Changes in physical and chemical properties of soil after surface mining and reclamation

Mining causes drastic disturbances in landscape and soil properties, and reclamation can restore soil quality over time. Thus, assessing changes in properties of reclaimed mine soils is essential to understanding the effects of the reclamation techniques. This study was aimed at quantifying the effects of mining and reclamation processes on physical and chemical properties of reclaimed soils for three dominant soil series in Ohio: Mahoning–Canfield–Rittman–Chili, Coshocton–Westmoreland–Berks, and Gilpin–Upshur–Lowell–Guernsey. Three newly reclaimed mine sites (< 1 year since reclamation) were identified from each of the three soil series. Three sampling locations were identified for each mine site. Each sampling location consisted of a paired, undisturbed reference site adjacent to the reclaimed mine sites (RMSs). Thus, there were 54 sampling locations distributed throughout eight counties in eastern Ohio. Composite and core samples were obtained from 0–15, 15–30, and 30–45 cm depths in 2008. Soil physical and chemical properties were measured and changes in properties of the RMSs in reference to the adjacent, undisturbed sites were quantified. The bulk density (BD) of the RMSs (1.11 to 1.69 Mg m− 3) significantly increased by up to 54% compared to that of the undisturbed sites (0.98 to 1.41 Mg m− 3) at the 0–15 cm depth but not at the lower depths. The BD of the RMS was also affected by soil series, a high BD in the Mahoning–Canfield–Rittman–Chili soil series. Mining and reclamation activities increased soil pH and electrical conductivity (EC), and decreased soil organic carbon (SOC) and nitrogen (N) pools. At the 0–15 cm depth, soil pH in RMSs (4.9 to 8.1) was 4 to 31% higher than that of the undisturbed sites (4.6 to 7.0). Likewise, EC in RMS (119 to 349 μS cm− 1) was > 200% higher than those for the undisturbed sites (43 to 154 μS cm− 1). In the 0–15 cm depth, SOC pools in RMSs (1.2 to 2.5 Mg ha− 1) declined by 52 to 83% of undisturbed sites (11 to 29 Mg ha− 1). Similarly, N pools in RMSs (1.2 to 2.5 Mg ha− 1) declined by 42 to 75% of undisturbed sites (3.1 to 5.1 Mg ha− 1). Clay content was positively correlated with SOC concentration in the RMSs but not in the undisturbed site. This trend indicates that a RMS high in clay content has a relatively high SOC sink capacity. The SOC, N, C:N ratio, and EC in the subsurface layer of RMSs were similar to those of the surface soil, although later received a topsoil cover. Such a trend suggests that topsoil materials require better handling during removal, storage, and application so as to preserve soil structure, nutrients, SOC, and N pools.

Research Highlights
► Mining and the reclamation process increased soil bulk density at the 0–15 cm depth.
► Clay content positively correlated with soil carbon in the reclaimed site.
► Mining increased soil pH and EC, and decreased carbon and nitrogen pools.
► Topsoil requires better handling to preserve soil structure, SOC, and N pools.