Watershed base-cation cycle dynamics modeled over forest regrowth in a Central Appalachian ecosystem

Watershed ecosystem analysis has been used to study aspects of nutrient cycles in many regions of the US. Here we quantify watershed input-output budgets and intrasystem cycling of the base cations Ca, K and Mg in a montane Virginia ecosystem. The intrasystem fluxes of uptake, return, canopy leaching and mineralization were simulated over the period of forest aggradation. A forest-dynamics model, based on previous models, was created to model biotically-driven fluxes at this site; biomass nutrient concentrations were parameterized with a field study. A two-year watershed mass-balance study was then conducted to estimate geologic fluxes for comparison with modeled biotic fluxes. Results show the major biotic fluxes to be much greater, highlighting the importance of considering biomass dynamics in ecosystem nutrient-cycling studies. Mineralization from forest-floor biomass compartments proved to be an increasingly important avenue for internal recycling during aggradation. Accumulation of base cations in biomass also corresponded to a production of H+ in soil at three times the H+ levels in atmospheric deposition at this location. Such high levels of base removal in soils could exceed weathering rates and may result in a depletion of bases from the soil exchange complex.