The True Cost of American Food14 April 2016

Corn/soy landscapes,water quality, and theGulf of Mexico ‘dead

zone’

R. Eugene TurnerLouisiana State University

(euturne@lsu.edu)

500 km

0.6%58%18%21%[w & w2.4%]

*

Our watershed

• up to 22,000 km2

• 4 - 5 m nearshore to 35 - 45 m offshore• 0.5 km nearshore to 100+ km offshore• widespread and severe in June – September

Source: N. Rabalais, LUMCON

Extensive, Severe Low Oxygen WatersExtensive, Severe Low Oxygen WatersTX MSLA

The  distribu,on  matches  theglobal  human  footprint  indeveloped  countries  and  isincreasing  in  developing

countries.

A  Global  Epidemic

Díaz  &Rosenberg2008

400  +100  moreof  concern

Why is it called the“DEAD ZONE”

???

Brown Shrimp • Fisheries resources at risk• Altered migration• Reduced habitat• Changes in food resources• Susceptibility of early life stages• Growth & reproduction

The Consequences

1 2 3 4

5 6

How does the bottom layer become hypoxic?

!

Hypoxia per unit nitrate: rising

Turner, R. E., N. N. Rabalais and D. Justic 2008. Gulf of Mexico hypoxia: Alternate states and a legacy. Environmental Science andTechnology 42: 2323 - 2327

More Silica than N:

Silica Loading from river:

diatoms as prey

Zooplankton as predators

Desirable fish

undesirable orreduced fish stocks O

More Silica than N:

Less Silica than N:

Silica Loading from river:

diatoms as prey

Zooplankton as predators

Desirable fish

flagellated algae as prey

Zooplankton reduced

Land use drives water qualityworldwide and also in this

watershed

Key variables: croppingpatterns, fertilizer use, tributary

size, drainage

Landscape influences

Crumpton et al. 2006

Land use and nitrate runoff

Percent crop land

Nitrate(mg N

L-1)

Nutrients  Delivered  to  GoM

http://water.usgs.gov/nawqa/sparrow/gulf_findings/Alexander et al. 2008 &

Impairments from nutrients are significant,but are not the only stressor

U.S. E.P.A. 2006. Wadeable streams assessment. A collaborative survey of the nation’s streams. Office ofResearch and Development, Office of Water. Washington, D.C. EPA 841-B-06-002.www.epa.gov/owow/streamsurvey

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