DEAD ZONE: Runoff from Midwest farms plagues Gulf

By Perry Beeman Gannett,
3 November 2012

CHAUVIN — For shrimpers, crabbers and oystermen who work these waters, locating their harvest has become an increasingly taxing game of hide-and-seek.

Nitrates from the fertilizer and manure that Iowa’s farmers apply to their fields, mixed with sewage and runoff from suburban lawns, flow 800 miles down the Mississippi River to the Gulf of Mexico.

There, the potent blend feeds algae that bloom, die and decompose, robbing the Gulf’s waters of oxygen and creating a so-called dead zone — also known as hypoxia — each summer along Louisiana and Texas. Shellfish and other creatures capable of moving to more hospitable waters do so.

Those that can’t perish.


Hypoxia is the low-oxygen condition that sends shrimp and crabs migrating in search of more hospitable waters.
When the Mississippi and Atchafalaya rivers spill into the Gulf, fresh water forms a layer on top of the salt water, acting like a lid that keeps surface oxygen from reaching deep water. In a typical year, that means the hypoxia, or low oxygen, lasts in the deep water from spring into fall.
Waters with dissolved oxygen of less that 2 milligrams per liter are considered hypoxic.
A sign at Martin’s Fresh Shrimp in Chauvin, La., last summer encouraged people to buy local shrimp, not imports that account for 90 percent of the U.S. market.
Shrimpers blame imports from China, Vietnam and elsewhere for depressing prices.
Shrimpers in July were getting about $3 a pound for their catch. Years ago, wholesalers were paying as much as $9 a pound.

Related Links
Some Louisiana farmers reduce runoff to trickle