Dead Zone

Dead Zone                In ecology, a relatively lifeless or hypoxic area in an ocean or sea that is devoid of or deficient in oxygen that results from an ecological chain reaction that is most likely precipitated by fertilizers, animal and human organic wastes, and runoff from land areas drained by one or more rivers and tributaries. These extensive areas that are typically devoid of higher forms of life (they do support bacteria and certain algae and thus are not completely “dead”) are thought to start with farmers using chemical fertilizers to provide nutrients to stimulate and maximize crop growth. But when rain water carries excess nutrients as run-off from the fields and into drainage basins and from there into rivers and the oceans, the excessive concentrations of nitrogen and phosphorus over-fertilize microscopic aquatic plant life, causing phytoplankton and algae to proliferate into massive blooms. When the phytoplankton die they fall to the sea bottom and are digested by microorganisms; that process removes oxygen from the water and creates low-oxygen or hypoxic zones. One of the world’s biggest, worst, and most persistent dead zone is in the Black Sea and extends over an area of about 5,000 square miles. The largest dead zone in the U.S. is a broad area of the Louisiana continental shelf in the Gulf of Mexico, extending across more than 8,000 square miles (projected at 8,800 sq. mi. in the summer of 2008), with seasonally-depleted oxygen levels (hypoxia) that begin in late spring, reach a maximum in midsummer, and disappear in the fall. This hypoxic or anoxic zone has formed in the middle of what had been the most important commercial and recreational fisheries in the coterminous United States and currently threatens the entire Gulf fishing economy.

Real World Examples: Approximately 400 dead zones are found around the world and range in size from small sections of coastal bays and estuaries to large sea beds of 30,000 square miles or more. Most but not all of those areas are found in temperate waters. They are concentrated off the eastern and southern coasts of the United States and in the seas of Europe, including the Mediterranean. Others have appeared off the coasts of Australia, Brazil, China, Japan, and New Zealand. The world’s largest dead zone is located in Northern Europe’s Baltic Sea and has in the past decade extended across 27,000 square miles. Author’s Note: Louisiana’s Dead Zone was discovered and documented in the mid-1980s by Nancy Rabalais and other marine scientists at Louisiana State University, who have been studying it since. It should be noted that dead zones are not necessarily permanent features. Between 1991 and 2001 the Black Sea dead zone shrank drastically and nearly disappeared after fertilizers became too expensive for farmers after the collapse of the Soviet Union and centrally planned agriculture in Eastern and Central Europe.

Real World Problem: Many if not most marine scientists have recently come to believe that dead zones, red tides, and other algal blooms are closely related through human agency. The purported connection is runoff from modern activities that is feeding an explosion of primitive life forms. An example, other than red tide, is the venomous fireweed, Lyngbya majuscule, a strain of primitive cyanobacteria, the type of simple life that flourished nearly three billion years ago. Outbreaks in Australia have decimated the fishing industry in certain areas as anyone contacting the weed can be affected by burns, blisters, painfully inflamed skin, and swelling of internal organs. That example is but one instance of a struggle in the world’s oceans of which many are unaware, that advanced life forms (fish, corals and marine mammals) are fighting for survival while primitive forms (algae, bacteria and jellyfish) are thriving. It is a scenario characterized by many marine scientists as “evolution in reverse,” as if life in the oceans is returning to a primeval state of many millions of years ago. Although a single cause has not been identified, most scientists point to myriad environmental changes that have altered the basic ocean chemistry by putting too many nutrients into the water — especially nitrogen but also carbon, iron, and phosphorous. The list of culprits includes large-scale agriculture, feedlots, sewage outfalls, inadequately treated sewage, leaking septic tanks, industrial spills and emissions, and residential lawn fertilizers. At the same time, over-fishing, the destruction of coastal wetlands and estuarine habitat, and the degradation of other ocean environments (such as warmer water) have stressed the more advanced organisms, weakening them, and making them more vulnerable to attack from many sides, including from the primitive life forms. The very real fear of marine biologists is that uncontrolled human actions will transform the ocean into a microbial soup.

Fun Stuff: The Dead Zone is not to be confused with Stephen King’s novel sporting the same name. Daffynition: The Dead Zone at colleges across the U.S. is the last several rows of students in many large lecture halls.