美国国家公共电台 NPR The Gulf Of Mexico's Dead Zone Is The Biggest Ever Seen（在线收听）

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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