Simulation of carbon cycling, including dissolved organic carbon transport, in forest soil locally enriched with 14C

The DyDOC model was used to simulate the soil carbon cycle of a deciduous forest at the Oak Ridge Reservation (Tennessee, USA). The model application relied on extensive data from the Enriched Background Isotope Study (EBIS), which exploited a short-term local atmospheric enrichment of radiocarbon to establish a large-scale manipulation experiment with different inputs of C-14 from both above-ground and below-ground litter. The model was first fitted to hydrological data, then observed pools and fluxes of carbon and C-14 data were used to fit parameters describing metabolic transformations of soil organic matter (SOM) components and the transport and sorption of dissolved organic matter (DOM). This produced a detailed quantitative description of soil C cycling in the three horizons (O, A, B) of the soil profile. According to the parameterised model, SOM turnover within the thin O-horizon rapidly produces DOM (46 gC m(-2) a(-1)), which is predominantly hydrophobic. This DOM is nearly all adsorbed in the A- and B-horizons, and while most is mineralised relatively quickly, 11 gC m(-2) a(-1) undergoes a maturing reaction, producing mineral-associated stable SOM pools with mean residence times of 100-200 years. Only a small flux (similar to 1 gC m(-2) a(-1)) of hydrophilic DOM leaves the B-horizon. The SOM not associated with mineral matter is assumed to be derived from root litter, and turns over quite quickly (mean residence time 20-30 years). Although DyDOC was successfully fitted to C pools, annual fluxes and C-14 data, it accounted less well for short-term variations in DOC concentrations.