Lichens may be canaries in the coal mine

For Linda Geiser, lichens record levels of nitrogen and acid rain in the Columbia River Gorge. (Steven Lane/The Columbian)

SEVEN-MILE HILL, Ore. — On a bluff overlooking The Dalles, Ore., and the east end of the Columbia River Gorge, Forest Service scientist Linda Geiser and two assistants climb out of their rig and set to work.

Geiser and graduate student Peter Nelson begin dismantling black plastic tubes called passive samplers that have gathered data on the nitrogen content of rain and fog at the site for the past three years.

Grad student Larissa Lasselle grabs two sample bags and heads downhill into a thicket of ponderosa pine and oak. Her job: to collect lichens from tree branches for laboratory analysis.

It was at this site that Geiser, a Forest Service ecologist, collected some of the first evidence that air pollution was damaging the gorge environment. The messenger — like a canary in a coal mine — was the community of lichens that grows here, both those that flourish and those that fail to thrive.

Lichens are neither plants nor animals. They belong to the fungi family, but are actually part fungus, part alga. They come in many shapes and colors, and reproduce both sexually and asexually. They can dissolve rock, survive severe cold, and remain dormant for long periods.

But for Geiser, their most useful characteristic is their sensitivity to nitrogen and acid rain, major forms of pollution in the gorge.

The Seven-Mile Hill site is 62 miles west of Portland General Electric’s Boardman, Ore., coal-fired plant, the largest source of nitrogen oxide and sulfur dioxide in the eastern gorge. Near the coal plant is a sprawling dairy feed lot, a major source of ammonia that contributes to acid rain and fog.

Together, those sources are responsible for most of the air pollution that blows west into the gorge during winter months.

In a nitrogen-rich environment like the Seven-Mile site, some lichens, including the crusty-appearing green-gold Xanthoria, thrive. But more sensitive lichens tend to grow slowly, in dense clusters.

In contrast, a healthy lichen in a low-nitrogen environment will leaf out in abundant lettuce-like layers or miniature branches.

Geiser’s chemical analysis has focused on four species that are moderately tolerant to nitrogen: Evernia prunastri (Oakmoss lichen), Hypogymnia inactiva, Letharia vulpin (Wolf lichen), and Platismatia glauca.

Geiser has recorded the abundance and health of those and other species at several sites in the gorge. Between 1993 and 2004, she and her assistants collected 20 grams each of the two most abundant species from each of 145 plots. Samples were sent to a University of Minnesota laboratory for analysis of their nitrogen and sulfur content.

The results set off alarms.

“Lichens indicating nitrogen-enriched environments were abundant,” Geiser wrote in a 2007 article published in the journal Environmental Pollution. “The atmospheric deposition levels detected likely threaten gorge ecosystems and cultural resources” such as Native American petroglyphs and pictographs rock art, she wrote.

Nitrogen levels were highest at the east and west ends of the gorge, indicating that both urban sources from the Portland-Vancouver area and agricultural and industrial sources from the Columbia Basin were contributing to the pollution. By far the most nitrogen-rich site was at Seven-Mile Hill.

“We’re sitting at the top of the hill,” Geiser said. “We have really good exposure to the whole gorge, and we’re at a high enough elevation that we get more fog.”

Prevailing winds funnel pollutants into the gorge mainly from the west in summer and from the east in winter. That’s one reason nitrogen and sulfur concentrations are two times higher in the gorge than in the surrounding national forests.

To the west, at a site north of Carson near the Wind River Canopy Crane, both the forest and the lichens are healthier. Lobaria oregana, also known as horse lettuce, which is plentiful in forests west of the Cascades, hangs from the branches of
Douglas firs and hemlocks. A nitrogen-fixing lichen, it’s an indicator of clean air.

A review of 12 years of federal air samples conducted for the Yakama Indian Nation confirmed that the Boardman coal plant is a major source of nitrogen and acid fog. The study, released in March, found that in November, when east winds push the air downstream along the Columbia River, the plant contributes 55.5 percent of the nitrogen measured at Wishram, in the east gorge.

Geiser said the Forest Service’s air quality managers decided to study lichens to give the agency more comprehensive coverage than it could get from its two permanent air monitoring sites, at Mount Zion in the west end of the gorge and at Wishram in the east.

“With the lichens, we were able to make a whole picture,” she said.

Recently, she has been gathering more data on nitrogen and acid fog levels at four of the lichen sites.

Passive collectors at the sites received rainwater and condensed fog, which flow into a resin tube and are filtered through gel ion exchange beads that record its chemical composition.

“We measured out in the open and under the canopy,” she said. “Once we put our samplers under the canopy, which is where the lichens are, we could experience what the soil is experiencing. That’s where we found the very highest levels.”

New data from the collectors will be integrated with what Geiser already knows about air pollution from her analysis of the lichens — when federal money is available to do the work.

Geiser began studying lichens in Southeast Alaska’s Tongass National Forest nearly 20 years ago.

A soil scientist by training, she knew nothing about lichens when she accepted a summer job that took her into the Alaska rainforest. “I just fell into it,” she said. “The lichens up there are so cool, such a diversity of colors and forms and habitats. They were just so vigorous and healthy.”

She went on to study with leading lichenologists in the United States and Canada.
Over the past 19 years, as a Forest Service ecologist, she has gathered and analyzed lichens at sites across the Northwest.

“One of our jobs is to determine whether there are ecological effects from pollution in the national forests,” she said. “We’re trying to make a connection between what’s in the air, what’s in the rainfall and what’s in the species.”