—by Marilyn Davis and Tim Crosby

Peat bogs might conjure images of misty, swampy wastelands. But an SIUC biologist wants you to think of them as giant stores of carbon that can have a major impact—good or bad—on global temperature.

Dale Vitt, professor and chair of plant biology, has worked for more than 30 years in Canada, Siberia, and other places to understand what makes these ecosystems tick. With funding mostly from the National Science Foundation (NSF), he and longtime scientific collaborator R. Kelman Wieder, a Villanova University biologist, have studied peatland formation, nutrient cycling, and carbon storage—the latter a pressing issue in an age of global warming.

Peat bogs and related peat-forming wetlands called fens (precursors to bogs) are found over large expanses of the far north. They are great reservoirs of carbon. Peat, which has been used as fuel since prehistoric times, is about 50 percent carbon, and deposits can be many feet deep.

"About one-third of the world's soil carbon is in these northern peatlands," Vitt says. "If all of it were released, it would double the carbon dioxide in the atmosphere."

During photosynthesis, plants draw CO₂ from the air. The carbon gets tied up in plant biomass. When bacteria break down dead plant material, they release the carbon, again as CO₂. In most ecosystems decomposition keeps pace with plant growth.

Not so in peatlands. Bogs and fens develop when thick vegetation grows in a waterlogged area. The bacteria in this oxygen-depleted water work more sluggishly, and some of the dead plant matter, instead of decomposing, builds up as peat. Sphagnum mosses are the species key to peat formation. Most bogs also host trees—usually spruces, which have special fungi that help them wrest nutrients away from the moss.

Carbon dioxide acts as a "greenhouse" gas, holding in the planet's heat and warming the environment. Because of peatlands' ability to store carbon, they affect how much CO₂ is in the atmosphere. In the lingo of climate change, they are helpful carbon "sinks" because they take in more CO₂ than they emit.

But they are very sensitive to climate change, Vitt says. "Raising the temperature just a little bit or changing precipitation regimes just a little bit could change [the system]" from a sink to a carbon source.

Across vast areas of western Canada, bogs and fens make up 40 to 70 percent of the landscape, interspersed with forest. Wieder, Vitt, and their students have established dozens of field sites in northern Alberta to study peatlands—most recently, the effects of wildfires on bogs.

Hydrologically speaking, bogs are islands. Peat buildup raises them above their surroundings, so they get no water runoff from neighboring areas. All of their water and nutrients come from the air.

The peat in bogs therefore holds a record of atmospheric deposition over time, as well as vegetation changes over time. That enables the team to study how bogs respond to climate variability and how they recover from wildfire over years and decades.

Despite being wetlands, bogs can burn during the dry season. Over the long term—maybe every 100 or 200 years—a bog actually needs to burn in order to keep its trees from getting too dense and drying it out. But the carbon released by fire adds to the global warming problem. And climate change models predict bigger, more frequent, and more severe fires in Canada, says doctoral student Brian Benscoter, as well as a longer fire season.

Vitt notes that it's possible to calculate what's called a "fire return interval"—how often, on average, a given area will burn. Tiffany Bone, one of his undergraduate students, did a tree-ring study at 45 peat bogs in Alberta in 2004-05. The longest fire interval she found was less than 150 years. Peatlands started forming in North America thousands of years ago, but it appears that any given bog periodically burns and starts over, like a phoenix rising from the ashes.

"This is a much faster dynamic than anyone ever thought," Vitt says, "and climate change may make it even faster" by shortening fire return intervals.

"When fire goes through a peatland, it kills all the trees and most of the vegetation, and it burns off carbon that was stored [in the peat]," Vitt says. "But decomposition continues. So all of a sudden you're going from a carbon sink to a carbon source. As things start to regenerate, how long does it take this ecosystem to make up for what it lost? No one knew."

Benscoter, who holds a three-year STAR Fellowship from the Environmental Protection Agency to study post-fire peatland recovery, tackled this question by doing peat-core and other analyses.

"It takes between five and 10 years for the peatland to become a sink again, where it's taking in more carbon than it's letting out," he says. "But it takes more than 70 years for the original carbon [store] to get back to where it was before the fire."

That means extra carbon in the atmosphere for decades.

Benscoter has found that the lie of the land affects carbon release during wildfires. Bogs are an essentially flat landscape made up of small hummocks and hollows. The elevation difference is less than two feet. But as Benscoter explains, "That creates a gradient of distances from the water table, and different species of Sphagnum separate themselves along this gradient."

