Bog Breath: Sleeper Factor in Global Warming?

Article excerpt

The vast northern peatlands do a good job of storing carbon, but the stuff they burp up may be an even more noxious player in the greenhouse equation.

Call it a sign of the times. Twelve years ago, NASA asked researchers at the USDA Forest Service's North Central Forest Experiment Station in Minnesota if it could sample the air above their bogs and peatland forests. NASA was curious about the cocktail of gases that peatlands inhale and exhale as plants grow and decay. Something about these gases, the space agency believed, would help researchers understand the atmosphere on distant planets such as Mars.

In 1985, NASA returned to the Marcell Experimental Forest, even more eager to know about bog breath. This time the space agency didn't mention extraterrestrial air. It was far more concerned about the changing atmosphere on the third planet from the sun, the life-friendly one we call home.

A growing segment of the scientific community would now echo NASA's concern. Carbon dioxide, the renowned greenhouse gas released by burning fossil fuels, has increased 13 percent since 1959. Many scientists believe its heat-trapping qualities may be causing global temperatures to change. Those of us in the forestry community are well aware of the role forests play in the global-warming debate. We know that tropical rainforests, for instance, provide a sink for carbon (carbon dioxide is turned into plant bodies), which in turn helps regulate the earth's temperature.

But tropical forests are only one player in the carbon shell game. A potentially more influential player that gets a lot less press is peatlands. To many people, these mysterious quaking mats, dotted with carnivorous plants, elfin shrubs, and incredibly tough trees, are little more than an asterisk in the earth's roster of habitats. They are throwbacks to a time when wilderness was forbidden - the edge of the map that warned "serpents lie here." Despite our disinterest, peatlands have been faithfully breathing for thousands of years, helping to keep the earth's composition of gases as regular as a top. What that has meant for us is just now beginning to come clear, thanks in part to a group of Forest Service scientists whose careers revolve around bogs.

THE BOG-TROTTERS

"Most people don't realize how extensive northern peatlands are," says Dr. Elon "Sandy" Verry, lead scientist at North Central's Water Quality Research Project. "We're talking about 500 million hectares (one hectare equals 2.4 acres) of the globe, a wide band that stretches through Siberia, Alaska, Canada, and across the Scandinavian countries. Peatlands represent up to half of the land base in northern latitudes, and contain up to a third of all the soil carbon in the world. There's no doubt bogs will play a part in the greenhouse effect - the question is, will they alleviate or aggravate global warming? That's what we want to find out."

Sandy Verry doesn't fit the 1950s stereotype of the white-coated laboratory scientist. In a polo shirt and jeans, he reminds me of the slow-talking, canny ranchers I know in Montana. Like them, he has a quiet wit, an encyclopedic knowledge, and a way of explaining the world so that anyone leaning against the fence with him can understand.

The story he shares with me is the cutting edge of what is known about bog habitats, much of it discovered by him and his colleagues at the Marcell Experimental Forest. For 20-odd years, Verry has explored how peatlands relate to surrounding watersheds, and how activities like forestry might affect those relationships. His studies have recently been used to write Minnesota's Best Management Practices for forest harvest in wetlands. Now he's completing the picture by studying how peatlands in Marcell's Experimental Forest interact with the atmosphere. He is joined by scientists from around the world who are equally fascinated by earth's equilibriators. The picture emerging from their papers is a good news/bad news story.

GOOD NEWS AND BAD NEWS

Verry explained it to me this way: In the cold, water-logged belly of a bog, plant decay - a job for living microbes - proceeds very slowly. That's good news for the atmosphere. The bog snatches carbon from the air, traps it in green plants, and then buries it for a long, long time. The bad news is that these cold, wet conditions spell paradise for microbes that emit methane, an even more serious greenhouse gas.

Methane, a.k.a. swampgas, is a compound to be reckoned with. Like carbon dioxide, it traps heat and reflects it back to earth's surface, acting like the sealed panes of a greenhouse. Methane makes a mightier seal than carbon dioxide, however, trapping 25 times more heat. In fact, although methane occurs in the atmosphere at 1/200th the quantities of carbon dioxide, scientists estimate that this more virulent gas may have caused 12 percent of the global warming over the last decade. And what is suspected to be the single largest source of methane? None other than the world's wetlands and their methane-breathing microbes.

