Understanding Aquatic Noise Pollution: Sources And Causes

Noise pollution is an invisible danger that can have harmful effects on human health, wildlife, and environmental quality. While noise pollution is commonly generated inside many industrial facilities and some other workplaces, it also comes from road, rail, and air traffic, as well as construction activities. In this context, it is important to discuss ocean noise pollution, which is caused by human activities such as commercial shipping, oil exploration, seismic surveys, and military sonar, among others. This form of pollution has severe impacts on marine life, especially those that rely on echolocation, such as whales and dolphins.

Commercial shipping

The total carrying capacity of the global shipping fleet nearly quadrupled between 1996 and 2020, with new and larger ships added to keep pace with the growing global economy. Scientists have found that noise from shipping is doubling roughly every decade. This is a serious issue as many marine species depend on sound to carry out their day-to-day activities. Whales, fish, lobsters, and other marine animals use sound to communicate with one another, find food, avoid predators, reproduce, and navigate. When ship noise overwhelms or "masks" these natural sounds, marine life has been observed leaving their preferred habitats and changing important behaviours, such as singing to attract mates.

Most of the underwater noise emitted by ships comes from propeller cavitation, which is a complex phenomenon that can be described as a breakdown in water flow over the propeller blades, resulting in significant noise and a loss of fuel efficiency. Cavitation can be addressed through design changes to the propeller and the hull of the ship or the use of new devices to smooth the water flow into the propeller. In 2017, the shipping company Maersk modified several of its ships by installing efficient propellers and reconfiguring hulls, resulting in a 75% reduction in noise energy emitted from the ship.

The International Maritime Organization (IMO) has issued guidelines to reduce noise pollution in the seas resulting from commercial shipping. The IMO is also designing a new project, the GloNoise Partnership, which aims to address the issue of underwater noise from shipping by building capacity in developing countries to implement the guidelines for the reduction of underwater noise from commercial shipping. The Marine Environment Protection Committee (MEPC) has approved revised guidelines for the reduction of underwater noise from commercial shipping to address adverse impacts on marine life.

Noise pollution from commercial shipping can have adverse effects on both human health and marine life. For humans, noise pollution can cause hearing loss, high blood pressure, irritability, anxiety, mental fatigue, sleep disruption, and communication interference. Marine animals, especially those that rely on echolocation such as whales and dolphins, are impacted by noise pollution as it interferes with their essential life functions, including finding prey, avoiding predators, locating offspring, and finding a mate.

Oil exploration

Oil and gas operations generate a diverse range of noise types, including intermittent and continuous sounds of varying intensities. For example, compressor stations produce a constant low rumble, while drilling a horizontal well is a loud and prolonged process that can operate 24 hours a day for four to five weeks. The use of large volumes of water at high pressure during drilling also results in pump- and fluid-handling noise. These varying noise levels and intensities can have detrimental effects on the health and well-being of nearby communities.

The environmental risks associated with oil exploration are significant, and accidents during exploration, refining, and distribution can lead to water pollution and marine life contamination. Oil spills, for example, have severe consequences for marine ecosystems and the coastal regions they affect. From 1970 to 2000, oil tankers spilled approximately 5.5 million tons of oil into the seas, with an average of 0.18 million tons per year and a maximum of 0.64 million tons spilled in 1979. Human error and negligence are often contributing factors in these accidents, highlighting the inherent risks of oil exploration to water resources and quality.

To address the noise pollution caused by oil exploration, researchers suggest implementing policies and mitigation techniques. These may include specifying setbacks from vulnerable communities, utilising noise mitigation measures such as perimeter sound walls, and incorporating natural noise barriers like hills and trees in location siting decisions. By taking these steps, it may be possible to reduce the impact of noise pollution on both human populations and marine life, minimising the negative consequences of oil exploration activities.

