Forest Soil Carbon Sequestration Measurement and Verification on Reclaimed Mined Land in the Appalachian Coalfield.
Beyhan Y. Amichev, Virginia Tech, Dept of Forestry, Blacksburg, VA 24061 and James A. Burger, Virgnia Tech., Dept of Forestry, 228 Cheatham Hall, Blacksburg, VA 24061.
Carbon accreditation of forest development projects is an essential approach to sequestering atmospheric C under the provisions of the Kyoto Protocol. The reforestation of mined land has the potential to sequester large amounts of atmospheric C on sites where previously productive forestland was disturbed during carbon-based fuel extraction operations. Today, existing at various stages of floristic succession – from abandoned grasslands to brush lands to forestlands, there are millions of hectares of land disturbed by surface mining across the United States. The rate and the extent to which reforested mined land captures and stores atmospheric C as Mine Soil Organic Carbon (MSOC) is still largely unknown due to the challenges associated with analytical measurement of MSOC and verification of sequestered MSOC at the landscape scale. Pedogenic soil C exists in two forms, soil organic matter and plant residues. A unique property of mine soils is the presence of coal and carboniferous rock particles, commonly referred to as geogenic carbon. Depending on their particle size and quality geogenic carbon particles could have the chemical and physical properties resembling those of soil organic matter. For most mine soils MSOC is largely overestimated by standard analytical procedures due to the effect of oxidizing agents on geogenic C particles in the soil, such as the dichromate used in a standard Walkley-Black procedure. This work was conducted to design an inexpensive method for MSOC analysis that will differentiate between pedogenic and geogenic carbon forms at accuracy and precision levels required for C sequestration measurement and verification of mined land reforestation projects. The new method was then used to determine the distribution pattern of MSOC down the soil profile and across the mined landscape and to determine the maximum cost effective depth of MSOC analysis on mined lands currently supporting abandoned grasslands. Estimates for MSOC were produced as the difference between total soil C and C present in geogenic and inorganic forms. Prior to C elemental analysis we removed all inorganic carbon using acid fumigation and we fully eliminated all pedogenic carbon present in mine soils via thermal oxidation pretreatment. The most significant contribution of our method to other thermal oxidation methods is that it provides a means to correct for the carbon loss from the more volatile constituents of coal fragments. We measured the soil carbon content on 9 minelands reclaimed after the passage of the Surface Mining Control and Reclamation Act (SMCRA) of 1977. Mine soil samples of the surface and the subsurface overburden material were collected to approximately 2m depth; chemical and physical soil properties were determined on the less-than-2mm fine soil fraction. The MSOC concentration ranged between 0.0 and 0.767% by weight and the geogenic C concentration ranged between 0.0294 and 4.53% by weight among all samples. The R2 of the MSOC predictions (g C m-2) was estimated at 60.6% and the shape of the prediction model resembled that of an exponential mathematical function. The cumulative MSOC content for the entire profile (0-150cm) was 17.6 Mg ha-1 with 95% confidence limits of the mean ranging from 0.32 to 42.3 Mg ha-1. The results indicated that one third of the total MSOC on mined lands was found in the surface 0-13cm soil layer and more than two thirds of it was located in the 0-53cm soil profile. MSOC below 50 cm is less valuable due to the higher cost of sample collection, especially in compacted and rocky mine soils. In most mined sites in the hard rock regions of the Appalachians 6 and 9 soil pits per hectare, respectively, need be sampled and analyzed in order to measure the sequestered MSOC at precision levels of 20% and 15% within the mean value at the 95% confidence level. Based on current C credit price listing of 22.8 Euros per ton of CO2,, and the standard costs associated with C sampling and analysis procedures, the cost-effective depth of MSOC analysis was estimated to be 7cm at the 20% precision level, and no MSOC analysis was justified at the 15% precision. In this paper we further present the direct relationship between C accreditation as an additional incentive to establish reforestation projects on mined lands and the horizontal and vertical variation of MSOC. In particular we investigated the potential use of Geographic Information Systems (GIS) and geostatistics as tools to more efficiently allocate soil pits across the landscape that would eventually allow for MSOC sequestered at lower soil depths to be measured and to be claimed as C credit, hence making reforestation a much more attractive alternative for mined land reclamation.