Annual Dead Zone Spreads Across

Annual Dead Zone Spreads Across the Gulf of Mexico

Marcy Broden

Purpose:

Most people may or not be familiar with the concept of a "dead zone". I'll admit that I had no idea what one was until I began my research for this project. The purpose of this web page is to explain a few different interrelated aspects about a dead zone. Although this page will contain information about a few different dead zones, the one that takes place in the Gulf of Mexico will be main the focus.

Contents:

What is a dead zone? How does a dead zone develop?

Dangers of the dead zone Clues of a dead zone

Future of the dead zone Coastal dead zones around the world

What can be done? Further reading

Bibliography

What is a Dead Zone?

A dead zone is an area of water that is unable to sustain many types of aquatic life due to the extremely low levels of oxygen that it contains. The term used to describe this is referred to as hypoxia. Fully oxygenated waters contain as much as 10 parts per million of oxygen. In some dead zones, oxygen hovers at 0.5ppm or lower for months (4). The dead zone in the Gulf of Mexico has been growing larger each year. It has now spanned up to 22,000 square kilometers, which is larger than the state of New Jersey. The appearance of this dead zone is an annual event, which can begin as early in the year as February and last as late until mid-fall. The only good news is that the dead zone disappears each winter. The picture below shows the area of the dead zone in light blue in the northern part of the Gulf of Mexico.

The following is a link to an article which describes the assessment reports developed as a response to hypoxia: Hypoxia in the Gulf of Mexico

How does a dead zone develop?

Dead zones tend to develop in quiet and deep water a few kilometers offshore. When excessive amounts of nitrates are deposited into the water, they cause the production of algae. A certain amount of algae is necessary for other aquatic life to survive but too much is where the problem begins. The numerous amount of algae goes through its normal life cycle and when it all dies it becomes a feast for bacteria. The bacteria consumes most of the oxygen from the bottom water. In the Gulf of Mexico, the Mississippi River deposits water that is heavily contaminated with nitrates which causes the dead zone to exist. The term hypoxia is applied to this oxygen-starved region. Hypoxia means an absence of oxygen reaching living tissues (1). In coastal waters, hypoxia is characterized by low levels of dissolved oxygen. Primarily, the excess nutrients being deposited into the Gulf Of Mexico are because of agricultural fertilizers being deposited into the Mississippi River. Runoff from developed land, soil erosion, sewage and industrial waste also can contribute pollutants (1).

Eutrophication

Dangers of the Dead Zone

The dead zone poses a very real threat to the biodiversity, ecological integrity, and fishery productivity of the Gulf of Mexico. The environmental impacts of low oxygenated regions include algal blooms that suffocate fish, shrimp and crabs and altered coastal phytoplankton. Phytoplankton is important because it's on the bottom of the food chain and most sea life depends on it for survival. The impact on fisheries includes fish kills, altered migration patterns for species of shrimp, and a loss of the essential habitat for spawning fish, shrimp and crabs. The dead zone poses a threat to the economy of the Gulf region. Fishermen can no longer depend on the waters and travel elsewhere around the dead zone for commercial fishing. The economic impacts will only continue to grow if it becomes larger and more severe. The dead zone can also cause harm to humans. A condition called methemoglobinemia can sometimes result in infants as well as adults. This condition is characterized by the hemoglobin molecules not being able to sufficiently carry oxygen to the different parts of the body. This is also referred to as "blue baby syndrome". If an infant drink water contaminated with a high enough concentration of nitrates , a baby would show signs of blueness around the hands, mouth and feet may appear purple in color. Treatment, more causes and information are available here.(3)

The cyanosis present in the lips, skin, and mucus membrane has been referred as "chocolate cyanosis" which may be due to the chocolate-brown appearance of the blood .

Clues of a Dead Zone

Scientists have not observed fish dying in the Gulf of Mexico, yet there are some indicators of what may be to come. J. Kevin Craig of Duke University has been observing what may become a crisis for shrimp populations (4). He has been studying two specific aspects of the shrimp's health; size and lipid content. Over the past 30 years, the average size and therefore price of Gulf shrimp has been decreasing, which Craig's data has closely followed. His data has also showed that the concentration of lipids in a shrimp's body representing the energy stores they carry tend to be 20-25% lower in animals caught in low oxygen areas than those caught in fully oxygenated areas. This suggests that hypoxia slows the animal's growth. Many fish also cannot survive in such a low oxygenated area. Nancy Rabalais, an aquatic ecologist with the Lousiana Universities Marine Consortium has been mapping the Gulf of Mexico's dead zone for approximately the past 20 years. When spring rains drench farm fields as far upstream as Ohio, Minnesota, and Montana, which spill large amounts of nitrogen into the Mississippi River, its only a matter of a few weeks before the oxygen concentrations in the Gulf begin to respond. Shrimp and bottom-dwelling fish tend to congregate around the area of the hypoxic region. This can lead to what appears as a fishing success but can really mean a future catastrophe. In Europe in the mid 1970's fisherman thought it was a joke that hypoxia was threatening bottom-dwelling aquatic life in the eastern end of the North Sea. Harvests of Norwegian lobsters remained plentiful through 1978. The next year these shellfish and many of the other sea's bottom-dwellers had vanished. Accounts of dead zones date back to 1884 when a Mobile, Alabama newspaper reported the abundance of fish and crabs. This abundance stemmed from the runoff of plant nutrients from local farms and towns which led to marine organisms fleeing a new dead zone (4).

