The Bear Brook Watershed in Maine is a long-term, paired watershed acidification study in northern New England. The West Bear watershed receives chronically elevated N and S amendments, and the East Bear watershed serves as a reference. The programme of research integrates studies of biogeochemical responses of streams, soils, and vegetation. Intensive hydrogeochemical measurements over the past decade provide for reasonably accurate measures of whole-watershed chemical budgets. The chapters in this book document atmospheric inputs of chemicals and water, internal cycling, transformation, and export of measured constituents. The research provides insights into ecosystem processes that govern ongoing N saturation, S retention and release, AI and P mobilization, and soil base cation depletion. This volume should of interest to researchers, managers, and policymakers concerned with the effects of air pollution on forested ecosystems.