FIGURE 9–5 Acidity of precipitation falling in the United States during June 1966. Source: Gene E.Likens, “Acid Precipitation,” Chemical and Engineering News, November 22, 1976, 54 (48):30.

maps in Figures 9–5 and 9–6 illustrate the increasing spread of the low-pH region over a period of some 15 years (1955–1972). These trends were confirmed in 1978.164

The ecological effects are greatest in waters that contain the least dissolved matter—waters that are poorly buffered. Thousands of lakes in southern Norway and Sweden have shown a decline in fish populations, associated with increased acidity of the water, in turn associated with acid precipitation. A similar trend has been reported for the Adirondack Mountain region. Effects on terrestrial systems have been more difficult to isolate unambiguously, perhaps because changes register less quickly. A recent report165 points out that as a result of acid precipitation, the forest-floor leaching mechanism in a New England coniferous ecosystem has changed from a carbonic-organic acid type to a mineral acid type, which may accelerate leaching and increase the concentrations of dissolved trace metals of potential toxicity. Damage to forests and sport fishing has been estimated at $100 million annually.166

Comparing various fuel cycles, it appears that the use of all fossil fuels involves some risk owing to the production of NO2, and the use of those containing sulfur (coal, oil) present an additional risk.

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