(c) Nancy Rabalais
What is the Dead Zone?
The Dead Zone is an area in the Gulf of Mexico where oxygen levels in
the water are too low to support life. The Dead Zone forms
seasonally off the coast of Louisiana and Texas. Those fish,
crabs, and shrimp that can swim away from the Dead Zone do so, while
others simply die. Since 1993, the size of the Dead Zone has
averaged 16,000 square kilometers, though its size varies every year.1
The lack of oxygen in the Dead Zone poses a serious threat to species
diversity in the Gulf and to the $2.8 billion commercial and
recreational fishing industry.2
For example, the amount of brown shrimp caught declines in years when
the Dead Zone is its largest, and shrimpers must look elsewhere for
their catch.3
The Creation of the Dead Zone
When the Mississippi River reaches the Gulf of Mexico, it is loaded
with nitrogen and phosphorus pollution. The polluted water acts as a
fertilizer of algae, resulting in large algal blooms. When the
algae die, they sink to the saltier water below and decompose,
depleting already low oxygen in the deeper water. Because the
salty bottom waters do not mix well with the lighter, fresh water from
the Mississippi River, oxygen in the water is not replenished,
resulting in a large dead zone in bottom waters.
The Causes of the Dead Zone
Courtesy of NASA
The cause of the Dead Zone is not a mystery. There has been an
almost threefold increase in nitrogen entering the Gulf from the
Mississippi River and its tributaries in the last 30 years.4
The actual size of the Dead Zone varies each year due to climate and
ocean dynamics, though nitrogen remains the prime factor in causing the Dead Zone.5
The largest source of nitrogen is commercial fertilizer used throughout
the Mississippi River basin – one of the agricultural centers of the
United States. Other sources include animal waste, sewage
treatment plants, and nitrogen in the atmosphere from fossil fuel
combustion.
What the GRN Does
The GRN advocates for reduction in the size of the Dead Zone through a number of strategies.
- As states develop limits for how much nitrogen and
phosphorus pollution is allowed in water bodies, we are working to
ensure that these limits will protect aquatic life and decrease
pollution entering the Gulf.
- Working with activists along the entire Mississippi River, we push for reduction of nitrogen and phosphorus pollution being dumped into the entire river.
- We monitor and push for enforcement of permits to polluters who are putting nitrogen and phosphorus into the water.
- We
advocate for changes in the way farm subsidies are distributed so that
farmers who are demonstrating conservation practices that reduce
nitrogen runoff recieve proper funding and taxpayers are not
subsidizing pollution.
What You Can Do
-
Educate your friends and neighbors about this problem.
- Ask your state to pursue aggressive nitrogen and phosphorus pollution reduction strategies.
- Ask to your legislators to push to fully fund the Dead Zone Action Plan.
- Reduce fertilizer application to your lawn (if applicable).
- Ensure that your septic system (if applicable) is regularly inspected and working properly.
Additional Resources
Check out two reports addressing the Dead Zone:
The first, Dead in the Water: Reforming wasteful farm subsidies can restore Gulf fisheries, looks at the role that federal farm subsidies play in creating the dead zone.
The second, Bringing Dead Zones Back to Life,
is a report released by American Rivers, Environmental Defense, and
Restore America's Estuaries on the impact of agricultural runoff on the
nation's most polluted bays and the role the Farm Bill can play in bay
clean-up efforts
[1] USGS. "The Gulf of Mexico Hypoxic Zone." http://toxics.usgs.gov/hypoxia/hypoxic_zone.html
[2] NOAA. "Gulf of Mexico Ecosystems and Hypoxia Assessment." http://www.cop.noaa.gov/stressors/pollution/current/gomex-factsheet.html
[3] Dybas, Cheryl Lyn. “Dead Zones Spreading in World Oceans.” BioScience. July 2005.
[4] NOAA. "Flux and sources of nutrients in the Mississippi-Atchafalaya river basin." http://www.nos.noaa.gov/products/hypox_t3final.pdf
[5]
Scavia et al. "Predicting the Response of Gulf of Mexico Hypoxia to
variations in Mississippi River nitrogen load." Limnology and
Oceanograpy. May 2003. http://aslo.org/lo/toc/vol_48/issue_3/0951.pdf
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