Chromium and arsenic in contaminated soils (Review of publications)

In the last decades, the chromium clarke in the world’s soils has been revised and reduced; at present, it is equal to 70 mg/kg. No maximal permissible concentration is accepted for the total chromium content in the soils of Russia; it appears reasonable to use the Western European and North American standards in Russia and to take the average value of the maximal permissible concentration equal to 200 mg Cr/kg. Chromium toxicity depends on its oxidizing status. The hazardous effect decreases with the reduction of Cr(VI) to Cr(III). There are various chemical reducers of Cr(VI), including sulfides, dissolved organic substance, aqueous Fe(II) and minerals enriched in Fe(II), and Fe(0). As-containing ore tailings represent a powerful source of technogenic arsenic. Significant environment contamination with natural As is registered in a number of Asian countries. The maximal permissible concentration of total arsenic is equal to 2 mg/kg in Russian soils; it is probably underestimated, because it is lower than the As clarke in soil (5 mg/kg). The approximately permissible concentration (APC) values for As look more reasonable. Arsenic toxicity depends on its oxidation degree: As(III) is 2–3 times more toxic than As(V).     

Postpyrogenic Polycyclic Soils in the Forests of Yakutia and Transbaikal region

Periodical forest fires are typical natural events under the environmental and climatic conditions of central and southern Yakutia and Transbaikal region of Russia. Strong surface fires activate exogenous geomorphological processes. As a result, soils with polycyclic profiles are developed in the trans-accumulative landscape positions. These soils are specified by the presence of two–three buried humus horizons with abundant charcoal under the modern humus horizon. This indicates that these soils have been subjected to two–three cycles of zonal pedogenesis during their development. The buried pyrogenic humus horizons accumulate are enriched in humus; nitrogen; total and oxalate-extractable iron; exchangeable bases (Са⁺² and Mg⁺²); and the fractions of coarse silt, physical clay (<0.01 mm), and clay (<0.001 mm) particles in comparison with the neighboring mineral horizons of the soil profile. The humus of buried pyrogenic horizons is characterized by the increased content of humic acids, particularly, those bound with mobile sesquioxides (HA-1) and calcium (HA-2) and by certain changes in the type of humus.     

Soil contamination with emissions of non-ferrous metallurgical plants

The upper soil horizons are strongly contaminated in the area influenced by the Mid-Urals copper smelter. In the technogenic desert and impact zones, the contents of a number of elements (Cu, Zn, As, Pb, P, and S) by many times exceed their clarke values and the maximum permissible concentrations (or provisional permissible concentrations). The degree of technogeneity (Tg) for these elements is very high in these zones. In the far buffer zone, Tg is about zero for many elements and increases up to Tg = 27–42% for four heavy elements (Cu, Zn, Pb, and As) and up to 81–98% for P and S. The buffer capacity of the humus horizon depends on the soil’s location within the technogeochemical anomaly and also on the particular pollutant. In the impact zone, it is equal to 70–77% for lead and arsenic, although other technogenic elements (Zn, Cr, S, and P) are poorly retained and readily migrate into the deeper horizons (the buffer capacity is equal to 14–25%). Nearly all the heavy metals enter the soil in the form of sulfides. The soils in the area affected by the Noril’sk mining and smelting metallurgical enterprise are subdivided into two groups according to the degree of their contamination, i.e., the soils within Noril’sk proper and the soils in its suburbs to a distance of 4–15 km. The strongest soil contamination is recorded in the city: the clarke values are exceeded by 287, 78, 16, 4.1, and 3.5 times for Cu, Ni, Cr, Fe, and S, respectively. The major pollutants enter the soil from the ferruginous slag. The soil’s contamination degree is lower in the suburbs, where heavy metal sulfides reach the soils with the aerial emission from the enterprise.     

