VERMONT'S FOREST FLOORS SOAK UP MORE MERCURY

by John Dillon; Times Argus and Rutland Herald; March 21, 1999

The clouds that often frame the summit of Mount Mansfield are picturesque--and potentially toxic. Recent research shows that clouds hovering around Vermont's highest peak bathe the area in acidic moisture, poisonous mercury and other airborne pollution. Cloud water is substantially more acidic--matching the level of vinegar or lemon juice--and contains higher concentrations of pollutants than snow or rain, according to research conducted by Vermont Forest Ecosystem Monitoring, Inc., a long-term research project administered jointly by the University of Vermont, the state Agency of Natural Resources and the U.S. Forest Service. For seven years researchers have measured and followed the movement of mercury pollution falling on Mount Mansfield. The work is the nation's longest continuos mercury monitoring project and is aimed at answering key questions about mercury's impact on the forest and the food web. About 140 tons of the toxic metal are released in the United States by coal fired power plants, trash incinerators, large industrial boilers, cement plants and other sources. Mercury accumulates in the food chain and is a potent neurotoxin at very low concentrations; it is particularly dangerous to developing fetuses and young children. Relatively high mercury levels in fish have led 40 states, including Vermont, to warn pregnant and children to limit their consumption of certain fish.

Sen. Patrick Leahy, D-Vt., last week reintroduced legislation that would require a comprehensive national mercury control plan. As Leahy renewed efforts to curb mercury pollution, Vermont scientists were meeting to discuss their latest research into how mercury moves through the ecosystem.

From their work on Mount Mansfield, the researchers have learned that much of the mercury drifting down from the sky stays in the forest, trapped in leaves and forest soil. By measuring how much mercury enters from the atmosphere--around 444 milligrams per hectare per year--and comparing that amount with how much flowed from a small upland stream, the researchers learned that only about 10 percent of the mercury falling on the forest is exiting through stream water. Some also vaporizes back into the atmosphere, scientists found.

While it may be good news that much of the mercury is not flowing downstream into Lake Champlain, where it would add to the toxins already building up in fish, scientists don't know yet what impact the pollution is having on the forest itself.

"The bad news is we believe a significant amount (of mercury) is accumulating in the forest," said Tim Scherbatskoy, an assistant professor at UVM's School of Natural Resources and research director at the Vermont Forest Ecosystem Monitoring project.

Mercury cold affect tree roots, forest microorganisms, and other critters like worms and the birds and animals that eat them, he said. "Right now (mercury) appears to be exclusively an aquatic problem. It's also possible that it is a terrestrial problem. We don't know. Is it putting our forests at risk? I think that is a very valid question," he said. The Mount Mansfield research has also allowed scientists to estimate how much of the mercury in Lake Champlain falls directly into the lake, and how much enters from rivers and streams. Although the land mass that drains into the lake is 18 times larger than the lake itself, the forest filters the mercury and only about half the metal in the big lake comes from the land sources, said James Shanley, a researcher with the U.S. Geological Survey in Montpelier.

Shanley has sampled mercury levels in a small headwater stream on Mount Mansfield and found that while much of the mercury remains in the forest, the amount that eventually entered the stream varied greatly during the year. The spring snowmelt in April washed much higher levels of mercury from the saturated soil, he said. The next phase of the research may examine mercury that enters streams from agricultural lands, he said. "We think just by looking at the forest system, we may be missing some due to the run-off (from farm fields)," Shaney said. Meanwhile, anouther UVM researcher is looking at the concentration of mercury and acid rain in the clouds that often hug Mount Mansfield's summit.

The pH level of the cloud water was between 2.1 and 3.2, with pristine rainfall usually showing a pH of 5.6.(Acid rain in the Northeast has an average pH of 4.3). Mercury levels in the Mount Mansfield clouds ranged from 6.1 to 34.4 nanograms per liter, graduate student Sean Lawson's work showed.

Scherbatskoy said he wasn't surprised by the finding that the clouds on Mount Mansfield are acidic and polluted. The physical and chemical properties of clouds enable them to contain more contaminants than are found in the larger and more diluted wter droplets that form rain.

Clouds "are just very good scavengers of atmospheric pollution," he said.

The concentrations "were higher than rain, just as we thought they would be."

However, Scherbatskoy said he was surprised that the acid levels have remained high, nine years after Congress passed amendments to the Clean Air Act to control acid-rain causing pollution. Mercury pollution from power plants was not regulated by the 1990 Clean Air Act amendments. Leahy's mercury bill is aimed at curbing one of the last major industrial pollutants that now lacks an overall pollution control strategy, his staff said. The bill would direct the Environmental Protection Agency to set mercury emission standards for fossi-fuel power plants, trash incinerators, cement plants, and other sources. It would also begin a phase-out of non-essential mercury-containing products.

"I think this call for a phase-out of non-essential mercury uses is the direction we have to go in this country if we're ever going to see mercury (pollution) eliminated," said Michael Bender, director of the Mercury Policy Project, a Montpelier-based organization. Leahy "is the clear leader in this area. I would hope the product manufacturers pay attention to this legislation and do the right thing."