Temporal changes in the microfabrics of virgin and reclaimed solonetzes at the Dzhanybek Research Station

In the past three decades, a trend of an increase in the climatic humidity has been observed in the southeast of European Russia; it has been accompanied by the rising groundwater level. The study of solonetzes at the Dzhanybek Research Station in the north of the Caspian Lowland indicates that the recent climate changes are reflected in the soil microfabric. A comparative examination of thin sections prepared from the soil samples taken in 1982 and in 2002 from the same points characterizing virgin and reclaimed solonetzes has shown the following changes in the soil microfabric: (a) an increase in the amount and diversity of the mesofauna excrements, (b) the accumulation of fine plant detritus at various stages of decomposition, (c) an increase in the content of the dispersed and flocculated brown-colored microforms of humus and charcoal particles in the surface horizons, and (d) the formation of hydrogenic gypsum in the middle and lower soil horizons. The character of changes in the microfabric of virgin solonchakous solonetzes attests to the enhancement of the eluviation of the silty-clayey-humus substances, solodization, and gleyzation. In the reclaimed solonetzes, the artificially turbated horizons have been subjected to desalination, and the gypsiferous and calcareous pedofeatures inherited from the previous stages of soil formation have been destroyed.     

Soil adsorption complex of the meadow-chestnut soils at the Dzhanybek research station in the northern Caspian region

Data on the composition and properties of soil adsorption complex in the virgin and ameliorated meadow-chestnut soils in the northern Caspian region are generalized. It is shown that the experimental values of the effective CEC in the A1 horizon are lower than those calculated on the basis of data on the organic matter content and the content and mineral composition of fine fractions. We explain this discrepancy by the interactions between the organic matter and clay minerals resulting in the blocking of a part of the exchangeable positions. In the BC horizon, the experimental values of the effective CEC are twice as high as those calculated from the data on the amount of labile clay minerals in fine fractions. This can be explained by the presence of sorption centers on poorly crystallized illites and chlorites in the clay fraction and by the partial aggregation of clay material into coarser fractions that cannot be destroyed upon the separation of clay fractions by the Aidinyan procedure, which leads to the underestimation of the clay content.     

Changes in the properties of solonetzic soil complexes in the dry steppe zone under anthropogenic impacts

Long-term studies of changes in the properties of solonetzic soil complexes of the dry steppe zone under anthropogenic impacts (deep plowing, surface leveling, irrigation, and post-irrigation use) have been performed on the Privolzhskaya sand ridge and the Khvalyn and Ergeni plains. The natural morphology of solonetzic soils was strongly disturbed during their deep ameliorative plowing. At present, the soil cover consists of solonetzic agrozems (Sodic Protosalic Cambisols (Loamic, Aric, Protocalcic)), textural (clay-illuvial) calcareous agrozems (Eutric Cambisols (Loamic, Aric, Protocalcic)), agrosolonetzes (Endocalcaric Luvisols (Loamic, Aric, Cutanic, Protosodic), agrochestnut soils (Eutric Cambisols (Siltic, Aric)), and meadowchestnut soils (Haplic Кastanozems). No features attesting to the restoration of the initial profile of solonetzes have been found. The dynamics of soluble salts and exchangeable sodium differ in the agrosolonetzes and solonetzic agrozems. A rise in pH values takes place in the middle part of the soil profiles on the Khvalyn and Ergeni plains.     