Biological mineralization of organic matter in the modern virgin and plowed chernozems,buried chernozems,and fossil chernozems

The phenomenon of mineralization (biological mineralization) of organic matter in chernozems has been studied. A decrease in the content of C_org with time can be considered an index of the organic matter mineralization. It is suggested that the humus horizons of modern chernozems contain the pools of organic matter of different ages: easily decomposable organic matter, labile biologically active humus, stable biologically active humus, and relatively inert humus. The composition and mean residence times of these pools and their contribution to the total organic matter content have been estimated. The particular types of the biological mineralization have been determined on the basis of the comparison between the velocities of mineralization (M) and humification (H) processes: total unidirectional mineralization (M ≫ H), equilibrium mineralization (M ∼ H), nonequilibrium mineralization (M> <H), and zero mineralization. The separation of subtypes is based on data on the relative rates (%) of the organic matter mineralization. On the basis of available experimental data on chernozems buried under kurgans and in loess sediments (with the age of up to 800 ka), the quantitative relationship of the humus content in the buried soils on their age has been found; it has an exponential shape. During the first 100 ka after the soil burial, the soil humus content gradually (with a slowing intensity) decreases from 100–75 to 6.5% of its content in the virgin chernozems. Then, 100–1000 ka after the soil burial, the soil humus content remains approximately constant (6.5% of the initial level, or 0.3% of the soil mass). The rates of mineralization have been estimated. It is shown that the elemental composition (C, H, N, O) of humic acids remains relatively stable for a long time due to the regeneration of the chemical structure of humus (matric restoration of humus). It is suggested that several different forms of humus related to pedogenesis should be distinguished in the biosphere. The renewable humus in the equilibrium state with the environment is typical of the open biospheric (soil) systems. The fossil humus, whose content decreases with time, and whose composition remains stable, is typical of the semiclosed and closed systems. With time, it transforms into residual humus, whose content and composition remain stable. The fossilized organic matter in the fossil soils and sediments of the past geological epochs (Mesozoic and Paleozoic) considerably differs from the renewable, fossil, and residual humus.     

Concentration and distribution of polychlorinated biphenyls in soils of Moscow

The concentration of polychlorinated biphenyls (PCB) in the soils of Moscow has been determined by gas chromatography and high-resolution mass spectrometry (GC-HRMS). The total concentrations of 19 indicator and dioxin-like congeners, as well as PCBs in surface soils, are 2.85–60.62 μg/kg (the most contaminated sample was 4591.99 μg/kg). The average value, excluding the most contaminated sample, is 14.44 μg/kg, which is characteristic of residential areas of industrialized countries. This indicator varies insubstantially depending on the functional zone of the city. The toxicity equivalent of 12 dioxin-like PCBs in soils is 1.92 ng I-TEQ/kg on average and varies in a range from 0.15 to 334.12 ng I-TEQ/kg. The fraction of PCBs in the total toxicity of dioxins and dioxin-like compounds in soil varieties is 16.7–85.4%.     

Monitoring of the humus status of soils of the Ingulets irrigation system

The results of long-term studies (1957–2007) of the changes in the morphology of soil profiles and in the reserves and fractional composition of the humus in the soils of the Ingulets irrigation system are discussed. After 50 years of irrigation, the boundaries of the genetic horizons shifted downward by 15–30 cm. The redistribution of the humus took place: its content decreased to a low level in the plow layer of the irrigated and rainfed soils and significantly increased in the layer of 60–100 cm so that the reserves of humus in the layer of 0–100 cm somewhat increased and corresponded to a moderate level. The distribution of humus in the soil profiles was characterized by the gradual lowering down the soil profile. The concentration of nitrogen in the humus of the irrigated southern chernozems was very low. The degree of humification of the soil organic matter was high. The humus was of the humate type in the upper horizons and of the fulvate-humate type in the lower horizons.     

Soil formation in the quarries for limestone and clay production in the Ukhta region

The soils forming on the overgrowing technogenic dumps of quarries for limestone and clay production were investigated in the northern taiga (the Ukhta region). The soils are formed under sparse herbaceous plant communities. In the soils on calcareous technogenic eluvium and clay dumps, the processes of humus formation and accumulation predominate. In the soils of the clay dumps, the leaching of carbonates is expressed to a greater extent than in the soils of the limestone quarries. The nitrogen content of organic matter is low in the soils on the technogenic lime substrates and very low on the clay ones. Fulvic acids predominate in the humus composition. At the stages of the soil restoration studied, the zonal trend of pedogenesis is manifested only in the humus accumulation. The calcareous technogenic eluvium is found to be more favorable for the development of microbial communities as compared to the clay substrates with their small microbial biomass. However, there are no features pointing to the development of zonal soil profiles. This fact attests that, in the first 20–30 years, the soil-forming potential in the northern taiga is insufficient for the initiation of the zonal processes.     

