It has become a rite of summer. Every year, a "dead zone" appears in the Gulf of Mexico. It's an area where water doesn't have enough oxygen for fish to survive. And every year, the National Oceanic and Atmospheric Administration commissions scientists to venture out into the Gulf to measure it.
This week, NOAA announced that this year's dead zone is the biggest one ever measured. It covers 8,776 square miles — an area the size of New Jersey. And it's adding fuel to a debate over whether state and federal governments are doing enough to cut pollution that comes from farms.
The debate actually goes back many years, at least to 1985, when Don Scavia was a scientist at the NOAA. He and his colleagues asked some scientists, for the first time, to go look for a dead zone in the Gulf.
"We expected it to be there," Scavia recalls. They expected to find it because they knew that the Mississippi River delivers a heavy load of nutrient pollution, specifically nitrogen and phosphorus, into the Gulf.
"Most of the nitrogen and phosphorus that drives this problem comes from the pper Midwest," Scavia says. "It's coming from agriculture."
Farmers use those nutrients on fields as fertilizer. Rain washes them into nearby streams and rivers. And when they reach the Gulf of Mexico, those nutrients unleash blooms of algae, which then die and decompose. That is what uses up the oxygen in a thick layer of water at the bottom of the Gulf, in a band that follows the coastline.
"Fish that can swim will move out of the way. Organisms that are living on the bottom, that the fish feed on, can't move, and they often die," says Scavia, who now is a professor of environment and sustainability at the University of Michigan.
The record-breaking dead zone this year is the result of unusually heavy rains in the Midwest, which flushed a lot of nutrients into the Gulf.
The dead zone is invisible from the surface of the ocean. Scientists lower instruments into the water to measure oxygen levels near the bottom. But Scavia describes it as a kind of hidden environmental disaster. "You know, it's 8,000 square miles of no oxygen. That can't be good!" he says. Potentially, it could have huge economic costs as well, because it imperils Louisiana's shrimp industry.
Federal and state agencies have promised to take action against the dead zone. As part of their "action plan" to shrink it, they're encouraging Midwestern farmers to try to keep nutrients from washing away by doing such things as planting wide grassy strips along streams to trap fertilizer runoff.
Scavia, however, recently published a blog post calling these voluntary measures inadequate. In a separate scientific paper, he also calculated that meeting the government's goal for a smaller dead zone will require dramatic cuts in nutrient pollution from farms.
Scavia argues that the Gulf should get the same kind of protection as the Chesapeake Bay, on the East Coast. The Chesapeake has had a similar dead zone problem. In 2010, though, despite fierce objections from farmers, the federal government set mandatory limits on nutrient pollution entering the bay. State governments spent billions of dollars to meet those targets. Now pollution in the bay is down, and some wildlife in the Chesapeake is starting to recover.
DAVID GREENE, HOST:
This summer, a record-setting dead zone has appeared in the Gulf of Mexico. This is a zone where water does not have enough oxygen for fish to survive. One major cause of this is pollution from farms. And this has provoked a debate about how to reduce that pollution, as NPR's Dan Charles reports.
DAN CHARLES, BYLINE: A dead zone appears every summer in the Gulf of Mexico, and we know this because 32 years ago, Don Scavia and his colleagues at the National Oceanic and Atmospheric Administration asked scientists to go look for it.
DON SCAVIA: We expected it to be there. We had no idea how big it actually was until we funded the work to go out and measure it.
CHARLES: They expected it because they knew that when the Mississippi River empties into the Gulf of Mexico, it brings a heavy load of nutrient pollution - nitrogen and phosphorus.
SCAVIA: Most of the nitrogen and phosphorus that drives this problem comes from the upper Midwest. It's coming from agriculture.
CHARLES: Farmers spread it on their fields as fertilizer. Rain washes it into nearby streams and rivers. And in the Gulf, those nutrients cause blooms of algae which then decompose. And that's what uses up the oxygen in a layer of water at the bottom of the Gulf along the coastline.
SCAVIA: Fish that can swim will move out of the way. Organisms that are living in the bottom that the fish feed on can't move, and they often die.
CHARLES: Scientists have continued to measure the dead zone. And this year, they found the biggest one yet - as big as the state of New Jersey, 8,776 square miles. It's because heavy rains in the Midwest flushed a lot of nutrients into the Gulf.
SCAVIA: You know, it's 8,000 square miles of no oxygen. That can't be good.
CHARLES: Don Scavia is now at the University of Michigan. He says the dead zone also has real economic costs. It puts Louisiana's shrimp harvest in danger. Federal and state governments have been trying to shrink the dead zone. They're encouraging Midwestern farmers to try to keep nutrients from washing away. For instance, by planting wide grassy strips alongside streams to trap fertilizer runoff. But Scavia says these voluntary measures are not enough.
SCAVIA: We definitely need to do a lot more.
CHARLES: Scavia argues the Gulf should get the same kind of protection as the Chesapeake Bay did on the East Coast. The bays had a similar dead zone problem, but in 2010, despite fierce objections from farmers, the federal government set mandatory limits on nutrient pollution there. State governments spent billions of dollars meeting those targets. Now, pollution in the bay is down. And there, some wildlife is starting to recover. Dan Charles, NPR News.
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