Vanished in the Haze

"I beheld with rapture and astonishment a sublimely awful scene of power and magnificence, a world of mountains piled upon mountains," proclaimed naturalist William Bartram on his first hike to the top of an Appalachian peak in 1776.

Unfortunately, 21^st century A.T. hikers are unlikely to see what Bartram saw. Clear mountain views from Springer to Katahdin are fast disappearing behind a noxious cloud.

"People come to the Smokies to view scenery and breathe the clean air," states Jim Renfro, air resource specialist for the Great Smoky Mountains National Park. "But those views are obscured ninety percent of the time by pollution. Air quality is unhealthy one out of three days in the summer. People notice the difference and get upset. The media call and ask, where did the mountains go?"

Air quality on the Appalachian Trail in 1999 was among the worst years ever, scientists report. During the summer, ozone pollution in the Smokies violated federal health standards on fifty-two days; skies were dirtier on the A.T. than in Washington, D.C. Visibility on some "clear" days was measured in feet instead of miles.

While the Smokies hold the record for the worst air quality of any national park, Virginia’s Shenandoah claims second prize. Annual average visibility there has shrunk from 93 miles to just 22 miles, obscuring long-views to the Washington Monument.

Northern skies are nearly as dirty. "From Mount Washington you should be able to see 130 miles," says Bruce Hill, Senior Staff Scientist for the Appalachian Mountain Club. "Last Memorial Day, one of the biggest hiking weekends, you could barely see to the valley below. The closest ridges looked like flat cardboard cutouts."

So what happened? Why have Bartram’s sublime scenes vanished in the haze?

Burning of fossil fuels—coal, oil and gas—causes most air pollution in the Appalachians. Increased auto traffic, a desire for bigger cars and cheap electricity has caught up to us.

Coal-fired power plants are a major offender, responsible for fifty-seven percent of all U.S. industrial pollution. A "grandfather clause" in the 1970 Clean Air Act exempted these outdated facilities from meeting tough new air standards. At the time, Congress assumed these Midwestern and Southern plants would eventually close. Instead, utility companies kept operating and repairing them to avoid costly emission controls. From 1992 to 1997, the amount of electricity made by coal-burning plants jumped sixteen percent, pumping 755,000 extra tons of smog into the air each year.

Every time we drive to the Trail, we also add to the noxious soup. Despite emission-reduced exhaust systems, nitrogen oxide levels from automobiles are expected to increase as cars get more numerous and Americans drive more miles. Even worse, sport utility vehicles (SUVs) and light trucks—some of the least efficient and most polluting vehicles on the road—now claim half of all auto sales.

The haze that is obscuring views all along the Appalachian Trail is just the visible symptom of the air pollution problem.

"What you see is what you breathe," notes Bruce Hill. Air pollution has been linked to respiratory illness, decreased lung function, and even premature death. It degrades soils and destroys plants. It kills lakes and streams. It is among the most serious problems plaguing the Appalachians – one about which scientists have yet to discern all the disturbing ramifications.

During the last half of the 20^th century, while volunteers labored to protect the Appalachian Trail corridor, the forest surrounding the path, and the earth and waters beneath it, were gradually poisoned by roughly 3000 human-made chemicals.

Three air pollutants have proven particularly troublesome to hikers and sensitive mountain ecosystems. Sulfates and nitrates produce acid rain, while ozone (an invisible airborne "bleach") adversely affects breathing and kills foliage.

The acid rain alarm was first sounded in the 1980s when scientists realized that tiny sulfate particles were being blown hundreds of miles east on winds from Midwestern power plants. The particles, chemically changed into sulfuric acid, were blamed for killing Adirondack Mountain lakes and ponds.

"The same sulfate particulates that obscure views also form acid rain in clouds," Bruce Hill says.

Natural rainwater should only be slightly acidic, with a pH of 5.3. But in the White Mountains, explains Hill, clouds can be as acidic as vinegar, with pH levels of 2.5 or 3.0. In the Smokies, a cloud pH of 1.9 has been recorded. It’s important to understand that the pH scale is logarithmic: a pH of 4.3 is ten times more acidic than normal precipitation. A pH of 3.3 is a hundred times more acidic than normal.

Acid rain has contributed significantly to the die-back of high altitude red spruce in Northern forests. In Vermont, on Camel’s Hump, fifty percent of red spruce trees are dead. In the southern Appalachians, where ninety percent of Frazer firs have died, scientists argue over the role acidification plays in the demise. While invasive insects finished off the trees, many suspect that acid rain weakened them.

Outcry over acid rain led the U.S. Congress to strengthen the Clean Air Act in 1990. Sulfur emissions have dropped twenty-five percent nationwide since then. But, they’ve increased in parts of the South where some Tennessee Valley power plants still belch sulfur dioxide. In New England, on Mount Washington, pH levels have stayed about the same since the mid-1980s.

In the last five years, scientists learned that the acid rain puzzle was more complex than first believed. While sulfates were thought to be the chief agent of acid rain, it’s now known that nitrogen oxides (NOx) – emitted from smokestacks and autos – play a huge role.

"Until recently, scientists thought increased nitrogen was beneficial to plants," explains Orie Loucks, an ecologist at Ohio’s Miami University. "Farmers typically add nitrogen to soils to spur growth." But, Loucks says, there comes a point when nitrogen saturation of soils threatens vegetation.

