A. V. Borisov

Comparative characterization of microbial communities in kurgans, paleosols buried under them, and background surface soils in the steppe zone of the Lower Volga region

A comparative analysis of the state of microbial communities in kurgans, paleosols buried under them, and background surface soils in the dry steppe zone of the Lower Volga region has been performed. It is shown that the population density of microorganisms of various trophic groups in the kurgans is an order of magnitude lower than that in the A1 horizon of the corresponding buried paleosols and background surface soils within the areas of chestnut, light chestnut, and solonetzic soils. The respiration activity of the microbial communities in the upper layer of the kurgans is comparable with that in the A1 horizons of the background surface soils; it decreases in the deeper layers of the kurgans. In the A1 horizon of the buried paleosols, the respiration activity is approximately the same as in the deep layers of the kurgans. In the buried paleosols, the spatial variability in the numbers of soil microorganisms is approximately the same or somewhat higher than that in the background surface soils. The spatial variability in the respiration activity of the buried paleosols is two to four times higher than that in the background surface soils.

The origins of terraced field agriculture in the Caucasus: new discoveries in the Kislovodsk basin

Terraced field systems are a feature of many regions of the world and have been dated as early as 6000 cal BC in the Levant (Kuijt et al. in Antiquity 81 (2007: 106–18)). The discovery of agricultural terraces in the northern Caucasus, reported here, extends their distribution into a new area. Relatively low population levels in the late medieval and early modern periods have preserved several blocks of terraced fields, some of them created at the beginning of the first millennium BC, others in the mid first millennium AD. The earlier terraced fields, associated with material and settlements of the Koban culture, culminated in over-exploitation of the land and exacerbated erosion during environmental change in the mid first millennium BC. The later series of terraced fields are of different form and are associated with the settlement in the area of communities of Alans in the first millennium AD. They largely avoided the areas rendered infertile by Koban period overexploitation. The morphology and chronology of the terraced field systems are explored using a combination of aerial photography, GIS analysis and field investigations.

Paleosols and climate in the southeast of the Central Russian Upland during the Middle and Late Bronze ages (the 25th–15th Centuries BC)

Paleosol studies of kurgans dating back to the Middle and Late Bronze ages (the Catacomb, Pokrovskaya, and Srubnaya cultural epochs; 4500–3500 BP) have been performed within the dry steppe zone in the southeast of the Central Russian Upland. The studied kurgans occupy the upper parts of local interfluves differing in the lithology of their upper horizons. The specificity of the Middle Holocene pedogenesis as related to the local lithologic and geomorphic conditions has been characterized. During the past 4500 years, local soils have been subjected to evolutionary changes related to climatic fluctuations. These changes manifested themselves at the subtype level with substitution of dark chestnut soils for chestnut soils. The climatic conditions during the Catacomb and Pokrovskaya cultural epochs (4.5–3.8 ka BP) were more arid than those at present. The maximum aridization of the climate took place at the end of the third and the first quarter of the second millennia BC. Detailed descriptions of the morphology of kurgan bodies and buried paleosols make it possible to hypothesize about the seasons of the kurgan construction and the technology of this work.

Ancient agricultural terraces in the Kislovodsk Depression: History and modern state of the soils

The results of the investigation into the history of soilscapes in the Kislovodsk Depression are discussed. It is shown that up to 60–70% of the area of slopes and interfluvial plateaus at the heights of 900–1500 m a.s.l. was terraced in the Late Bronze-Early Iron ages, during the Kobansk cultural stage (1200–600 BC). Under these conditions, a sharp change in the climate with a considerable increase in the annual precipitation in the middle of the first millennium BC resulted in the activation of erosion and the formation of a layer of colluvial sediments overlying the buried soil on the terraces. Thus, the middle of the first millennium BC can be considered the zero moment for the modern stage of soil formation in the region. Problems of the current state of the terrace complexes and the development of erosion on them are also discussed.

Production of CO2 by surface and buried soils of the steppe zone under native and moistened conditions

Modern light chestnut and chestnut soils and their analogues buried under steppe kurgans in the southeastern part of the Russian Plain were studied in order to determine the rates of the CO2 production by these soils under the native (with the natural moisture content) and moistened (60% of the total water capacity) conditions. It was found that the rates of the CO2 production by the soil samples in the native state are relatively close to one another and vary from 0.3 to 1.4 μg of C/100 g of soil/h. The rates of the CO2 production in the moistened state increased by two orders of magnitude for the modern surface soils and by an order of magnitude for the buried soils.

