Luvisols or Cambisols? Micromorphological study of soil truncation in young morainic landscapes — Case study: Brodnica and Chełmno Lake Districts (North Poland)

Abstract

Eight soil profiles in Brodnica Lake District and Chełmno Lake District were described and sampled. The profiles were divided into four pairs (study areas) dissimilar in lithology, relief or land use. Each pair of profile contained soil located on the crest or upper slope (exposed to erosion) and back slope (slightly exposed to erosion) positions. The relief of this area is inherited from the last (Vistulian) glaciation and represents mostly flat and hummocky moraine plateau landscapes. All investigated pedons have a B-horizon. Five profiles have vertical contrasting texture and contain a significantly developed eluvial zone (A and E horizons) above B horizon. In three cases, pedons have A–B–C horizon sequence. To date, numerous studies have shown that the soils with A–B–C profiles developed on moraine tills should be treated as Cambisols. On existing soil-agricultural maps, these soils are also marked as Cambisols. The B-horizons are enriched in the clay fraction and contain low amount of carbonates in comparison with the parent material. All these criteria can be used to distinguish a cambic horizon but analysis of thin sections revealed the presence of significant amounts of clay and silt illuvial features. The illuvial pedofeatures resulted in these horizons being classified as argic horizons (Bt). These soils cannot be classified as Cambisols which are characterized by absence of appreciable amounts of illuvial silt and clay. Instead the A–B–C profile forms represent truncated Luvisols in which the material from eluvial horizons was entirely removed. The soils described in this study occur in areas where soil erosion is common — the upper part of slopes and crests in arable areas. The illuvial origin of B-horizons in truncated pedons (A–B–C) was also confirmed by the presence of eluvial horizons in nearby soils on the back slope position (slightly or non-exposed to erosion).The results showed that accelerated erosion had a significant role in development of soil cover in agriculture moraine landscapes of Brodnica and Chełmno Lake Districts. The micromorphological analysis confirmed that the loamy soils with the A–B–C profile developed on ground moraine tills should be classified as truncated (eroded) Luvisols. The B-horizons of these soils have significant accumulation of clay and silt features. The illuvial microforms are the relic feature of eluviation–illuviation (lessivage) process. The material from the eluvial horizons of Luvisols was entirely removed. This study is important to understand the influence of soil erosion processes on soil cover development in young-glacial regions. Further investigations concerning formation and characteristic of A–B–C-soils and appropriate classification of described pedons are very important for understanding the impact of accelerated erosion in young glacial landscapes.