Robert Diaz is a researcher with the College of William and Mary's Virginia Institute of Marine Science in Gloucester Point, Virginia. He and his colleagues have found evidence for more than a hundred dead zones worldwide. They range in size from 0.4 to 27,000-plus square miles (1 to 70,000-plus square kilometers).
In the U.S. these oxygen-depleted, or hypoxic, zones develop annually in western Long Island Sound off New York and Connecticut, the Chesapeake Bay off Maryland and Virginia, and the Neuse River in North Carolina.
Outside the U.S., dead zones are found in the North, Adriatic, Baltic and Black Seas and Japan's Seto Inland Sea.
Scientists first noted the annual formation of the Gulf of Mexico dead zone in the 1980s.
In 2001 a multilevel government task force led by the U.S. Environmental Protection Agency set a goal of reducing the Gulf of Mexico dead zone to a five-year running average of less than 2,000 square miles (5,000 square kilometers).
Donald Scavia, a marine scientist at the University of Michigan in Ann Arbor who led the science team that advised the task force, said the figure "represents conditions that were likely to be typical in the early 1970sand a significant reduction from the current conditions."
Whitall, the NOAA coastal ecologist, said, "To achieve this goal, a 30 percent reduction in nitrogen load from the Mississippi and Atchafalaya Rivers is being implemented."
The effort focuses on refining agricultural practices in the watershed. Such tactics include timing of fertilizer applications better, plowing more efficiently, restoring natural wetlands, and improving manure management.
Computer modeling by Scavia and colleagues suggest that, to reduce the Gulf of Mexico dead zone to 1970s levels, a 40 to 45 percent reduction in nutrient runoff may be necessary.
"This does not negate the original agreement," Scavia said. "In fact, it supports it. This basin is a massive, slow-moving system. And moving toward practices that produce [a] 30 percent or 40 percent [reduction] is appropriate."
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