"If nature was left to her own devices," Verry says, "the methane bubbling up from peatlands wouldn't be a problem. There are plenty of carbon sinks and sources that would balance out the equation. The problem is that humans have added methane to the atmosphere in unnatural concentrations, and now the finely balanced scale is surfing to tip."

Though you don't hear much about it, methane in the atmosphere is increasing at a rate of 1 percent a year, double the increase in carbon dioxide. Human sources of methane are partly to blame, as is the fact that the atmospheric defuser of methane - the hydroxyl radical - is in short supply because of ozone depletion. Activities that release methane include rice-paddy agriculture, waste treatment, biomass burning, venting during coal and natural gas exploration, and, most especially, livestock production. Each and every cow belching contentedly in a field launches more methane into the air each day, the waste product of bacteria that live in the cow's gut, breaking down the cellulose.

Strangely enough, though scientists have studied the methane emission of cows, we can't yet quote a figure for bogs. Part of the problem is the enormous variability in methane production from site to site, season to season, even day to day. In fact, when global-climate-change models were being developed in the late 1980s, peatlands were not factored in because of this lack of consensus. Sandy Verry is determined to change that.

"We're now soliciting representative peatland hydrology data from 15 sites around the world," he says, "and hopefully we'll be able to create models that will estimate average methane loss from bogs. Once we get a handle on methane emission, we can ask what effect it might have on global warming."

The next question Verry poses is even more ominous. As the world becomes wetter or drier, hotter or cooler, might the amount of methane emitted by peatlands change? Might warming or cooling cause wetlands to release even more methane than normal? Is there a chance the process is already feeding on itself?

RESEARCH PORTAL

Marcell Experimental Forest is an ideal place to probe for answers. It's 200 miles north of Minneapolis, Minnesota, where the boreal peatland ecosystem dips into the U.S. and makes its final southern stand. When glaciers melted from this landscape 10,000 years ago, they left shallow depressions that eventually filled with bog vegetation - sphagnum mosses, heath-like shrubs, and black spruces and tamaracks. Because cold air tends to settle in bog hollows, these arctic dwellers could survive long after their counterparts had migrated north with the retreating glaciers. But being this far south also left them vulnerable. As Verry says, "Boreal peatlands in Minnesota are already pushing the envelope of what they can endure temperature-wise. In a way, the bogs on the Marcell are like miners' canaries. They'll be the first affected by global warming, showing us what might happen to the southern fringe of the vast peatlands farther north."

Another part of Marcell Experiment Forest's allure is its rich legacy of baseline data. Ever since its establishment in 1960, researchers have been collecting information about the geology, biology, and hydrology of peatlands, making Marcell a senior partner in the study of wetlands. The 2,200-acre mix of open bogs and forests is owned by the U.S. Forest Service, Minnesota Department of Natural Resources, Itasca County, and a private landowner. All research is administered by North Central Forest Experiment Station, one of 10 regional stations in the Forest Service's research arm. A wide range of monitoring, trial, and hypothesis-testing studies have gained Marcellites a worldwide reputation, as well as kudos from their local national forests. "The Water Quality Project findings help us manage upland forests in a way that protects lowland peatlands," says Steve Eubanks, who supervises Chippewa National Forest, where the map shows 50 percent lakes and wetlands. "We're lucky to have the leaders in bog research living right next door."

Verry and his team cooperate with a host of other groups including the National Atmospheric Deposition Program, universities both here and abroad, state agencies, the National Science Foundation, and NASA. Scientists are drawn to the site because so many of the studies are long-term, a rare treasure in an era when evaporating budgets cut studies short. "Marcel has 34 years of baseline information to compare our results against, and that lends more meaning to the data we're collecting now," says one cooperator.

