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Hydrological Hazards: Flushing out America’s Heartland


“The sea is the universal sewer.” ~Jacques Yves Cousteau, Oceanographer

The Mississippi River and its tributaries drain 41 percent of the United States and carry the nutrients that cause the Gulf of Mexico’s dead zone.

Map of the Mississippi River Basin

Map of the Mississippi River Basin and Watershed. Made using USGS data. Image: Wikipedia


Map of the Mississippi River watershed.

Map of the Mississippi River watershed. Image: National Park Service via Wikipedia

The Floods’ Lingering Effects: New Study Shows Gulf “Dead Zone” One of the Largest on Record

The Gulf “dead zone” threatens seafood production, recreation and marine life.

Gulf of Mexico Dead Zone

One of the largest dead zones forms in the Gulf of Mexico every spring. This data visualization discusses the causes of hypoxia in the Gulf of Mexico. (Credit: NOAA/

“Dead Zones” or Hypoxic zones are areas in the ocean of such low oxygen concentration that animal life suffocates and dies, and as a result are sometimes called “dead zones.”

Extremely heavy rains and melting snows washed massive amounts of nutrients—particularly nitrogen and phosphorus—from lawns, sewage treatment plants, farm land and other sources along the Mississippi River into the Gulf of Mexico. Once in the Gulf, these nutrients, which are required for plant and crop growth, trigger algae blooms that choke off oxygen in water and make it difficult, if not impossible, for marine life to survive.

The National Oceanic and Atmospheric Administration, or NOAA, which funded the scientists’ research, estimates that the dead zone costs U.S. seafood and tourism industries $82 million a year. The impact could be devastating to the Gulf’s seafood industry, which accounts for more than 40 percent of the nation’s seafood. Louisiana is second in seafood production only to Alaska.

Because fish and other commercial species usually move out to sea in order to avoid the dead zone, fishermen are forced to travel farther from land—and spend more time and money—to make their catches, adding stress to an industry already hurt by hurricanes and the oil spill. Those species that can’t move—or can’t move fast enough—die off, leading to the name “dead zone.”

A team of NOAA-funded scientists from the Louisiana Universities Marine Consortium, Louisiana State University and the University of Michigan recently analyzed nutrient runoff from the recent floods and predicted the dead zone in the Gulf would reach historic proportions. Fortunately, their findings show the dead zone didn’t hit an all-time record, but the news was nothing to celebrate. The report underscores the need to invest in our natural resources. The Mississippi River, its tributaries and floodplains, and the Gulf are an inner-connected system that affects—and is affected by—people. We must work collaboratively to find solutions that address the connectivity of this system—solutions that benefit people and nature. Learn how the Conservancy is working to reduce the Gulf’s dead zone.

The Nature Conservancy (edited)

See Also

The Mother-of-all-Dead Zones: “Fossil site shows impact of early Jurassic’s low oxygen oceans”

More Information

Hypoxia in the northern Gulf of Mexico – LUMCON

Center for Operational Oceanographic Products and Services – NOAA

Harmful Algal Bloom Forecasts – NOAA

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