Poison from Above

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THE DRAMATIC DAMAGE

The impact that acid rains have on aquatic ecosystems can be dramatic . . . and those systems occurring in areas with granite, quartz, or similar rock are especially vulnerable. Such rocks — which have a low capacity to neutralize (or "buffer") the acidity — are widespread in the Appalachian and Rocky Mountains and throughout much of Canada, New England, and northern Europe. The lakes of southern Norway, for example, are in severe trouble. Populations of micro-organisms crucial to the lakes' economies have been altered, and fish populations have declined or disappeared.

The situation is especially critical in the Adirondacks. Not only are the rains acidifying the water there, but the sulfuric and nitric acids are causing chemical reactions in the soil that are releasing large quantities of aluminum. The acids accumulate in the snowpack in the winter. Then, when the snow melts in the spring, they pour into the lakes . . . creating a flush of aluminum pollution. As a result, all fish have been killed in some 300 Adirondack lakes, and brook trout and other sensitive species may have been exterminated over the whole area. (Spotted salamanders, for example, cannot breed in acid snowmelt.)

In Canada, scientists have now identified 48,000 lakes that will become sterile in 20 years or so if the acid rains continue. And — along with dams, overfishing, poaching, pesticides and other kinds of pollution — the rains threaten the economically valuable Atlantic salmon with extinction.

THE EFFECTS ON SOIL

While the most dramatic immediate effects of acid precipitation appear in ponds and lakes, it may seriously damage terrestrial ecosystems as well. The acids can apparently harm soil micro-organisms, including those that participate in the crucial nitrogen cycle. They also can influence the rates at which toxins are mobilized in the soil, and those — in turn — tend to worsen the effects of other pollutants.

At the moment we cannot give accurate estimates of the damage potential of acid rains. There is evidence, for example, that they are stunting forest growth (indeed, recently it has been claimed that much of Europe's woodland is already doomed). But it may be decades before the full impact of acidic precipitation on trees will be understood. Similarly, there's laboratory evidence that some lichens may be very sensitive to this pollutant from the skies, a situation that could portend serious changes in both arctic and alpine ecosystems.

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