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			Ecological Effects of Acid Deposition Ecological Society of America 02.01.01 Base Nutrient Depletion: Acidification of soils causes the removal of nutrients (a process known as leaching) from terrestrial ecosystems. These nutrients, known as base cations, are critical in neutralizing acids. As forest soils lose nutrient cations, they become more vulnerable to further acidification and as a result, trees become more sensitive to disease and stress. An example of this occurs in western Pennsylvania where a high rate of sugar maple and red spruce mortality is blamed on the depletion of nutrient cations caused by chronic acidification. Aluminum Toxicity: The release of the heavy metal aluminum from the soil due to increased acid deposition can create unsuitable living conditions for many freshwater fish species. High concentrations and extensive exposure of lakes and streams to aluminum is a main symptom of systems suffering from chronic acidification. Nitrogen Saturation: Nitrogen saturation occurs when excessive additions of nitrogen overwhelm an ecosystems’ capacity to store nitrogen. Since nitrogen is a nutrient normally in limited supply in forest and estuarine ecosystems, the addition of large amounts of nitrogen from nitric acid deposition can have significant ecological effects. At first, increased nitrogen inputs may stimulate forest growth, but too much nitrogen in ecosystems overwhelms the holding capacity of these systems and eventually causes soil, forest, and aquatic ecosystem degradation. Eutrophication (nutrient enrichment): When nitric acid enters terrestrial and aquatic systems from the atmosphere, a portion of this added nitrogen eventually reaches coastal areas, with the potential to create eutrophic conditions. Increased inputs of anthropogenic (human) nitrogen have caused harmful impacts on coastal ecosystems that include hypoxia/anoxia (low oxygen levels), fish and shellfish kills, and changes in algal community composition. Biodiversity in coastal ecosystems can be greatly threatened under these ecologically stressed conditions.


			Prepared by the Ecological Society of America 1707 H Street NW, Suite 400 Washington, DC 20006 (202) 833-8773