Catena linking of landscape-geochemical processes and reconstruction of pedosedimentogenesis: A case study of defensive constructions of the mid-17th century, South Russia

The 'catena concept', along with previously proposed meanings of this term, has recently acquired a soil evolutionary content. The prospects of wider special and chronological study of dated pedotopocatenas include the possibility of a more detailed analysis of the mutual dependence of soil-geomorphological relationships through distinguishing relatively homogeneous climatic stages of pedogenesis and denudation. With this purpose, the present study comprised earthen defensive constructions, which, within the 'rampart/ditch' system, combine erosive, trans-accumulative catenas and accumulators of pedolithosediments. The goal was to develop a system of the most information-rich pedogenetic indicators to reconstruct the dynamics of erosion-accumulative processes on the basis of dated earthen defensive constructions of a historical period (using the example of a frontier rampart within a ditch from the mid-17th century). Soil samples were collected within the limits of the erosion and trans-accumulative catenas, as well as in the closing alignment of the ditch (over the vertical profile in eight strata of pedosediments of up to 1 m high). The granulometric composition, concentration of macroelements and trace elements (25 metals and oxides) in soils and in particles with sizes < 1 mm, and the fractional composition of the humus were analysed in soil samples taken from different points in the catena and along the profile of the pedosediments. For the reconstruction of the humidity conditions over 3.5 centuries based on dendrochronological data, the cross-relation approach was applied. This allowed us to represent the chronostratigraphy of pedosediments as stages differing in the rate of accumulation processes. The system of soil indicators in pedosediments including the percentage of particles 0.001-0.005 mm and > 0.01 mm in size, the content of organic carbon and its qualitative composition, the sum of the elements accumulated in the soil (P, Ca, K, Mg, Mn, Cu), as well as the geochemical ratios which reflect the processes of leaching, can serve as palaeogeographic tracers of the climatic variability at the level of intra-secular changes under forest-steppe conditions. The history of the formation of pedosediments over 3.5 centuries in the forest-steppe zone of Eastern Europe comprises two wet periods (1890-1935, 1976-2013) when the average annual rates of pedosedimentogenesis were similar (2.80-2.85 mm yr(-1)) and two periods of geomorphological 'lull' and a xeromorphic climatic condition span (1821-1890 and 1666-1741). These periods correspond to diminution of the average rate of accumulation of sediments down to 2.47 mm yr(-1). The results of the present study suggest the need for purposeful research and wide inclusion of dated sites of the anthropogenic relief formation with flow-geochemical series over the topographic gradient into studies of soil-geomorphologic interrelations and calibration of mathematic models of natural processes using on-site data.