Rachel Carson in Silent Spring depicts such a chilling scene – the sound of birdsong that once echoed in the fields and woods disappeared without a trace, leaving only silence covering the earth.
Carson described this horror scene to awaken people’s vigilance of artificial chemical pollution, but at the same time, he said the fact that a healthy ecosystem is always full of all kinds of sounds.
Running, swimming, flying, breathing, eating… Every move of living things will make sound. Many animals will also take the initiative to make sounds and use them as tools. From insects, fish to croons, many animals make their own unique sounds to attract and look for their mates. Monkeys, chimpanzees and other animals will make sounds to warn their companions that natural enemies are approaching. Animals such as bats and dolphins will make high-frequency sounds to find prey and locate obstacles through echoes.
The more vibrant a habitat is, the more diverse the sounds there are. The sound in the primeval forest is usually the richest and most diverse. The secondary forest is much thinner than the former, and the sound of living things can hardly be heard in the human-cultivated farmland, and the night is silent. Therefore, some ecologists want to assess the health of ecosystems and biodiversity through “soundscapes”. The so-called soundscape refers to the sum of various sounds in the environment. The research method of recording the sounds of wild animals has been around for a long time, but researchers used to focus only on the sounds of a specific animal. In recent years, with the progress of recording equipment and sound analysis technology, more and more research has been made on recording and analyzing the whole sound scene.
In September 2015, researchers from the University of Freiburg in Germany set up 300 recording devices in Brandenburg and other places. These devices record the sound of nature every 10 minutes, and each recording lasts for 1 minute. By September of the following year, they had collected 120 TB of data. If a person listens to these recordings 24 hours a day, it will take 30 years to finish listening. Of course, researchers don’t need to do this. Computers can help them analyze sound. They focused on the composition and diversity of sound, and analyzed the artificial sound in it. The results show that the amount of artificial sound is obviously related to the composition of sound, that is to say, human activities affect biodiversity, thus changing the whole soundscape. Since then, researchers have continued to record soundscapes in Germany and other places to monitor the impact of climate change on the ecological environment through changes in soundscapes.
Like the land, the biological habitats in the ocean are also very noisy, especially the diverse coral reefs with a large number of “residents”. But this is only suitable for healthy coral reefs, and when corals die for various reasons, resulting in the degradation of coral reef ecosystems, the sound here also becomes much more monotonous. In the waters west of Sulawesi Island in Indonesia, coral reefs were once severely damaged by blasting and fishing. From the 201st, environmental organizations began to restore coral reefs here, placing steel frames attached to coral worms on degraded coral reefs. How effective is this repair method? Researchers at the University of Exeter in the United Kingdom tried to make an evaluation through the soundscape.
Researchers divide local coral reefs into three categories: healthy coral reefs, degraded coral reefs and restored coral reefs. In 2018 and 2019, they set up water listeners in multiple locations of the three types of coral reefs, and recorded 1 hour of sound continuously at different times of the day (sunrise, morning, afternoon, sunset). Researchers analyze the recording in two ways. One is to manually identify whether it contains 10 special sounds. According to previous research, scientists can be sure that these sounds come from coral reef fish, such as the squeaking sound of fish chewing harder food. If the special sound of a place is relatively complete, the researchers will determine that the sound here is more abundant. Another method is to analyze the entire sound scene and calculate the sound complexity and sound pressure. The results show that the soundscape of restored coral reefs is similar to that of healthy coral reefs, and the richness and complexity of sound are significantly higher than that of degraded coral reefs. It can be seen that the local coral reef restoration has made considerable progress.
Because artificial identification is too time-consuming and labor-intensive, scientists mostly use a second method to analyze the soundscape as a whole, rather than looking for the sound of a specific species from it when using soundscapes to study ecology. Therefore, they designed many indicators to describe the soundscape, such as the diversity, complexity, uniformity, difference, sound entropy, etc. mentioned previously. Each indicator has a complex formula. Fill in the frequency, time, intensity and other information of the sound in the original data into the formula to calculate the indicator. These indicators can reflect different ecological information, such as biodiversity, population number, etc. However, with the rapid development of artificial intelligence technology in recent years, the work that could only be done by manual recognition in the past can also be handed over to computers. Deep learning algorithms can quite accurately identify species based on sound.
