Although the Dead Zone* in the Gulf of Mexico tends to receive the most publicity in the US, there are an increasing number of dead zones around the world and the area covered by dead zones is doubling about every ten years (reported in NY Times, original study in Science).
As reported by Bina Venkataraman in the New York Times,
“What’s happened in the last 40, 50 years is that human activity has made the water quality conditions worse,” the study’s leader author, Robert J. Diaz, said in an interview.
The trend portends nothing good for many fisheries, said Dr. Diaz, a professor at the Virginia Institute of Marine Science at the College of William and Mary. “Dead zones,” he said, “tend to occur in areas that are historically prime fishing grounds.”
Indeed, while the size of dead zones is small relative to the total surface of the oceans, scientists say they account for a significant part of ocean waters that support commercial fish and shellfish species.
The authors of the study conclude their report in Science with this observation:
Currently, hypoxia and anoxia are among the most widespread deleterious anthropogenic influences on estuarine and marine environments, and now rank with overfishing, habitat loss, and harmful algal blooms as major global environmental problems. There is no other variable of such ecological importance to coastal marine ecosystems that has changed so drastically over such a short time as DO [dissolved oxygen].
The major cause of dead zones is the flow of too many nutrients down our rivers and out into coastal waters. These nutrients come from agriculture (fertilizers), animal waste (from raising cows, pigs, poultry, etc.), and also from sewer overflows, air pollution, and other smaller contributors. The entry of these nutrients into the rivers is made easier when wetlands and other riverside vegetation systems are destroyed for farmland or for other development.
Better management of crop fertilization, manure disposal, and the requirement of ‘buffer zones’ of nutrient-absorbing vegetation and soil can all help lessen the problem of nutrient pollution (eutrophication) of our rivers and coastal zones. Because the pollution often takes place across state and even national boundaries, this problem needs to be managed, and managed responsibly, at the highest levels.
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*A dead zone is a low-oxygen area in the ocean; the term tends to refer to areas where this low-oxygen (hypoxic) area is persistent in time, often leading to the death of sedentary and sessile organisms and attempts by mobile species to leave the area.
