Contributing to a Cleaner World

The Hubbard Brook Experimental Forest is home to the longest continually operating ecosystem study in the United States. In 1955, scientists began research on the 8,000-acre site in New Hampshire's White Mountain National Forest to figure out what makes a forest tick. NSF began funding research at the site in the 1960s; Hubbard Brook joined the LTER network in 1987.

The main research aim at Hubbard Brook is suitably large scale: by measuring all the chemical energy and nutrients that enter and leave this experimental site, researchers hope to learn what makes a forest, a forest.

"The approach we use is called the small watershed approach," says Charles Driscoll, an environmental engineer at Syracuse University in Syracuse, New York and a principal investigator for the Hubbard Brook LTER. A watershed is the whole area drained by a particular stream and its tributaries. The watersheds at Hubbard Brook span mountain valleys from ridgeline to ridgeline, encompassing the hillsides and the tributaries that drain into the streams on the valley floor. Researchers learn about the effects of both human and natural disturbances by measuring and comparing the transport of materials, such as water and nutrients, in and out of different watersheds.

The small watershed approach at Hubbard Brook has proven crucial to understanding the effects of acid rain. The term "acid rain" describes precipitation of any kind that contains acids, largely sulfuric and nitric acids. Natural processes release sulfur and nitrogen compounds into the air, where they react with water vapor to form acids. By burning gasoline, coal, and oil, humans are responsible for releasing even greater amounts of sulfur and nitrogen compounds, creating snow and rain that can carry life-stunting levels of acids into waterways and forests. By the 1970s, numerous lakes and streams in the heavily industrialized northern hemisphere became inhospitable to fish and other organisms. The link to forest degradation has been harder to prove, but in Europe people have coined a new word—Waldsterben—to describe the kind of "forest death" thought to be caused by too much acid rain.

Acid rain in North America was first documented in 1972 by Gene E. Likens, F. Herbert Bormann, and Noye M. Johnson at Hubbard Brook. Because Hubbard Brook researchers using the small watershed approach had long been monitoring the quality, not just quantity, of precipitation, they could tell that rainwater wasn't quite what it used to be and that the acid problem was getting worse. Their work was important in the establishment of the National Acid Precipitation Assessment Program and the passage of the landmark Clean Air Act Amendments in 1990, which mandated reductions in sulfur dioxide emissions from power plants.

Although precipitation over the U.S. is not quite as acidic as it was in 1972, forests are still showing worrisome signs of decline. A 1996 Hubbard Brook study determined at least one reason why: Acid rain ravages the soil's ability to support plant life.

"A lot of people thought that acid rain changes surface waters, but not the soil," says Likens, director of the Institute of Ecosystem Studies in Millbrook, New York, and lead author of the 1996 Hubbard Brook study. "This was one of the first studies to clearly demonstrate the substantial effects of acid rain on soil."

As it turned out, numerous minerals essential to life, including calcium and magnesium, dissolve more readily in highly acidic water. Thirty years of Hubbard Brook data on the chemical composition of soil, rain and stream water showed that acid rain was and is seriously leaching calcium and magnesium from the forest soil—as rain falls, it reacts with soil minerals and washes them into the streams.

Can anything be done to bolster the soil's resistance to acid rain? In 1999, Hubbard Brook researchers set out to address this question by sending up helicopters to drop a load of calcium pellets on a thirty-acre watershed that, like the rest of the forest, has been depleted of calcium over the years.

"We're going to look at the trees, the herbaceous plants, how salamanders respond, how microbes respond, and how aquatic organisms respond," Driscoll says. In a few years, the researchers may be able to report whether calcium enrichment shows any signs of helping to restore damaged soil. Such a finding would be welcome news to New Englanders in the tourism and maple sugar industries, where concern is high about whether calcium levels in the soil have something to do with the notable decline in the region's sugar maple trees. A full understanding of calcium's role in the environment will take longer. That's why Driscoll says the new study—like most Hubbard Brook studies—will continue "not just for a few months, but for fifty years."