Soil and geochemical study of chernozems and settlement cultural layers (dated from Paleolithic to Medieval ages) in the mining Urals region

The aim of the study was to characterize soil and geochemical properties of the cultural layers (CL) and chernozems of eight settlements dated from the Paleolithic to the Medieval Ages in the mining Southern Urals. Methodology. Together with archeologists we studied pedological, geochemical and microbiological properties of soils and CL of eight settlements, dating 136–2,5 ka BP and located along the slope of the Southern Urals mountains. The sites are located on the terraces of small rivers of the Ural River basin, used as moderately grazed pastures, except for one site (Telyashevo-4, 3,9–3,45 ka BP) used as arable land. Samples were collected sequentially from each 5-cm layer to the parent rock. From the 0–30 cm layer samples were taken in three replicates. The chemical and physical characteristics of soils and cultural layers were determined by conventional methods. Microbial biomass was estimated by substrate-induced respiration with glucose addition; soil basal respiration was measured by gas chromatography after seven days of moist soil incubation. Determination of 15 macro- and trace elements was performed by X-ray fluorescence analysis on the Spectroscan Max-GV device. Main results. Most of the CL had developed on chernozems, at a depth from 3–25 cm to 40–60 cm. The 0–10 cm CL layer contained 6–13,7% of organic matter (Corg) due to current soil processes. In the Ishkulovo CL (0,6–0,8 ka BP), located below 80 cm, Corg decreased to 1,3% due to the lack of fresh organic material. The CL and soils were found to have good structure, no salinization, increased anthropogenic phosphorus (0,2–0,4%) and exchangeable calcium, near neutral pH. In the Tashtuy-1 CL (19th century AD) pH was alkaline due to the carbonate presence. The development of ancient settlements took place in periods with a favorable paleoclimate, according to the published data. Such climate facilitated productive landscapes, ensuring the development of husbandry and agriculture. Due to their properties, chernozems have a high buffering capacity, a strong bond with heavy metals, high content of microbial biomass (520–680 μg C/g of soil in the 0–10 cm layer) and soil respiration rate (0,2–1,0 C-CO2 μg/g of soil per hour). Conclusion. In chernozems and cultural layers of ancient settlements of different ages at the Southern Urals, accumulation of pollutants of the I (arsenic, lead, zinc, chromium) and II (cobalt, copper, nickel) hazard classes was shown to be several times higher than the lithosphere сlark value, albeit rarely higher than the permissible content for humans, which is mainly due to the natural anomaly of the Urals Mountains and, to a lesser extent, the proximity (18–60 km) to the Magnitogorsk Metallurgical plant. Favorable properties of soils and CL, namely high content of Corg, fine fractions and exchangeable calcium, absence of salinization, near neutral pH cause strong adsorption of heavy metals, not affecting negatively soil microbial biomass and soil basal respiration. The study provided detailed data on the chemical elements content throughout soil profiles and CL, thus supplementing the information about their accumulation in the geochemical anomaly of the Southern Urals in the respective database, which is important for monitoring.