Modifications of the mineralogical composition and surface properties of soils as related to steppe climate dynamics in historical time

This work presents the results of a study of changes in the soil mineral components and the related modifications of the chemical composition and surface properties of soils in the desert-steppe zone in the southern part of the Ergeni Upland. Burial mounds dating back to the Bronze epoch have been investigated. According to radiocarbon data, their ages are estimated at 5100 ± 50, 4410 ± 100, 4260 ± 120, 4120 ± 70, and 3960 ± 40 years. The substantial transformation of the clay minerals, the molar chemical coefficients, the magnetic mineralogy, and the surface properties of the soils permits us to assess the rates of the mineralogical transformations caused by the climate change during the time interval of less than <∼100 years. The ratio between the content of the mineral phases in the buried soils of different ages testifies to the primary importance of climatic factor in comparison with the total duration of weathering or the soil existence on the land surface prior to its burial, i.e., the soil age.

Microbial Biomass in Paleosols under Burial Mounds as Related to Changes in Climatic Conditions in the Desert-Steppe Zone

The contents of carbon in the total microbial biomass (C-TMB) and in the microorganisms reactivated with glucose (C-RG) and the portion of glucose-reactivated microorganisms in the microbial community (C-RG/C-TMB) were determined in paleosols buried under desert-steppe kurgans (burial mounds) 5100–3960 years ago and in the background surface light chestnut soils. In the paleosols, the corresponding indices reached 986 μg/g (C-TMB), 14.6 μg/g (C-RG), and 1.5% (C-RG/C-TMB) and were considerably lower than those in the background surface soil. The lowest values were found for the paleosols buried 4260–3960 years ago, which confirms a conclusion about the paleoecological crisis during this time interval.

Variability of Microbial Biomass in Paleosols of Different-Age Burial Mounds of the Lower Volga Region in Relation to the Dynamics of Climate Humidity

The microbial biomass variability in buried chestnut and light chestnut soils of different ages under burial mounds and their modern background analogs in the Volga and Ergeni uplands were studied. It was shown that almost all microorganisms in chestnut paleosols of the Bronze Age are in the dormant state and provide no respiratory response to the addition of glucose. In the paleosol buried in the most arid period, an increase in the total microbial biomass and the abundance of colony-forming units was revealed. The maxi-mum values of active microbial biomass upon the minimum number of cells were found in soils buried in rel-atively humid periods. The increase in the total microbial biomass and the proportion of microbial cell carbon in the organic carbon of soils buried in extremely dry seasons at the turn of the III–II millennium BC may indicate the adaptation of microbial communities to unfavorable environmental conditions.

Evolution of soils and dynamics of the climate of steppes in the southeast of the russian plain during the late eneolithic and bronze ages (fourth to second millennia BC)

On the basis of studies of subkurgan pedochronoseries, the main mechanisms of the development of soils of arid and desert steppes in drained landscapes of the southeastern Russian plain in the Late Eneolithic and Bronze ages (6000−3000 years ago) were established. During the fourth to third millennia BC, evolution of soils took place at the level of subtypes with a shift of boundaries of soil subzones toward the north. In each of the studied natural regions (Central Russian Upland, Volga Upland, Ergeni Hills, and Caspian Depression), an increase in the aridization of the climate in the second half of the third millennium BC can be distinctly traced, owing to which a convergence of the topsoil with the transformation of dark-chestnut, chestnut, and light-chestnut soils in chestnut-like semiarid soils, which dominated the region 4200–3900 years ago, occurred. In the first half of the second millennium BC, another change in the conditions of soil formation occurred that was caused by an increase in the degree of atmospheric humidity. It induced the divergence of the topsoil with a secondary formation of areas of zonal chestnut soils and solonetzes in place of chestnut-like soils by the middle of the second millennium BC. The obtained data gives reason to suggest that the age of modern chestnut solonetz complexes of the region does not exceed 3500 years.

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.