GETTING TO THE ROOT OF NONPOINT SOURCE POLLUTION IN ABANDONED MINE LANDS: BIOGEOCHEMICAL CYCLING OF MANGANESE IN FORESTED COAL MINE SPOIL

Soils that have experienced human perturbation can become reservoirs for potentially toxic heavy metal(loid)s that can disrupt local ecosystems. Abandoned mine lands often contain piles of waste rock (spoil) that continue to leach toxic metal(loid)s and acid to stream water long after mining operations have ceased. Revegetation of abandoned coal spoil is a commonly used reclamation technique, but more research is needed to evaluate how vegetation impacts the mobility and consequent leaching of metal(oid)s into groundwater and surface waters. In this study, we evaluated the geochemistry of soils, rain water, pore waters, and foliage collected from forested coal spoil in the Appalachian region in Ohio to examine the potential of forest vegetation to mitigate leaching of the metal manganese (Mn) out of actively weathering coal spoil. We also examined solid-phase Mn in soils using a sequential extraction procedure targeting exchangeable, acid-soluble, reducible, and oxidizable soil fractions. Manganese oxides (reducible fraction) are the dominate solid–phase fraction of Mn in soils at 60 – 120 cm depth, indicating an enrichment of Mn oxide minerals deep in the soil profile. This Mn-oxide-enriched layer overlies soil that contains a relatively large fraction of reduced material (organics and sulfide minerals) and may represent a redox interface. High concentrations of Mn in green leaves (2,383 mg kg⁻¹) indicate substantial uptake of Mn by trees; however, concentrations of dissolved Mn in pore water were highest at 120 cm depth (< DL – 768 mg L⁻¹), suggesting leaching of Mn from the Mn-oxide-rich layer below the rooting depth. Mass balance models were used to determine that vegetation uptakes 3xs more Mn than what is leached from mine spoil in pore water, but uptake only occurs within surface soils where roots access water. Pockets of reduced material may release acid and promote the leaching of Mn at depth in soils forming in forested piles of abandoned coal spoil. Our study provides insight into the geochemical evolution of forested coal mine spoil and biogeochemical cycling of Mn in soils.