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.