Acid assessment: the state of the science.

Acid assessment: The state of the science

Only 10 years ago, respected researchers contended that "there is no reason to state that pollutants in modern time are the chief reason for the acidification of surface waters," recalls Patricia M. Irving, associate director of the National Acid Precipitation Assessment Program (NAPAP). Since then, NAPAP has gathered ample evidence to the contrary. In a mammoth draft report unveiled last week, this $500 million federal program -- one of the largest research efforts in history -- concludes that the sulfur- and nitrogen-based air pollutants emitted during fossil-fuel combustion are indeed responsible for most of the acidification plaguing sensitive lakes and streams in the eastern United States.

While refuting those who once downplayed the problem, the new study also contradicts the doomsayers of a decade ago who predicted widespread collapse of aquatic and terrestrial ecosystems under assault from acid rain. NAPAP reports that only about 4 percent of the lakes sampled in the National Surface Water Survey -- the largest analysis to date of vulnerable U.S. waters--are acidic. In addition, the authors conclude that ambient levels of acidic precipitation in the United States are "not responsible for regional crop yield reductions" or for damage to "the vast majority" of North American forests.

NAPAP has "changed the way the world thinks about acid rain," says Michael R. Deland, chairman of the President's Council on Environmental Quality, which administers the interagency research program.

In 1980, President Carter created NAPAP as a 10-year program to study not only the causes and effects of acid deposition but also the best strategies for controlling iti(SN: 2/16/80, p.106). At an international NAPAP meeting in Hilton Head Island, S.C., last week, more than 600 scientists shared new findings and debated how well the draft report -- entitled "State of Science and State of Technology" and spanning more than 15,000 pages -- sums up what NAPAP scientists have learned.

Each book in the 28-volume series was anonymously peer-reviewed by at least three scientists before the meeting and by an identified reviewer at the conference. In general, critics deemed the study comprehensive and reasonably balanced. However, most also noted data gaps that leave several important questions unanswered. Among those questions: Which chemical constituents, whether in rain, snow, fog or dry particulates, have the greatest effect on the health of humans and other species? Which of the many new computer models of toxicology described in the report (and showcased for the first time at last week's meeting) best predict the effects of acids on aquatic species? And to what extent do brief but acute acidic episodes -- such as runoff of acid snowmelt -- reduce the species diversity of sensitive waters?

Because data collection and analysis financed through NAPAP will essentially shut down later this year, such questions will likely remain unanswered for many years to come. Some of the 1,000-plus researchers employed through NAPAP, especially the atmospheric modelers, may secure financing to continue their investigations through the rapidly growing and congressionally popular "global change" program (SN: 2/3/90, p.71), but most ecologists say they will be left high and dry when NAPAP's large aquatics programs wind to a close.

In general, the draft report concludes that:

* The average pH of precipitation in remote--and therefore relative pristine -- regions of the world is about 5 rather than 5.6 as scientists once assumed. Moreover, "no site anywhere in the world is at all times free from long-range transport of [human-generated acidifying] pollutants" -- a problem that complicates numerical comparisons with industrial areas. The NAPAP data do indicate, however, that in the United States the median annual concentrations of sulfates are generally eight times higher, nitrates 10 times higher and hydrogen ions four times higher than those in most remote regions. At the same time, the report shows that about seven times more acidneutralizing ammonium ions fall upon the United States than on most remote areas.

* As aquatic pH drops to a level of 6 to 6.5, sensitive fish species and other vulnerable organisms in the water begin to lose their ability to reproduce and survive. Below a pH of 5, the whole ecosystem may start falling apart, although some naturally acidic Florida lakes support diverse fish communities, including game fish, at a pH of 4 to 4.5. While the study did not determine how many U.S. lakes have been seriously impaired or killed by acid rain, new data from a survey sponsored by New York State and a consortium of electric utilities show that 23.5 percent of the 1,469 Adirondack lakes surveyed are "entirely fishless," reports aquatic ecologist Joan P. Baker, a Raleigh, N.C.-based consultant who both participated in the Adirondack study and coauthored the NAPAP report's aquatic biology volume. And in roughly one-third of these lakes, fishlessness appears due to acidic air pollutants, she says.

* North American forests are not suffering substantially from acid pollutants, according to the report, "with the possible and notable exception of high-elevation red spruce in the northern Appalachians." Data collected on these high-elevation stands over the past two years indicate that acid-mediated soil changes are fostering nutrient imbalances and a general weakening of red spruce -- changes similar to those now held responsible for European forest declines (SN: 7/22/89, p.56).

* Technologies have so improved that U.S. emissions standards for new fossilfueled power plants could be cut to just one-tenth the current standards and could be met by systems costing no more than those available in 1979, says former NAPAP Director J. Laurence Kulp of Federal Way, Wash.

Over the next few months, the authors of each volume will formally address their reviewers' criticisms and incorporate changes where warranted. The revised version of this encyclopedic series, due out this fall, should provide the scientific underpinnings for NAPAP's swan song -- a much shorter report now referred to only as the "integrated assessment." Due out by year's end, that final report is expected to include comparisons of the likely environmental and health impacts of more than 30 pollutantemissions scenarios of the future. The "integrated assessment" is intended to help policymakers choose among various levels or patterns of pollutant controls, including those proposed by President Bush last year in his clean air legislation (SN: 6/17/89, p.375).