Modeling carbon and nitrogen dynamics in disturbed ecosystems: A case study of coal surface-mined lands in eastern Ohio

The quantification of carbon (C) and nitrogen (N) cycling in ecosystems is important for (a) understanding changes in ecosystem structure and function with changes in land use, (b) determining sustainability of ecosystems, and (c) balancing the global C budget as it relates to global climate change. Estimating future dynamics of C and N is complicated by the projected changes in climate including increased atmospheric CO₂ and temperature. Regional climate change can differ significantly from average global change and should be accounted for if accurate changes in C and N budgets are to be obtained. In the State of Ohio, increased precipitation and existing tropospheric aerosols need to be considered in addition to expected increases in CO₂ and temperature. A meso-scale study was conducted to determine regional effects of climate change on C and N cycling within disturbed ecosystems. Objectives of the research were to quantify (a) sediment yield, (b) current C storage in vegetation and soils, and (c) C efflux from soils from both abandoned and rehabilitated coal surface-mined lands in Ohio. A process-based, dynamic model was developed to simulate sediment yield, grassland production, and C and N cycling on mined lands. Verification of plant production and soil erosion submodels with data sets from surface-mined lands in the mid-western U.S. showed r2 values of 99.5% and 97%, respectively. A spatial model was developed with land cover and topographic data in a geographic information system to supply the dynamic model with land area, percent slope, and slope aspect values for the study region. From the land cover theme and other documented sources, the estimated extent of surface-mined lands was 102 km2 of abandoned, unvegetated, surface-mined land and 565 km2 of rehabilitated surface-mined land. Simulations from the dynamic model estimated that unvegetated surface-mined lands in Ohio produce approximately 441,325 t yr−1 of sediment and between 2,000 and 20,000 t yr −1 of C emissions to the atmosphere from decomposition, depending on the initial values of SOC used in the model simulation. While rehabilitated lands in Ohio had a higher C efflux rate than barren lands, a positive net C sequestration of 5.5 t km−2 yr−1 was estimated as a result of organic matter additions. This sequestration rate increased considerably under projected climate change scenarios, while decreasing when simulated rehabilitated grasslands were harvested for hay. Carbon and N dynamics are altered by changes in land use and land cover which may be caused by changes in management practices and climate regimes, respectively. Ecological modeling helped to quantify the changes in C and N dynamics while estimating current productivity and future sustainability. Regional models will continue to be important in ecological studies because of the increasing need for ecological information at levels between the micro- and macro-scales and because the models may serve as a basis for policy decisions since the results can cover the spatial extent within political boundaries.