Sleeping Bear Dunes National Lakeshore: Acoustic monitoring report, 2022
Olstad TA. 2025. Sleeping Bear Dunes National Lakeshore: Acoustic monitoring report, 2022. Science Report. NPS/SR—2025/257. National Park Service. Fort Collins, Colorado. https://doi.org/10.36967/2309412
This study was conducted in response to Technical Assistance Request (TAR) 20133, which identified a need for a baseline acoustic inventory within a discontinuous parcel of Sleeping Bear Dunes National Lakeshore (SLBE). Although the Bow Lakes parcel is frequented by visitors seeking a quiet refuge away from crowds, it is bordered by three privately owned and operated sand and gravel mines. The park needs information about existing and natural ambient sound levels to evaluate the effects of mining noise on the parcel. In March-April 2022, the Natural Sounds and Night Skies Division (NSNSD) gathered acoustic data at two sites in the Bow Lakes parcel in SLBE, discontinuous from the popular areas along the shoreline as well as the Sleeping Bear Dunes Wilderness but bordered by three privately owned and operated sand and gravel mines. On average, noise was present 71.2–77.3% of the time at these sites, with vehicles the most common identifiable source of non-natural noise, audible an average of 22.9–23.2% of the time, and heavy equipment the main contributor. Existing median ambient sound levels (LA50) ranged from 24.1–24.2 dB at night and 30.2–30.9 dB during the day. Natural ambient sound levels (LAnat) ranged from 20.9 dB at night to 26.9–27.6 during the day. The median influence noise has on the acoustic environment, defined as the difference between LA50 and LAnat, was 3.2–3.3 dB, representing a detectable increase in sound levels due to anthropogenic noise. In the ANS-weighted frequency range, the sound level of 35 dB (LAeq, 1s), indicative of quiet environments, was exceeded 14.27–14.35% of the day and 7.36–10.49% of the night. All other key sound levels (i.e., 45 dB and above) were exceeded less than 0.4% of the time. To summarize, the Bow Lake parcel receives consistent but low-level anthropogenic noise that would be noticeable to a listener. A geospatial sound model designed to estimate sound levels over larger areas predicts existing median sound level (L50) of 37.0 dBA and a median natural L50 of 33.6 dBA across the park, with lower sound levels in the Wilderness Area and Bow Lakes parcel and localized effects from anthropogenic noise, especially along M-22.
- Type
- Published Report
- Authors
- Olstad, Tyra
- Date of Issue
- 2025-03
- Publisher
- National Park Service
- DOI
- 10.36967/2309412
- Units
- NRSS , NSNSD , SLBE
- Keywords
- Acoustic monitoring, baseline ambient, natural sound, noise, sound level, soundscape