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.