Acid and Mercury Deposition Effects on Forest and Freshwater Aquatic Ecosystems

Acidic deposition is comprised of sulfuric and nitric acids and ammonium. Although released naturally to the atmosphere, humans greatly increase emissions of these compounds by the burning of fossil fuels and agricultural activities. Acidic deposition has impacted soils, forests, streams, and lakes in eastern North America, northern and central Europe, and southeastern China. Human activities have also increased atmospheric mercury deposition globally. Atmospheric deposition of ionic mercury can be converted to methyl mercury largely by bacteria that process sulfate. Methyl mercury bioaccumulates along aquatic and terrestrial food chains by a factor of a million to 10 million, resulting in exposure to humans and wildlife and potential health effects.