Carbon and nitrogen pools in reclaimed land under forest and pasture ecosystems in Ohio, USA

The long-term changes of ecosystem carbon (C) and nitrogen (N) pools in reclaimed mine soils remains poorly understood. Thus, age chronosequence sites, ranging from <1 to 25 years of reclamation, under forest and pasture land use, were identified to determine ecosystem C and N pools. Ecosystem C and N pools and selected soil properties were measured for 42 reclaimed sites across northeast Ohio. Soil organic C (SOC) was estimated by determining coal C and inorganic C, and subtracting these from the total soil C. Of the total soil C in reclaimed soil, coal C ranged from 0.2 to 15%, and inorganic C from <1 to 42%, depending on soil depth and land use. The C sequestered in the minesoil ecosystem followed a polynomial function, with the highest rate of sequestration of 6.59 Mg ha(-1) after 14 years of reclamation in the forest and 1.61 Mg ha(-1) after 6 years under pasture. After 25-year of reclamation, C sequestration was 107 Mg ha(-1) under forest ecosystem and 21 Mg ha(-1) under pasture. In the forest ecosystem, a major portion of ecosystem C consisted of soil C (94%) during the initial period (<1 year) and biomass C (66%) during the later period (>14 year). In the pasture ecosystem, soil C contributed a major portion of ecosystem C throughout the reclamation period: 95% for <1 year and 89% for >25 years of reclamation. However, soil N contributed a significant portion of ecosystem N in both the forest and pasture ecosystems. Ecosystem C and N pools and bulk densities were strongly related with reclamation age for both forest and pasture. The rates of ecosystem C and N sequestration peaked at about 10 to 15 years of reclamation. After 10 to 15 years of reclamation, the rate of sequestration decreased as reclamation age increased. (C) 2010 Elsevier B.V. All rights reserved.