Nature Section - Page E1
IMPACT OF ACID RAIN ON SOILS
by Staff Science Writers, The Daily Repubican OnLine NewspaperFRESNO - Agricultural soil research scientists have found that a New England forest whose soil chemistry has been subjected to acid rain fallout from automobile and factory air pollution contaminants has stopped growing nearly ten years ago and will probably be a long time in recovering.
The Ag science study of the impact of acid rain on American forest soil is part of a 10-year federal assessment of the problem concluded in 1990. The findings of the study failed to establish any clear evidence linking acid precipitation to any important harmful effect on forests.
Many Ag scientists argue, however,that the impact of changes in soil chemistry was not yet clear and that those changes would probably have long range damaging effects.
Ag science investigators have examined more than three decades of data from the Hubbard Brook Experimental Forest in the White Mountains of New Hampshire and discovered that increased acidity has deprived the soil of alkaline chemicals, mainly calcium, that are essential for plant growth. At the same time, they found that the annual rate of accumulation of forest biomass (its total plant material)dropped to nearly zero in 1987 and has remained there.
Finally, they discovered that the soil was recovering its calcium and other alkaline chemicals very slowly because precipitation contains about 80 percent less of them than it is estimated to have contained in 1950.
The alkaline chemicals, or cations, are leached from the soil by acid precipitation and carried away by streams. The precipitation contains sulfuric acid and nitric acid, produced by the burning of coal, oil and gasoline.
A major source of these chemicals raining down on the Northeast has been the sulfur dioxide and nitrogen oxides emitted by Midwestern power plants and borne eastward by prevailing winds; they form sulfuric acid and nitric acid when they mix with water.
Congress amended the Clean Air Act in 1990 in an effort to cut the emission of sulfur dioxide and nitrogen oxides in half by 2000. But the findings from the Hubbard Brook forest suggest that this will not be enough if forests are to recover any time soon, said Dr. Gene E. Likens, the leader of the study.
Likens, an ecologist, is the director of the Institute of Ecosystem Studies at Millbrook, N.Y., a nonprofit research and educational institution formerly associated with the New York Botanical Garden. The institute has been collecting a wide range of data since 1963 on the functioning of the Hubbard Brook forest, a 7,500-acre tract owned by the U.S. Forest Service.
It is one of only a few ecological research projects looking at ecosystem behavior over the long term, and it is probably the only one to come up with decades-long detailed measurements on the effects of acid rain on American forests.
The report of the new findings appears in the current issue of the journal Science. It was prepared by Likens, Dr. Charles T. Driscoll of Syracuse University and Donald C. Buso of the Millbrook institution.
"It's just a landmark paper," said Dr. David Schindler, a prominent acid-rain researcher at the University of Alberta in Edmonton, Canada. "Hubbard Brook has the only data set that's thorough enough and long enough to show this happening."
Until now, Schindler said, the idea that acid rain is harming deciduous forests has amounted to a "robust" hypothesis. The Hubbard Brook results are "the clincher," he said, adding: "I think there's concern for the whole northeastern United States and eastern Canada that this is occurring."
Some other researchers were more cautious. "The large majority of forests in the eastern U.S. seem to be growing quite well," said Dr. Jay S. Jacobson, a plant physiologist at the Boyce Thompson Institute at Cornell University.
While the Hubbard Brook results are suggestive, he said, other factors should be considered before reaching a firm conclusion on the effects of acid rain. These include the effects on forests of climatic changes and possible changes in the deposition of nitrogen, a critical forest nutrient.
Assuming that forests are recovering slowly, Jacobson said, "are we as a nation willing to accept slower growth of forests in order to avoid placing additional controls on emissions of pollutants?"
In their paper, the Millbrook researchers stopped short of asserting a firm cause-and-effect relationship between the depletion of cations in the soil and the slowing of forest growth. Pinpointing the cause of the slow growth, they wrote, "should become a major area of research." Likens said, "If indeed the forest has become limited in its growth by the disappearance of these base cations -- and I emphasize the 'if' -- then that's a very serious implication of these results."
Likens compared the action of acid rain in depleting the soil of cations with that of stomach acid eroding an antacid tablet. In the case of the Hubbard Brook forest's soils, he said, "it's like half the antacid has been eroded away, and you've only got half of it left." The continuing deposition of acid is making the system even less able to neutralize it. "The system is now very sensitive," he said.
The observed effects on soil chemistry were unexpected, Likens said, and neither those effects nor other data based on long-term observations were reflected in the 10-year federal study, the National Acid Precipitation Assessment Program. The study found that acid rain generally causes significant ecological damage, but not so much as originally feared.
Among other things, the study concluded that acid rain was harming aquatic life in about 10 percent of Eastern lakes and streams, that it was reducing the ability of red spruce trees at high altitudes to withstand the stress caused by cold and that it was contributing to the decline of sugar maples in some areas of eastern Canada. While forests otherwise appeared healthy, the study said, they could decline in future decades because of nutrient deficiencies brought on by acid rain.
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