An assessment of the ecological effects of acidic deposition

Abstract

Research on the ecological effects of acidic deposition has yielded information that currently permits a partial assessment of these effects. Establishing a relationship between deposition of acidity and ecological effects is a difficult, lengthy process; the complexity of ecosystems requires an integrated mechanism-level approach in order to obtain quantitative and predictive information. Known ecological effects of acidic deposition appear in surface waters and probably forest eco-systems in eastern North America, northern, and central Europe. Almost all documented anthropogenically acidified surface waters in North America occur in the Adirondack Mountains. The effect of anthropogenic acidification on fish, expressed regionally, seems to be small compared to the total resource at risk. The current rate of acidification of surface water in North America appears to be slow. Acidification of surface water is temporarily reversed with addition of CaCO3. Fish tend to have higher Hg body burdens at lower pH of ambient water. Vertebrates other than fish and amphibians have not been affected by acidification, with the possible exception of local populations of piscivores and insectivores. Some lakes are apparently culturally acidified in southern Scandinavia and southern Scotland, but the limitations of the data restrict assessments. Forest decline is a widespread natural process that may be exacerbated by air pollution. Acidic deposition may contribute to forest decline by interaction with ozone and by the leaching of nutrients from soil. In North America, high elevation red spruce is in an unexplained decline to which both ozone and acidic deposition may be contributing. Acidic deposition may be exerting some unmeasured effect on forest decline in Germany by the further leaching of nutrient deficient soils. Extensive experimental work has failed to disclose unambiguous effects of acidic deposition on crops.