Scientists know that soundscapes can reflect the health of ecosystems, and wild animals are instinctively aware of this truth. Just as people are attracted to bustling cities, animals are also more willing to live in bustling and vibrant places. Therefore, artificially playing the sound of nature and “falsifying” healthy sound scenes can attract animals to settle down. That is to say, we can not only use the soundscape to monitor the ecological environment, but also accelerate the recovery of the ecosystem.
In 2016, after being hit by typhoons for two consecutive years, the world’s largest coral reef group, the Great Barrier Reef, had a large-scale bleaching phenomenon. The so-called bleaching is the symbiotic algae excreted by coral worms in the body and die due to the loss of nutrient supply. As the basis of the ecosystem, the death of coral worms has made many coral reefs lose their vitality. In 2017, scientists from the University of Bristol in the United Kingdom tried to use the power of sound in the Great Barrier Reef Restoration Project. They set up speakers underwater to play the sound recorded in the healthy coral reef for 40 days. The results showed that the healthy soundscape successfully attracted a large number of young fish looking for a place to live. In the coral reef with speakers, the number of fish has doubled and the variety has also increased by 50%. And the increase in fish contributes to the recovery of the entire coral reef ecosystem.
Not only fish with complex auditory organs will pursue healthy sounds, but invertebrates with very simple body structures, such as coral worms, can also perceive sounds and use force clues to find suitable habitats. In the U.S. Virgin Islands, scientists at the Woodshall Institute of Oceanography have set up solar-powered speakers on degraded coral reefs to play the sound of healthy coral reefs. Scientists have found that on average, more than 70% of Porites astreoides settled on reefs with speakers.
In Australia, researchers from the University of Adelaide are also using soundscapes to rebuild oyster reefs. Oyster Reef is a biological reef formed by oysters breeding on rocks for generations and shells accumulating layers. Similar to coral reefs, oyster reefs are also home to many marine creatures. There used to be endless oyster reefs along Australia’s coast, but these biological reefs were severely damaged by large quantities of oysters and shells dug for lime. In order to attract young oysters that could swim freely in the water and rebuild the oyster reef, the researchers recorded healthy sounds near the undamaged oyster reef and then played these sounds near the stones at the bottom of the sea. This method is surprisingly effective. In places with artificial soundscapes, there are thousands more oysters per square meter. Five months later, the volume of oyster reefs in these sites was four times that of the silent control sites.
What’s more surprising is that when restoring ecology, soundscapes can not only enrich and attract creatures, but also have a more magical effect. Researchers at Flinders University in Australia found that sound can promote the growth of Trichoderma harzianum. And this fungus can protect plants from harmful microorganisms and promote the growth and development of trees. The researchers used a single white noise in the experiment, which is only for the convenience of operation. They believe that the effect will be better if the complete soundscape of healthy soil is used. As for why sound has such a miraculous effect, researchers are still unclear. They speculated that the cell membranes of the fungus may have sensed vibrations, starting or turning off the expression of certain genes.
Healthy soundscapes enable living things to live in peace. When the noise generated by human activities is inserted into the soundscape, it will inevitably have a negative impact on living things. Many ecological studies have found this kind of phenomenon. As mentioned before, young fish will look for an ideal habitat based on the soundscape. In order to study whether artificial sounds, such as the sound of ship propellers, will interfere with fish’s search for homes, researchers at the University of Bristol conducted an experiment on Apogondoryssa. They played the sound of coral reefs, the sound of coral reefs mixed with the sound of propellers, the sound of open sea and white noise to the young long-spined catfish. When a normal coral reef sound is played, 69% of the young fish are attracted by the sound source. With the addition of the propeller sound, only 56%, and 44% of the young fish will stay away from the sound source mixed with the propeller sound. And only 8% will completely avoid the sound of coral reefs. The experimental results show that the sound of the ship’s propeller may indeed make the fish lost and unable to find a suitable habitat.
