Lava Beds National Monument: Acoustic monitoring report

Pipkin, Ashley

In 2014, the Natural Sounds and Night Skies Division (NSNSD) received a request to collect baseline acoustic data at Lava Beds National Monument (LABE). From August 2014 to September 2014 three acoustic monitoring systems were deployed across the park. These stations were configured to collect sound pressure level data and continuous audio recordings for approximately thirty days. The baseline data collected during this period will help managers and planners assess the current condition of the acoustic environment at LABE. Results of this study will help assess future impacts of a new designated military airspace over the park. The measured existing and natural ambient conditions may also be used as a baseline for noise modeling efforts. LABE offers a variety of unique pristine natural sounds not found in most urban or suburban environments. This quiet setting provides a very special dimension to the park experience. The quiet affords visitors an opportunity to hear faint or very distant natural sounds such as grass blowing in the wind, and the call of a coyote. Sources of noise at LABE include trains, vehicles, and aircraft. For the purposes of this document, we will refer to “noise” as any human-caused sound that masks or degrades natural sounds (Lynch et al. 2011). Table 1 displays percent time audible values for each of the most common noise sources during the monitoring period as well as ambient sound levels. Ambient sound pressure levels were measured continuously, every second, over the 30-day monitoring period by calibrated, Type 1, Larson Davis 831 sound level meters. After monitoring was complete percent time audible metrics were calculated. See the Methods section for protocol details, equipment specifications and calculation of metrics. Median existing (L50) and natural ambient (Lnat) metrics are also reported for daytime (7 am – 7 pm) and nighttime (7 pm – 7am). In determining the current conditions of an acoustic environment, it is informative to examine how often sound pressure levels exceed certain values. Table 2 reports the percent of time that measured levels were above four thresholds during the monitoring period (daytime and nighttime). The top value in each split-cell focuses on frequencies affected by transportation noise (20-1250 Hz) and measures a truncated (T) set of frequencies, whereas the lower values represent the conventional full frequency range (12.5-20,000 Hz). Recent studies suggest that sound events as low as 35 dBA, the lowest value in table 2, can have adverse effects on blood pressure while sleeping (Haralabidis, 2008). The second value addresses the World Health Organization’s recommendations that noise levels inside bedrooms remain below 45 dBA (Berglund et al., 1999). The third value, 52 dBA, is based on the EPA’s speech interference level for speaking in a raised voice to an audience at 10 meters (EPA 1974). This value addresses the effects of sound on interpretive presentations in parks. The final value, 60 dBA, provides a basis for estimating impacts on average voice communications at 1 meter. Hikers or other visitors viewing scenic areas in the park would likely be conducting such conversations. This report shows that overall anthropogenic noise is very commonly audible at the three sites, however overall acoustic impacts and exceedance levels are low, meaning that while noise is audible, it does not introduce substantial sound energy to the acoustic environment. In many cases only listeners with very sensitive hearing would find a majority of the anthropogenic sound sources identified at LABE audible. If unchecked, impacts could increase over time, but if sound levels are kept low or are reduced through mitigation, this could result in one of the most natural soundscapes in the area. Efforts to maintain the low levels of impacts could include (but are not limited to) interpretive signs about the acoustic environment, educating small craft pilots especially when flying over w

Lava Beds National Monument: Acoustic monitoring report

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