Modern tendencies of changes in the properties of virgin and post-irrigational soils of solonetzic complexes on the Privolzhskaya ridge

The study of post-irrigational and virgin soils of solonetzic complexes on the Privolzhskaya sandy ridge has shown that the morphological features of paleohydromorphism and the features acquired during the 30-year-long irrigation period are well preserved in the soil profiles. After the cessation of irrigation, the upper boundary of effervescence has shifted closer to the soil’s surface; fine-crystalline gypsum has appeared in channel pores. When the groundwater level is deeper than 4 m, the boundary of effervescence is higher than the boundary of the gypsum concentrations. When the groundwater level is about 3 m, these two boundaries coincide. If the groundwater level is higher than 2.5 m, the boundary of the effervescence is found deeper than the boundary of the gypsum concentrations. Salinization and solonetzization of the post-irrigational soils have not been identified. In the virgin soils with the groundwater level of 2.3–3.0 m, the content of exchangeable sodium in the upper 30 cm is similar to that in the post-irrigational soils. In the deeper layers, the exchangeable sodium content in the solonetzes and chestnut soils rises up to 25% and more; in the meadow-chestnut soils, it constitutes up to 4% of the sum of exchangeable bases.     

Mathematical simulation of water and salt transfer in geosystems of solonetzic soils in the Northern Caspian region

The Dzhanybek two-dimensional radial-axial mathematical model was developed for water and salt transfer in geosystems of solonetzic complexes of the Northern Caspian region; the model is capable of considering the geochemical links and revealing the features of migration processes between the conjugated elements of the microcatena. The simulation results suggested that the stabilization of salinization-desalinization processes occurs under stable weather conditions within approximately 100 years. When the weather conditions changed (the total moisture pool of the area increased from 1978), the simulation results indicated a tendency toward salinization of dark-colored soils in microdepressions and removal of salts in the upper 1-m thick soil layer on microhighs and microslopes. Predictions for 2040 showed that a deep accumulation of salts in microdepressions and desalinization of soils of microhighs and microslopes will occur under the current weather conditions. Thus, the changes in the halogeochemical capacity of geosystems of solonetzic complexes primarily depend on the climatic conditions, although the capacity value remains almost constant with increasing total water reserves; the changes occur only between the conjugated soils of solonetzic complexes, which is of great importance for predicting the soil-geochemical status of the entire landscape.     

Temperature regime of solonetzic meadow-chernozemic permafrost-affected soil in a long-term cycle

The characteristics of temperature dynamics in a solonetzic meadow-chernozemic soil of alas depression in Central Yakutia are described on the basis of long-term (2005–2014) stationary studies. Quick changes in weather conditions accompanied by changes in the soil temperature regime were observed during that period. Thus, the beginning of soil thawing in the spring shifted to earlier dates, and the beginning of soil freezing in the fall shifted to later dates. Temperature trends demonstrate an increase in the mean annual soil temperatures at all the depths. In total, the period of the frozen state of the soil became considerably shorter: in the middle-profile horizons, by 30–39 days. The obtained results attest to the high dynamism in temperature parameters of meadow soils in alas depressions of Central Yakutia under conditions of global climate changes.     

The boron content in soils of solonetzic complexes in the Irtysh Region of Omsk oblast and the boron resistance of plants

Data on the boron content in the main soil types of solonetzic complexes in the Irtysh Region of Omsk oblast are given. They attest to the boron salinization of the soils. It is shown that there is a risk of excessive boron accumulation in natural plants and crops. The boron resistance of crops cultivated on the boronsaline soils has been examined in the field and in pot experiments. Approximate normal and toxic levels of the boron content in soils and in plants and the corresponding Ca-to-B ratios in the aboveground phytomass are suggested. Amelioration of solonetzes with application of gypsum and phosphogypsum reduces the degree of their boron salinization and the boron uptake by plants.     

The structural state of buried and surface soils of solonetzic complexes in the dry steppe zone of the Lower Volga basin

The structural state of modern (surface) soils and the soils buried under Anna Ioannovna??s rampart (1718?C1720) was studied. These soils are the components of solonetzic soil complexes in the southern Privolzhskaya Upland. The dehumification and the high content of calcium in the exchange complex determine the state of the macrostructure of the chestnut soil buried about 300 years ago. The dehumification drastically lowers the water stability of the soil aggregates, and the predominance of calcium ions in the soil exchange complex prevents the destruction of the chestnut paleosol aggregates and preserves their aggregate state upon moistening. For the last 300 years, no significant changes in the macrostructure of the solonetzes have been observed.     

