America’s Protected Natural Areas Are Polluted, By Noise

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Cars line up at the south entrance to Zion National Park in Utah.

Education Images/UIG via Getty Images

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There are thousands of parks, refuges and wilderness areas in the U.S. that are kept in something close to their natural state. But one form of pollution isn’t respecting those boundaries: human-made noise.

New research based on recordings from 492 protected natural areas reveals that they’re awash in noise pollution.

Researchers from Colorado State University spent years making the recordings, setting out microphones in natural areas across the country. They caught all sorts of wildlife sounds, such as rutting elk and howling wolves. But they were also after “background” sound — wind, rain, birdsong, flowing streams and rivers, even bubbling mud pots in Yellowstone National Park.

They compared the decibel level of this natural background with the kind of intrusive noisiness from human activity. And they’ve discovered that in two-thirds of the places they studied, the median decibel level of human-made sound was double the normal background sound. These were sounds that came from within the area, such as road traffic, as well from as outside, such as passing jets or mining and logging equipment.

And in more than 20 percent of the areas studied, the unnatural sounds were 10 times as loud as the natural background. “So, fairly shockingly high levels of noise pollution within protected areas,” says Rachel Buxton, lead author of the study, which appears in the journal Science.

Buxton, an ornithologist, points out that adding just a few decibels of artificial background sound, like of a jet plane, means it’s harder to hear what’s around you: a stream, or wind through the trees, or wildlife. Even with an increase in unnatural sound of three decibels, “if you could hear a sound before at 100 feet, now you can only hear it from 50 feet,” she explains.

The National Park Service is well aware of the problem. They have a scientist dedicated to studying noise in parks: biologist Kurt Fristrup. He says people who are used to urban soundscapes might not know what they’re missing.

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