Phantom Menace: Air Pollution Threatens Western National Parks

It’s just past 8 on a June morning in Colorado’s Rocky Mountain National Park, and the sun already beats down through a cloudless sapphire sky. Jill Baron jams on a floppy-brimmed hat, shoulders a bulging pack, and starts hiking. A handful of graduate students follow her; they’re laden with bamboo poles, metal stakes, and other scientific equipment. The three-mile trail to Loch Vale—a glacier-sculpted valley cupping several pristine alpine lakes—is a well-worn route for Baron, an ecologist with the U.S. Geological Survey and Colorado State University. She or one of her colleagues has trekked through these wildflower-studded aspen and conifer groves every week, year-round, for the past 25 years. “Every day is a perfect day up here,” Baron says. But she knows better than anyone that an invisible menace has been creeping in for decades, threatening to wreak havoc on the park’s raw beauty.

The culprit? Nitrogen, an element that makes up 78 percent of the air we breathe. Nitrogen in the air is not reactive; it is converted to a reactive state through combustion processes or fixation by plants. In normal concentrations, nitrogen is a crucial building block of DNA, proteins, and enzymes, and a vital part of plant growth. But in excess, reactive nitrogen leads to adverse effects, causing nutrient imbalances that can send shockwaves through an ecosystem. Too much nitrogen in the ecosystem means fast-growing, aggressive grasses could overwhelm the slower-growing, showy alpine flora—such as moss campion, a violet-hued wildflower that springs up in dainty bouquets throughout high-alpine regions—that have become perfectly adapted to their low-nutrient conditions. Add even more nitrogen, and the nutrient begins to act like a poison, bleeding nutrients out of the soil and water and eventually killing fish and the organisms they feed on. Here at Rocky Mountain, Baron has discovered that nitrogen levels on the east side of the park are three to four times higher than normal, and have been increasing by about 2.5 percent per year since the early ‘80s.

By sifting through historic layers of sediment, Baron found that nitrogen levels began to rise around 1950—right about the time when nearby Front Range cities began booming and farmers started using nitrogen-based synthetic fertilizers. Nitrogen is released into the air from vehicle exhaust, power plants, fertilizers, and even the manure from feedlots. How that nitrogen is reaching the park is not entirely clear, says Baron, but recent studies point to the upslope movement of air pollution from the Front Range. And the problem is not isolated to Rocky Mountain National Park. Nitrogen deposition is increasing at a number of national parks in the West and East, including Mount Rainier in Washington, Grand Teton in Wyoming, Great Smoky Mountains in North Carolina, and Acadia in Maine. Heightened nitrogen deposition occurs in “hot spots” that are downwind of agricultural and metropolitan areas.

Strapping gaiters over their bare legs, Baron and her team traverse calf-deep snow patches to reach their field sites. They bushwhack through low-hanging limbs, maneuver over fallen trees and gnarled roots, and slide down the snowpack, occasionally postholing, in pursuit of the experimental plots that Baron and her team set up in 1992. Stopping at one plot, Baron empties a baggie of tiny ammonium nitrate pellets into the soil. These pellets will release nitrogen throughout the flagged area, leaving a Hansel-and-Gretel trail of white pebbles on the forest floor—and allowing researchers to see what effects this excess nutrient will have.

Telltale signs of over-fertilization in the park are already apparent. At lower elevations, weedy, aggressive species, such as several non-native European grasses, now crop up along trail margins, and the park’s historically rich variety of diatoms (doily-shaped algae that form the base of the food chain) have been replaced by just two dominant native species. The differences are subtle—but if trends continue on the current trajectory, the park’s ecosystems could be severely impacted. “These biological changes are portents of more serious things to come,” says William Bowman, an ecologist at the University of Colorado at Boulder. In the worst-case scenario, that could mean acidified soil, heavy metals leaching into park lakes and streams, dead fish, and a profoundly different environment.

And unfortunately, nitrogen is just the beginning. A National Park Service study released in February 2008 found that a slew of toxic airborne chemicals—including DDT, Dieldren, and mercury—have accumulated in disturbingly high levels in the streams, soils, and plants of America’s most pristine wildernesses. The effects of these contaminants echo up the food chain: Fish at several parks were found to contain levels of pesticides and mercury that exceed safe consumption limits for humans, birds, and other wildlife. “Parks are our last bastions of cleanliness,” says Baron, “so this kind of insidious stuff coming in out of the sky is a terrible thing for an area that is our last, best hope to keep ecosystems in their natural state.”

But it’s not too late. Colorado adopted the Nitrogen Deposition Reduction Plan in 2007, a road map (based largely on Baron’s and Bowman’s work) aimed at bringing the nitrogen influx at Rocky Mountain National Park down to acceptable levels by 2032. Farmers and ranchers are closely involved, working to learn how they can better manage livestock operations and fertilization practices to minimize unwanted nitrogen. And ordinary hikers can do plenty to help. Actions that combat climate change—such as biking to work, driving cleaner-burning vehicles, reducing energy use and buying more efficient products—will also slash airborne pollutants like nitrogen, mercury, and other heavy metals.

As storm clouds gather in the west, Baron hurries to complete her tasks. The glistening lake has now turned steely blue, and a cool breeze sends a shiver through the meadow grasses. Surrounded by granite towers and glaciers, the setting is postcard-perfect—and hard to imagine any other way. If enough people listen to Baron’s alarm, there won’t be a need to.