Nitrogen oxide—converted to nitric acid in the atmosphere—falls as acid rain and bonds with the earth’s natural calcium and magnesium. It flushes these vital nutrients out of soils, denying them to plants. The acid also leaches aluminum from rock and soil. Toxic aluminum destroys root hairs; it prevents trees from absorbing water and minerals.

Trees weakened by acid rain may be more prone to blowdown, insect and disease damage. Loucks contends that nitrogen saturation and leaching of bases causes increased limb breakage and tree snap-off. "Less calcium means weaker cell walls, which means weaker wood," Loucks argues. "For trees, it’s like having a pack-a-day cigarette habit for fifty years." The degradation is gradual, cumulative and eventually fatal. In time, it may cause Appalachian Mountain forests to come crashing down around our ears.

Some long-time Appalachian Trail maintainers feel that Trail-blocking blowdowns are already increasing. Bob Proudman, ATC Director of Trail Management Programs, worries about a recent rise in "hazard tree" incidents—the number of trees reported to have fallen on lean-tos, bridges, and even hikers. While such anecdotal evidence can’t be tied directly to acid rain, Orie Loucks agrees that severe damage to sugar maples during New England’s devastating 1998 ice storm may have been intensified by pollution-sapped trees.

The loss of soil nutrients and a lack of forest growth were conclusively linked to acid rain in 1996 at New Hampshire’s Hubbard Brook Experimental Forest. Investigators studied three decades of data. They found that the annual accumulation rate of forest biomass—the total plant material added to the forest—dropped to zero in 1987 and has remained static ever since.

"The hypothesis is that when nitrogen depletes soils, overall biomass stops increasing," explains Bruce Hill. "In a sense, the forest stops growing."

Acid deposition also diminishes the number of organisms which help decompose organic matter, so plant nutrients stay locked in unrotted leaf litter. "At a pH of 6.0, soils are rich in earthworms," Loucks reports. "In soils acidified to a pH of 4.0 by pollutants, only one earthworm per square meter survives."

Hikers who are also anglers have reason to resent acid rain. The golden glint of native brook trout is disappearing from mountain streams. In the Adirondacks, where the problem was first detected, twenty-five percent of lakes and ponds no longer support life. Only fifty percent of Virginia’s 304 trout streams are now rated "not acidic," compared to eighty-two percent in pre-industrial times. If acid deposition levels stay the same, thirty-five percent of Virginia trout streams could be dead in forty years.

On summer days when visible haze is at its worst above the A.T., the invisible pollutant called ozone also peaks. "Ozone may be the eight-hundred pound gorilla no one notices," Loucks speculates. "While public attention has focused on acid rain, ozone is having extreme impacts on forest ecology."

Ground-level ozone (not to be confused with the high altitude "ozone hole" over the Antarctic) forms when NOx combines with natural atmospheric gases in the presence of heat and sunlight. Ozone acts like a powerful bleach: it discolors clothing, drapes, and wallpaper, and decomposes rubber. It hampers human breathing and kills plant cells.

A 1998 AMC study showed that ozone harms hikers. "On summer days in the White Mountains, the air gets dirtier the higher you climb," says Bruce Hill. "Air atop Mount Washington can be one-third dirtier than at its base." Small doses of ozone, even at levels below the national health standard, caused a two percent decline in normal lung function, and a seven to eight percent decline in asthmatic hikers.

"Smoky Mountain ridgetop monitoring stations have recorded the highest cumulative ozone levels in the Eastern U.S.," Jim Renfro adds. "On bad ozone days, people find themselves wheezing, or with scratchy throats."

At least hikers with pulmonary disease or asthma can stay indoors on bad ozone days. That’s a choice not open to vegetation. Ozone disrupts plant photosynthesis, producing ugly dark blotches of dead cells on foliage—an effect called "stippling." Some leaves are so injured they change color as early as June and drop off.

"We tested forty-six plant species and found that thirty showed symptoms," Renfro says. "In some test plots, ninety percent of trees exhibited visible injury." Black cherry, tuliptree, and sassafras are among the most sensitive plants. Sixty more plant species show ozone-like symptoms, he said, but funding cuts prevent researchers from being sure.

The full extent of ozone damage is unknown. Loucks suggests that reduced photosynthesis hinders the healthy growth of tree diameters and roots. He worries that since the plants produce fewer carbohydrates, they also generate fewer secondary metabolites, the defensive chemicals made by trees to inhibit insects and disease. Ozone may, in a sense, disable a plant’s immune system.

Representatives of the automobile and energy industries deny that air pollution harms people or trees. They say there is no smoking gun implicating acid rain and ozone in human or forest health impacts.

Bruce Hill disagrees.

"Air pollution is like AIDS in the forest," he counters. "Forest ecosystems are complex. So, determining precise cause and effect will always be difficult. But you can draw a strong connection between air pollution and forest decline."

"We need to recognize that we’re in the midst of a major forest health crisis," asserts Orie Loucks. "Some of my younger colleagues, who are in their forties, say that the tree growth we see today is normal, but I point out that they’ve never really seen a healthy forest." Loucks fears the gradual decline in ecological stability that he has observed and documented may continue leading down toward the edge of a cliff, beyond which forests will not recover.