Vanadium in landscape components of western Transbaikalia

Vanadium in soil-forming rocks, soils, and vegetation of forest-steppe, steppe, and dry-steppe landscapes of Transbaikalia has been studied. The mean element contents in rocks and soils are equal to its mean natural abundances (clarke values). The content of vanadium in soils is strictly determined by its content in parent materials; its dependence on the vanadium concentration in plants and on the soil pH and humus is less pronounced. With respect to the coefficient of biological uptake by plants, vanadium is assigned to the group of elements of slight accumulation (0.10–0.33) on mineral soils and of moderate accumulation (1.1–1.5) on peat bog soils. The mean vanadium concentration in steppe, meadow, and cultivated vegetation exceeds the norm for animals by 1.7–2.6 times but does not rich toxic levels. Vanadium uptake by plants is most intensive in meadow cenoses and is less intensive in dry-steppe cenoses.     

Availability of elements in tundra soils on acidic and ultramafic rocks in the Polar Urals

The chemical properties of soils and their particle-size distribution in ecotopes of the Polar Urals mountain tundra were considered in relation with the lithological and geochemical features of the parent rocks. In the soils of ecotopes on the ultramafic massif, the contents of the total Ni (2830 mg/kg) and the total Cr (2327 mg/kg) were found to exceed their clarke values, which suggested the accumulation of these elements by plants and their migration with water. In the soils of the ultramafic massif, the average content of mobile Ni was 46.8 mg/kg, which exceeded the Ni MPC by 11.7 times. The average concentration of mobile Cr in the soils of the massif made up 0.35 MPC. In the soils of geochemical acidic rocks, the contents of mobile Ni and Cr were lower than their MPC levels. A higher content of particles with an average diameter ≥5 μm was found in the soils of the ultramafic massif.     

Bottom–up or top–down control in forest soil microcosms? Effects of soil fauna on fungal biomass and C/N mineralisation

A major question in soil ecology is whether soil food webs are regulated by resources or by predators, i.e. bottom–up (donor) or top–down controlled. We tested the hypothesis that meso- and macrofaunal soil predators can regulate fungivore populations and, thereby cause a top–down cascade effect on fungal biomass and decomposition/mineralisation processes in boreal forest soils. The study was performed as a microcosm experiment with two contrasting soils (humus layers), one poor and one rich in N, and with different combinations of fungivore and predator soil fauna added to “defaunated” soil. In comparison with control microcosms lacking mesofauna (but with nematodes and protozoans), the presence of a diverse Collembola and Oribatida fungivore community significantly reduced the FDA-active fungal biomass or tended to reduce the ergosterol fraction of the fungal biomass in the N-poor humus, but no clear effect could be detected in the N-rich humus. Fungivores as well as fungivores plus predators (a predator community consisting of gamasids, spiders and beetles or a subset thereof) reduced C mineralisation and increased net N mineralisation in both soils. The presence of predators (particularly gamasid mites) reduced collembolan numbers and alleviated the negative effect of fungivores on fungal biomass in the N-poor soil. In the N-rich soil, the presence of predators increased fungal biomass (ergosterol) in relation to the “defaunated” soil. Therefore, a top–down trophic cascade could be detected in the N-poor humus but not in the N-rich humus. Our results suggest that the degree of top–down control in soil fauna communities depends on resource quality and soil fertility.     

Changes in the physical properties of soils in the Kamennaya Steppe under the impact of shelterbelts

The physical properties of ordinary chernozems and meadow-chernozemic soils under different land management practices (maple, larch, birch, and pine sections of the shelterbelts; continuous (since 1959) fallow; and arable field (since 1952)) were studied in the Kamennaya Steppe. The soils had favorable physicochemical properties, light clayey texture, and high microaggregation independently from the type of land management. The long-term impact of the shelterbelts improved the soil structure in the upper part of the humus horizon: the content of agronomically valuable aggregates increased, the content of coarse aggregates (>10 mm) decreased, the aggregation coefficient increased by 3.7–4.3 times, and the water stability of the aggregates became by 8–12% higher. The soils under the shelterbelts were characterized by minimum values of the bulk density and solid phase density and by maximum values of the total, active, and air porosities. At the same time, no considerable differences between water reserves in the studied range of soils were detected. The ratio of the optimum productive water range to the active (productive) water range (OPWR/AWR) within the upper soil meter varied from 0.42–0.44 to 0.45–0.54. This points to changes in the character of perched water: the content of intra-aggregate capillary-perched water decreases, and content of film perched water increases down the soil profile.     