Animals that rely on voice communication are often the most affected. For example, a scientific case of the University of Glasgow in England and the German Institute of Horseman’s Cakes found that the common blackbirds in the urban environment gets up earlier in the morning. They put radio trackers on the male common blackbirds in the city and surrounding villages, and found that the birds in the city get up early for 40 minutes and sleeps 9 minutes late on average every day. The male common blackbirds should use its chirping to attract its mates, divide the territory and deter its competitors. And the artificially noisy urban soundscape forced them to start chirping earlier to avoid interference. Other studies have also found that in places where there is more artificial sound, birds will fight interference by increasing the volume and sound frequency.
Human-made noise not only affects other creatures, but also harms human beings themselves. Nowadays, people are more and more aware that protecting the soundscape is also an important part of protecting the environment. On the one hand, when in contact with nature, we should minimize the disturbance of the natural soundscape; on the other hand, we should also design and optimize the soundscape in the city where human beings live.
In order to protect ocean sound and scenery, the International Maritime Organization and countries are developing stricter standards and regulations to limit underwater noise from ships. Some enterprises and research institutions are also vigorously developing ship technologies that can reduce noise. Most of the noise produced by ships comes from their propellers, and the reason why propellers generate noise is mainly due to the bubble effect, that is, bubbles are generated when the propeller stirs the water flow. When these bubbles burst, they not only make noise, but also bring additional resistance to the ship. Therefore, scientists’ research on reducing ship noise is mainly aimed at the bubble effect. For example, the University of Sclyde in the United Kingdom cooperated with a ship power company to develop a propeller with many small holes at the edges. This kind of propeller can significantly reduce the generation of bubbles and reduce the noise volume by 10 decibels.
In cities, soundscape researchers are not only satisfied with reducing noise, but also creating a healthier soundscape so that residents can have a pleasant auditory experience. There are many ways to achieve the goal, such as using sound-absorbing materials in buildings and using more natural elements such as plant and water bodies. New York’s High Line Park is a successful example of improving the soundscape of the city. The New York High Line is an elevated railway in central Manhattan. After the railway was suspended, New York City did not demolish it, but reused it and converted it into a suspended park. The park has not only become a well-known scenic spot, providing a place for people to relax, but also improving the sound of the surrounding blocks. A lot of sound-absorbing materials (such as sound-absorbing floors) were used in the park, and many plants were planted, and even the fences on both sides were full of climbing vines. These designs can absorb and scatter sound, reducing urban noise.
In addition to reducing the noise, the park also brings pleasant natural sounds, such as the sound of water flowing from fountains and canals, and the sound of birdsong. The plant configuration of the park is specially designed by plant landscape designers, including plants from different ecosystems such as woodlands, grasslands and wetlands, and taking into account the changes of the four seasons, so that there are seeds for birds to eat for most of the year. The park does not use pesticides in daily management, so that insectivorous birds can also find abundant food. These designs attract many birds to stop in the park. As planners and designers realize that soundscapes are as important as visual landscapes, there will be more and more such cases.
In this era of convenient and easy-to-use recording equipment, almost everyone can record the soundscape around them. Researchers around the world have launched many public scientific projects to enable ordinary people to participate in soundscape research. The National Aeronautics and Space Administration (NASA) has launched a solar eclipse soundscape project to let people record the soundscapes around them during the two solar eclipses in 2023 and 2024 to study how the solar eclipse will affect wildlife. Researchers at Sonoma State University in the United States recruited volunteers to set up thousands of recording devices in the countryside of California, recording tens of thousands of hours of natural sound in five years. Through these data, researchers can analyze changes in biodiversity.
More and more research in related fields enables us to re-understand the easily overlooked side of the environment – the soundscape. And facts have proved that it should indeed be paid attention to and is worthy of our careful creation.
