ABSTRACT
Soil physical properties at post-mining sites can substantially affect plant growth. One reason is that texture extremes are very common because sedimentation of material overlying the coal layer in many cases causes separation of material of similar grain sizes. The frequent result is overburden from sand and gravel or clay sediments (Bradshaw 1997), both extreme textures that can affect soil properties and the water regime of the dumps (Kuraz 2001). Given a choice between the two extremes, clay overburden is usually better for soil and fauna development because clay holds more water. In addition, a clay overburden is often consolidated by carbonates or organic matter (Kribek et al. 1998) because mudstones do not generally break directly into amorphous clay but disintegrate into small stone-like fragments that slowly break into clay. The remaining fragments can play the role of sand and gravel and improve soil physical properties, as documented by analysis of 20-year-old clay post-mining substrate near Sokolov by different preparation methods. When Kuraz et al. (2012) used the FAO method (which is quite aggressive and disintegrates carbonates and organic matter-bound fragments), they found 70% clay. However,
1Institute for environmental studies, Faculty of Science, Charles University, Benátská 2, Prague, 128 00, Czech Republic. 2Faculty of Civil Engineering, Czech Technical University of Prague, Takurova 7, Prague, 16000, Czech Republic. *Corresponding author
more gentle preparation methods, which might better refl ect the action of natural forces, identifi ed only 30% clay. The difference was small stonelike fragments of mudstone fi rmly encrusted with carbonates and organic matter.
