Today, the tranquil stillness of night or the symphony of an early morning bird chorus are likely to be replaced with the discordant sounds of automobiles, jackhammers, or water boat engines. Common human activities, such as transportation and urban construction, produce outdoor noise pollution that is unhealthy for people but also has a negative impact on nearby fauna. This understanding has led to new areas of research focus: understanding soundscape ecology and testing the effects of anthropogenic noise pollution. Many studies have examined these topics using wildlife, marine mammals, and fish. However, studies examined the effect of invertebrates on the composition of natural soundscapes and their response to anthropogenic noise pollution has not been well studied. Furthermore, early studies focused on the effect of noise pollution on a relatively few species of birds and whales. These studies have provided valuable insight into the bioacoustics ecology of many ecosystems. However, the increasing threat of anthropogenic noise pollution in freshwater ecosystems has only recently been understood.
In many parts of the world, traffic is one of the biggest contributors to the increasing levels of anthropogenic noise. Researchers Arevalo and Blau studied the impact of road networks on protected areas. They found that soundscapes in many areas were directly affected by road proximity and that natural sounds were often masked near roads with heavy use or large vehicle traffic. They proposed that this contributes to the degradation of habitats through the loss of natural sounds. Others have recommended management efforts in national parks should not only maintain good quality habitat, but also preserve the natural soundscapes. Thus, research is needed to identify characteristics of natural soundscapes and also test how they are altered in areas with noise pollution.
In my first study, I used recorded sound to investigate the impact that submersed aquatic vegetation had on sound transmission in shallow wetland habitats. Understanding the movement of sound in shallow vegetated habitats, like freshwater wetlands, is important to understand the bioacoustic environment of those areas. Overall, sound transmission was effectively reduced by submersed vegetation and distance from sound source. There was a predictable negative linear relationship between sound loss and plant density. Furthermore, this effect was greater on high frequency tones. While most of the sounds were still audible at 1 m even in dense vegetation, by 15 meters only the low tones were still audible. Mixed tones, (i.e. those composed of high tones and low tones), showed a similar pattern.
My results indicate that aquatic organisms in densely vegetated wetlands may be restricted to using acoustic signals only at short distance. However, since wetland vegetation senesces in the autumn in temperate climates, it is possible at times of year that form of acoustic communication is more effective. These data also indicate that wetland management practices that reduce dense stands of emergent and submergent vegetation (e.g. herbiciding, mowing, water level drawdowns) may have an unintended impact on the biotic community. While sounds used to communicate information would be enhanced, predators that use acoustic signals to locate their prey might have a higher success rate. Therefore, further research should examine how changes in underwater soundscapes. Furthermore, enhancing submersed vegetation may have a positive impact by reducing the transmission of underwater anthropogenic sounds such as motorboat engine noise. Further research in this area is needed on various types of vegetation and a variety of wetland types. These results would likely vary in a wetland with different characteristics and proper understanding and management will require knowing the acoustic behavior of different ones.
In my second study, I researched how natural soundscapes of freshwater wetlands in northeastern Ohio are affected by road noise. I studied this by recording soundscapes in three seasons in rural wetlands away from roads and wetlands near to roads. My results indicated that wetlands near roads had higher overall sound intensity (70 dB) and more anthropogenic sound components as part of their soundscape. Most anthropogenic noise occurred in the low (0-5 kHz) frequencies while natural sounds occurred across a wider frequency range from 0-15 kHz. The soundscapes also changed throughout the year with Spring having the most natural sounds and the highest acoustic diversity. Unexpectedly, I also found rural wetlands had more natural sounds both above and below the water line and more diverse soundscapes. This may reflect a lower aquatic and terrestrial biodiversity in wetlands near roads or a change in calling behavior of the fauna. My findings indicate that traffic noise altered natural soundscape in freshwater wetlands by masking natural sounds, and that anthropogenic noise impact may play a role in reducing wetland biodiversity if they disrupt vital natural behaviors such as mating, hunting and predator avoidance. Future research focusing on how to analyze soundscape data to identify changes in species assemblages and research testing the impact of human noise on biodiversity and acoustic ecology would add valuable knowledge to this particular area of research.
In my third project, I investigated how a native invertebrate, Procambarus acutus, react to short term (20 minute) exposure to anthropogenic noise (motorboat engine sounds). I also was the first to describe the acoustic characteristics of sounds produced by this species. Crayfish are an important component of aquatic ecosystems, particularly wetlands, because they are important predators, herbivores and can alter resource availability with their burrowing activity. Therefore, factors affecting their behavior and survival could have cascading ecological effects in their habitats. This experiment showed that crayfish exposed to anthropogenic sound reduced their overall activity levels, but their sound production did not change. These results indicate that anthropogenic noise can alter crayfish behavior. Further study in the area of crayfish sound production is needed to gain a better understating of why the sounds are made and how they are used. Understanding how they and other key species react to anthropogenic noise will be an important aspect of developing new wetland management strategies.
My fourth research study investigated how P. acutus were affected by chronic exposure to anthropogenic motorboat noise. Crayfish in the sound treatment were held outdoors in wading pools and exposed to continuous anthropogenic sounds for 4 weeks. Similar to the short-term sound exposure study (Project #3), anthropogenic sounds again suppressed crayfish activity levels but did not affect sound production. However, I also found that aggressive behaviors were the most reduced. This response can have an effect on crayfish reproductive success and defense of their home territories. Furthermore, there was a positive correlation between activity levels and sound production, although no specific behavior was associated with sound production. Overall, these results indicate that anthropogenic noise can alter the behavior of this crayfish species. Because crayfish are a dominant species in many aquatic habitats, changes to their populations can affect many other aspects of their ecosystem. Future research should investigate how anthropogenic noise affect other freshwater invertebrate species and any impacts on the ecosystem processes.
The primary goals of applied ecology are to understand the effect of anthropogenic factors in natural habitats, to protect biodiversity, and to develop management strategies to enhance valuable ecological services. My research provided useful data on this topic, including characteristics of underwater sound transmission, a comparison of soundscapes in rural and roadside wetlands, and the effects of anthropogenic noise on the ecology of a native aquatic invertebrate species. Future research on soundscape ecology can help provide a better understanding on how mitigate negative impacts of noise pollution in freshwater ecosystems.