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University of Missouri

The Ungrateful Dead Zone

Water pollutants from agricultural runoff are killing Gulf of Mexico marine life.

skeleton fish

©shutterstock.com

Every summer, a portion of the Gulf of Mexico the size of Connecticut chokes in abundance. Nitrogen and phosphorous, applied as agricultural fertilizer, are ferried by river and stream through the 1.24 million square-mile Mississippi River basin and deposited in the Gulf. They spark a massive bloom in algae, which quickly die and decay, a process that consumes oxygen and kills marine life. Scientists call it the dead zone.

The U.S. Environmental Protection Agency’s Mississippi River/Gulf of Mexico Watershed Nutrient (Hypoxia) Task Force, formed in 1997, works to contain the dead zone. In 2014, it brought 12 land-grant universities, including Mizzou, onto the task force to help support state-level strategies to reduce pollution in the 2,300-mile Mighty Mississippi — the world’s second-largest watershed and a flyway to more than 325 migratory bird species.

College of Agriculture, Food and Natural Resources (CAFNR) scientists are already providing data on the effectiveness of variable-rate fertilizer application and livestock manure management.

Jason Hubbart, associate professor of forest hydrology and water quality, and director of the Center for Watershed Management and Water Quality in CAFNR, is MU’s research representative to the task force.

“MU has expertise in statewide soils, climates, people and solutions and is, therefore, a highly trusted source of objective research-based information,” Hubbart says.

Cornbeans

Nitrogen-based fertilizer is the most popular agricultural fertilizer in the U.S., and nearly half of the 13 million tons used in 2011 went to the country’s most popular crop, corn.

Unlike soybeans, corn can’t pull nitrogen from the air and covert it to a usable form in the soil — what’s called nitrogen “fixing.”

If it could, the need for nitrogen fertilizer would plummet.

Strictly speaking, soybeans don’t fix nitrogen either. Rather, it’s done by the Rhizobia bacteria that thrive on their roots. Rhizobia give off a chemical signal that inhibits soybeans’ immune response, allowing the bacteria to take up their root residence.

In a 2013 paper published in the journal Science, Gary Stacey, Curators Professor of Plant Sciences in CAFNR, showed that corn and tomatoes, though they don’t allow Rhizobia on their roots, nevertheless recognize the bacteria’s signal and reduce their immune response.

The finding is a potential breakthrough on the way to Stacey’s goal of developing a nitrogen-fixing corn variety.

Oh, Gee. Algae.

One way to prevent nitrogen and phosphorous from flowing into the ocean is to remove it from streams.

Mizzou’s Zhiqiang Hu, associate professor of civil and environmental engineering, and Baolin Deng, C.W. LaPierre professor in the same department, with a joint appointment in chemical engineering, are working on just such a method.

Using an advanced filtering system and a particular algae, the professors hope to improve existing technology and use high-density algae cultivation at municipal treatment plants to skim nitrogen and phosphorous from wastewater.

The system filters the sediment and dissolved nitrogen and phosphorous from the water and feeds it into an algae-filled tank that digests the nutrients. The algae are then harvested and broken down through anaerobic digestion, the products of which are methane, which can be burned to produce electricity, and nitrogen and phosphorous, which can be returned to fields and reused as fertilizer.

Using lab prototypes, they have identified optimal conditions for the process, which don’t include cold, Hu says. So a full-scale system likely won’t be seen in Columbia but rather in warmer climes such as California, Florida or perhaps Mississippi.

The approach improves water quality, produces energy and reuses fertilizer for farmers, something Deng likes. “Food, water and energy are all related,” he says, and can’t be treated in isolation. “It’s a system.”