Marine Dead Zones
What are Dead Zones?
Dead zones are areas in bodies of water that have little to no oxygen. As a result aquatic life suffocates and the area becomes lifeless.
What Causes Dead Zones?
The culprit is human-made pollution created on land that is flushed into rivers, waterways, and watersheds, which then transport the excessive nutrients to the seas:
Runoff from farmland that carries fertilizers and animal manure.
Runoff from urban areas, such as garden fertilizers, septic systems, and other pollutants
Wastewater released from treatment plants, which can still contain large amounts of nutrients
Air pollution from power plants, factories, cars, all machines that burn fossil fuels.
Image by teachoceanscience.org
The added nutrients are overpowering the natural system and create explosive algae blooms that have multiple negative effects. A dense algae bloom blocks sunlight that seagrasses need to grow, which in turn can be detrimental to the animals that live in and feed on the grasses. Excessive algae will also choke the life out of corals. When the algae die they sink to the bottom where they are decomposed by bacteria. This decomposition process sucks oxygen from the water.
Sea temperatures and wind can affect how big a dead zone will grow by affecting how warmer shallow water and deeper, cold water mix. Dead zones become more deadly and intense when the surface temperatures are high because it essentially creates a lid of warm water that prevents the exchange of oxygen.
HOW MANY DEAD ZONES ARE THERE?
Read this great article by NRDC. It is from 2014, so the estimates are likely to be much higher by now. Devil in the Deep Blue Sea. “There are more than 400 known dead zones worldwide, covering about 1 percent of the area of the continental shelves. That number is almost certainly a vast undercount, though, since large parts of Africa, South America, and Asia have yet to be adequately studied. Diaz estimates that a more accurate count is 1,000-plus dead zones globally.”
NOAA’s latest report on the dead zone in the Gulf of Mexico. The numbers are in. The 2021 Gulf of Mexico Hypoxic Zone, or Dead Zone, an area of low oxygen that can kill fish and marine life near the bottom of the sea, measures six thousand three hundred and thirty-four square miles. This year's dead zone is larger than the average measured over the past five years.
ARE THERE SOLUTIONS?
Scientists Find New Way to Reduce Marine ‘Dead Zones’. “When it rains, excess nutrients — mostly nitrogen and phosphorus from Midwest farm and livestock operations — wash into the Mississippi and Atchafalaya rivers. Those nutrients make their way to the Gulf, fueling an overgrowth of algae which deprive the waters of oxygen, driving away or killing marine life.” Over the past five years the average size of the Gulf of Mexico's dead zone has stretched to more than 5,400 square miles. But these hypoxic areas are also found in other parts of the United States and across the world. And climate change, experts predict, will cause them to get bigger and persist for longer.
In a recent study published in Nature, researchers from the University of Waterloo and the University of Illinois Chicago found that efforts to restore wetlands in the United States "are often carried out in an ad hoc manner," meaning they lack a comprehensive strategy. Read the full article on TheRevelator.