Diversity of clay minerals in soils of solonetzic complexes in the southeast of Western Siberia

Data on the mineralogical composition of clay in soils of solonetzic complexes of the Priobskoe Plateau and the Kulunda and Baraba lowlands have been generalized. The parent materials predominating in these regions have loamy and clayey textures and are characterized by the association of clay minerals represented by dioctahedral and trioctahedral mica–hydromica, chlorite, kaolinite, and a number of irregular interstratifications. They differ in the proportions between the major mineral phases and in the qualitative composition of the minerals. Mica–hydromica and chlorites with a small amount of smectitic phase predominate on the Priobskoe Plateau and in the Kulunda Lowland; in the Baraba Lowland, the portion of mica–smectite interstratifications is higher. An eluvial–illuvial distribution of clay fraction in solonetzes is accompanied by the acid–alkaline destruction and lessivage of clay minerals, including the smectitic phase in the superdispersed state. This results in the strong transformation of the mineralogical composition of the upper (suprasolonetzic) horizons and in the enrichment of the solonetzic horizons with the products of mineral destruction; superdispersed smectite; and undestroyed particles of hydromica, kaolinite, and chlorite from the suprasolonetzic horizons. A significant decrease in the content of smectitic phase in the surface solodic horizons of solonetzic complexes has different consequences in the studied regions. In the soils of the Priobskoe Plateau and Kulunda Lowland with a relatively low content (10–30%) of smectitic phase represented by chlorite–smectite interstratifications, this phase virtually disappears from the soils (there are only rare cases of its preservation). In the soils of the Baraba Lowland developed from the parent materials with the high content (30–50%) of smectitic phase represented by mica–smectite interstratifications, the similar decrease (by 10–20%) in the content of smectitic phase does not result in its complete disappearance. However, the smectitic phase acquires the superdispersed state and the capacity for migration.     

On the dynamics of salts in solonetzic soil complexes of the Pallas irrigation system in relation to fluctuations in the groundwater level and changes in the regime of irrigation

Changes in the salt status of solonetzic soil complexes within the Pallas irrigation system were estimated for a field surveyed in 1990 and 2003. The irrigation of this field was stopped in 2000. In 2003, the depth of the groundwater table lowered by 1 m, and the groundwater salinity decreased considerably in comparison with the corresponding values obtained in 1990. The concentrations of Na⁺ and SO ₄ ^2? ions in water extracts, as well as the ESP values in the upper horizons of solonetzes, became lower. In meadow-chestnut soils, dealkalization processes were active in the entire profile.     

Quantification of the areas of saline and solonetzic soils in the Ural Federal Region of the Russian federation

Soil Salinization Map of Russia on a scale of 1: 2500000 (the paper version) has been used for compiling an electronic map of the Ural Federal Region and an attribute database containing twelve characteristics of soil salinization. The areas of saline soils have been quantified for the entire region and its administrative districts. The total area of saline soils in the 0- to 200-cm layer averages up to 6.85 million ha or 5.53% of the plains in the region. The area of soilssaline in the 0- to 100-cm layer averages up to 4.91 million ha, including 4.13 million ha of weakly solonchakous soils (84%) and 0.78 million ha of solonchakous ones (16%). More than half of them (58.3%) are assigned to the moderately and strongly saline soils. The soils saline in the 0- to 100-cm layer are characterized by the neutral salinization type (45%) or the types of soda salinization and neutral salinization with soda (55%). The areas of the region with saline soils are dominated by solonetzic microassociations. The average area of the solonetzes is about 3 million ha. The area of solonchaks is about 0.09 million ha. The area of saline soils is the greatest in Kurgan oblast and the lowest in Sverdlovsk oblast and the Yamal-Nenets autonomous okrug. The formation of saline soils in the Ural Federal Region is related to the climatic conditions of the steppe zone with insufficient moistening and lithologicgeomorphologic conditions (saline Paleogene-Neogene deposits and poor drainage of the area).     

