Ecological Effects of Acidic Deposition

Detailed studies by a large community of scientists for more than four decades have provided considerable insight into the ways in which atmospheric deposition alters ecosystems. When it was first identified, acidic deposition, or acid rain as it is commonly called, was viewed as a simple problem that was limited in scope. Scientists know now that acids and acidifying compounds enter ecosystems largely from atmospheric deposition and are transported through soil, vegetation, and surface waters, resulting in a range of adverse ecosystem effects. Controls on emissions of air pollutants, which were initiated in North America and Europe in the 1970s, have resulted in some recovery of ecosystems from the adverse effects of historical acidic deposition. In this article, information on patterns of acidic deposition, the effects of atmospheric deposition of sulfur and nitrogen on sensitive forest and freshwater resources, and the recovery that has resulted from controls on emissions of air pollutants is synthesized. A brief summary of the effects of acidification on marine environments is also presented.