Hummocks, being higher, are drier. The Sphagnum species that can grow there form dense mats that hold water like a sponge. Wildfires, unless they're very severe, burn only the top of the moss on hummocks.

Hollows usually are watery, so their Sphagnum species don't need to be water-holding specialists. But during the dry season, hollows can dry out. In a fire, Benscoter found, they burn almost twice as much as hummocks do, releasing much more carbon. "The mosses just go up like a candle," he says. And hollows take longer to begin accumulating peat again.

What's the significance of the fire studies? If you know the rough ratio of hollows to hummocks in a bog, you can better estimate the carbon released by a fire and how long it will take the bog to recover. Such information will become increasingly important for scientists trying to model climate change and decision makers trying to put the brakes on global warming.

To aid their efforts, says Vitt, "We want the whole picture of what happens to peatlands post-fire."

Another threat to bogs is air pollution in the form of excess nitrogen. And since bogs are the only ecosystem to receive all of their nitrogen from the air, they offer a unique opportunity to "differentiate [the ecological effects] of what comes from the atmosphere and what comes from other sources," Vitt says.

To understand how the peatland system changes with more and more nitrogen, doctoral student Bin Xu is adding different levels of nitrogen to field plots. He's then tracing the movement of the nitrogen to see how it's used and where it's stored. He's also looking closely at shifts in microbial communities, since most plants other than mosses rely on microbes to make nutrients available to them.

Peat is full of nitrogen, yet peat bogs are considered nitrogen-limited environments. That's because the Sphagnum grabs the nitrogen and hoards it. Other plants, besides the spruces, can't get a foothold.

If extra nitrogen deposits onto a bog, perhaps from vehicle or power-plant emissions, the mosses will initially grow more. But eventually they reach a point where nitrogen leaches out of the moss.

"Once you pass the nitrogen limits for Sphagnum, nutrients become readily available [in the system]," Xu says. "That could change the microbial and plant communities, affecting ecosystem functioning."

When other plants get well established, says Vitt, "they overtop and shade the mosses, the Sphagnum dies, and the whole system breaks down."

What's the tipping point for a bog? The research team has determined that it's about 14 kilograms of nitrogen per hectare (roughly 2.5 acres). Western European nations that would like to restore their harvested peatlands are out of luck, because nitrogen deposition there is high. Fortunately, says Vitt, "We're not anywhere close to the limit in western Canada."

That could change, however. Underlying many of the bogs in Alberta are oil-rich sands, which are being intensively surface-mined. Mining not only destroys peatland, but its industrial and transportation processes emit nitrogen, which deposits on surrounding peatlands.

Wieder and Vitt have industry funding to monitor the effects of nitrogen, as well as to study how best to restore peatlands. Restoration is no simple matter, as doctoral student Rose Bloise can tell you. Simply creating a wetland in northern Canada is not going to net you a peatland down the road, her research shows.

"If we're going to re-create peatlands today, maybe we can learn some lessons from how they form naturally," Vitt says. "Rose's project has been to look at natural, undisturbed peatlands and marshes [non-peat-forming wetlands] and see how they got started.

"Of the 26 peatland sites she studied, it turns out that none started out as marshes. They started out as uplands; then the water table rose and saturated the surface soil."

Reclaiming a peatland, then, will take much more than "some water and a few cattails," Vitt says. It will take complicated reconstruction of the original hydrology and topography to make conditions favorable for peat formation.

To reach deeper deposits of oil-bearing sand, some companies are now using steam-injection wells. The potential for peatland restoration may be much better for these smaller sites. Vitt and Wieder just received a new industry grant to look at that issue. "The next [phase] of our project is to help oil companies develop methods to put in infrastructure that's less invasive than it's been in the past," Vitt says.

Pooling knowledge about peatlands is important if we're to preserve these ecosystems. Wieder and Vitt recently edited a book, Boreal Peatland Ecosystems (Springer, 2006), that gives a thorough overview of peatland characteristics and management. With an NSF Research Coordination Network grant, they have started a website called PEATNET to link together experts and provide scientific and financial resources. And another NSF grant to Vitt and Wieder helped fund efforts to coordinate U.S.-Russian research on Siberian peatlands.

Meanwhile, Vitt and his students are preparing for their next field trip to Alberta, where they'll expand the number of sites they're studying.

With so much carbon at stake, Vitt says, "We should think carefully about what we do with bogs."