Gulf of Mexico's dead zone expected to grow

Heavy Midwest rains will wash more destructive fertilizer into the water, scientists say.

By Jessie Higgins
The Mississippi River delta is seen from the International Space Station on April 26. Photo courtesy of NASA
1 of 3 | The Mississippi River delta is seen from the International Space Station on April 26. Photo courtesy of NASA

EVANSVILLE, Ind., Aug. 7 (UPI) -- Scientists expect the size of the Gulf of Mexico's massive dead zone to grow in coming years, as changing global weather patterns pound the Midwest with heavier rains and more severe flooding.

The Gulf's dead zone is an area that spans thousands of square miles just off the coast and where no fish can survive. It is created year after year, mainly by fertilizers that run off Midwestern agricultural fields.


The fertilizers travel to the Gulf down the Mississippi River. Once there, they stimulate intense algae growth. That overly thick algae consumes all the oxygen in the water, choking out the other marine life.

"Just like people, anything living in the water requires oxygen to breathe," said David Kidwell, a lead scientist with the National Oceanic and Atmospheric Administration's National Centers for Coastal Ocean Science. "That oxygen is dissolved in the water. And when that dissolved oxygen level is low, it causes things to die off."


Thousands of species of marine plants and animals live in the Gulf, including shrimp, crabs, oysters, squid, octopus and corals. Animals that can swim, like fish or shrimp, simply leave the zone once the oxygen is depleted. Those that cannot swim usually die.

This low-oxygen -- or hypoxic -- area has existed in the Gulf for decades. Scientists began measuring it in the 1980s.

On average, the dead zone has not changed much for decades, said Dan Obenour, an assistant professor of civil, construction and environmental engineering at North Carolina State University who works with a team of scientists to predict the dead zone's annual size.

"The nutrient load ... plateaued in the late 1980s, and we haven't had much success at changing that," Obenour said.

But the situation could worsen because, while the amount of fertilizer applied to America's cropland hasn't changed, the percentage of that fertilizer carried into the Gulf is expected to increase, said Craig Cox, senior vice president for agriculture and natural resources at the Environmental Working Group.

The latest climate models, produced by the federally mandated U.S. Global Change Research Program, predict that springtime in the Midwest will become wetter. The rains will arrive in heavy downpours that will cut through fields, washing away tons of fertilizer-dense soil -- far more than over the previous decades.


It already has started. This year, historically heavy rains and flooding inundated the entire Midwestern region, delaying or preventing farmers from planting millions of acres of agricultural fields.

"All the climate models predicted what is happening now," Cox said. "Across the Midwest, it is going to be wetter. And, more importantly, most of the rainfall will come in heavy downpours."

When the water is delivered in a downpour, it creates more intense erosion, Cox said. Instead of washing off the fields in a more level sheet -- as happens with gentle rain -- the water creates a channel through the dirt.

"They look like small streams flowing through the fields," Cox said. "And that creates much more erosion. The estimated amount of soil and material that erodes is anywhere from two to four times more than what happens in a normal year. It's tons and tons and tons of soil and fertilizer."

It's already having an impact. Scientists this spring predicted that the Midwestern flooding would create a larger-than-average dead zone.

On June 10, NOAA released a forecast predicting the zone to span more than 7,829 square miles -- well above the five-year average size of 5,770 square miles, and nearing the record set in 2017 of 8,776 square miles.


"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," a statement from NOAA said. "This past May, discharge in the Mississippi and Atchafalaya rivers was about 67 percent above the long-term average between 1980 and 2018."

NOAA scientists measured the zone in late July at 6,952 square miles -- nearly 1,000 square miles smaller than predicted. But, the agency was quick to warn that the area probably would grow substantially.

The scientists measured the zone shortly after Hurricane Barry swept through the Gulf in mid-July. The storm churned up the water, bringing more oxygen into the dead area.

"Tropical storms will mix up the water and make the hypoxia go away," Obenour said. "But it is a temporary effect. It only lasts a couple weeks. So, the size they measured was a little smaller than what we predicted, probably because of the storm. It was kind of bad luck because now we don't have a clear picture of the zone's size."

The scientists who measured the area saw evidence that it was growing, Kidwell said.


The forecast may look bleak, but there are efforts being made to reduce the dead zone's size over in the coming years, Kidwell said.

In 2008, the Environmental Protection Agency formed the Mississippi River/Gulf of Mexico Hypoxia Task Force, bringing together multiple federal and state agencies to find ways to reduce the nutrient load in Mississippi River.

Much of their work focuses on stopping Midwestern soil -- and fertilizer -- from ever leaving agricultural fields. There are several ways to do this, one of the most promising is when farmers plant "cover crops" on their fields during the winter.

Most fertilizer runoff occurs during the fall, after the crop is harvested, and spring, before it is planted. During these periods, the fields are bare, and that allows rain to easily wash away large quantities of heavily fertilized soil.

Cover crops stop this by securing the soil.

There are other methods that can help, like planting perennial grasses in strips throughout the fields that remain permanently. These strips act as a buffer, blocking the runoff.

The use of these methods is increasing across the Midwest.

"A lot of farmers are trying it out," said Paul Overby, a farmer in North Dakota who has used cover crops for six years. "They're at the point where I was five or six years ago, where they're planting 50 acres with cover crops and seeing how it goes. It's coming."


It may not be coming fast enough, though, Cox said.

Between 2015 and 2016, less than 3 percent of Iowa's cornfields were planted with cover crops, according to an EWG survey. The same was true in Illinois. Indiana did a little better, with about 7 percent of fields covered.

"You'll hear the use of cover crops is increasing, and that is true," Cox said. "But it is at a snail's pace compared to what is needed. It's just not happening at the rate that it needs to happen to protect the Gulf."

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