Technogenic soils (Technosols) developed from fly ash and bottom ash from thermal power stations combusting bituminous coal and lignite. Part I. Properties, classification, and indicators of early pedogenesis

Abstract Large amounts of fossil fuel combustion wastes (e.g. fly and bottom ash) are discharged on land surface all over the world. The uppermost layer of disposal sites is subject to soil-forming processes after the development of plant cover due to natural succession or reclamation works. The present study presents the analysis of technogenic soils (Technosols) developed from ashes after combustion of bituminous coal and lignite. The study involved the determination of their properties, their classification, and discussion of the indicators of early pedogenesis. Technosols located on the surface of settling ponds and landfills of selected thermal power stations in Poland combusting both bituminous coal and lignite were examined. Standard pedological methods for the determination of soil morphology and physical-chemical properties were applied. Dithionite and oxalate extractions of Fe, Al, Si, and Mn were used in order to determine transformations of soil substrate during pedogenesis. Moreover, optical microscope observations permitted finding microscale effects of soil-forming processes in the studied Technosols. The properties of the analysed Technosols are primarily influenced by the properties of the parent material (i.e. ash from thermal power stations) which in turn are strongly dependent on (1) the type of ash (fly ash vs. bottom ash), (2) the kind of fuel (bituminous coal vs. lignite), as well as (3) the mode of ash deposition and type of disposal site (settling pond vs. dry landfill). Properties of the studied soils are also controlled by the following soil-forming factors: vegetation (input of soil organic matter), human (acceleration of soil-forming processes by reclamation), and climatic/weather conditions (leaching of soluble compounds by water from precipitation). The most important morphological and physical-chemical indicators of pedogenesis of the studied Technosols over several decades of soil formation are as follows: (1) the development of soil structure in A horizon related to the accumulation of soil organic matter, (2) the decrease in pH (a change in reaction from strongly alkaline towards less alkaline or acidic), (3) the formation of pedogenic carbonates and their subsequent leaching from the topsoil after several dozen of years of pedogenesis, and (4) the release of oxalate-extractable Al and Si during the pedogenesis. The studied soils were classified according to WRB as Spolic Technosols (or Leptic Spolic Technosols) with various supplementary qualifiers (Alcalic or Eutric, Arenic and/or Loamic, Calcic or Protocalcic, Fluvic, Hyperartefactic, Laxic, Relocatic, Tephric or Vitric). Certain suggestions to improve the WRB soil system are discussed in the paper.