Spatial variability of Brunic Arenosols and associated soils along the slope of the Słupia River valley (middle Pomerania, northern Poland)

Abstract

This study was aimed at evaluating the spatial heterogeneity of the soil cover along the slope of the Słupia River valley (Middle Pomerania, northern Poland). Various soil properties are discussed in a context of parent material origin and its transformation through post-depositional processes, and the role of relief as a factor influencing the spatial variability of the soils and sediments. A broad spectrum of soil characteristics, including texture, contents of elements and indicators of soil eco-chemical state, weathering and pedogenesis, were determined from 10 soil profiles using standard procedures. Brunic Arenosols were a major component of the studied sequences. However, their morphology varied, reflecting the impact of the post-depositional transformation of their parent materials by water erosion and other processes typical for slopes. The Ti:Zr ratio suggested only a local-scale transformation of the primary deposits. Typically, soils from the upper slope locations and the transitional zone between the valley slope and the supra-flood terrace were characterised by lower solum thicknesses when compared to the slope foot, middle slope and valley bottom. The presence of colluvial horizons in some locations constituted evidence downslope sediment transport. Weathering features in the studied soils were evidenced by the presence of brown or rust coloured B horizons enriched in pedogenic forms of Fe and Al. The distribution of free Fe and Al along the studied slope suggested lateral transport of those elements. The soils strongly varied in terms of total organic C and N contents and stocks, the highest stocks of these being noted in soils from higher locations and the slope foot, and being the lowest in mid-slope locations. The P, K, Ca and Mg contents were typically low in these sandy soils. All the soils were characterised by typical pH and sorptive characteristics, although their spatial variability was considerable.