16 May 2019
Scientists are predicting a “large to very large” Gulf of Mexico dead zone this year.
It may even wind up being the largest on record.
Experts discussed their forecast at a Thursday morning meeting of the Mississippi River/Gulf of Mexico Hypoxia Task Force, a coalition of state and federal leaders working under the U.S. Environmental Protection Agency.
An official estimate of the size of the dead zone is not expected until June to give researchers a chance to collect complete May data. Concentrations of nitrates in the water continue to fluctuate and rose just Wednesday night, LSU oceanography professor Gene Turner said in an interview.
The dead zone forms when nitrates and phosphates enter the Gulf, where algae feed on them. When the supply of nutrients runs out, the algae die and decompose, sucking the oxygen out of the water, a condition known as hypoxia.
Nutrients are produced by wastewater treatment facilities and ranches, but the biggest concern is nutrient-rich fertilizer runoff from farms. All the rain that has soaked the Mississippi River Basin this spring is also expected to wash the nutrients that feed the dead zone down the Mississippi River, said Steven Thur, director of the National Centers for Coastal Ocean Science at the National Oceanic and Atmospheric Administration.
Thur declined to speculate on a precise forecast but noted that rains have washed into waterways “significant loads” of nutrients that are likely to feed a “large to very large” dead zone. Turner said scientists are considering whether it could be the largest ever recorded.
Last year, scientists measured a very small hypoxic area, but Thur said researchers now believe those findings were skewed due to high winds mixing the water just before they went out to take samples. Had they collected their data a week before or after, they likely would have found the dead zone was much larger.
LSU oceanographers are also investigating whether it might be more productive to discern the volume of hypoxic zones rather than just the surface area.
“The researchers’ model simulations indicate that even under a modest 25% nitrogen load reduction, the thickness of the hypoxic layer in the northern Gulf of Mexico decreases markedly, and hypoxia remains localized to a relatively thin layer near the bottom that most fish and other mobile organisms can more effectively avoid,” the LSU College of the Coast & Environment wrote in a February news release.
Louisiana contributes only one percent of the nutrients that wind up in the Gulf, said Louisiana Department of Environmental Quality Secretary Chuck Carr Brown. The agriculture-heavy “I caucus” — Indiana, Illinois and Iowa — supply much more.
Brown discussed DEQ’s intent to implement by the end of the year a pollution credit program in which polluters who make improvements can earn credits they can sell to other sites. The trick, he said, will be making sure the measures stick. So if a farmer builds a retention pond that helps keep fertilizer out of the river, the state needs to ensure that pond stays there, even if the farmer sells the land.
He suggested that in the future, participants could sell credits across state lines to encourage the best technology and conservation-oriented practices.
“We have to find collective solutions,” he said.
Several speakers also said the planned mid-Barataria and mid-Breton sediment diversions south of New Orleans will have the added benefit of helping strip nitrates and phosphates from river water. Conference attendees hope pushing the water through wetlands would give the flora there a chance to soak up some of the nutrients.
“Our main strategy is to intercept nutrients that have already entered the system and prevent them from reaching the Gulf of Mexico,” said Chip Kline, chairman of the Coastal Protection and Restoration Authority.
Yet much of the emphasis remains on sustainable agricultural practices: installing buffer zones, practicing no-till farming, planting cover crops, employing prescribed grazing, and other strategies.
Not everyone has been pleased with the Hypoxia Task Force. In the nearly 20 years since the group formed, the nutrient load has continued to increase, and the dead zone gotten larger, said Matt Rota, senior policy director of the nonprofit Healthy Gulf. He said organizations like his up and down the Mississippi have tried to pitch in, but the task force doesn’t respond to their letters or heed their advice.
“We feel like we’re being ignored. It’s frustrating,” Rota said.