Carbon accumulation and changes in soil chemistry in reclaimed open-cast coal mining heaps near Sokolov using repeated measurement of chronosequence sites

Abstract

Summary: Accumulation of soil organic matter and associated changes in soil chemistry are important drivers and indicators of ecosystem recovery at post-mining sites. To understand the temporal changes in the ecosystem properties of these sites, researchers typically use a chronosequence approach and at one time they compare similar sites of various ages. Although useful, this approach has an important limitation, which is site variability. In this study, we amended the chronosequence approach by repeated measurements of sites after extended periods. We used post-mining sites near Sokolov where the soil C stock and soil chemistry variables had been measured in 1999, 11 years before the current study. In 2010, we used the same methods to repeat these measurements at the same sites, allowing us to assess real-time changes in the investigated variables in individual plots. All sites had been reclaimed by planting of alder in the graded overburden without topsoil application; the overburden consisted of alkaline clay shales. Sites were 4-45 years old in 1999 and 15-56 years old in 2010. Soil pH gradually deceased with site age; this decrease was more pronounced in the upper soil layer. Changes in pH between 1999 and 2010 were negatively correlated with the initial pH; as a consequence, pH decreased in alkaline sites and increased in acidic sites. Soil carbon (C) increased with site age but the rate of increase declined with site age. The average increases in C stock were similar as determined by the chronosequence and real-time approaches. Changes in soil nitrogen content were similar to changes in soil C content. Phosphorus content did not differ significantly among sites but tended to be less at older than at younger sites.