Sensitive receptors such as soil and fresh bodies of water are at the end of a long chain of events in the process of regional acidification. This chain begins thousands of kilometers upwind at the emitters of acidifying pollutants. The topics covered in this book are important in the study of regional acidification for two reasons. First, it is important to assess the sensitivity of terrestrial and aquatic ecosystems to the deposition of acidifying pollutants. If the sensitivity of an ecosystem is known, then international control strategies can be developed to reduce deposition in the receptor areas of greatest importance. This is an impor­ tant factor in designing the most effective strategies because of the very high costs of reducing emissions of acidifying pollutants. Second, it is important to be able to predict changes in ecosystems for decades into the future, whether it be an improvement owing to decreases in aci­ difying emissions or, alas, a further deterioration because control strategies are nonexistent or inadequate. In either event, it is important to be able to judge the results of our actions. Decision makers tend to be mistrustful of models unless they can judge their reliability. The application and testing of the models in Part III of this book cover, therefore, an important facet of model building.

I: Terrestrial Effects.- 1. Philosophy, structure, and application methodology of a soil acidification model for the Netherlands.- 2. Effects of acid deposition on agricultural soils during and after use.- 3. Analysis of regional changes in forest growth.- II: Aquatic Effects.- 4. Mapping groundwater sensitivity to acidification in Europe.- 5. Modeling the impacts of acidification on fisheries in Ontario, Canada.- 6. Present and future acidification of Swedish lakes: Model calculations based on an extensive survey.- 7. A regional model of surface-water acidification in southern Norway: Calibration and validation using survey data.- 8. Regional modeling of acidity in the Galloway region in southwest Scotland.- 9. Modeling regional acidification of Finnish lakes.- 10. Identification of a Direct Distribution model from a regionalized mechanistic model of aquatic acidification.- III: Model Reliability and Model Use.- 11. Estimating the reliability of regional predictions of aquatic effects of acid deposition.- 12. Evaluating the performance of Monte Carlo calibration procedures.- 13. A regional model of surface-water acidification in southern Norway: Uncertainty in long-term hindcasts and forecasts.- 14. Atmospheric deposition assessment model: Applications to regional aquatic acidification in eastern North America.- Conclusions.- References.- Authors.