Soil formation on calcium carbonate-rich parent material in the outer Carpathian Mountains - A case study

In this study, ten stratified calcium carbonate rich soil profiles from the Polish Outer Carpathians were investigated in order to identity the influence of parent material variability and slope processes on soil diversity and their evolution. Moreover, we evaluated the morphological and physico-chemical soil properties to recognize the diagnostic horizons and classification of such soils. While it is usually thought that carbonate-rich soils are considered as formed in situ, these study soils clearly presented layering and contribution of materials, as they were developed from mixed substrates of different origin, e.g. as the result of mass movements and possible aeolian silt contribution. Irrespective of the type of parent material, every investigated soil showed traces of slope processes, resulting in heterogeneous soil profiles. Further, a few different patterns of primary calcium carbonate arrangement were found. In general, the studied soils were characterized by enrichment with calcium carbonate, not only due to inheritance from calcium carbonate rich parent material but also translocation of calcium carbonate within soil profiles, the latter depending on soil stratification. Based on the obtained results, four pathways of soil evolution were formulated. Leptosols, which represent initial calcium carbonate rich soils, may evolve in different directions. First, formation of the thick layer suitable for cambic horizon development under deciduous forests, which enables the classification of such soils as Cambisols, depends on slope processes and allochthonous material deposition. In turn, the decrease of mineralization rates for organic matter, delivery of soil material from the upper parts of the slope as well as mixing of organic matter by mesofauna result in the formation of mollic horizons and transformation of Leptosols into Phaeozems. Further erosion and redeposition of fine soil material provide two types of slope sediments: i) those with silt loam texture dominance, and ii) clay brims interstratified with silty substrates. The first type of sediments are more suitable for water percolation, and after carbonate leaching clay dispersion and translocation occur. In such materials, Luvisols may develop. Sediments with a prevalence of clay loam aided Stagnosol formation, in which pools of carbonates were stabilized due to the reduction of water percolation, leading to stagnation.