Assessment of the microbial biomass using the content of phospholipids in soils of the dry steppe

Microbiological and biochemical investigations of chestnut soils and solonetzes were conducted in the dry steppe of the southern Privolzhskaya and northern Ergeni uplands. The living biomass of the microbial communities in the soils was estimated based on the content of phospholipids in the soils. Significant correlations were revealed between the contents of phospholipids and the main soil properties (the contents of humus, r = 0.66, P = 0.999; clay, r = −0.41, P = 0.95; physical clay, r = −0.57, P = 0.99; and pH, r = −0.59, P = 0.99). The content of phospholipids varied from 69 to 192 nmol/g of soil in the A1 horizons; with depth it decreased down to 36–135 in the B1 horizon and to 26–79 nmol/g of soil in the B2 horizon. The microbial biomass in the solonetzes was lower by 5 to 38% than that in the chestnut soils. A trend of the decreasing of the microbial biomass in the soils from the north to the south was revealed. Based on the content of phospholipids, the number of living microbial cells was assessed; the weighed averages of their number varied from 0.7–3.2 × 10¹⁰ to 7.5–13.6 × 10¹⁰.     

Boron in soils and plants of the West Transbaikal region

Some particularities of the distribution of boron in the main types of soils were studied. A close dependency between the boron content in the soils and its concentration in the soil-forming rocks (r = 0.85) was established, as well as the absence of a correlation between the content of boron and that of humus. It was found that boron is an element with an average intensity of accumulation in plants: the coefficient of its biological absorption from the soil of the steppe, meadow, and agrocenoses varied from 1.2 to 3.2. A correlation between the bulk content of boron in the soils and its accumulation in plants was absent (r = −0.07–0.11). The vegetation of a significant part of the steppe, dry-steppe, and forest-steppe landscapes had a boron deficiency (30–75%).     

Cobalt in soils and plants of the Selenga River delta

The contents and distribution of cobalt in soils and plants of the Selenga River delta (the Buryat Republic) have been studied. It is shown that the cobalt content in the studied soils does not exceed the clarke value and is somewhat higher than the regional background value. Its distribution in the soil cover of the region is rather uniform. The concentration of cobalt in the aboveground phytomass is usually lower than its normal concentration in the vegetation of the world.     

Accumulation of organic matter in the mineral layers of permafrost-affected soils of coastal lowlands in East Siberia

On the basis of a large volume of literature and original data, the high content (1–7%) of organic matter in the mineral layer of loamy permafrost-affected soils of coastal lowlands in East Siberia (from the lower reaches of the Lena River to the lower reaches of the Kolyma River) has been statistically proved. In most cases, the reserves of C_org in the mineral layer of these soils exceed those in the surface organic horizons and constitute 60–90% of the total soil pool of C_org. The enrichment of the mineral layer with C_org is due to the cryogenic retention (retenization) of humus (the illuviation and accumulation of colorless humic substances above permafrost) and the cryogenic mass exchange (mechanical admixture of organic matter from the upper organic horizons into the mineral layers). The analysis of 60 soil profiles showed that the accumulation of organic matter above the permafrost table is observed in 43% of cases; in general, the organic matter distribution in the soil profiles is highly variable. A specific type of colorless humus is accumulated above the permafrost table. The mechanisms of its precipitation and transformation in the profile require further studies.     

Carbon budget in arable gray forest soils under different land use conditions

The effect of different land-use practices on the carbon budget in old arable gray forest soils of Russia was studied in field experiments. A short-term (for 6–7 years) cessation of mineral fertilization had no negative effects on the carbon budget in the agrocenoses studied. Only the combination of zero fertilization with the return to monoculture and the introduction of black fallows created a negative budget of humus in the soil. The regrassing of the eroded arable soil for 24 years increased the humus reserve in the 0- to 60-cm layer by a factor of 1.6–1.7. The average annual accumulation of carbon and nitrogen after the restoration of the perennial vegetation was 106–128 g C/m² and 11–16 g N/m², respectively.     

