COLUMBUS, Ohio -- Researchers are studying ways to control the rush of nitrogen and other chemicals that flow into the Mississippi River watershed each spring and ultimately turn more than 7,000 square miles of the Gulf of Mexico into a “dead zone.”
Nitrogen and other nutrients cause hypoxia, or the depletion of oxygen in a body of water. Hypoxia in the Gulf stems from human activities in the Mississippi River watershed, which encompasses more than 40 percent of the United States. A federally-appointed task force is currently looking into ways to manage the hypoxia problem.
“The answers to controlling hypoxia essentially come down to using nature to take care of our problems while protecting its biodiversity,” said William Mitsch, professor of natural resources at Ohio State University. “These solutions embrace ecotechnology, which includes restoring or building wetlands and riparian buffer zones along waterways.”
Mitsch leads one of six task force committees currently studying the hypoxia problem in the Gulf of Mexico. His committee is responsible for developing ways to control the pollution that causes hypoxia in the Gulf. The group presented their preliminary results June 9 at an Ecological Society of America meeting in St. Louis.
“Hypoxia is the result of living in an over-fertilized society,” Mitsch said. “We fertilize the living daylights out of the Midwest.” Ecotechnology may be the answer.
“Ecotechnology establishes some degree of natural landscape between human activity and waterways,” Mitsch said. Riparian zones, belts of vegetation next to a waterway, and wetlands both serve as filtering systems. Each essentially “cleans” runoff water of fertilizer by-products.
Hypoxia happens when excess nutrients, such as nitrogen and phosphorus, accumulate in a body of water and cause algae to flourish into algal blooms. These blooms thrive on nitrates and phosphates and deplete the water of nearly all dissolved oxygen.
Dissolved oxygen content in the Gulf is normally 5 parts per million (ppm). Hypoxia occurs when this level dips to 2 ppm or lower. The lack of oxygen either forces aquatic life to relocate or kills it.
Hypoxia affects many coastal areas of the world, such as the Baltic Sea and Chesapeake Bay. It is also on the increase in shallow coastal areas such as the Gulf of Mexico, which means a reassessment of priorities is in order, Mitsch said.
“Hypoxia may be a standard of living issue,” he said. “If we decide not to cut back on our pesticides and fertilizers, we may not be able to solve the problem.” The main problem, he added, comes from farming. According to the U.S. Geological Survey, about 56 percent of the nitrogen entering the Gulf is from fertilizer runoff.
“It’s hard for a farmer in the Midwest to connect his activities to problems in the Gulf of Mexico,” Mitsch said, adding that the far-reaching Mississippi River watershed encompasses Midwestern farm fields.
Other potential solutions to the hypoxia problem include reducing the initial disposal of nutrients into waterways; increasing the ability of a watershed to assimilate nutrients; and changing the hydrology of the Mississippi Basin.
“Humans levied the river to make it behave, while the river used to have the ability to naturally flood over its banks and spread nutrients over the landscape,” Mitsch said. “When water naturally spills over the banks, it can drain through a riparian corridor and come back as cleaner ground water.
“It’s our job to assess how well these proposed ecotechnologies will work in dealing with the hypoxia problem,” Mitsch said. “It just makes ecological sense to try these kinds of things.”