Seismic surveys

The impact of seismic surveys extends beyond the reduction in cetacean sightings. Cetaceans, such as whales and dolphins, rely heavily on echolocation for navigation, communication, and foraging. Exposure to intense noise from seismic surveys can cause these animals to change their diving patterns, surfacing more frequently or spending less time at depth. This can lead to reduced mating success, disrupted migration patterns, and even stranding events. In some cases, extremely loud sounds from seismic surveys can trigger mass strandings, where entire groups of disoriented animals beach themselves, leading to high mortality rates.

Furthermore, chronic exposure to noise from seismic surveys can cause elevated stress levels in marine animals, leading to increased production of stress hormones like cortisol. Intense acoustic events can also rupture the eardrums and other sensitive tissues of whales and dolphins, resulting in disorientation, hearing loss, and even death.

The global proliferation of seismic surveys and the large propagation distances of airgun noise highlight the urgent need to address the impacts of underwater noise pollution on marine species. By recognizing and mitigating these impacts, we can work towards protecting the vital acoustic habitats that marine life depends on for their survival.

Military sonar

Sonar, or sound navigation and ranging, is a system that was first developed by the US Navy to detect enemy submarines. Military sonar devices emit sound waves of up to 235 decibels, which can travel for hundreds of miles underwater and retain an intensity of 140 decibels as far as 300 miles from their source. To put this into perspective, the world's loudest rock bands top out at only 130 decibels.

The use of military sonar has been linked to injuries and deaths of whales, dolphins, and other marine life. In January 2005, 34 whales of three different species became stranded and died along North Carolina's Outer Banks during nearby offshore Navy sonar training. This is not an isolated incident, as there have been other cases of whale strandings and deaths linked to sonar testing. Evidence shows that whales will swim hundreds of miles, rapidly change their depth (sometimes leading to bleeding from the eyes and ears), and even beach themselves to get away from sonar sounds.

The frequency and volume of military sonar can interfere with whale biology and cause behavioural changes, such as altered feeding behaviour, increased swimming speed, and changes in social behaviour. These changes can lead to decompression sickness and even death. In addition to whales, other marine mammals such as dolphins and porpoises may also be affected by sonar, as they rely on sound to communicate, locate mates and prey, avoid predators, navigate, and defend their territories.

While the use of military sonar has been met with opposition from environmental groups and lawsuits, the Supreme Court has ruled that the Navy should be allowed to continue some mid-frequency sonar testing for national security reasons. However, efforts are being made to find a balance between protecting marine life and preserving national security.

Wind turbine installation

Noise pollution is defined as unwanted or excessive sound that can have detrimental effects on human health, wildlife, and environmental quality. It is particularly harmful to marine animals that rely on echolocation, such as whales and dolphins, with naval sonar devices being one of the loudest and most detrimental sources of noise in the sea.

Wind turbines, as a source of renewable energy, have gained prominence in recent years. However, wind turbine noise (WTN) has been identified as a potential cause for concern, particularly regarding its impact on nearby wildlife. WTN can affect the physical well-being, vital survival mechanisms, social and reproductive processes, and habitat continuity of certain species. Despite this, planning guidelines in some countries, such as the US, Germany, and Israel, do not adequately address these adverse effects.

To mitigate WTN, developers employ several methods during the planning and installation of wind farms. These include:

• Micro-placement and impact assessments: Careful positioning of wind turbines can help reduce their impact on wildlife and nearby communities.
• Zoning: Establishing specific zones for wind turbines can help maintain a safe distance from protected areas and sensitive habitats.
• Sound mitigation techniques: Researchers are working on designing quieter turbines by modifying blade shapes, soundproofing gearboxes, and generators, and optimizing blade positions to reduce low-frequency and impulsive sound.
• Collaboration with regulatory bodies: Developers work with organizations like the Bureau of Ocean Energy Management to establish limits and guidelines for wind turbine noise.
• Community engagement: Operators of wind farms communicate with local communities to address potential noise pollution concerns, such as by adjusting turbine operating modes based on wind conditions.

It is important to note that research on the effects of WTN is ongoing, and more studies are needed to fully understand and mitigate its impact on wildlife and human communities.

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