Occurrence, formation, and micromorphology of gypsum in soils from the Central-German Chernozem region

Abstract

Occurrence of gypsum in soils from loess of the Central-German Chernozem region indicates that local climatic conditions with low precipitation (average <500 mm a −1) and a real evaporation between 450 and 460 mm do not allow leaching of weakly soluble gypsum from soils. At a site close to the strip mine Etzdorf, gypsum is accumulated in the Ck-horizon of a Haplic Chernozem down to a depth of about 1.5 m, its distribution being nonuniform. Calculated total gypsum in the Haplic Chernozem amounts from 10–20 t ha −1. The highest accumulation of gypsum, obviously by solution transport and evaporation, can be observed in a profile exposed to the air since about 1960. In this profile maximum, SO 4 2– values, however, are not found on the surface of the outermost aggregates with whitish efflorescence, but at 20 cm depth in the profile. In a Eutric Podzoluvisol, the precipitation of gypsum developed on living roots as well as in pores of former roots. In a buried Chernozem, large euhedral gypsum crystals with a diameter of up to 1.5 cm were found. Gypsum crystals occur in different shapes and sizes such as euhedral lenticular, rosette-like, and equigranular ones. Even soils having undergone leaching processes reveal unusual increases of SO 4 2− at 40–50 cm depth. This may be an indicator of more recent SO 4 2− input due to atmospheric deposition since the beginning of industrialization. It is supposed that gypsum is formed by the reaction of atmogenic sulfuric acid with different Ca sources in the soil.