Dead Zone the Size of Connecticut Blossoms in Gulf of Mexico

By Tom Yulsman | July 30, 2013 3:09 pm

Sediments and nutrients darken the waters of the Gulf of Mexico from the Mississippi River and its distributaries, as seen in this image captured by NASA’s Aqua satellite on May 6, 2013. (Image: NASA)

This summer’s “dead zone” in the Gulf of Mexico measures some 5,840 square miles, or roughly the size of Connecticut, according to the National Oceanic and Atmospheric Administration.

A dead zone is an area where oxygen levels in the water drop so low that most forms of life cannot survive. Thanks to huge amounts of nutrients coursing down the Mississippi River from America’s agricultural heartland, formation of a dead zone along the Louisiana coast has become an annual occurrence, threatening commercial and recreational fisheries valued in 2011 at $818 million.

This map shows the extent of low oxygen in the Gulf of Mexico along the Louisiana coast this summer. (Source: LUMCON/Rabalais)

A wet spring that brought more runoff of fertilizer from farmlands was projected to trigger formation of a larger than average dead zone this summer. But windy conditions in the Gulf of Mexico churned and oxygenated the waters, limiting its size to only slightly above average.

Even so, it’s more than 3,000 square miles larger than the goal being pursued by a task force consisting of federal and state agencies and Indian tribes. And while American farmers have become more efficient in their use of fertilizer, “we don’t see less in the way of nutrients coming out at the end of the Mississippi, and we still have dead zones,” says Alan Townsend, a scientist at the University of Colorado who conducts research on the cycling of nitrogen, a key nutrient, on global and regional scales.

For more of Townsend’s perspective, keep reading. But first, how do dead zones form? The image at the top of this post, captured by NASA’s Aqua satellite on May 6th, helps illustrate the process.

Two big plumes of sediment are visible. Toward the right edge of the picture, one is emptying into the Gulf from the main branch of the Mississippi. To the left another plume is coming from the Atchafalaya River, a distributary of the Mississippi.

The whole Mississippi system dumps some 230 million tons of sediment from farm fields and other sources into the Gulf every year, according to the U.S. Geological Survey. These sediments are accompanied by nitrogen, phosphorous and other nutrients — 1.7 million tons of the stuff, ultimately from from fertilizer, treated sewage from cities, and other sources.

When the nutrients hit the Gulf, they stimulate blooms of algae in the water. And when these tiny, photosynthesizing organisms die, they sink toward the bottom and decompose — a process that sucks so much oxygen out of the water that there is too little to support life. Thus the name “dead zone.”

For more detailed information on the formation and impacts of dead zones, check out this explainer from the Mississippi River Gulf of Mexico Watershed Nutrient Task Force.

Some progress has been made in mitigating the flow of nutrients off farm fields, according to Townsend. (Full disclosure: He is a colleague of mine at the University of Colorado.) American farmers used to over-apply fertilizers as an insurance policy. But now, driven in part by economics — using too much fertilizer is simply a waste of money — “they are using less fertilizer in the heartland. They have become much more efficient,” he says.

Why does a dead zone still form in the Gulf every summer despite these efforts? It’s not entirely clear, Townsend says. It may be partly due to a lag effect — it takes awhile for excess nutrients to be flushed all the way out of the system. Another factor may be increased production of corn, with its attendant use of fertilizer, to produce ethanol as a biofuel.

Townsend also points out that less than 1 percent of the U.S. corn crop now winds up on our plates as corn. The overwhelming majority goes to animal feed. So-called concentrated animal feeding operations, or CAFOs, where large numbers of cattle are fattened on corn and other grains, produce huge quantities of waste loaded with nutrients, which can run off into streams and rivers.

“So in some ways you’ve just outsourced the problem from the field to the feedlot,” Townsend says.

Dead zones are by no means limited to the Louisiana coast:

Dead zones worldwide. (Source: EPA, from “Spreading Dead Zones and Consequences for Marine Ecosystems,” Diaz and Rosenberg, Science, 2008 )

As of 2008, researchers had identified more than 400 dead zones around the world, covering almost 95,000 square miles.

