CARBON STORAGE AND CYCLING OF RECLAIMED MINE SOILS IN SOUTHEASTERN KENTUCKY

Since the passage of the Surface Mining and Reclamation Act (SMCRA) in 1977, the most common type of surface mine reclamation is heavy compaction followed by grass seeding. To promote better vegetative recovery after mining, the Appalachian Regional Reforestation Initiative (ARRI) promotes leaving the top four feet of fill material loose and planting a seedling mix of native hardwood trees. This study aims to quantify the effects of the resulting soil bulk densities on decomposition processes through the analysis of carbon storage and cycling in the soil column. Soil carbon storage mechanisms are divided into specific size classes/pools, each corresponding with a general turnover rate: labile at 2000µm<d<500µm, recalcitrant at 500µm<d<53µm, and inert at d<53µm. Using these size classes and their soil organic carbon (SOC) content, decomposition rates can be estimated for sites of varying bulk density.

Sampling sites for compacted and loose soil were selected by similar reclamation ages in southeastern Kentucky. Compacted sites were 2, 9, 12, and 14 years since reclamation, and uncompacted sites were 2, 5, and 14 years. Soil samples were taken at four depths (0-5, 5-10, 10-25, and 25-50 cm) and wet-sieved to isolate the SOC pools. A chronosequence of previously collected data from these sites reveal that SOC is predominantly sequestered in the top 5 cm of reclaimed mine soil; thus, the top 5 cm for all sites was analyzed to assess pool distribution and carbon content over time. A full depth analysis was conducted on samples from the compacted 12-year and uncompacted 14-year sites to evaluate carbon storage allocation with depth. Samples were analyzed by an isotope ratio mass spectrometer for %Corg and d13C. A mass balance unmixing model was applied to differentiate the geogenic organic carbon fraction from soil organic carbon in the samples, using d13C signatures from litter and coal samples.

Preliminary results indicate that for both bulk densities, size class dominance shifts from labile to recalcitrant over time; however, uncompacted sites exhibit a faster change in pool dominance compared to compacted sites. Both compacted and uncompacted sites reveal a transfer of carbon storage over time toward the inert pool, once again occurring sooner in uncompacted sites, demonstrating decompositional progression.