Human Population Expansion = Oceanic Dead Zones

By Greg Bungo

Every spring and summer, a huge dead zone appears in the Gulf of Mexico. It's never exactly the same size, but it's often around 7,000 square miles, about the size of New Jersey. What causes this is a complex chain of events that is partly based on overpopulation in the giant Mississippi, Missouri, and Ohio River basins.

Nitrogen and phosphorus compounds enter the river drainage system as byproducts of agricultural fertilizer use, farm animal waste, human sewage, and yard fertilizers. When this rich mix of plant nutrients reaches the Gulf of Mexico, it promotes the growth of algae and cyanobacteria. After a while these plants and plant-like bacteria die, and they sink to the bottom of the Gulf. There they are consumed by bacteria and other bottom dwelling animals. The animals and the bacteria use large amounts of oxygen as they feast on a smorgasbord of dead algae. Before long, there's not enough oxygen in the water to support animal life, a condition known as hypoxia, and the Dead Zone appears and expands.

Ironically, life dies in 7,000 square miles of the Gulf of Mexico because too many nutrients flowed there. The balance of nature is broken, and the result is hypoxia and death. It's a little bit like someone who eats too much candy for Halloween, and is sick the next day. Or a person who develops heart disease or diabetes from a fast food diet heavy in saturated fat, cholesterol, and refined sugar.

What can be done about this problem? We must reduce the amount of nitrogen and phosphorus reaching the Gulf. This is a very large problem, and there's probably no single action that can completely solve it.

One possibility is to reduce how much fertilizer farmers and suburban lawn owner's use. Fertilizer runoff is a big part of the problem. The waste from large factory farms, or CAFOs (Concentrated Animal Feeding Operations) needs to be treated properly, which often does not happen. Wetlands must be preserved and expanded, since they provide a natural filtration system that removes much of the waste and excess nutrients from the water before it enters the main rivers.

But the continuing growth of the U.S. population will reduce the effectiveness of these solutions to the problem. As the population grows, the people will need food to eat. This means that farmers will want to continue fertilizing their fields in an effort to provide the maximum output. More large factory animal farms will be built, and it will be harder to monitor and regulate the increasing number of these "farms". When there are more people, naturally there will be more sewage. And homes for these people will be built in areas where there should be wetlands that can filter the waste and nutrients.

In October 2003, the population of the United States was over 292 million people ( The population is growing by about 3.1 million people per year. If we wish to protect the Gulf of Mexico from an expanding Dead Zone, we must stop the growth of the U.S. population. Without population stabilization, the wetlands, fertilizer reduction, and CAFO regulation won't have a chance to adequately reduce the eutrophication of the Gulf of Mexico.

For more information, here are some websites and books:
There are many documents that can be downloaded from this NOAA site. (836 Kilobytes)
Information about the relation between population growth and the environment.
Environmental ratings for the members of the U.S. Congress.

Cycles of Life: Civilization and the Biosphere,
by Vaclav Smil. Published by Scientific American in 2001. 221 pages. This covers many of the biogeochemical cycles of our planet, including the processes of eutrophication.

Coastal Hypoxia: Consequences for Living Resources and Ecosystems,
Nancy N. Rabalais and R. Eugene Turner, Editors. Published by the American Geophysical Union in 2001. 460 pages. For readers who already know something about the subject.