SIX HOURS IN A BOG

Much of the data gathered at Marcell can't be collected by satellite cameras or weather balloons - it must be logged in by hand. When it came to conducting the world's first full-year studies of methane loss, Dr. Nancy Dise and, later, Dr. Sandy Verry and an assortment of technicians took turns monitoring between eight and 24 recording stations in Marcell's peatland. They spent six hours a day drawing gas samples with a syringe, even in the heart of a character-building Minnesota winter. Every one of them built a special relationship with their bog.

"Bogs have an eerie beauty," says Doug Meade, the research technician who currently spends two days a week sampling the bog breath. Even on the sunniest morning, the Bog Lake bog is usually cloaked in a wooly fog that stubbornly lingers, stilling the air and blanketing sounds. Meade plunges in around 7:30 a.m., taking his place on a small wooden platform for the first sampling. Later, when the fog lifts, he is treated to hundreds of glittering spider webs, florescent green and crimson mosses, and a constantly changing soundtrack of wild calls. He sees indigo buntings, black bears, deer, and even a turkey vulture that circles by occasionally "to see if I'm still alive." The show is enough to make a researcher's mind wander, Doug admits, but not for long. Every four minutes, he syringes 60 milliliters of air out of a "chamber" - an aluminum box turned upside down on the bog surface to capture its exhalations. He takes five samples, then rotates to a new spot in the bog. Back at the lab, he'll expose the 40 samples to a gas chromatograph, giving the concentration of methane at various times throughout the day.

These measurements are cross-checked with exotic laser "sniffers" and air-sensing devices called eddy correlation systems. Data is gathered under different nutrient conditions, water-table depths, temperatures, times of day, and during all four seasons. Soil temperatures are always recorded, and at the end of the season, researchers trim a season's worth of moss that has grown in each chamber to gauge how much biomass (carbon) the bog has cached.

The Water Quality Project uses this data to zero in on the key factors that affect methane "flux" - the milligrams of methane released per square meter of bog per day. In between peatlands, they found the water table plays a role in how much methane bubbles up. In peatlands themselves, however, the temperature turned out to be the No. 1 determinant, accounting for 80 percent of the variation in emissions.

"Methane counts really soar when the bog is cooking," says Doug Meade. The reason? "Microbes like it warm."

THE INVISIBLE HAND

The real behind-the-scenes stars of bog breath are tiny single-celled microbes swarming in numbers as dense as 23 million per gram of peatland soil. In the oxygen-starved zone, microbes that can live without oxygen systematically (albeit slowly) break down peat for energy and carbon, releasing methane as waste. The gas bubbles easily through the water, but before it hits the air it has a tougher gauntlet to run. The scientists call it the acrotlem.

The acrotlem, or aerated top layer of a bog, is like a drier sponge laying atop a soaking sponge - that's why you're likely to trust a footfall and be surprised when your boot comes up dripping. This drier, live-plant zone is more like the litter layer in your garden - it is home to microbes that break down plant matter by using oxygen. It is also home to bacteria that use methane as a source of carbon and energy. They welcome the methane bubbling up from below, and if there are enough of them, they'll gobble it all up before it can escape into the atmosphere. These methane gobblers are like gatekeepers, deciding via their appetites how much methane gets through. As such, they are as important to the mystery of methane flux as the methane-generating microbes.

Because these methane gobblers need oxygen, they can't live in saturated conditions. That makes water-table level the second most important factor affecting methane flux. When water is high, the acrotlem becomes wet, and there is not enough methane consumption to keep up with the supply. Much of it sneaks by. When the water table drops, the oxygen-loving microbes flourish, and less methane sneaks by. This phenomenon explains why less methane comes from high, dry hummocks than from soggy hollows in the bog.

As you can see, the seesaw relationships of methane, temperature, and water table are far from straightforward. Talk to bog researchers long enough, and you'll begin to admire their doggedness. The riddle they're solving is convoluted, and complicating factors keep cropping up. After all the experimenting, the clearest harbinger of future methane emissions still seems to be temperature change. What do Marcell scientists predict for their backyard bogs? As you might have guessed, it's not exactly good news.

