Advocate staff 10 June 2019

The 2019 “dead zone” in the Gulf of Mexico could be the second largest on record because high water in the Mississippi River watershed will funnel excessive nutrients and fertilizer downstream this year.

Every year, nutrients and fertilizer rush down the Mississippi River into the Gulf to create a zone of low oxygen known as hypoxia. The area is commonly referred to as the “dead zone” because it holds too little oxygen to support marine life.

Louisiana scientists predict this year’s dead zone will cover about 8,717 square miles, or an area about the size of New Hampshire.

Hypoxic conditions form when nitrates and phosphates feed nutrients feed algae, which die and then decompose on the sea floor, using up oxygen from the bottom up in an area along the coasts of Louisiana and Texas. These chemicals are present in runoff from ranches, sewage treatment facilities and especially farms that use nitrogen-rich fertilizer.

“A major factor contributing to the large dead zone this year is the abnormally high amount of spring rainfall in many parts of the Mississippi River watershed,” the National Oceanic and Atmospheric Administration said in a news release Monday. It predicted a slightly smaller dead zone, at 7,800 square miles.

LSU professor Nancy Rabalais said if the hypoxic area becomes as large as predicted, then it will be about 4.5 times the size of the Hypoxia Action Plan goal to reduce it to less than 5,000 square kilometers, or around 1,900 square miles. No reductions in nitrate loading from the Mississippi River to the Gulf of Mexico has occurred in the last few decades.

Rabalais, of the Louisiana Universities Marine Consortium, will measure the dead zone during a July trip offshore. She has been measuring the hypoxic zone since 1985.

The record dead zone occurred in 2017 at 8,776 square miles.

Scientists had said previously that widespread flooding made a large dead zone likely this year.

A task force of federal, tribal and state agencies from 12 of the 31 states that make up the Mississippi River watershed set a goal nearly two decades ago of reducing the dead zone from what was then an average of about 5,800 square miles.

“While this year’s zone will be larger than usual because of the flooding, the long-term trend is still not changing,” said University of Michigan aquatic ecologist Don Scavia, professor emeritus at the School for Environment and Sustainability. “The bottom line is that we will never reach the dead zone reduction target of 1,900 square miles until more serious actions are taken to reduce the loss of Midwest fertilizers into the Mississippi River system.”

Storms before last year’s mapping cruise reduced that hypoxic zone to about 2,720 square miles, or about 40 percent of the average size that had been predicted, and among the smallest recorded.