Microbial biomass carbon in the profiles of forest soils of the southern taiga zone

In the mineral horizons of the soils under different southern taiga forests (oak, archangel spruce, and aspen in the Kaluzhskie Zaseki Reserve of Kaluga region and the green moss spruce and spruce-broadleaved forests of the Zvenigorod Biological Station of Moscow State University in Moscow region), the carbon content in the microbial biomass (C_mic), the rate of the basal respiration (BR), and the specific microbial respiration (qCO₂= BR/C_mic) were determined. The C_mic content was measured using the method of substrate-induced respiration (SIR). In the upper humus horizons of the soils, the C_mic content amounted to 762–2545 μg/g and the BR ranged from 1.59 to 7.55 μg CO₂-C/g per h. The values of these parameters essentially decreased down the soil profiles. The portion of C_mic in the organic carbon of the humus horizons of the forest soils was 4.4 to 13.2%. The qCO₂values increased with the depth in the soils of the Biological Station and did not change in the soils of the Reserve. The pool of C_mic and C_org and the microbial production of CO₂ (BR) within the forest soil profiles are presented.     

The formation of the humus profile of chernozems in the Azov province

The regularities of the formation of the humus profiles in chernozems of the Azov province (“priazovskii chernozems”) were revealed from studying the paleosols of burial mounds (archeological monuments) of the Bronze Age, Early Iron Age, and Middle Ages. The principal differences in the geneses of different parts of the humus profiles were revealed. From 40 to 70% of the current humus reserves in the 1-m-thick layer were shown to be accumulated by the late 3rd and early 2nd millennia BC. In the following 4000 thousand years, the development of the upper soil layers was cyclic. In favorable climatic periods, the humus content increased and accumulation processes predominated. Under aridization, the humus mineralization was intensified, the humus content decreased to 3%, and its reserves did not exceed 18 kg/m². The fluctuations in the humus reserves in the past were not higher than 30% as compared to the recent reference soils. They were most actively replenished from the 1st to the 8th centuries A.D., and the rate of this process reached 0.5 kg/m² for 100 years. In the same period, the thickness of the layer with the humus content above 1% drastically increased. The illuviation of peptized organic matter and its further bioturbation upon the development of the solonetzic process had the greatest importance in the formation of the lower part of the humus profiles.     

Soil formation in the technogenic forest-steppe landscapes of the Nazarovskaya Depression in western Siberia

The soil formation was studied in the 21- to 35-year-old pine plantations created on the overburden dumps of the Nazarovskaya Depression without applying the material of the humus horizon. The surface technogenic formations under the pine plantations belong to the group of naturfabricats (surface formations devoid of the humus horizon and composed of natural substrate). The morphological characteristics, bulk chemical and particle-size compositions, and labile properties of the soils indicate that the accumulation and transformation of organic matter are dominant processes in the artificially planted forests. The accumulation of organic residues and destruction and humification are tightly related to the environmental conditions transformed by the technogenesis and conceal other processes forming the soil profiles. Quasizems created for agricultural production purposes were the objects of the study. They were formed by covering the technically planned overburden rocks with the material of humus layers. The thickness of the humus horizons of the quasizems varies greatly (25–64%); the variation of the humus reserves in them is 34–122%. Middle-profile horizons have not been formed by the present time.     

Temperature regime of some soil types in Georgia

The thermal regime of the different soil types of Georgia has been studied on the basis of soil temperature records obtained at 60 weather stations in 1947–1995. It is shown that the thermal conductivity and temperature gradients in the soil profiles depend on the soil type. In the upper 0–20 cm of the soils in the intermontane depressions, the lowest temperature gradients in the summer are typical of the red ferrallitic soils (0.5–1.1°C/dm), and the highest gradients are observed in the chernozems of eastern Georgia (1.0–1.3°c/dm). The soil temperature gradients are especially high in the late spring (1.4–1.8°c/dm), when the atmospheric convection is formed. In the mountains, the lowest gradients in the summer are observed in the cinnamonic soils (0.4–0.9°c/dm), and the highest gradients are established in the brown forest soils (0.5–1.3°c/dm). The redistribution of the temperatures in the deeper layers depends on the soil texture. The lowest temperature gradient is in the soils of Telavi (3.1°c/m), where a stony layer is found at the depth of 60 cm, which causes the good heating of the deep layers. The highest gradients are seen in the clayey and loamy soils of western (Chakva, 3.8°c/m) and eastern (Tbilisi, 3.9°c/m) Georgia. This is probably related to the high water content in the heavy-textured soils.