Future of the Dead Zone

The federal government only seeks voluntary controls on runoff so there hasn't been much action to lessen it. The Gulf's dead zone may continue to get worse. According to Robert W. Howarth of Cornell University, "There comes a time when the fisheries collapse, not only will commercial harvests plummet, but fish and shrimp reproduction will also drop off"(4). No one knows how close the dead zone may be to this point. The climax of this problem may happen fast and leave irreversible damages. Laurence Mee of the University of Plymouth in England understands this problem well. He has studied this transformation in the Black Sea. A recurring dead zone emerged there in 1973 caused by heavy fertilizer use in Eastern Europe. The dead zone at times was much bigger than the Gulf's dead zone and completely changed the Black Sea's ecosystem. Commercially valuable fish such as the turbot declined while other invaluable fish increased their populations. An alien species-comb jellyfish present on ships from the Chesapeake Bay took over the Black Sea. There were about one million tons of these jelly fish and their mass exceeded the weight of the entire world's commercial fish catch. A short time later a bigger species of jelly fish emerged and began consuming the smaller original species of alien jellyfish. Currently the Black Sea's ecosystem is improving. The fall of communism reduced the agricultural spending on fertilizers therefore nitrate runoff into the sea decreased.

Coastal Dead Zones Around the World

Source:United Nations Environment Programme, GEO Yearbook 2003 (Nairobi: 2004), compiled from Boesch 2002, Caddy 2000, Diaz et al. (in press), Green and Short 2003, Rabalais 2002.

The world's largest dead zone is found in the Baltic Sea. A combination of agricultural runoff, the release of nitrogen burning from fossil fuels, and human waste discharge have contributed to the formation of this dead zone (2). There are other problems similar to this in the northern Adriatic Sea, the Yellow Sea and the Gulf of Thailand. Offshore fish farming is another cause of nutrient buildup in some coastal waters. Forty-three of the world's known dead zones occur in U.S. coastal water. The dead zone in the Gulf of Mexico is the world's second largest. The Kattegat straight between Denmark and Sweden has been infiltrated with hypoxic areas and fish kills since the 1970's. In 1986, the Norway lobster fishery collapsed. Since then the phosphorus levels in the water have been reduced by 80 percent. The dead zone on the northwestern shelf of the Black Sea peaked at 20,000 square kilometers in the 1980's. Phosphorus was cut by 60 percent due to the collapse of many centralized economies and the dead zone shrank. In 1996, it was absent for the first time in 23 years. Although farmers cut down on the amount of fertilizers they were using, their crops did not suffer. It is possible for some dead zones to shrink in as little time as a year with careful management (2).

What Can Be Done?

Researchers are trying to decrease the amount of plant nutrients into rivers and eventually seas. The U.S. government limits major releases of nitrate into the environment because high concentrations can be toxic even to people. Without new regulations, U.S. attempts to reduce low-level nitrate pollution relies heavily on voluntary efforts by farmers and others whose organizations lead to the problem. Some programs can be as simple as encouraging cuts in fertilizer use. Other projects may be more creative and require more work. Some of these options include changing crop choices or expanding and creating wetlands. The most important thing is to get these programs started. There has been no major damage to fisheries yet but without programs in use damages will occur. Fertilizer used on crops is the greatest factor that contributes to the pollution causing the dead zone in the Gulf of Mexico. Farmers find that other than water, fertilizer is the primary limiter of growth in most plants. Farmers usually use more fertilizer than what is actually needed to avoid the possibility of decreased productivity. The U.S. Department of Agriculture provides an estimate, called the agronomic rate, of how much fertilizer is needed in a typical year. For example, a farmer might be advised to use 150 pounds of nitrate per acre of planted corn. However, every 4 or 5 years rainy weather creates an environment in which plants can grow better with extra fertilizer. Most farmers apply fertilizer without really knowing what the weather will bring. If there isn't enough rain, the excess fertilizer remains in the soil until after the harvest rains wash it into nearby bodies of water. Conservation groups are looking for ways to convince farmers to limit the amount of fertilizers that they use. There has even been a low-cost insurance program that's been suggested to farmers. If a farmer is left with over-fertilized patches of land at harvest, and these patches out perform the other areas, the farmer would be compensated for the diminished yield. The insurance would cost about $8.50 per acre but it would save farmers from buying extra fertilizer which costs around $18.00 per acre. The federal government approved the plan as a pilot program, but insurance companies and farmers alike aren't interested in participating.(6) The contacts found in this link can be written to in helping to tackle the problem of the dead zone. There are a few things that should be included when addressing this issue for action to be taken:

Identify the best nutrient management practices for habitat protection

Ensure that the scientific assessments currently being planned are funded immediately

Direct funds to on the ground efforts

Establish a formal organization for citizens to become involved