Evaluation of an integrated biogeochemical model (PnET-BGC) at a northern hardwood forest ecosystem

An integrated biogeochemical model (PnET-BGC) was formulated to simulate ch emical transformations of vegetation, soil, and drainage water in northern forest ecosystems. The model operates on a monthly time step and depicts th e major biogeochemical processes, such as forest canopy element transformat ions, hydrology, soil organic matter dynamics, nitrogen cycling, geochemica l weathering, and chemical equilibrium reactions involving solid and soluti on phases. The model was evaluated against soil and stream data at the Hubb ard Brook Experimental Forest, New Hampshire. Model predictions of concentr ations and fluxes of major elements generally agreed reasonably well with m easured values, as estimated by normalized mean error and normalized mean a bsolute error. Model output of soil base saturation and stream acid neutral izing capacity were sensitive to parameter values of soil partial pressure of carbon dioxide, soil mass, soil cation exchange capacity, and soil selec tivity coefficients of calcium and aluminum. PnET-BGC can be used as a tool to evaluate the response of soil and water chemistry of forest ecosystems to disturbances such as clear-cutting, climatic events, and atmospheric dep osition.