SAN FRANCISCO – Forest resources experts at the University of Washington suspect that Asian air pollution has contributed to dramatic increases of nitrate, sulfate and acidity in precipitation during four of the last six years at their research site on Washington’s Olympic Peninsula.
The West Twin Creek watershed in the Hoh River Valley experienced the biggest change in 1994 when precipitation had between seven and eight times more nitrate than expected, says Robert Edmonds, UW professor of forest resources.
He, his graduate students and colleagues have been monitoring the area, a part of the Olympic National Park some 20 miles from the Pacific Ocean, since 1984. Georgia Murray, UW research scientist, presents information, Tuesday, Dec. 8, at the American Geophysical Union about measurements from the site including those starting in 1993 when the upward trend was first recorded. The amount of nitrate and sulfate remained high in ’94, ’95 and ’96 then tapered off in ’97 and early ’98, perhaps because of the effects of El Nino, Edmonds and Murray say.
Air pollution from ’93 through ’96 quickly affected water quality in the 128-acre watershed when trees and other plants failed to take up the excess nitrogen. Instead the nitrate made its way into streams where it, and to a lesser degree the sulfate, lowered the pH of the water from its typical 7.3 to an acidic level, the lowest of which was recorded in 1996. Such rapid changes were unexpected says forest-health researcher Edmonds, who thought the forest appeared capable of taking up most of the excess nitrogen.
The pollutants could be from Asia, Pacific Northwest cities or some other source but the researchers hypothesize it is probably from Asia because of the location of their research area.
Work led by Dan Jaffee, a scientist at the University of Washington Bothell, shows that air pollution from Eastern Asia at times travels directly across the Pacific to the West Coast of the United States, particularly to the Pacific Northwest, where it makes a small contribution (maybe 10 percent of the total) to the air pollution that is homegrown in cities such as Seattle.
Edmonds and Murray say NASA research aircraft (part of the Pacific Exploratory Mission-West work) have measured two plumes of pollution over the Pacific in recent years that originate in Asia, have trajectories to take them over their research site and that carry the chemicals found at their site.
Pollution from Seattle also could reach the site if wind currents carrying pollutants make their way to the west side of the Olympic Mountains, Edmonds says.
From whatever source or combination of sources, Edmonds and Murray say even remote forest sites such as the West Twin Creek watershed will no doubt be subjected to the effects of air pollution in the future, much of it bearing additional nitrogen.
“Nitrogen is the most important nutrient element in these forest systems but is a pollutant, especially in waterways, when there is too much of it,” Edmonds says. “A lot of people are very concerned that we are simply putting too much nitrogen into the atmosphere through our use of fertilizers and burning fossil fuels. When it makes its way to Earth, it can have large ecological impacts.”
Edmonds points to the West Twin Creek site as an example. The forest is old-growth, with some trees more than 600 years old, yet Edmonds would have predicted that the plants at the site could have taken up the relatively small amounts of excess nitrogen being deposited. That it failed to do so makes Edmonds wonder about the ability of similar forests, many of them in British Columbia and Alaska, to absorb excess nitrogen.
Long-term monitoring at the West Twin Creek site is funded by the U.S. Geological Survey and in recent years has involved Edmonds, Murray, James Marra, who holds a post-doctoral position at the UW, and Roger Blew, a former post-doc who is now with the Environmental Science and Research Foundation in Idaho Falls.
FOR MORE INFORMATION:
Edmonds, (206) 685-0953, firstname.lastname@example.org, is unable to attend the AGU meeting.
Murray, (206) 543-8242, email@example.com, will be at the AGU meeting the afternoon of Dec. 6 through Dec. 10. Messages can be left at the AGU press room, (415) 905-1007.