THE MICROBIAL POOL AND SOIL CARBON CYCLING ON RECLAIMED SURFACE MINE SITES

The southern Appalachian region is an important source of coal resources. The wide scale practice of surface mining in this region leads to the landscape-scale removal of surface material and soils, a large carbon reservoir and important component of the carbon cycle. To date, few scientific studies have examined the development of the soil carbon cycle on post-reclamation mine sites in this region. In particular, development of the microbial pool and its role in carbon cycling in post-reclamation mine soils remains poorly understood.

This study measured microbial biomass and soil respiration, as well as bulk soil total organic carbon, total nitrogen, carbon and nitrogen stable isotope fractionations, C/N ratios, water holding capacity and bulk soil density for recently reclaimed mine soils. Study plots of five soil pits were set up on three grassland reclaimed ridgetop surface mining areas aged 2, 8, and 10 years after reclamation from Robinson Forest in eastern Kentucky. Soil pits were dug to 50cm below the litter layer and samples were taken from the litter, 0-5cm, 5-10cm, 10-25cm, and 25-50cm depths. Samples were also taken of the litter, 0-5cm, and 5-10cm layers for biomass and respiration experiments. Where possible, bulk density samples were taken using soil cores of known volume.

Analysis of geogenic organic carbon and soil organic carbon contributions employing a two-phase unimixing model showed limited penetration of soil organic matter into the soil column. Microbial biomass was found to be better correlated to total organic carbon than to soil organic carbon. Soil respiration was shown to be correlated with the exponent microbial biomass shortly after collection and better correlated with total organic carbon. While soil respiration experiments suggest limited soil microbial activity, microbial biomass shows a strong relationship with soil total organic carbon. This suggests that geogenic organic matter may act as a replacement for soil organic matter, either as a nutrient source or soil additive. Results also suggest a need to adjust the standard two-phase unmixing model to account for fractionation of soil organic matter during soil formation.