Modern geochemical evolution of lagoon-marshy landscapes in the western Caspian Sea region

The landscape-geochemical consequences of the full cycle of Caspian Sea fluctuations (regression-transgression-stabilization) that has taken place in the recent decades are analyzed. The regressive and lagoon-transgressive sets of landscape-geochemical processes (LGPs) are characterized. The impact of the regressive stage on the environment is seen in the development of the regressive LGPs in the soils and sediments of the coastal landscapes with a predominance of salinization and weak humus accumulation. The transgression of the sea was accompanied by the formation of specific lagoon-marsh landscapes, in which the accumulation of sulfides, gleyzation, iron oxidation, and humus formation were clearly pronounced. The general scheme of the evolution of the LGPs within the past 30 years is discussed. The rates of the humus accumulation and salinization during the stabilization stage are estimated. The organic matter reserves in the coastal soils increased by 1.5–2 times in a decade. The transformation of the particular forms of chemical elements in the lagoon-marsh landscapes upon fluctuations in the sea level is shown. The rise in the Caspian sea level was accompanied by the enhanced migration of elements with varying valences, such as Fe and Mn (as well as Zn, Cu, Pb, Ni, and Co) due to their mobilization in the slightly alkaline and neutral reducing conditions and their precipitation at the geochemical barriers.     

苏北滨海盐土区河流入海口土壤盐分及养分分布特征

为系统了解淮河入海口两侧盐渍土养分及盐分分布状况,采用野外调查取样和室内分析相结合的方法,分析淮河入海口土壤养分(有机质、速效氮和速效磷)指标和盐分质量分数的空间分布特征.结果表明:1)研究区有机质和速效氮总体贫乏,随距入海口越来越远,呈缓慢上升趋势,速效磷总体适量.土壤养分有明显的表聚现象,与河漫滩相比较,对应堤防外侧土壤有机质、速效氮变异深度偏低,速效磷差异不明显.2)北堤河漫滩、南堤河漫滩、北堤外和南堤外临界脱盐位置分别在距入海口3 200 m、2 800 m、3 400 m和600 m处,土壤盐分剖面主要为表聚型、低聚型和平衡型,其分布较为集中,分别位于重度盐渍化区、中度盐渍化区、轻度盐渍化及脱盐区.3)有机质与速效氮呈极显著正相关,二者与土壤盐分呈显著性负相关,速效磷与其他3个指标相关性均不显著.该结果可为淮河入海口盐渍土的分区、改良和合理利用提供参考.     

The solonetzic process in surface soils and buried paleosols and its reflection in the mineralogical soil memory

The development of the solonetzic process in paleosols buried under kurgans and in the modern surface soils has been studied on the basis of the analysis of the clay (<1 μm) fraction. The revealed changes in the textural differentiation of the soils and the mineralogical composition of the clay fraction during 4500 years are assessed from the viewpoint of the “memory“ of the solid-phase soil components. The mineralogical characteristics show that the solonetzic process in the modern background soil is more developed. The mineralogical approach allows us to reveal the long-term changes in the soil status; it is less useful for studying the effect of short-term bioclimatic fluctuations. In the latter case, more labile soil characteristics should be used. The mineralogical method, combined with other methods, becomes more informative upon the study of soil chronosequences. Our studies have shown that the data on the clay minerals in the buried paleosols may contain specific information useful for paleoreconstructions that is not provided by other methods.     

