In U.S. protected areas, human activities raise the noise level above the natural background sound levels from 1.25 decibels (dark blue) to 10 decibels (lighter blue-green). | R.T. Buxton et al., Science, 2017
Humans are doubling the background sound levels in 63% of the nation's protected areas, where manmade disturbances are supposed to be reduced, changing wild areas that spread primarily across the Western states, a new study reveals.
The results, published in the May 5 issue of Science, highlight the extent to which human noise pollution is encroaching into more remote expanses.
Noise pollution can have a profound effect on wildlife, by reducing the ability of prey to hear predators approaching or interfering with the ability of animals to find a mate. Even plants can be affected by noise pollution if animals, such as rodents that disperse plant seeds, alter their behavior or location because of the sound disturbance.
Designated protected areas include national parks, monuments, federal wilderness areas and nature preserves. The National Park Service manages these areas to minimize the impact of humans on these natural ecosystems, including the impact of noise. Yet sounds from such sources as jets flying overhead, car and boat traffic and oil and gas extraction operations are increasingly resonating within these areas.
Acoustic recording station at Alcatraz Island in San Francisco Bay, California.| National Park Service
"Protected areas in the United States provide important places for respite, recreation and natural resource conservation," explained Rachel Buxton of Colorado State University, an author of the study. "Because of the known negative impacts of noise pollution, for both human visitors and wildlife, it is important to quantify the threat caused by noise in these high value areas."
Over a decade, the team gathered data to quantify noise pollution in U.S. protected areas, measuring sound levels at 492 sites across the country. They then used a computer algorithm to establish a baseline, or natural sound level, for the various areas given each site's unique features. For example, areas near a roaring waterfall will have a naturally higher background noise level than a dense forested area where trees help muffle sound.
"This acoustic data collection has occurred over about a decade through the National Park Service, requiring an impressive collaborative effort, from engineering appropriate acoustic recorders, to storing and processing terabytes worth of data. The sound model itself took a tremendous effort from [National Park Service and Colorado State University] engineers," said Buxton.
The team found that background noise exceeded 3 decibels (dB) in 63% of protected areas, and 10 dB in 21% of protected areas; essentially, a doubling and ten-fold increase in background noise, respectively, in these locations.
Buxton was most surprised about the percentage of protected areas that are experiencing a ten-fold increase in background noise. "This represents a 90% reduction in listening area, or rather, if you could hear a sound at 100 feet, you can now only hear that sound at 10 feet. This has serious implications for both visitors and wildlife."
Acoustic recording station at Devils Tower National Monument in Wyoming.| National Park Service
Wilderness areas, which receive the highest level of conservation protection including barring the construction of permanent roads and buildings to retain as much of their natural condition as possible, were found to have the lowest exposure to noise pollution, yet 12% of these areas still experience sound levels of 3 dB above natural levels, the authors report.
Wilderness areas subject to more stringent land use regulations had less human-related excessive noise; for example, these extra noise levels were 56% lower in designated critical habitat within protected areas, compared to habitats in unprotected areas.
In a related podcast, Buxton noted that the data collected by her team points to "low-hanging fruit" for mitigating noise pollution. For example, a protected area that would normally be fairly quiet but contains one particularly noisy patch would benefit greatly by management efforts to reduce sound in the louder subregion, limiting the ambience of manmade sound across the region as a whole.
Buxton said, "Our paper provides valuable general information about decision-making for noise management and enhancing enjoyment of natural quiet … Noise is an often overlooked issue, yet we show that it is widespread, even in protected areas. Thus, educating the public about the importance of natural sounds and encouraging them to appreciate these natural sound resources is becoming more important."
[Credit for related image: National Park Service; Credit for related podcast: Michelle Hampson/ Carla Schaffer/ AAAS]