The content and distribution of Mn, Fe, Ni, Cu, Zn, and Pb in automorphic soils of Polistovsky Reserve

The intensive human impact on the environment leads to a significant change in the components of landscapes, in general, as well as the soil cover in particular. Currently, areas with undisturbed soils are mainly preserved within specially protected natural areas. The characteristics of reference soils serve as a starting point for environmental monitoring. One of these objects is Polistovsky Reserve in Pskov region, created to protect the upper marshes. On the territory of the reserve among the wetlands, unique landscapes are present, i.e. mineral islands, formed by postglacial morainic deposits, not buried under a layer of peat, on which soils, that are unusual for the given terrain, developed under mixed forests. Automorphic soils, formed within the boundaries of these isolated formations, remain poorly understood. The relevance of the presented research is due to the importance of mineral island soils as one of the key components of the natural systems of the Polistovo-Lovatsky bog massif. Data on the composition and properties of autonomous soils can be used in the planning of environmental protection measures, as well as to predict their stability in the intensification of anthropogenic impact. The aim of this research is to identify accumulation and distribution of total content and mobile forms of Mn, Fe, Ni, Cu, Zn, and Pb in various types of automorphic soils in Polistovsky State Nature Reserve. The automorphic soils of Polistovsky Reserve (57°10'N, 30°30'E), formed within the mineral islands, were investigated: Eutric Cambisol, Haplic Luvisol, Rendzic Leptosol and Rubic Arenosol (See Fig. 1). We studied soils using profile and genetic methods based on the Classification and Diagnostics of Russian Soils (Shishov LL et al., 2004). International names are given according to the World Reference Base of Soil Resources, version 2015 (IUSS Working Group WRB, 2015). The following soil properties were determined: particle size fractions by pipet analysis (Katschinski NA, 1956, Burt R, 2011), organic carbon content by bichromate oxidation method according to IV Tyurin, exchangeable bases by complexometric method, cation exchange capacity by ammonium acetate method, KCl pH and pH of aqueous suspension by potentiometric method (Vorobeva LA, 2006; Burt R, 2011). The total content of Mn, Fe, Ni, Cu, Zn and Pb was determined by X-ray fluorescence analysis using a spectrometer Spectroscan MAX-GV “Spectron” (Russia), and the content of mobile forms extracted from the soil by ammonium acetate buffer (Motuzova GV et al., 2014) was determined by atomic absorption using a spectrometer NOVAA300 “Analytik Jena” (Germany). Clarkes of concentration and Clarkes of dispersion of elements in the studied soils were calculated relative to the clarke of elements in the soils according to AP Vinogradov (1957). A correlation analysis was carried out to evaluate the relationship between the physical and chemical properties of soils and the content of elements with the calculation of Spearman's rank order correlation coefficient. In this research, we found out that the lithological heterogeneity of the soilforming rocks of mineral islands leads to a significant differentiation of soils both by morphological features and by physicochemical properties. Eutric Cambisols form on moraine loams on the slopes under oak forests with thin grass cover, while Haplic Luvisols are characteristic of spruce forests. Rubic Arenosols are common in binomial deposits under a mixed birch and spruce forest. Rendzic Leptosols are confined to sandy sediments. The considered soils are quite different in a range of parameters (See Table 1). The typical differentiation of the profile according to the content of physical clay is characteristic of Eutric Cambisols and Haplic Luvisols. In terms of pH values, Eutric Cambisols and Haplic Luvisols are defined as acidic soils, Rubic Arenosols are slightly acidic or neutral, and Rendzic Leptosols are slightly or moderately alkaline. The organic carbon content in the horizon AY of Rendzic Leptosols is 2 times lower, while in Eutric Cambisols and Haplic Luvisols it is 4-7 times lower than in Rubic Arenosols. The studied soils are differentiated by the content and profile distribution of elements (See Table 2). With the depths, the total content of elements in Haplic Luvisols and Rubic Arenosol increases, while in Rendzic Leptosol it decreases. It was established that the total content of elements in automorphic soils was reduced in the following order: Fe> Mn> Zn> Ni> Cu> Pb. The proportion of mobile forms relative to the total content was minimal for Fe (0.002-0.08%), especially in Rendzic Leptosols (0.003-0.02%), for other elements it varied from 0.3 to 10.7%. The total content of Ni, Pb and Fe is higher in Rubic Arenosols than in a Haplic Luvisols and Rendzic Leptosols (See Table 3). The chemical composition and physical properties of moraine deposits determine the conditions for migration and accumulation of elements (See Table 4). An increase in the total content of Ni, Cu, Zn, and Fe is linked with an increase in the proportion of silty particles in the soils; their maximum values are noted in the lower horizons of the soil. Mn accumulation was observed in sandy horizons with high humus content. High pH values lead to accumulation of mobile forms of Ni and Mn, while low values lead to accumulation of mobile forms of Fe. Mobile forms of Mn, Fe, Ni and Pb are accumulated in the organogenic horizons. It was revealed that Fe and Mn in the soils of the considered landscapes were typomorphic elements whose content significantly influences the behavior of Ni, Cu, Zn and Pb. The results show that the soils of autonomous positions, even despite the limited distribution area within Polistovsky Reserve, demonstrated significant diversity. Differences in the composition and properties of rocks affect soil properties, the severity of soil-forming processes, and the contrast of geochemical differentiation of the profile, which should be taken into account when planning environmental monitoring of both the lands protected and affected by human activity in the territory under consideration. The paper contains 1 Figure, 4 Tables and 32 References.

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