as an integral complex of interrelated hydrocarbons is almost not analyzed. Hydrocarbons of a single class (polycyclic aromatic hydrocarbons, hydrocarbon gases, n-alkanes, etc.) are usually characterized in each publication.

Factors and features of the hydrocarbon status of soils

The hydrocarbon status (HCS) of soils has been characterized using a set of quantitative parameters, which can be obtained in the routine laboratory studies of soil samples. This is a general quantitative and qualitative characterization of hexane bitumoids and individual polycyclic aromatic hydrocarbons prevailing in natural objects. Field survey of soil air has been performed in order to determine the composition and content of gaseous hydrocarbons. The features and factors of soil HCS formation have been studied in soils of eight key sites in forest, steppe, and dry-steppe landscapes of European Russia. Along with zonal diversity, the presence of any local anomalous natural or technogenic factor capable of affecting the soil HCS (gas emanations from the deep lithosphere, specific parent rocks, pollutant fallout from the atmosphere, confinement to an oil field, etc.) has been used as the criterion of their selection. It has been shown that, just as the humus and salt statuses of soils have become their important integrated characteristics, so the study of soil HCS allows reaching a new level of knowledge of the nature of soils and their processes. The parameters of soil HCS adequately reflect the features of bioclimatic and topolithological factors of pedogenesis, the properties of soils, and the level of technogenic impact on the soil cover. Accumulation of new factual data and refinement of soil-geographical studies are necessary for more thorough study of soil HCS.

Soil properties in the Tol’yatti pine forest after the 2010 catastrophic wildfires

The results of the studies of soil changes after the 2010 fires in the forest outliers of the city of Tolyatti have been reviewed. The morphological analysis of postpyrogenic soils has showed that the fire touched only the upper part of their profiles. It has been revealed that the surface fires favor the more intense loss of organic carbon than the crown fires (2.85 and 2.37%, respectively). However, the crown fires are more destructive for soils, because, first, they are a continuation of the surface fires and, second, sheet and linear water erosion of soils develops because of the complete denudation of the soil cover. It has been found that forest fires result in the dehumification of soils, which is related to the destruction of the organic horizons, the mineralization of root residues, and the almost complete absence of fresh plant waste on the postfire areas. The pyrogenic impact increases the portion of humic acids in the organic matter. Along with the transfer of the clay fraction, the translocation of polycyclic aromatic hydrocarbons resulting from the fires to the accumulative geochemical positions is also possible.

Polycyclic aromatic hydrocarbons in pyrogenic soils of swampy landscapes of the Meshchera lowland

The composition and distribution of polycyclic aromatic hydrocarbons (PAHs) were studied in organomineral and organic soils of the Meshchera National Park. It was found that the background oligotrophic peat soils unaffected by fires in central parts of the bogs are characterized by the increased PAH concentrations due to their high sorption capacity. The fires of 2007 and 2010 resulted in the transformation of the plant cover and soil morphology, the formation of new horizons, and the change in the PAHs content and composition. Significant burn-off of organic matter was found in oligotrophic-eutrophic soils and resulted in the decrease of PAHs content after fire. Only partial burn-off of organic horizons and intense formation of PAHs were recorded in the soil with initially great thickness of peat horizons. Pyrogenic accumulation of PAHs was identified in organomineral soils of the marginal parts of bogs and of forest sites.

Soils on overburden dumps in the forest-steppe and mountain taiga zones of the Kuzbass

The properties of the soils forming on coal dumps significantly depend on the properties of the parent rocks and the technology of creating the dumps. In the forest-steppe and mountain taiga zones of the Kuznetsk Coal Basin, argillites, siltstones, and sandstones are the overburden and enclosing rocks. They are responsible for the alkaline reaction and the same microelement composition in almost all the soils studied. The nonselective formation of the dumps and the predominance of the coarse fraction in the rocks composing the dumps is a cause of the wide distribution of petrozems and humus petrozems on their surface. The presence of a great amount of coal particles in the substrates and the incorrect planning of the dumps may be the reasons for their self-ignition, which can change the composition of polycyclic aromatic hydrocarbons in the soils of the dumps.

Laboratory Assessment of Forest Soil Respiration Affected by Wildfires under Various Environments of Russia

Pyrogenic carbon emission rates were estimated in the soils of three natural zones in Russia: forest-tundra, south-taiga, and forest-steppe. Postfire soils were found to be characterized by essential losses of soil C due to the combustion fire effect. Soils lost 3 or 5 parts of initial carbon content and showed an essential decrease in the C/N ratio during the fire effect. The pH values increased due to soil enrichment by ash during the fire events. CO2 emission rates were highest in natural soil samples, because the amount of organic matter affected by mineralization in those soils was higher than in natural ones. Simultaneously, the total values of mineralized carbon were higher in postfire soils because the SOM quality and composition were altered due to the fire effect. The only exception was in forest-tundra soils, where a high portion of dissolved organic compounds was released during the surface fire. The quality of initial SOM and intensity of the wildfire play the most important roles in the fate of SOM in postfire environments. Further study of CO2 emissions is needed to better characterize postfire SOM dynamics and develop an approach to model this process.