“dead zone” in the gulf: addressing agriculture’s...

The Northern Gulf of Mexico’s hypox-ic (oxygen-deficient) waters represent oneof the Western Hemisphere’s largest “deadzones”—areas where lack of oxygen killsfish, crabs, and other marine life. The sizeof the zone varies but at its peak, itstretches along the inner continental shelffrom the mouth of the Mississippi Riverwestward to the upper Texas coast, cover-ing about 7,000 square miles, an area aslarge as New Jersey. Long-term conse-quences to biodiversity, species abun-dance, and biomass in the Gulf are not yetknown, but experience with other coastaldead zones has shown significant ecologi-cal deterioration and depleted fisheries.

Scientists believe that Gulf hypoxia iscaused by nitrogen loads from theMississippi River. Nitrogen fuels the rapidgrowth of large populations of algae andplankton. When they die and sink to thebottom, their decay robs the water of oxygen.

Because two-thirds of the nitrogen inthe Mississippi River comes from use offertilizer and manure on agriculturallands, reducing agricultural nitrogen is a

major component ofthe strategy for con-trolling the hypoxiczone. Two basicapproaches can betaken: (1) inducechanges in the appli-cation and manage-ment of nitrogen fer-tilizer on farm fields,or (2) restore wet-lands along riversand streams to inter-cept and filter out the nitrogen before itreaches surface waters. Because the geo-graphic scale of the problem is so large,any policy to reduce nitrogen from agricul-ture will affect commodity prices, and con-sequently farmers and consumers bothinside and outside the basin.

An ERS analysis of the two approach-es found farm-based controls on nitrogenfertilizer use to be more cost-effectivethan restoring wetlands when up to 1.2million metric tons (26 percent) of basin-wide nitrogen losses (nitrogen leaving theland and entering the water system) must

be eliminated. Until thatpoint, crop yields are littleaffected by the controls onnitrogen use. But whennitrogen losses must becut by more than 1.2 mil-lion metric tons, a turn-around occurs and wet-land restoration becomesthe more cost-effectivestrategy. The reason forthe turnaround is thatwhen reduction in nitro-

gen use reaches a certain point, crop yieldsdecline significantly, causing subsequentincreases in prices of some agriculturalproducts. The price increases also result inmore intense production of the commodi-ties outside the Mississippi Basin, increas-ing erosion and nutrient runoff in thoseregions. However, these calculations don’tinclude (because of insufficient data)other environmental benefits of wetlandsnot related to nitrogen reduction, such asincreased habitat for wildlife. Inclusion ofthese benefits would cause the wetlandoption to become the more cost-effectiveapproach at a lower level of nitrogen

reduction.

Marc Ribaudo, mribaudo@ers.usda.gov

This finding is drawn from . . .

“Least-cost Management of Nonpoint Source

Pollution: Source Reduction Versus

Interception Strategies for Controlling

Nitrogen Loss in the Mississippi Basin,” by

Marc O. Ribaudo, Ralph E. Heimlich, Roger

Claassen, and Mark Peters, in Ecological

Economics, May 2001. Abstract available at:

www.ers.usda.gov/publications/

erselsewhere/eejs0207/

RESOURCES AND ENVIRONMENT

6

5

4

3

2

1

0

Controls on nitrogen fertilizer use are more cost- effective than wetland restoration up to 1.2 million tons of nitrogen loss reduction

0 0.2 0.4 0.6 0.8 1 1.2 1.4 1.6 1.8

Reduction in nitrogen loss within the Mississippi Basin (million tons)

Cost per unit ($1,000/ton)

Wetland restoration approach

Fertilizer reduction approach

1.0

“Dead Zone” in the Gulf:Addressing Agriculture’sContribution

MississippiRiver Basin

Missouri

Hypoxic Zone

UpperMississippi

Arkansas-Red-White

Gulf of Mexico

Ohio

TennesseeLower

Mississippi

F I N D I N G S

8

AM

BE

R W

AV

ES

ECONOMIC RESEARCH SERVICE/USDA

VO

LU

ME

1 �

ISS

UE

5

F I N D I N G S