Environment

Scientists predict giant ‘Dead Zone’ the size of Massachusetts in the Gulf of Mexico

As rain deluged the Midwest this spring, commercial fisherman Ryan Bradley knew it was only a matter of time before the disaster reached him.

All that water falling on all that fertilizer-enriched farmland would soon wend its way through streams and rivers into Bradley’s fishing grounds in the Gulf of Mexico, off the Mississippi coast.

The nutrient excess would cause tiny algae to burst into bloom, then die, sink and decompose on the ocean floor – a process that sucks all the oxygen from the water, turning it toxic. Fish would suffocate or flee, leaving Bradley and his fellow fishermen nothing to harvest.

Scientists from the National Oceanic and Atmospheric Administration and Louisiana State University confirmed Bradley’s worst fears in forecasts published Monday, predicting this spring’s record rainfall would produce one of the largest-ever “dead zones” in the Gulf of Mexico.

An area the size of New Jersey could become almost entirely barren this summer, posing a threat to marine species – and the fishermen who depend on them.

“It’s just a major punch in the gut,” said Bradley, a fifth-generation commercial fisherman from Long Beach, Mississippi. Bradley is executive director for Mississippi Commercial Fisheries United, a nonprofit group that supports the state’s fishermen.

Bradley said he plans to travel to Washington this month to ask federal lawmakers to declare a fisheries disaster, making relief funds available to affected fishermen.

“To have a total wipeout,” he said, “which is what we’re going to have here now, I don’t know if our guys are going to be able to make it.”

Nancy Rabalais, an LSU marine ecologist who developed one of the recent forecasts, called the outlook one of the most severe she has seen.

“It’s perennial,” she added. “And it shows no signs of diminishing.”

Unoxygenated “dead zones” appear in waterways wherever algae are overfed by runoff from human activities such as urbanization and agriculture – a phenomenon called eutrophication.

NOAA estimates that 65 percent of American estuaries and coastal waterways are moderately to severely degraded by this phenomenon. The hundreds of dead zones around the world cover a combined 100,000 square miles (259,000 square km) and have caused nearly 10 million tons of biomass to either move or die.

The dead zone in the Gulf of Mexico, fueled by the nutrient-laden water spilling from the mouth of the Mississippi River, is the second-largest in the world.

It blooms every summer, when warming waters accelerate the metabolisms of microorganisms, and it is expected to get even worse as the climate continues to change.

The Midwest’s recent extreme weather will almost certainly exacerbate the problem, said David Scheurer, a NOAA oceanographer who worked on the agency’s dead-zone forecast.

The National Weather Service reported this week that the Mississippi River is in the midst of its longest cycle of flooding since 1927.

Analyses from US Geological Survey monitors in the Mississippi and Atchafalaya watersheds showed that discharge from these rivers was 67 percent greater than the 1980-2018 average.

The amounts of nitrogen and phosphorus spilling into the Gulf were 18 percent and 49 percent above average, respectively.

Those nutrients, Scheurer said, “provide the foundation for [and] the fuel for the dead zone itself.”

NOAA’s model forecasts this summer’s dead zone to cover 7,829 square miles (20,000 square kilometers); Rabalais’s prediction puts the size at 8,717 square miles (22,576 square kilometers).

These numbers are far above the five-year average of about 6,000 square miles (15,500 square kilometers). It would have to be cut 75 percent in the next 15 years for the Environmental Protection Agency to meet a target size for the dead zone of 1,900 square miles (4,900 square kilometers) by 2035.

The Gulf of Mexico yields commercial fish catches in the hundreds of millions and generates tens of billions of dollars in revenue, according to the National Marine Fisheries Service.

But Rabalais, who conducts an annual cruise into the affected area, said the summertime dead zone can turn the Gulf into a wasteland. Bottom-dwelling organisms such as eels and shrimp will swim 60 feet (18 meters) to the surface just to get some oxygen.

The carcasses of any creatures that can’t flee – worms, burrowing crabs, brittle stars – lie motionless in the mud. Vast mats of bacteria, which thrive in low-oxygen environments, form a carpet over the seafloor.

Scientists are only beginning to understand the ecological and economic consequences, she said. But studies have shown that eutrophication reduces the abundance of Atlantic croaker and affects the price of shrimp; both are important commercial species.

Fisheries on the eastern side of the Mississippi will endure a double whammy, Bradley said, after the opening of the Bonnet Carré Spillway, which redirected floodwaters from the river into Lake Pontchartrain.

The move protected the city of New Orleans from flooding, but it spewed problematic nutrients into Mississippi’s inland waterways.

“So we’ve created a dead zone in our near-shore environment too,” Bradley said. “We’re really going to feel a big hammer this year.”

The only long-term solution to the dead zone is to treat it at its source: in the farms and cities of the 31 states of the Mississippi watershed, Rabalais said. The EPA has developed a “hypoxia task force” that aims to reduce the amounts of nitrogen and phosphorus that make it into the region’s waterways.

Even if nitrogen runoff was eliminated today from the Mississippi River, a 2018 study in the journal Science found, it would take at least 30 years for the Gulf dead zone to recover.

2019 © The Washington Post

This article was originally published by The Washington Post.

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