Large scale aquatic effects of acidic deposition have become a prominent environmental issue in North America and Europe. Models are required to assess the potential future impacts of current levels of acidic deposition, and the potential benefits of emission controls. This paper presents a model that uses measurements of current lake chemistry and assumptions about the processes governing acidification, to first estimate original (i.e. preacidification) lake chemistry and then predict the eventual chemistry expected given a specified level of acidic sulphate deposition. The model is deliberately kept simple, so that its input requirements are modest and thus can be met on a regional scale. When applied on a regional scale the model predicts the expected eventual distributions of alkalinity and pH. Application of the model is illustrated for a watershed in north-central Ontario, which includes the area immediately to the south and west of Sudbury. Model-based estimates of current alkalinity are very similar to observed alkalinities. The predicted eventual alkalinity distributions, given current levels of deposition, indicate a trend towards recovery, consistent with other observations in the Sudbury region. A sensitivity analysis of the model indicates that its outputs are highly sensitive to estimates of preacidification lake sulphate levels, and less so to assumptions about the catchment's ability to neutralize incoming acidity. Simple, regional models such as the one presented in this paper should play a more central role than they presently do both in assessment and in the definition of future research and monitoring needs.
Acidic Deposition in the Northeastern United States: Sources and Inputs, Ecosystem Effects, and Management Strategies