PREDICTIONS FOR THE FUTURE

The global-climate-change models call for Minnesota to be 5 degrees Fahrenheit warmer and somewhat wetter in the coming years. According to Verry's models, the warmer soil temperatures and longer growing season will increase bacterial metabolism and perhaps allow the methane generators to increase in number as well. Because the water table will remain steady, the methane consumers won't have room to multiply or gobble up the excess. "We expect to see as much as a 50 percent increase in methane evolution," says Verry.

Already, methane is released in Minnesota at much higher rates than farther north (the annual average flux there is 140 milligrams/square meter/day, versus a flux of only 50 at a Hudson Bay site). In part that's because Minnesota is already racking up warmer temperatures. The problem with gases like methane is that they are self-reinforcing: They warm the atmosphere, which causes some bogs to produce more methane, which warms the atmosphere. To use an inappropriate metaphor, the process snowballs.

SO WHAT'S AN INDUSTRIAL SOCIETY TO DO?

I hesitated before asking what I knew would be a trick question. "The answer to the methane problem seems too easy," I said. "If a lower water table means less methane, why not drain peatlands?" Sandy Verry smiled his slow smile, as if he'd been asked this before. "Sure, you might do away with methane. But when the peat dries out, all that carbon is free to decay in the oxygen-rich environment. Dried-out peat is essentially a fossil fuel, and the microbes that burn it through oxidation will release carbon dioxide. And, remember, there's six to seven feet waiting to decay in the average peat bog. That's a lot bigger stash than you would find on most forest floors, where there's only three to four inches of organic soil."

But won't plants grow on the drained site and begin to remove carbon from the air? "Yes and no," says Verry. "Plant growth on the site may absorb some carbon, but usually not enough to compensate for the decay process. Trees make the best carbon sinks, but if the water level drops below a certain point, even trees won't grow. Responsible drainage requires vigilance to keep the water table within 24 to 18 inches of the surface."

Besides, he reminds me, we need peatlands just as they are. Peatlands control flooding, filter water, buffer lakes from acid rain, provide nurseries and feeding stations for wildlife, and, of course, sequester all that carbon. The years of undecayed remains, piling up like moldy blankets, are potentially more important to the carbon cycle than are tropical rainforests. Peatlands are so influential, in fact, that Minnesota recently passed a Wetland Conservation Act of 1991 that would make it imperative to replace acre-for-acre any wetland destroyed by development or draining: a no-net-loss policy.

The real answer, says Verry, is to reduce our dependence on fossil fuels and to curtail activities that upset the natural balance of atmospheric gases. After all, if you don't like the temperature, it doesn't help to yank the thermostat from the wall.

Thankfully, nothing so draconian has been attempted to solve the methane dilemma. But peatlands are being systematically drained and harvested for other reasons. For instance, we vacuum up thousands of acres each year to condition the soil in our gardens. (Recently, however, fears of losing the last of England's bogs have many gardeners boycotting agricultural peat and looking for substitutes.) We also use peat for fuel, filtration material, and absorbant for oil spills; we process it to produce carbon, coke, ethyl alcohol, tars, and waxes.

Peatlands are equally prized for what they might become after draining. Finland, where peatlands comprise half the country, has already converted half of its bogs to forestry and agriculture. Peatlands sometimes are flooded instead of drained, as thousands of acres have been in Canada - part of the giant hydroelectric project in St. James Bay. When drained or flooded, peat-lands function differently, and we need to monitor their reactions closely. Protection for peatlands is good news. Since these irreplaceable systems took thousands of years to form and reach maturity, we might be wise to view them as laboratories for the likes of Sandy Verry, Nancy Dise, and Doug Meade. We don't yet know all the roles that bogs play in making life possible on our planet. What we do know is that they have been here for at least 10,000 years, and in that time, atmospheric gases have enjoyed a steady state, making life possible.

"Destroying bogs and other wetlands is akin to deflating Earth's lungs," says Professor Eville Gorham, a peatlands expert at the University of Minnesota. "Until we understand them better, we tamper with them at our peril."

JANINE BENYUS is a Montana-based writer employed by the USDA Forest Service's North Central Forest Experiment Station. Her books include The Field Guide to Wildlife Habitats (Eastern and Western U.S. editions) and Watcher's Guide to How Animals Act and Why.

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