Mark Schleifstein | NOLA.com 3 August 2022
Scientists measuring the low-oxygen dead zone in the Gulf of Mexico this summer found a mix of good and bad news: It covered only 3,275 square miles of bottom waters, less than half the size of last year. But that was still larger than the combined areas of Rhode Island and Delaware, or five times the size of Lake Pontchartrain.
And even with this year’s drop, the dead zone’s five-year average size equals 4,280 square miles, more than double the national goal under a plan for reducing it. That goal calls for shrinking it to less than a 5-year average of 1,900 square miles by 2035.
Marine biologist Nancy Rabalais, who has overseen the dead zone mapping cruises along the Louisiana and east Texas coasts since it began in 1985, also warned that data collected this year show the reductions did not occur because of state and federal efforts to reduce emissions of nitrogen and phosphorus nutrients, mostly from fertilizer used in Midwest farming.
Instead, she said, they resulted from an unusual combination of weather events, some related to global warming. Spotty drought conditions in a number of locations among Midwest farmland dramatically reduced rainfall runoff in the Mississippi River basin between mid-June and mid-July, when the monitoring cruise began, she said. Rabalais is a marine biologist at Louisiana State University and the Louisiana Universities Marine Consortium.
Normally, the dead zone is created when nutrient-rich freshwater enters the Gulf from the river’s vast watershed, which includes parts of 32 states and two Canadian provinces. That freshwater creates a layer atop the salty Gulf waters that blocks the normal mix of oxygen from air above the surface into deeper waters, and stays in place until it is mixed by tropical storms in the summer or frontal systems in the fall.
In the spring and summer, nutrients in the surface water feed blooms of phytoplankton that eventually die, sink to the bottom and decompose, using up oxygen in that bottom layer.
When oxygen levels reach 2 parts per million, it’s defined as hypoxia. Fish, shrimp and crabs in those areas are able to swim to more oxygen-rich areas and survive, while bottom-living organisms die.
This year, however, the amount of freshwater measured during the cruise in the upper layer dropped off dramatically from the river’s mouth to the state’s western border.
The result was that there was a smaller area where freshwater at the surface blocked the ability of oxygen to mix into the water column, resulting in more oxygen being found by the crew aboard the M/V Polaris in measurements near the Texas border, compared to the low-oxygen readings near the river’s mouth.
This year’s results are an indication of the complexities facing efforts to reduce the size of the dead zone, said Rabalais and officials with federal agencies participating in the news conference.
What remains clear, Rabalais said, is that both federal and state agencies must continue to try to reduce the nutrients entering the river, if the long-term dead zone reduction goal is to be met.
A 2020 study by the Union of Concerned Scientists concluded that hypoxia is causing up to $2.4 billion a year in damage to fisheries and marine habitat.
Steve Thur, director of NOAA’s National Centers for Coastal Ocean Science, said during the news conference that NOAA Fisheries scientists based at North Carolina State University are working on an experimental model to help fishers identify where shrimp have been driven after leaving low-oxygen areas.
Officials with NOAA, which finances the dead zone monitoring, and the Environmental Protection Agency, used the news conference to highlight $60 million in bipartisan infrastructure law funds being provided to states over the next five years for research and projects aimed at that goal.
That money is in addition to a variety of long-running programs funded by the U.S. Department of Agriculture and EPA aimed at getting farmers to change methods and reduce fertilizer use. There are also programs seeking to turn marginal farmland into wetlands or grass buffer strips to capture nutrients before they enter waterways as well as reduce sewage effluent from both individual home treatment systems and urban wastewater systems from entering the river.
Iowa Agriculture Secretary Mike Naig said his state was a good example of how the infrastructure money will assist in ongoing efforts to reduce nutrients, using the $1 million a year his state expects to receive to match about $42 million a year it’s already spending on nutrient reduction efforts.
He said Iowa has enlisted 350 public and private partners in developing both agricultural and urban projects, including assistance to Ames, Cedar Rapids and Des Moines urban areas to assist in sewage treatment efforts.
Naig, co-chair of a federal-state Hypoxia Task Force that set the dead zone reduction goals, also pointed to similar projects in Ohio, including 20 wetland restoration projects and six wastewater infrastructure projects.
“They’re providing countywide grant assistance, including to nine counties for home sewage treatment system repairs in the Ohio River basin,” he said.
In Louisiana, the state Department of Environmental Quality this week filed an initial proposal with EPA on how it would like to use its share of the infrastructure money over the next five years.
One proposal is to fund a Coastal Protection and Restoration Authority plan to create a string of monitoring sites extending from Barataria Pass into the Gulf to measure nutrients, hypoxia and the effects of climate change.
That system also would help monitor the potential effects on water quality along the shoreline of the proposed Mid-Barataria Sediment Diversion, which could direct up to 75,000 cubic feet per second of river water into the Barataria basin to restore land.
Another proposal in the state plan would assist ongoing efforts of the federal Natural Resources Conservation Service to get farmers along Lake St. Joseph in Tensas Parish to adopt no-till farming practices to reduce nutrient runoff into the waterway, which connects to the Mississippi River.