Specific Water Regime in Technogenic Soils: Preferential Water Flow Formation

Abstract

Technogenic soil (technozem) was created on the surface of the former sludge pond of the iron-ore quarry in the course of land rehabilitation. The upper chernozemic layer in the technozem was underlain by sandy or loamy layers. The soil land reclamation constructions were created 20 years ago: the chernozemic 60-cm layer with classical granular fine and medium-size aggregates (1-5mm) was sprinkled on the deep layer of sand. This construction was in agricultural use during the last 20 years. At present, the layers of prismatic coarse peds (>50mm) bounded by flat to rounded vertical faces and columnar, very thick, vertically oriented blocks (>100mm) have been formed at the depths 20-40 and 40-60cm. The water regime of these soils differed from that of the background automorphic natural soils and was characterized by periods of water stagnation at the boundary between the two layers. In the course of 20 years, this type of water regime resulted in the development of a columnar structure in the lower part of the chernozemic layer. The coatings on the ped faces in this part of the profile had an increased content of Fe and Ca ions. There was no differentiation of the carbon of organic substances and carbonates in the soil profile. Field studies of water flows in this soil based on starch label and laboratory experiments on infiltration of salt solutions though the soil columns with determination of breakthrough curves demonstrated the existence of preferential water flows in technozem. Rapid infiltration of water through preferential water paths in chernozemic layer after abundant rainfalls and during the snowmelt season leads to the development of perched water above the textural boundary. This preferential water and matter flows are generated along the faces of the peds and form the perched water layer on the sand. Such kind of water phenomenon with preferential flows and perched water table formation transforms the granular aggregates into columnar blocks by the temporary gleyzation process.