Pollutant is increasingly found in national parks

A pollutant that can slowly trigger changes in the lives of plants and animals is increasingly being found in 16 National Park Service sites, mostly in the Western United States.

Air quality data obtained by The Associated Press shows significant worsening trends for ammonium in several flagship parks, including Yellowstone, Mount Rainier and Utah's Canyonlands. At Colorado's Rocky Mountain National Park, researchers have already seen subtle shifts in the alpine tundra, where some of the park's trademark wildflowers are being replaced by grass.

Scientists worry that increases in nitrogen-rich ammonium could gradually transform other national parks' sensitive ecosystems, affecting everything from microscopic algae and plants to fish, frogs and other wildlife.

"We're in the early stages of seeing impacts to the parks, but the longer we let it go, the harder it is to fix later," said Tamara Blett, an ecologist with the National Park Service's air quality branch in Denver.

Ammonia is a mix of hydrogen and nitrogen. When it mixes with water, it becomes ammonium and acts as an extra dose of fertilizer when it reaches the ground. It's commonly associated with fertilizers, large animal feeding operations, vehicle exhaust and factory emissions. It also occurs naturally.

After it is emitted, it gets swept up into the atmosphere and hitches a ride back to Earth on bits of rain and snow.

And more often in recent decades, it has found its way to national parks, detected by a network of air and precipitation monitors.

The latest data from the Park Service, which analyzed trends from 1998 to 2007, raises particular concern about seven national parks and monuments in Arizona, New Mexico, Colorado, Utah, Wyoming and Washington state.

"Nitrogen is a fertilizer," Blett said. "It's used on lawns to help them grow and be green. That's fine for lawns but not good for national parks where we want them functioning in a natural way."

In large enough doses, excess nitrogen can change soil and water chemistry, affect species diversity or provide extra nutrients for exotic grasses that facilitate the spread of wildfires.

Much of what's known about the effects of ammonium in national parks comes from studies at Rocky Mountain National Park, north of Denver.

Scientists there watch vulnerable high-elevation tundras and lakes for signs that nitrogen is overloading the system and setting off a chain reaction that alters which native species survive and which don't, according to Jim Cheatham, a biologist at the park.