Southeast waterways will face an acid test.

Southeast waterways will face an acid test

Strengthened U.S. acid-rain controls proposed last June (SN: 6/17/89, p. 375) may prevent further degradation of Northeast lakes and streams, but they appear unlikely to improve conditions significantly in the Northeast waterways now suffering most from acid rain, a new study suggests. Instead, the findings indicate such controls could offer the biggest benefit to Southeast waters currently headed for serious acidification.

EPA researchers in Corvallis, Ore., used three computer models to forecast changes in soil and water chemistry. All three models indicated that if current rates of sulfate emissions continue over the next 50 years, Northeast waterways -- currently the most acidified by rain -- will at most worsen slightly.

"This sort of surprised us," says Chemist M. Robbins Church, who directed the study. It appears acid fallout has already stripped most Northeast soils of their beneficial capacity to sequester sulfates deposited by rain and snow, he explains. In effect, he says, much of the damage possible in this region "has apparently already occurred."

The damage may also prove difficult to reverse. When the computer models cut sulfate deposition rates 30 percent, suface-water sulfate levels fell about 36 percent. However, beneficial increases in the water's acid-neutralizing capacity -- which is more closely related to their pH and their life-sustaining capacity -- averaged only 7 percent area-wide, or about 10 microequivalents per liter. In the most acidic waters, the neutralizing capacity increased only half as much -- about 5 microequivalents per liter.

In the Blue Ridge mountains of the Carolinas, Tennessee and Georgia, where soils today retain about 75 percent of sulfates deposited by rain, EPA data suggest no streams have yet become chronically acidic and only three are vulnerable to fleeting episodes of damaging acidity. But the study predicts that if sulfate deposition continues at today's levels, it will saturate area soils, diminishing their ability to protect the streams.

Within 50 years, according to the new predictions, aquatic sulfate concentrations in the southern Blue Ridge will double, the number of waterways qualifying as acidic could climb from zero to about 130 (or 10 percent of those deemed vulnerable), and the number of streams susceptible to periodic acidification could increase from three to 203. Though the researchers have not yet forecast the effects of decreasing sulfate depositions, Church says it appears that even 10 percent decreases in sulfate emissions will not halt the increasing acidification of these waters.