Human-induced development of mollic and umbric horizons in drained and farmed swampy alluvial soils

Abstract

River regulation since the 17th century, large-scale drainage, and intensive farming have seriously transformed soils in the river valleys of Poland. Flood suppression and groundwater lowering have created oxidizing conditions in topsoil and allowed biological activity and plant rooting, which has retarded original stratification of the alluvial substratum. However, ploughing has led to the development of thick humus horizons. In particular, soils with organic topsoil horizons have been changed, i.e. they have lost their initial swampy nature and have undergone an anthropogenic transformation to mineral soils. Despite the long-term agricultural land use, it is still possible to recognize the peaty character of organic matter in some soils and this allows reconstruction of their origin. This study investigated a sequence of soils in the valley of the river Barycz: (i) occasionally flooded, very moist Fluvic Histic Gleysols, with a Murshic organic layer, (ii) weakly drained soils with a high groundwater table, deeply ploughed, where the sandy plough layer contains easily recognizable peat-derived organic material, weakly bound to the mineral fraction (Fluvic Anthromollic Gleysols), and (iii) deeply drained soils, deeply ploughed, where organic carbon content in the plough layer is below 10%, but peat-derived particles of organic matter are still recognizable and are weakly bound to the mineral fractions [(Endogleyic Phaeozems (Anthric) or Endogleyic Umbrisols (Anthric)]. None of the thick plough layers, although intentionally created by humans by mixing the organic layer with underlying sandy material, fulfill the requirements of the anthropogenic diagnostic horizons. Therefore, two new qualifiers are proposed to the WRB classification in relation to the recent addition of the “Murshic” qualifier, namely “Anmooric” and “Atric”, to allow accurately naming the postswampy soils at subsequent stages of their transformation.