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Assessing levels and trends of acidic deposition in Northeast

The northeastern part of the United States has been viewed as a region heavily affected by acidic deposition, and much of the impetus for the acid rain control sections of the 1990 Clean Air Act Amendments was the result of the acidification of lakes and forests in New York’s Adirondack Mountains. To follow up on this concern, scientists from several universities and federal agencies, including EPA’s Western Ecology Division, have published a current assessment on acidic deposition in the region. Effects of acidic deposition in the region include the acidification of soil and water, which stresses terrestrial and aquatic biota. Their report, in the March 2001 issue of the journal Bioscience, provides detailed answers to three critical questions: 1) What are the spatial patterns and temporal trends for emissions, precipitation concentrations, and deposition of anthropogenic sulfur, nitrogen and acidity across the northeastern U.S.? 2) What are the effects of acidic deposition on terrestrial and aquatic ecosystems in the area and how have these ecosystems responded to changes in emissions and deposition? 3) How do scientists expect emissions and deposition to change in the future, and how might ecosystems respond to these changes?

In related research, a WED scientist joined two colleagues from the Norwegian Institute for Water Research in an examination of trends in the acidification of surface waters in Europe and North America. In recent years, reductions in emissions have decreased atmospheric deposition of sulfur up to 50 percent, though deposition of nitrogen has remained almost constant. The scientists examined data from 98 surface water sites to test whether changes in deposition have resulted in recovery from acidification. Testing large-scale, regional trends found that all regions had highly significant downward trends in sulfate, the primary acidifying compound in fresh waters. However, nitrate concentrations show no regional patterns of change. The study found that all regions showed tendencies toward increased amounts of dissolved organic carbon. The scientists found the largest rates of recovery in the most acidic surface water sites. (Contact J.L. Stoddard, 541-754-4441; stoddard.john@epa.gov)

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