Regional application of the PnET-BGC model to assess historical acidification of Adirondack lakes

The Adirondack region of New York has high inputs of acidic deposition and large numbers of acidic lakes. The biogeochemical model, PnET-BGC, was applied to 44 statistically representative Environmental Monitoring and Assessment Program (EMAP) lake watersheds in the Adirondacks. Model simulations help provide an understanding of historical effects of acidic deposition on soils and lake waters. Model simulations indicate that median annual concentrations of SO42- and NO3- in the 44 EMAP lakes were 15.9 mu eq/L and 3.8 mu eq/L, respectively, in 1850, compared to the median current measured values of 88.8 mu eq/L and 20.0 mu eq/L. Simulated median values of pH, acid-neutralizing capacity (ANC), and soil percent base saturation were 6.63, 67.7 mu eq/L, and 12.3%, respectively, in 1850, compared to the median current measured values of 5.95, 27.8 mu eq/L, and 7.9%. The estimated historical surface water acidification was greatest in lakes having low ANC below values of 100 mu eq/L. This pattern of historical acidification is in agreement with a previous paleolimnological investigation.