7.8 - Noise Pollution

Learning Objectives

I. Urban Noise Pollution and Terrestrial Impacts

• Measuring noise (decibels): sound is measured in decibels (dB), a logarithmic scale where every 10 dB increase means 10 times more sound intensity. So 90 dB is $10^{(90 - 60)/10} = 10^3 = 1{,}000$ times more intense than 60 dB (about the level of normal conversation).
• Hearing loss: long or repeated exposure to sound at or above about 85 dB can destroy the tiny hair cells in the inner ear, and they don't grow back. At 85 dB you have to raise your voice to be heard by someone 3 feet away. NIOSH's limit for workers is 8 hours at 85 dB, cut in half for every 3 dB louder, so 100 dB is safe for only 15 minutes a day.
• Physiological stress: constant noise raises stress hormones, blood pressure, and heart rate, and it disrupts sleep, even below the levels that damage hearing. Long-term exposure to traffic noise is linked to heart disease.

• Urban sources: Construction (jackhammers, trucks), transportation (cars, buses, trains), industrial activity (manufacturing plants, metal factories), and domestic activity (loud neighbors, home repair projects).

• Effects on wildlife: Noise can cause hearing loss, confusion, headaches, or disorientation in animals.
• Disrupted communication: Animals, particularly birds, rely on vocalizations or calls for activities like migration or mating, and those get disrupted when they can’t hear each other.
• Physiological stress: Studies subjecting caterpillars to simulated highway noise showed a substantial increase in their heart rate. That stress may prevent proper growth and reproduction, which could lead to a decline in pollinator species.
• Predator-prey dynamics: Noise pollution disrupts the predator’s ability to find food and the prey’s ability to avoid the predator, which dramatically affects survival.
• Example: some bats hunt by listening for the faint rustling of insects on the ground. Near loud highway noise, they catch less prey because the noise masks those sounds.
• Changes to migration routes and stopovers: animals avoid noisy areas, even when the habitat is otherwise good. In the "phantom road" experiment in Idaho, researchers played recorded traffic noise in a roadless area where songbirds rest during fall migration. Bird numbers there dropped by more than a quarter, some species avoided the area almost completely, and the birds that stayed gained weight more slowly.

II. Aquatic Noise Pollution and Marine Impacts

• Aquatic sources:
• Tanker ships: Really large ships carrying oil, natural gas, or other products create a lot of noise with their engines.
• Military grade sonar: Navies send out powerful sound pulses to find submarines. In March 2000, more than a dozen whales, mostly beaked whales, stranded in the Bahamas during a U.S. Navy exercise, and a joint Navy and NOAA investigation concluded the Navy's mid-frequency sonar was the most likely cause.
• Seismic air blasts: Sent down by surveying ships looking for oil and natural gas deposits under the ocean floor. They're among the loudest human-made sounds in the ocean, fired over and over for days or weeks, and they travel really long distances: underwater microphones in the middle of the Atlantic Ocean picked up blasts from surveys off northeast Brazil and West Africa, almost 4,000 km (about 2,500 miles) away.

• Effects on marine organisms: Marine organisms can experience physiological stress like a faster heart rate, hearing loss, confusion, and disturbed communication.
• Whale disruption: This is especially problematic for whales, which rely on sound based vocalizations for communication. Noise pollution disturbs their communication about danger or migratory paths.
• Whales also change their swimming and migration paths to avoid loud areas. For example, migrating bowhead whales in the Arctic detour around active seismic surveys.
• Behavioral changes: Loud noise can make whales stop feeding, change how they dive, or swim away from an area. In experiments off California, some blue whales exposed to recordings of navy sonar stopped feeding and swam away (Goldbogen and others, 2013).
• Predator-prey dynamics: Noise disrupts the ability of aquatic predators to locate prey and the ability of prey to hear and escape predators.