Carbon sequestration on mined lands supporting abandoned grasslands: Soil organic carbon accumulation and distribution

Abstract

Reclaimed surface coal mines in the eastern United States are commonly revegetated with grasses and legumes. The productivity and carbon sequestration potential of the vegetation varies with the condition and nature of the mined site and soil. This study was conducted to determine the distribution pattern of soil carbon stock on 9 mined grasslands reclaimed after the passage of SMCRA in 1977. Mine soil samples of the surface and the subsurface overburden material were collected to approximately 2m depth and chemical and physical soil properties were determined on the less-than-2mm fine sample fraction. Results are presented for the vertical distribution of soil organic carbon concentration (SOC-Cwt%), fine earth (<2mm particle size) fraction (Fines vol%), coal-derived carbon concentration (Coal-Cwt%), and the bulk density of the fine earth fraction (BDfines,gcm-3) down the mine soil profile. The SOC-Cwt% ranged between 0.0 and 0.767% and the Coal-Cwt% ranged between 0.0294 and 4.53% among all samples. The R2 of the soil organic carbon content (SOC) predictions (g C m-2) was estimated at 60.6% and the shape of the prediction model resembled that of an exponential function. The results for a hypothetical scenario indicated that at an assumed cost of $24 per 1cm thick spoil layer across 1 hectare of homogenous project area, labeled as cost of SOC analysis within the soil profile, and $97.4 per Mg of elemental C, labeled as C credits for the analyzed SOC the maximum cost effective sampling depth was 48cm. One third of the total sequestered SOC was located beyond the cost-effective sampling depth for this experiment based on these sample analyses.