Mercury in the Aquatic Environment of the Village of Caimito at the Mojana Region,North of Colombia

During May–September 1999, several aquatic environmental samples were collected from the village of Caimito, in the San Jorge River basin area, state of Sucre (Colombia), and analyzed for total mercury (T-Hg). Mean T-Hg concentration in sediments from surrounded marshes was 0.155 ± 0.016 g Hg/g. Low Hg concentrations were found in the phytoplanktivorous fish species Prochilodus magdalenae (0.087 ± 0.01 g Hg/g), while four-fold greater concentrations were found in all the carnivorous species. In average, T-Hg concentrations for fish samples did not exceed the limit consumption level (0.5 g Hg/g). However, risk assessment based on the hazard index suggested that the consumption of 0.1 kg per day of carnivorous fish could increase the risk of mercury poisoning in local population.     

Morphological and chemical properties of the meadow-semidesert soil complexes of the Khaki playa (the Caspian Lowland) and the influence of the biogenic factor on them

The initial stage of the development of the complex soil cover pattern in the Caspian Lowland was studied. The obtained data made it possible to reveal the specific features of the morphological and chemical properties of the soils on terraces of the Khaki playa and the role of burrowing animals in the formation of the microtopography and complex soil cover patterns on the youngest surfaces. The soil cover of the studied area consists of three-component complexes: light-humus quasi-gley solonetzes on relatively flat background surfaces, zooturbated solonetzes on microhighs, and humus quasi-gley soils in microlows. The layered deposits of the Khaki playa terraces and the shallow depth of the saline groundwater are responsible for the specificity of the modern salinization of the studied solonetzes. The distribution of the salts in their profiles has a sawshaped patter, which is related to the nonuniform texture of the deposits. On the microhighs composed of the earth extracted from 5- to 7-year-old suslik burrows, specific zooturbated solonetzes are formed. The known age of these formations makes it possible to determine the rate of the desalinization of the gypsum- and salt-bearing material extracted onto the soil surface and the rate of the salt accumulation in the lower part of the solonetzic horizon and in the subsolonetzic horizons in comparison with the data on the solonetzes of the background flat surfaces. The specific features of the soils in the closed microlows suggest that these soils have a polygenetic origin. The features of the recent hydromorphism predetermine the specificity of their morphology.     

Characterization of the microbial communities in the modern and buried under kurgans soils of solonetzic complexes in the dry steppes of the Lower Volga region

The microbial communities were studied in the modern and buried under kurgans (1st century AD) soils of solonetzic complexes on the dry steppes of the northern part of the Yergeni Upland. It was found that the changes in the numbers of microorganisms from different trophic groups and in the biomass of the fungal mycelium along the profiles of the modern and buried solonetzic chestnut soils and solonetzes do not differ significantly. The quantitative estimate of the impact of the solonetzic process on the spatial variability of the microbiological parameters of the soils was given on the basis of the ANOVA. As a rule, the values of the microbiological parameters in all the horizons of the modern and buried chestnut soils were 1.2–2.8 times higher than those in the modern and buried solonetzes. The influence of the degree of solonetzicity of the buried paleosols on the microbiological parameters manifested itself in the entire profile, though in each particular horizon it was only seen in the numbers of some particular trophic groups of microorganisms. The comparison between the mean weighted values of the microbiological parameters in the entire soil profiles (the A1 + B1 + B2 horizons) demonstrated an inverse relationship between the population density of the microorganisms utilizing easily available organic matter and the degree of solonetzicity of the buried paleosols. The maximum biomass of the fungal mycelium was found in the solonetzic chestnut paleosol; it exceeded the biomass of the fungal mycelium in the other paleosols (which did not differ significantly in that parameter from one another) by 1.5–1.6 times.     

Lateral variability in the agrophysical parameters of soil complexes

The main principles and criteria used to assess spatial variability in the agrophysical parameters of soils are discussed. The agrolandscape approach applied by us suggests the collection of field data on the physical properties of soils with the use of a regular-grid sampling pattern, the interpretation of this information with the use of GIS technologies, and the delineation of areas with different physical parameters of soils according to existing classifications. This approach has been realized in the area of gray forest soils of the Vladimir opolie region. The lateral differentiation of the agrophysical parameters as dependent on the soil cover patterns and the morphology of soil profiles is analyzed.