WATERSHED BASE-CATION CYCLE DYNAMICS MODELED OVER FOREST REGROWTH IN A CENTRAL APPALACHIAN ECOSYSTEM

Watershed ecosystem analysis has been used to study aspects of nutrien t cycles in many regions of the US. Here we quantify watershed input-o utput budgets and intrasystem cycling of the base cations Ca, K and Mg in a montane Virginia ecosystem. The intrasystem fluxes of uptake, re turn, canopy leaching and mineralization were simulated over the perio d of forest aggradation. A forest-dynamics model, based on previous mo dels, was created to model biotically-driven fluxes at this site; biom ass nutrient concentrations were parameterized with a field study. A t wo-year watershed mass-balance study was then conducted to estimate ge ologic fluxes for comparison with modeled biotic fluxes. Results show the major biotic fluxes to be much greater, highlighting the importanc e of considering biomass dynamics in ecosystem nutrient-cycling studie s. Mineralization from forest-floor biomass compartments proved to be an increasingly important avenue for internal recycling during aggrada tion. Accumulation of base cations in biomass also corresponded to a p roduction of H+ in soil at three times the H+ levels in atmospheric de position at this location. Such high levels of base removal in soils c ould exceed weathering rates and may result in a depletion of bases fr om the soil exchange complex.