This article first appeared in the St. Louis Beacon, March 15, 2009 - Acid rain has all but disappeared from the headlines ... but not from the environment. The U.S. took action in the last century to reduce acid rain, but it remains a problem and a threat to the planet, says Gene Likens, founding director and president emeritus of the Cary Institute of Ecosystem Studies in Millbrook, NY.
Likens, the winner of the 2001 National Medal of Science for his work in ecology, has conducted more than four decades of field research in the White Mountains of New Hampshire and around the world. On Tuesday, March 17, he will discuss his work at the Missouri Botanical Garden. His lecture, "Acid Rain: An Unfinished Environmental Problem," will be held at 7:30 p.m. in the Garden's Shoenberg Auditorium.
Likens and his research team were the first to observe acid rain in North America in the 1960s and then link it to air pollution from burning fossil fuels. His work has influenced legislation like the Clean Air Act.
Off the Radar, but Still in Air
While global warming has dominated environmental news in recent years, Likens' research shows that acid deposition -- as rain, snow, sleet, hail, fog, and even dry dust particles -- continues to fall on our forests, lakes, streams, towns, and cities. Acid rain made a lot of news in the 1980's, a period Likens calls "the acid rain wars." Clean Air Act Amendments in 1990 did reduce pollution leading to acid rain. Reduce, Likens hastens to point out, not stop.
With this continuing problem in mind, Patrick Osborne, a freshwater biologist and executive director of the Whitney R. Harris World Ecology Center at the University of Missouri-St. Louis, helped bring Likens to St. Louis. According to Osborne, the issue of acid rain has fallen off the public radar. "And it shouldn't have done so," he said. "There is an opportunity to work on acid rain and climate change. The chemistry is very different, but the sources are the same." Sources like coal fired power plant emissions and automobile exhaust continue to drive both global warming and acid rain.
Nature's Antacid
Today's rain is less acidic than in the 1980s or 1990s. Low-sulfur coal, scrubbers on smokestacks, catalytic converters in cars, and other measures have reduced sulfur dioxide and nitrogen oxide emissions. Despite these improvements, the rain has not returned to natural levels of acidity and remains a threat to delicate ecosystems. In addition, soils continue the struggle to recover from damage already done -- especially in the northeastern United States.
"In terms of the chemistry, it took those soils literally thousands of years to develop," Likens said in a phone interview. Over the past 70 years, however, with the increased acidity of the rain, the soil has lost much of its ability to neutralize acids. Calcium and magnesium in soils help buffer the acids, but the acid rain itself has caused these minerals to leach out. "We've used up all the Tums and Rolaids in the system," Likens said.
The Experimental Forest
Nestled in the rolling, forested hills of New Hampshire's White Mountains, the Hubbard Brook Experimental Forest is devoted to ecological research and home of the Hubbard Brook Ecosystem Study, co-founded by Likens in 1963. Far from industrial factories and traffic jams, it seems an unlikely place to find damage from human pollution. But prevailing winds bring sulfur dioxide and nitrogen oxide gases from cars and from coal burning power plants (many in the Midwest).
These gases react with water vapor in the air and form sulfuric and nitric acids. These acids fall to earth's surface, acidify soils, lower the pH of rivers, lakes, and streams, and set off a cascade of events that endanger plant and animal life. Likens points to the plight of the sugar maple. "Sugar maple mortality is much higher than it should be if it weren't stressed by this pollution," he said. According to Likens, long term measures going back to 1965 show the forest is now in decline, halting its growth in 1982.
When forests stop growing, they stop sequestering carbon; when trees die, they emit carbon and carbon contributes to global warming. Acid rain and global warming are often thought of separately; but as Osborne observes, there are synergies between them. "If an organism is stressed from impacts of acid rain and you compound that through stresses from higher temperatures, the organism may succumb because the two are operating in tandem," he said.
Acid rain's effects are not limited to the natural world, damaging buildings, bridges, cars, and other man-made structures. Even though soils in the Midwest are not as sensitive as those in the Northeast, acid rain still does damage to lakes, streams, buildings, and human health. The particles that cause acid rain reduce visibility and can harm lungs.
Globe Trotting Scientists
Indeed, observing acid rain is easy. Revealing its cause was the challenge. After first measuring acid rain in the 1960s, Likens needed to show that it was more acidic than rain would be naturally. "What was it like before all these emissions?" Likens asked. To find out, he sought a baseline -- rain free of emissions from smokestacks and automobiles.
"My colleagues and I went to some of the most remote places on the planet to try to answer that question," said Likens. "We went to southern tip of Chile, the southern tip of Africa, an island in the middle of the Indian Ocean, a remote site in northern Australia, to find out what the background values were," he said.
In the end, "Acid rain is a pretty simple phenomenon," said Likens. "But it took us years to figure it all out." He will present information from long term studies on Tuesday evening. "Those long term records give us insights that we could not get any other way. It's compelling information to see what changes have occurred and what the trends are," he said.
Julia Evangelou Strait is a freelance science writer based in St. Louis. She has a master's degree in biomedical engineering and works in hospital epidemiology at BJC Healthcare.