The True Cost of American Food 14 April 2016 Corn/soy landscapes, water quality, and the Gulf of Mexico ‘dead zone’ R. Eugene Turner Louisiana State University ([email protected])
The True Cost of American Food14 April 2016
Corn/soy landscapes,water quality, and theGulf of Mexico ‘dead
zone’
R. Eugene TurnerLouisiana State University
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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