The dead zone in the Gulf of Mexico is getting bigger. That’s the bad news. But we’re making progress in figuring out why—and potentially how to reduce it.
Dead zones are areas of low oxygen caused by excess algae growth, which in turn is caused by high levels of nutrients in the water. Last year, a common comparison—and one I used in this column—to describe the dead zone was to say it was about the size of the state of Connecticut. This year, it’s 28% larger than in 2014, or about the size of Connecticut and Rhode Island combined. Researchers have been closely mapping the Gulf’s dead zone for the past three decades, and this year’s is the 11th largest recorded—not the worst, but moving in the opposite direction from what we want it to be.
Why the change? It’s well established that discharge from the Mississippi River, particularly the nutrient load from agricultural and urban areas in the river’s watershed, is the single biggest influence on the size and characteristics of the dead zone. The nitrate load in May of this year was in line with the yearly average, as measured over several decades. But heavy rains in June led to greater runoff to the river and record high discharges.
A disturbing detail is not just the overall size of the dead zone, but its severity. Hypoxia is said to exist when water has 2 milligrams per liter of oxygen or less. The oxygen concentrations in much of this year’s dead zone are even lower, less than 1 milligram per liter.
The Louisiana Universities Marine Consortium released data last month on this year’s conditions. (Executive director Nancy Rabalais was the subject of a Reader Profile in our November/December 2014 issue.) Survey cruises along the Gulf coast have been helping to identify specific areas of low oxygen, and researchers can then trace the potential causes upstream, such as heavy rains or high nutrient loads in particular watersheds. Texas A&M University and the National Marine Fisheries Service are two of the organizations conducting these data-gathering cruises.
And the information they provide is crucial. According to the Marine Consortium, “Long-term research and observations are the best ways to test and calibrate ecosystem models, the recognize the dynamic nature of our changing environment(s), and to improve the basis for sound management decisions.” There are many programs in place—mostly voluntary ones in the case of agricultural operations—to limit nutrient loading. Detailed measurements from multiple locations in the Gulf can tell us which ones are working.
Hypoxic conditions and dead zones occur all over the world, of course; in the US they occur off every coast, sometimes causing bans on commercial and recreational fishing and—as in the much-publicized case of Lake Erie a few years ago, where a toxic cyanobacteria bloom erupted—disrupting drinking water supplies. But the Gulf of Mexico’s is the largest one in the US, and currently the second-largest in the world. (The Baltic Sea has a larger one.) Research performed in the Gulf can help not only improve local conditions but also tell us more about the relationship between conservation efforts and results.
Maps of the dead zone and other information are available at www.gulfhypoxia.net.
Janice Kaspersen
Janice Kaspersen is the former editor of Erosion Control and Stormwater magazines.
