Acid/dirt/rocks/fish

By Alex Danoff

On an autumn day, the leaves of trees in the deciduous forests of Shenandoah National Park are brilliant shades of amber and burgundy. Yellow poplars, red oaks and sugar maples, among many other varieties of trees, cover the landscape of the park.

In the valleys below, streams run through the dense foliage like arteries. Beneath the clear waters swim the copper and cobalt speckled native brook trout. These fish, one of the region's most popular species, represent an important role in both the natural ecology and recreational activity in Shenandoah.

"Brook trout is a major player in our streams," said Rolf Gubler, biologist for the park. "A lot of people come to fish for brook trout."

But because of acid deposition from air pollution and acid rain, the habitats of these fish are unlikely to recover from previous damage, according to studies conducted by the Shenandoah Watershed Study (SWAS) program.

"The impact on aquatic life is such that some of the more acidic streams only have one or two species of fish in them at most," said Rick Webb, projects coordinator of SWAS.

"Acid rain" falls on mountain soils in the form of rain, snow, fog, and dry particles that include acid-forming sulfates and nitrates. Webb and other scientists at the University of Virginia program have been studying acid rain effects in the park since 1979. They have found that even if acid rain diminishes, mountain forest ecosystems will only improve very slowly.

Webb said numerous SWAS studies have shown that dramatic recovery in mountains across the central Appalachian region is unlikely because current laws do not provide enough regulation of air pollution. Soils have been damaged because acidic materials have leached the minerals that provide buffering capacity from the soils over time, he said. Soil in the South is especially susceptible to this process because it is highly absorbent and retains some of the sulfur that is deposited.

The sulfur has accumulated through acid rain, which is a product of sulfur dioxide emissions from power-generation facilities and manufacturing plants. Unpolluted rainfall tends to be anywhere from 5.0 to 5.6 on the pH scale, which ranges from 0, the most acidic, to 14, the most alkaline. But rainfall in the Shenandoah Valley, with a pH close to 4.6 or 4.7, is significantly more acidic than normal rainfall. This, predictably, leads to lower pH levels in nearby streams.

Many fish, such as rainbow trout and the fathead minnow, cannot survive in water with a pH lower than 5.5. Brook trout are one of the more resilient organisms, as they are able to survive in an environment with a pH as low as 4.5.

"They're relatively hardy when it comes to acidified streams," Gubler said. "They're able to exist at the 'five' pH level, whereas other species like rainbow trout are more susceptible to lower pHs."

But while brook trout can survive at relatively low pH levels, many of their food sources cannot. The species most at risk are invertebrates, and a decrease in invertebrate populations directly affects vertebrate species like amphibians and fish that depend on the invertebrates.

"As far as I'm concerned, acid deposition is one of those situations that is the most significant, the most damaging consequence of bad air because it has immediate impacts on the aquatic resources, starting at the bottom of the food chain," said Bill Wade, former superintendent of Shenandoah National Park.

"Changes in the pH in streams in the parks, for instance, materially change the populations of microscopic resources and then as you go up the food chain that affects every level. While brook trout themselves may be able to stand some narrow changes in the pH of the water that they're in, perhaps some of the organisms that they feed on can't."

It is not just the immediate effects of acid deposition, however, that lead to the pollution of water sources. In addition to the acid that reaches streams via rainfall and runoff, it also is absorbed into the surrounding soil, where it can remain for long periods of time. Wade said this is a bigger issue than current acid levels in watersheds because it has the potential to affect water quality in the years ahead.

"The more insidious problem is the fact that over time, acid rain changes the composition of the soils that are in the area and drain into the streams," Wade said. "Even in an ideal world, if we were able to stop acid rain from occurring tomorrow, the problem is that the soil composition has changed already so much that it's going to take years before that gets back to normal without some sort of manual attempt to change that. So the consequences of years of acid rain are going to be felt by the resources far into the future."

Part of a watershed's ability to withstand acid deposition has to do with the bedrock beneath the soil. In order to neutralize, or "buffer" the acid effectively, the bedrock must have high levels of alkaline and must "weather," or break down, relatively quickly. In Shenandoah, there are three different classes of bedrock, each with its distinct buffering abilities.

Siliclastic rock is mostly found in the southern regions of the park, and is the most susceptible to acidification because of its enduring properties. It does not break down easily and is thus less able to buffer acid. Granitic rock is found mostly in the northern sections of the park and is intermediate in alkaline levels and weathering ability. Basaltic rock is fairly evenly distributed throughout the park's boundaries and provides the best buffering of the three types because it deteriorates somewhat quickly and adds minerals to the water, which helps neutralize the acid.

Still, none of the park's three classes of bedrock are especially adept at buffering acid. Even basaltic rock cannot completely counteract the effects of continual acid rain on Shenandoah's watersheds. Because of this, additional measures are often necessary to protect the streams, said James Damron, president of the Thomas Jefferson Chapter of Trout Unlimited.

"There are ways of buffering [acid]," he said. "There are a couple of projects that have been done by Trout Unlimited where they've added limestone deposits to streams to help bolster the ability to ward it off. It's a short term repair but it keeps the watershed alive."

In the long term, the way to slow acidification would seem to be to get at the source of the pollution. Unfortunately, this is more difficult than it seems. Much of the polluted air that reaches Shenandoah is from Midwest and the Tennessee Valley, hundreds of miles away.

"While you can maybe control a little bit the coal fire generating plant that's built 25 or 35 miles from the boundary of Shenandoah, you have very little control or influence over what happens in the state of Tennessee or the state of North Carolina," Wade said. "When those sources have been there for 30, 40 or 50 years, it makes it even more complex. It's just not one of those issues that there are easy solutions for, unfortunately, and not a situation that's gonna be resolved any time in the near future."

Such changes take years, as evidence by the federal Clean Air Act, passed in 1970. Although the legislation has reduced sulfur emissions and decreased the rate of acidification, the soil has been damaged beyond simple restoration, Damron said.

"Since the Clean Air Act... emissions have been cut back to a certain extent and we've seen some changes in the amount of runoff and what's in it," he said. "But it's still there and it builds up and it's going to continue to run off."

Still, Damron said, he is encouraged by the progress made over the last few decades.

"I'm 45 years old, so I've been fishing a long time in these mountains," he said. "I think that [the streams] are healthier now than they've been in the past 20 to 30 years. Most of the streams in Shenandoah National Park, particularly on the east side, are pretty much as healthy as they can be, given the circumstances they've encountered over the past couple hundred years."

But Catharine Gilliam, Virginia Field Representative with the National Parks Conservation Association, said that despite relative progress, enforcement of the Clean Air Act has been considerably less aggressive in the last few years. Because of this, states have begun to pass their own state air pollution control laws. Gilliam stressed the importance of Virginia following suit and addressing pollution sources within the state.

"The misconception is that... in state sources are not a problem," she said. "But they're a huge problem and that misconception has made it harder to get greater controls in reduced emissions on the plants within the state... I think that the Virginia sources are significant enough that that is the greatest opportunity to reduce the pollution: To address the sources within Virginia."

Photo courtesy of SWAS. Graphics courtesy of Rolf Gubler.

Nationwide pH levels