Top Paper in Environmental Science: Leaving a legacy of dead zones

Erika Engelhaupt in Environmental Science & Technology: “Gulf of Mexico Hypoxia: Alternate States and a Legacy” by R. Eugene Turner and Dubravko Justic, Louisiana State University; and Nancy N. Rabalais, Louisiana Universities Marine Consortium, 2008, 42 (7), 2323−2327; DOI 10.1021/es071617k.

In 1974, biologist R. Eugene (Gene) Turner was tossing about in a tiny 15-foot boat off the Louisiana shore when his handheld oxygen meter started showing strangely low readings. Turner was scouting the coastal waters as a new faculty member at Louisiana State University, and what he discovered led to a career-spanning quest to understand low-oxygen “dead zones”, or hypoxia, in the Gulf of Mexico. His longtime collaboration with coauthors Nancy N. Rabalais and Dubravko Justic (affectionately dubbed “Dubi” by his teammates) has now resulted in ES&T’s top science paper of 2008.

“Other people had measured low oxygen before, but it had never been followed up,” Turner says. He initially wondered if the low-oxygen areas were related to the large number of oil and gas rigs nearby, but soon he realized that high levels of nutrients flowing down the Mississippi River to the Gulf of Mexico were to blame. Most of the nutrients come from fertilizers used in the Midwest, and these nutrients stimulate excessive growth of algae that later rob waters of oxygen when they die and decompose.

In 1985, Turner and Rabalais received a small grant to map hypoxic zones. Rabalais then had her own turn bobbing about 25 miles offshore in an undersized Boston Whaler with a handheld oxygen meter. “I came back and told him I wasn’t going to die doing this research,” she says. For more than 20 years since then (and in successively larger boats), the now husband-and-wife team of Turner and Rabalais has surveyed hypoxia in the Gulf, with only one exception in 1989 when funding ran dry.

This year’s award-winning paper is a culmination of research that led the team to conclude that coastal ecosystems in the Gulf are becoming more sensitive to nutrient loads. “It’s not the same system as in the 1960s. It’s taking less nutrients now to fuel this hypoxic situation,” Rabalais says.
Over time, large nutrient-fueled algal blooms have deposited loads of organic matter to coastal sediments, and the slow decay of these remnants in the sediments continues to use oxygen. This extra demand for oxygen adds to the problem created by each year’s new blooms, and as a result, the potential size of the hypoxic zone doubled for a given nitrogen load from 1980 to 2000.