Dead zones are low-oxygen areas found in large lakes and oceans. In a dead zone, oxygen has been depleted to the point where marine life is drastically reduced, particularly throughout the lowest portion of the water column and along reef bottoms and seabeds. The number and severity of dead zones has been increasing since the 1970's; in particular, they tend to occur along inhabited coastlines, in areas where aquatic life should be highly concentrated. When discussing dead zones, oceanographers make it clear that the vast, central portions of seas and oceans, which tend not to support much life, are not considered to be dead zones. What causes these dead zones, and what can be done to reverse them? The answers to these questions are surprisingly simple.
Ocean Dead Zones on the Rise
In March of 2004, the UN Environment Program published its first-ever Global Environment Outlook Yearbook, in which it reported 146 dead zones worldwide. The smallest of these covered as little as a square kilometer, while the largest covered 70,000 square kilometers. Even more frightening, the number of ocean dead zones worldwide increased to 405 by 2008. Some dead zones expand during the warmest months of the year, and recede when water gets cooler; this is mainly due to the fact that many ocean dead zones can be attributed to algal bloom.
While algal bloom is a natural phenomenon, it is accelerated, and made denser via a process called eutrophication, which takes place when chemical nutrients, especially phosphorus and nitrogen, make their way into the water. These nutrients are fertilizers - and you might be surprised to discover that the massive farms which produce a majority of the world's food, along with chemicals from common household products, urban land use, and sewage are actually the source of the nutrients algal blooms need to thrive.
These chemicals enter the environment due to runoff, making their way into rivers, lakes, and oceans. As algal blooms grow in size, massive fish die offs occur, particularly in shallow areas where water exchange is minimal. Natural contributions to ocean dead zones are intensified when concentrated chemicals are present. These include changes in wind and water patterns, along with coastal upwelling.
Where are the Dead Zones?
NASA has produced a map showing dead zones worldwide, along with a gallery of photos shot from space which illustrate just how ubiquitous these areas are becoming. While dead zones can happen anywhere, some of the world's largest are located off the coasts of the United States, China, India and Russia. The Gulf of Mexico, the Baltic Sea, the eastern portion of the topical Pacific, and the northern portion of the Indian Ocean have permanent or semi-permanent dead zones; the Chesapeake Bay is affected, and so is the Mississippi River basin. Areas off South America are quickly deteriorating due to deforestation and subsequent factory farming, and dead zones in the Great Lakes get larger as unsustainable farming practices continue in the Midwest regions of the United States and in Canada.
What Can Be Done About Ocean Dead Zones?
Just as human activity is the main contributing factor to dead zones, so humanity can act to reverse them. This is illustrated by the rapid reversal of the Black Sea dead zone. Between 1991 and 2001, when the Soviet Union collapsed, commercial fertilizers were too costly for most famers to use, and runoff containing these fertilizers stopped entering the Black Sea. Today, the dead zone has all but disappeared, and fishing is once again a major economic activity throughout Eastern and Central Europe. While this cleanup was, for the most part, unintentional, it proved illustrative. Today, the U.N. advocates reduction in industrial emissions and sewage; nonprofit groups around the world are promoting farming techniques which rely on organic matter to build up soil, rather than fast-acting chemical fertilizers often used by major agricultural enterprises.
You can make a difference by selecting detergents which contain no phosphorous, and by choosing local, organically grown foods whenever possible. Avoiding factory farmed foods, including soy grown where rainforests once stood, is another way you can vote with your wallet. Supporting groups, like Ocean Champions, who work to promote sound environmental policies, is another way you can make a difference. If we all work together, corporations will eventually get the hint - and our oceans can spring back to life. It's not too late to put a stop to dead zones.