Hypoxia sounds like a treatment that pop stars would use to keep from aging, but it’s actually one of the most serious—if underreported and invisible—environmental threats in the world. Hypoxia occurs when coastal waters become overloaded with nutrients like nitrogen and phosphorus—often from sewage or fertilizer running off the land. All those tasty nutrients encourage blooms of phytoplankton, which steadily suck the levels of oxygen from the water through respiration. (Phytoplankton do breathe.) When those phytoplankton die, they sink to the bottom of the water, where bacteria use oxygen to break them down, further stripping oxygen from the water. The result can be a “dead zone“—an area where water has almost been stripped of oxygen, killing any sea life that can’t swim or crawl away.
The Gulf of Mexico has long been home to a gradually expanding seasonal dead zone, thanks at least in part to fertilizer from the rich farmlands of the Midwest, which runs off and flows down the Mississippi River and into the Gulf. (Over the past two decades the Gulf dead zone has averaged about 5,200 sq. mi.) As my colleague Tara Thean wrote earlier this summer, scientists predicted that this summer’s Gulf dead zone might reach record size because of the catastrophic floods that hit the upper Midwest earlier this year. More floods can mean more fertilizer runoff—and that can mean more hypoxia.
Well, the results are in, and it turns out the Gulf dead zone is larger than average—but not record size. Scientists from the Louisiana Universities Marine Consortium (LUMCON) embarked on their annual research cruise to measure the size of the dead zone last week, and found that hypoxia covered an estimated 6,765 sq. mi of the Gulf. (You can download a PDF of LUMCON’s press release here.) That makes it one of the biggest dead zones since scientists began studying the phenomenon back in 1985, but it’s significantly less than the 8,500 to 9,421 sq. mi scientists predicted at the start of the summer.
That’s good news, right? Well, not exactly. The LUMCON researchers made their measurements just as Tropical Storm Don was plowing through the Gulf of Mexico and headed towards Texas. As Nancy Rabalais, the executive director of LUMCON, said in a statement, the storm likely threw off the study:
Chief Scientist, Dr. Nancy Rabalais, reported that “the major disruptor of the size was Tropical Storm Don that followed the Research Vessel Pelican across the Gulf of Mexico towards Texas and whipped up the winds and waves.” Mixing of the water column re-supplies oxygen to the lower layers and reduces the area of low oxygen, at least temporarily.
That means even during a period when a strong storm was churning up oxygen-rich waters from the ocean floor, the dead zone was still much larger than average. That’s not a good sign for the Gulf of the Mexico, and it shows that we still have a long way to go in reducing fertilizer runoff in the Midwest and other sources of coastal pollution.
Nor is hypoxia only a problem for the Gulf. In 2008, researchers in Science reported that there were more than 400 dead zones around the globe, covering 95,000 sq. mi of seabed—nearly the size of Wyoming. And it’s likely to get worse—as the British science writer Mark Lynas describes in his great new book The God Species, humans will likely intensify fertilizer use as we seek to increase agricultural productivity and meet a growing global population’s rising demand for food. If we can’t use fertilizer more efficiently—which companies like Pepsi are actually working on—and curb runoff, more of those nutrients will end up in the oceans. And the dead zones—as stripped of life as the surface of the moon—will keep growing.