Noise pollution is invading even the most protected natural areas

The great outdoors is becoming a lot less peaceful. Noise pollution from humans has doubled sound levels in more than half of all protected areas in the United States—from local nature reserves to national parks—and it has made some places 10 times louder, according to a new study. And the cacophony isn’t just bad for animals using natural sounds to hunt and forage—it could also be detrimental to human health.

The study, which maps noise levels across the United States, is “a call to arms,” says Nathan Kleist, an ecologist at the University of Colorado in Boulder, who was not involved in the work. The noise maps could help scientists identify key areas to keep quiet, such as critical habitats for endangered species, he adds. “If you’re missing noise, you’re missing a huge driver of habitat suitability.”

Noise pollution—from honking cars to clanging construction equipment—can disturb sleep, cause stress, and impair concentration. In 1972, U.S. officials enacted the Noise Control Act, which gave the Enironmental Protection Agency the authority to impose limits on noise from motor vehicles and machinery. But regulators have largely ignored noise in parks, wilderness, and other protected areas, which cover 14% of the country. And 80% of the United States—including many parks and protected areas—is now within 1 kilometer of a road, thanks to rapidly growing residential and industrial areas.

Concerned about the clamor, researchers at the National Park Service and Colorado State University in Fort Collins (CSU) recorded noise at 492 sites across the country with varying levels of protection. They used the recordings to predict noise throughout protected areas in the rest of the country. Using a computer model, they also estimated the ambient noise naturally present at each site. The scientists then compared two scenarios: protected areas with and without humanmade noise.

They found that noise pollution doubled sound levels in 63% of protected areas and caused a 10-fold increase in 21%, the team reports today in Science. Such levels can harm wildlife and annoy visitors in natural areas. Generally, the more remote or restricted an area, the less noise. Parks and open spaces managed by local governments, often adjacent to cities, were the noisiest. State and federal lands allowing logging, mining, and oil and gas extraction were also noisy. National parks and wilderness areas were notably quieter but still not safe. Noise pollution doubled sound levels in 12% of all wilderness areas.

“We were surprised we found such high levels of noise pollution in such high amounts of protected areas,” says lead author Rachel Buxton, a conservation biologist at CSU.

The excess noise can do more than just annoy park visitors. It can also undo the benefits of spending time in nature, like improved mood and memory retention. For plants and animals, the ruckus can disrupt entire communities. Some plants need silence for seed dispersal—revving cars can scare away rodents that might otherwise do the job. Animals need silence to hear predators approaching or to communicate with their mates: A bird whose song would normally travel 100 meters would, with a 10-fold increase in noise, have its melody stifled to a 10-meter radius. “In so many landscapes, both people and other organisms are living in shrunken perceptual worlds,” says Clinton Francis, an ecologist at California Polytechnic State University in San Luis Obispo, who was not involved in the work.

Many protected areas already use noise-reducing strategies, like operating shuttles to reduce traffic or concentrating highways and flight paths into “noise corridors.” Buxton’s hope is that her map of noise will help land managers make decisions about where to implement such measures so that the greatest number of wildlife and humans can benefit.

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