But dead zones are everywhere around the globe, totaling perhaps as many as a thousand. Although the number of oxygen-poor aquatic habitats may no longer be increasing, the size of many is expanding, oxygen is dropping to even lower levels, and the number of months they linger is lengthening.
How do dead zones work?
When there are excessive amounts of nitrogen and phosphorus in the water, algae can bloom to harmful levels. Dead zones form when the algae die, sink to the bottom, and are decomposed by bacteria—a process that strips dissolved oxygen from the surrounding water.
Where are dead zones found?
Dead zones occur in coastal areas around the nation and in the Great Lakes — no part of the country or the world is immune. The second largest dead zone in the world is located in the U.S., in the northern Gulf of Mexico.
How does a dead zone form?
Dead zones occur because of a process called eutrophication, which happens when a body of water gets too many nutrients, such as phosphorus and nitrogen. Human activities are the main cause of these excess nutrients being washed into the ocean. For this reason, dead zones are often located near inhabited coastlines.
How many dead zones exist?
After the 1970s, dead zones became more widespread, almost doubling each decade since the 1960s. A 2008 study found more than 400 dead zones exist worldwide—anywhere excess nutrients travel downstream and into a body of water. (Read about a large dead zone in the Baltic Sea.)
How does a dead zone start?
What is a dead zone and how are they formed?
Dead zones begin to form when excess nutrients, primarily nitrogen and phosphorus , enter coastal waters and help fertilize blooms of algae. Major nutrient sources include fertilizers, wastewater, and the burning of fossil fuels.
How do dead zones occur naturally?
Dead zones can be caused by natural and by anthropogenic factors. Use of chemical fertilizers is considered the major human-related cause of dead zones around the world. Natural causes include coastal upwelling and changes in wind and water circulation patterns.
What is the largest dead zone in the world?
The largest dead zone in the world encompasses the entire bottom of the Baltic Sea. Others dead zones occur in the Chesapeake Bay, off the coast of Oregon, Lake Erie, and the most famous dead zone is located in the Gulf of Mexico.
What causes the Dead Zone?
Thus, a “dead zone” is created where no organisms can live anymore. Although nitrogen and phosphorous from agricultural fertilizer runoff are the primary causes of dead zones around the world, sewage, automobile and industrial emissions, and some natural factors can also cause dead zones to develop.