One country to watch: China. “They are using fertilizer at a rate that has never been seen before,” Townsend says. “They’ve done an unbelievable job in creating astounding yields, but they’ve done it on the back of an incredibly inefficient system.”

Of course this also means that Chinese farmers could save money by becoming much more efficient, just as American farmers have done. In other words, the problem is amenable at least in part to a solution that would be a win/win for farmers, fishermen, and aquatic ecosystems.

  • Susan Moran

    Potent images and descriptions of a huge pervasive problem, Tom. Thanks for that. On China, check out images of Lake Taihu, which looks like a golf course from all the N and P pollution. Cheers!

    • Tom Yulsman

      Thank you Susan! I will definitely check out that lake.

      • Tom Yulsman

        Turns out I was very close to the shore of that lake this summer — in Souzhou, which is just a bit to the east. Lovely city! There’s a fabulous museum there designed by I.M. Pei. (Souzhou is his ancestral home: But I missed the lake masquerading as a golf course. Maybe it’s just as well…

  • Enopoletus Harding

    Why the heck does Russia have no human footprint? Its human footprint is certainly much larger than that of Canada; I’ve seen it myself.

    • Tom Yulsman

      Not sure, but it looks like they made no distinction between Siberia and the more developed parts of Russia.

  • Paul Strode

    I discuss this every year with my students. The irony is that the dead zone in the Gulf of Mexico is a product of our incredible demand for meat in this country. Most of the land that is the source of this extra phosphorus and nitrogen is in corn and soybean row crop production which are fed to livestock. The anglers in the Gulf who suffer economically from the dead zone shake their fists with one hand at the farmers of the Midwest, while holding a burger in the other hand.

    • Tom Yulsman

      Hi Paul, thanks for commenting here. And your point is well taken.

    • Mark Skinner

      Well stated ! We need more vegetarians !

  • NoBigGovDuh

    I’m not sure the word blossom sounds correct when discussing a

  • Scott

    It might also be worth mentioning more about nitrogen chemistry: the history of discovering how to make organic nitrogen from inorganic nitrogen in WWI so that Germany didn’t have to import bat guano from Brazil to make munitions to the use of synthetic nitrogen for fertilizer to get to the point now where the amount of synthetic organic nitrogen far outnumbers the amount of organic nitrogen our ecosystem naturally puts out each year.

  • Abinico Warez

    Dead zone blossoms – funny choice of words.

  • Michael Courtney

    Most conscientious citizens are aware of the environmental pseudoscience of “Global Warming” portraying something as benign as CO2 as a major pollutant requiring Draconian government restrictions on energy production. There has been less recognition of attempts to reduce agricultural fertilizer use by 45% in the Mississippi River watershed by demonizing nitrogen and phosphorus fertilizers as “pollutants” by publishing exaggerated claims of a purported Gulf of Mexico “dead zone.” The fact is that runoff of agricultural fertilizers has greatly enhanced fisheries production in the effected areas of the Gulf of Mexico and that the seasonal area of hypoxic bottom water affects less than 2% of the Gulf for only a few weeks each summer. Reducing fertilizer use by 45% would not only reduce agricultural production and drive up prices of farm products, it would also reduce fisheries production and increase seafood prices. See also:

  • Mark Skinner

    We worry about what’s happening on the land when we should be looking towards the seas and oceans.



ImaGeo is a visual blog focusing on the intersection of imagery, imagination and Earth. It focuses on spectacular visuals related to the science of our planet, with an emphasis (although not an exclusive one) on the unfolding Anthropocene Epoch.

About Tom Yulsman

Tom Yulsman is Director of the Center for Environmental Journalism and a Professor of Journalism at the University of Colorado, Boulder. He also continues to work as a science and environmental journalist with more than 30 years of experience producing content for major publications. His work has appeared in the New York Times, Washington Post, Audubon, Climate Central, Columbia Journalism Review, Discover, Nieman Reports, and many other publications. He has held a variety of editorial positions over the years, including a stint as editor-in-chief of Earth magazine. Yulsman has written one book: Origins: the Quest for Our Cosmic Roots, published by the Institute of Physics in 2003.


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