Ecosystem Carbon and Nitrogen Dynamics in Reclaimed Forest and Pasture Land-Uses.

The long-term dynamics of ecosystem carbon (C) and nitrogen (N) in forest and pasture ecosystems established on reclaimed mined land remain poorly understood. Thus, an age chronosequence of <1 to 25 years was identified to determine the dynamics of ecosystem C and N following reclamation of coal mined soils in Ohio. Components of ecosystem C and N pools and selected soil properties were measured under forest and pasture ecosystems at 42 reclaimed soil age chronosequence sites across northeast Ohio. Soil organic C (SOC) was estimated by determining coal C and inorganic C and subtracting these from the total C. Of the total C, coal C ranged from 0.2 to 15%, and inorganic C from <1 to 42%, depending on soil depth and land use. The ecosystem C sequestration in mine soil followed a polynomial pattern, with the highest rate of C sequestration of 6.59 Mg ha^-1 after 14 years of reclamation for forest ecosystem and 1.61 Mg ha^-1 after 6 years of reclamation for pasture ecosystem. After a 25-year reclamation, terrestrial C sequestration was 107 Mg ha^-1 in the forest ecosystem and 21 Mg ha^-1 in the pasture ecosystem. In the forest ecosystem, soil C (94%) contributed a major portion of ecosystem C during initial period (<1 year) and biomass C (66%) contributed a major portion of ecosystem C during later period (>14 year). In the pasture ecosystem, soil C contributed a major portion of ecosystem C throughout the reclamation period: 95% in <1 year to 89% in >25 years of reclamation. However, soil N contributed a significant portion of ecosystem N in the both forest and pasture ecosystems. The ecosystem C and N pools and bulk density under both forest and pasture land uses were strongly related to the duration since reclamation, but pH and electrical conductivity were not. The rapid accumulation of ecosystem C and N pools in the pasture and forest land uses occurred within 10- to 15-years of reclamation. The rate of increase in ecosystem C and N pools was lower under older than younger reclaimed sites.