A team led by researchers from Louisiana State University has measured the largest anoxic "dead zone" in the Gulf of Mexico ever recorded.
The 8,800 square mile zone is the product of algal blooms, which are fed by high levels of agricultural fertilizer in the outflow from the Mississippi River. The algae grows and decomposes, using up the dissolved oxygen in the water in the process. Aquatic species are forced to move outside this plume in order to survive, with effects on fisheries.
The size of this year's zone stems from higher-than-normal discharge from the Mississippi, the researchers said. Heavy rains carried large amounts of phosphorus and nitrogen fertilizer off of fields and into the river drainage, and the recent measurements confirmed NOAA forecasts for a super-large dead zone. “We expected one of the largest zones ever recorded because [of] the Mississippi River discharge levels, and the May data indicated a high delivery of nutrients during this critical month which stimulates the mid-summer dead zone,” said study leader Nancy Rabalais, Ph.D., a professor at LSU.
The federal government has targets for the maximum size of the dead zone, and it has voluntary measures in place for farmers to reduce runoff. But Prof. Donald Scavia of the University of Michigan, a specialist in forecasting algal blooms, contends that these steps are insufficient.
"In the Mississippi River basin this approach has failed. In spite of more than 30 years of research and monitoring, over 15 years of assessments and goal-setting, and over $30 billion in federal conservation funding since 1995, average nitrogen levels in the Mississippi have not declined since the 1980s," he recently wrote. He points to the success of the states in the Chesapeake Bay watershed in reducing runoff and reviving fisheries: these states asked EPA to formulate a target maximum for fertilizer pollution in the watershed, then each came up with a management plan to meet it. Agricultural pollutant levels have fallen over the years since and Chesapeake fish stocks are on the rise.
Scavia notes that reducing nutrient outflows into the Mississippi and the Great Lakes would require more serious changes – notably, cutting down on fertilizer-intensive corn production, including the 40 percent that goes into making ethanol for gasoline blends.