Evolution of Chemical Characteristics of Technosols in an Afforested Coal Mine Dump over a 20-year Period

Coal mining in areas containing pyritic materials frequently leads to a remarkable impact on the environment because of sulphide oxidation. We studied the evolution of chemical characteristics of Technosols derived from sterile materials, in a lignite mine located in As Pontes (northwest Spain), over a 20-year period. Three plots, which had different management practices, were selected. The mine spoil was deposited randomly in two of the plots (CSP with low S concentration and CSA with high S concentration), while it was selectively managed in the other one (P206). Twenty years after the first sampling, CSA continued to show the highest acidity (pH(water) 3.7-3.9), whereas the lowest acidity was that of P206 (pH(water) 5.0). Regarding the surface layer, C increased 1.1% in P206, 0.3% in CSP and 0.2% in CSA. Nitrogen increased 1% in P206. The C/N ratio increased in all plots. Phosphorus, Ca, Mg, K and effective cation exchange capacity decreased in 2002 and experienced a slight increase in 2012. Exchangeable Al and Al saturation increased in CSP and P206 and decreased in CSA. Electric conductivity levels of Ca, Mg, Na, Al and SO42- concentrations decreased in the soil solution in all plots during the 20-year period. Twenty years after the first monitoring, the plots that were built based on selective management of the mine spoil showed lower acidity and acidity-derived consequences. These facts confirm the necessity of an appropriate selection of sterile materials, avoiding the placement of pyrite-rich spoils on the surface or near-surface zones, which is essential to facilitate proper restoration of this kind of dumping areas. Copyright (c) 2015 John Wiley & Sons, Ltd.