Scientists say this year’s Gulf of Mexico “dead zone” is almost guaranteed to be the worst one on record. In truth, they say that every year — and they’re usually right.
Every summer, like clockwork, the Gulf of Mexico develops a huge area of oxygen-depleted water near the mouth of the Mississippi River.
When Gulf oxygen levels hit rock bottom, nothing can survive. The fish and shellfish that can leave the area will flee. Creatures that can’t leave will die.
It’s a problem that harms the Gulf ecosystem and the commercial fisheries that depend on the Gulf to survive. According to estimates, this year’s dead zone may be as large as the entire state of New Jersey.
What Causes the Gulf of Mexico Dead Zone?
Scientists have been studying the dead zone phenomenon in the Gulf of Mexico since 1985.
The problem is caused by nutrient runoff — mostly nitrogen and phosphorous — from farms and livestock operations throughout the Midwest.
Spring flooding carries fertilizer and livestock waste from the heartland to the Mississippi River, which in turn carries the nutrient runoff south. Eventually the runoff spews into the Gulf, triggering huge green algae blooms.
The blooms cause a dead zone when the algae eventually sinks to the bottom of the Gulf. Bacteria move in to feast on the dying algae, decomposing it and quickly consuming the oxygen at the bottom layer of water. When oxygen concentrations fall below the level necessary to sustain most life, the area becomes “hypoxic” — a dead zone.
Dead Zones: Weather Can be a Friend and a Foe
Weather can also affect dead zone development, in both positive and negative ways.
Anything from wind speed to temperature to hurricanes can affect how serious a dead zone is in any given year. For example, a hurricane that hits the Gulf in the middle of the summer will move the water around enough to keep the bottom layer from being completely smothered.
Blame the weather for what’s going on this year. Minnesota, Illinois, Wisconsin and Iowa had extremely wet springs in 2013. The significant flooding this year means that the Mississippi River carried exponentially more agricultural runoff to the Gulf.
Why Study Dead Zones?
“It’s important because most often those areas that become uninhabitable by fish, are preferred habitat for fish. To draw on an analogy that’s ironic, it would be like taking thousands of square miles of land in the Midwest out of production. People wouldn’t like it,” University of Michigan aquatic ecologist Donald Scavia told National Geographic.
It’s also about finding out what is contributing to dead zone growth.
The amount of nitrogen flowing into the Gulf of Mexico over the past 50 years has increased by approximately 300 percent, mostly thanks to agricultural runoff.
In May 2013 alone, an estimated 153,000 metric tons of nutrients washed down the Mississippi and Atchafalaya Rivers, according to the U.S. Geological Survey. That’s 16 percent more than the average nutrient load over the past 34 years.
What’s going on? In a nutshell, we’re growing more corn. Corn, unlike many other crops, must have fertilizer to grow. Much of the corn we’re growing isn’t even intended for us to eat. About 40 percent of the corn we raise is used to make fuel — ethanol, which renewable fuel mandates require us to blend with gasoline. Another third of our corn crop feeds domestic livestock.
All that corn farming means we’re using fertilizer galore. When it rains in the spring and summer, much of that fertilizer washes away, eventually making it to the Mississippi and Atchafalaya Rivers. Clearly, before we choke off the Gulf completely, we need to solve our agricultural runoff problem.
Can We Reduce the Size of the Dead Zone?
The Mississippi River/Gulf of Mexico Watershed Nutrient Task Force, a coalition of Federal, state and tribal agencies along the Mississippi Watershed formed in 1997, aims to do just that. The group set a goal in 2001 and again in 2008 to reduce the size of the Gulf hypoxic zone to an average 1,950 square miles by 2015.
It doesn’t look like they will make it. Since 1995, the annual Gulf dead zone has been about the size of Connecticut — 5,960 square miles, give or take. The only year it was smaller than projected was in 2012, when drought along the Mississippi River Basin limited the amount of runoff that ended up in the Gulf.
We’ll know for sure how bad this year’s dead zone is when scientists conduct their official measurement in late July.
Even if it’s not Jersey-big, it will be huge, and that’s not a good sign.
Photo Credit: NASA