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AN EVALUATION OF PROCESSES REGULATING SPATIAL AND TEMPORAL PATTERNS IN LAKE SULFATE IN THE ADIRONDACK REGION OF NEW YORK
Citation:
Impact/Purpose:
To assess the impact of changes in acid deposition on the Adirondacks.
Description:
As a result of the Clean Air Act Amendments of 1970 and 1990, there have been significant decreases in sulfate (SO4^2-) concentrations in surface waters across the northeastern U.S. The 37 Direct/Delayed Response Program (DDRP) watersheds in the Adirondacks receive elevated levels of atmospheric S deposition and showed considerable variability in lake SO4^2- concentrations. In response to decreases in atmospheric S deposition, these sites have generally exhibited relatively uniform decreases in surface water SO4^2- concentrations. In this study, an integrated biogeochemical model (PnET-BGC) was used to simulate the response of lake SO4^2- concentrations at these DDRP sites to recent changes in atmospheric S deposition. Using default parameters and algorithms, the model underpredicted lake SO4^2- concentrations at sites with high SO4^2- concentrations and overpredicted at sites with low SO4^2- concentrations. Initial predictions of lake SO4^2- were relatively uniform across the region. Initial model simulations also underpredicted decreases in lake SO4^2- concentrations from 1984 to 2001. We identified seven hypotheses that might explain the discrepancies between model predictions and the measured data. Model inputs, parameters and algorithms were modified to help test these hypotheses and better understand factors that control spatial and temporal patterns in lake SO4^2- in this acid-sensitive region.