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Gulf of Mexico Dead Zone

This map generally illustrates how runoff from farms (green areas) and cities (red areas) drains into the Mississippi, delivering nutrients into the Gulf of Mexico and fueling the annual hypoxic zone. Image: NOAA

The Inertia

Every summer for decades now, the Gulf of Mexico has endured something called a dead zone, and the National Oceanic and Atmospheric Administration (NOAA) forecasts for this summer aren’t looking too hot. They’re expecting it to come in at around 8,000 square miles, which is roughly the size of Massachusetts. A dead zone, as the name implies, is a place so devoid of oxygen that nothing can live.

In short, dead zones occur when a variety of factors come together. As they say, all rivers lead to the sea, and the Mississippi River watershed running into the Gulf of Mexico just so happens to be the jumping off point for vast amounts of agricultural runoff used to feed our insatiable lust for more of everything.

“The Mississippi River watershed drains 1.245 million square miles, including all or parts of 31 U.S. states and two Canadian provinces, the NOAA explains. “Runoff from farms and cities drains into the Mississippi, delivering nutrients into the Gulf of Mexico and fueling the annual hypoxic zone.”

Here’s an interesting related aside: according to a study Mighty Earth did in 2015, the average American ate 211 pounds of meat. The CDC put the average American’s weight at 195 pounds for the same year, which means, of course, that we’re eating more than our weight in meat each year.


In the wake of the NOAA’s forecast, Mighty Earth laid the blame squarely at the feet of America’s biggest meat companies.

“In 2018, JBS was responsible for generating 80 million tons of raw sewage – and that’s just what we know about,” said Mighty Earth Campaign Director Lucia von Reusner. “Dumping that much manure and slaughterhouse waste into our waters is clearly a major threat to our health and downstream prosperity, but the new forecast shows just how disastrous and out of hand the industry’s pollution has become. The environmental catastrophe is rivaled only by the economic damage this will do to the Gulf economies later this year.”

When the fertilizer-laden runoff from the corn and soy grown for the vast cattle ranches inevitably makes its way into the waterways and, eventually, into the Gulf, the fertilizer continues to do what it does: fertilize. Only now, it fertilizes algal blooms, which occur naturally. When algae are given a massive dose of nitrogen and phosphorus, however, they flourish, and they flourish in a big way.


The phytoplankton milling around in the area have a feeding frenzy on that algae and the populations explode. Then, since there are just so many of them, huge portions die off, sink to the bottom, and the even-tinier creatures that break them down use up way more dissolved oxygen than they should. And there you have a dead zone. It seems odd that this has been happening for so long we can put a number on the average size of it every year, but so it goes.

The five-year average is 5,770 square miles, but two years ago in 2017, the record was smashed. It came in at 8,776 square miles, just a little more than 2019’s expected dead zone. The reason this year’s dead zone is expected to be so much larger than average is – as you probably already guessed – related to the changing climate.

You may have noticed that this winter was a wet one. Enormous storms pummeled the globe, bloated with moisture sucked up when the ocean is warmer than it usually is. Those storms soaked the country, filling rivers and soaking the earth that grows our food. Then, as water tends to do, all that precipitation, now choked with fertilizers, drained into the water table and into the creeks and rivers nearby.

“A major factor contributing to the large dead zone this year is the abnormally high amount of spring rainfall in many parts of the Mississippi River watershed, which led to record high river flows and much larger nutrient loading to the Gulf of Mexico,” the NOAA wrote in a press release. “This past May, discharge in the Mississippi and Atchafalaya rivers was about 67 percent above the long-term average between 1980 and 2018.”

According to the United States Geological Society, the larger-than-average discharge carried 156,000 metric tons of nitrate and 25,300 metric tons of phosphorus into the Gulf in May alone. That’s nearly 20 percent more nitrates than the long-term average and a staggering 49 percent more phosphorus.


Now, bear in mind that this is all still a prediction, but it’s a prediction based on years of data. Every year, the NOAA’s Hypoxia Task Force uses the previous models to set nutrient reduction targets and better understand how dead zones are linked to nutrients.

“The forecast assumes typical coastal weather conditions, but the measured dead zone size could be disrupted and its size could change by major wind events, hurricanes and tropical storms which mix ocean waters, as occurred in 2018,” the NOAA wrote. “A NOAA-supported monitoring survey will confirm the size of the 2019 Gulf dead zone in early August, a key test of the accuracy of the models.”

The Mississippi River/Gulf of Mexico Watershed Nutrient Task Force, a group working to reduce the Gulf dead zone through nutrient reductions within the Mississippi River watershed, has set a five-year average measured size target of 1,900 square miles, far smaller than the current average.

Throughout much of the country, nitrogen loading into coastal estuaries has decreased in recent years, but in the Gulf of Mexico, it’s a different story. Nitrogen and phosphorus loads continue to pour into it each year simply because of the way we get much of our food.


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