Print

Print


Fertilizer Run-off From Agricultural Activities Blamed For Gulf Dead  
Zone In Gulf Of Mexico



Gulf dead zone, June 15 - July 16, 2005. Dark red areas have the  
lowest oxygen content (0-.5 mg/l).
(Credit: NOAA)

ScienceDaily (Apr. 24, 2008)  Improved management of crops and  
perennials could go a long way toward alleviating the problem of  
hypoxia, which claims thousands of fish, shrimp and shellfish in the  
Gulf of Mexico each spring.

An assessment by a team led by Virginia Dale of Oak Ridge National  
Laboratory's Environmental Sciences Division concludes that low oxygen  
levels in water, or hypoxia, causes problems throughout the ecosystem.  
The death zone, scientifically documented in the Gulf since 1985, has  
consistently covered about 6,000 square miles, usually off the coast  
of Louisiana west of the Mississippi River's mouth.

The problem is caused in part by fertilizer run-off from agricultural  
activities in the Mississippi basin, which drains about 48 percent of  
the U.S. land. These nutrients combined with stratification caused by  
warm freshwater from the Mississippi and Atchafalaya rivers running  
into the colder saltwater of the Gulf sets up the deadly process.  
Algae grows, then dies and sinks to the bottom, where it decomposes,  
using up oxygen in the process.

"The oxygen-depleted water at the bottom is not replenished because of  
the lack of circulation," Dale said. "The more water that flows into  
the Gulf and the more nutrients in the water, the worse the hypoxia  
becomes."

While scientists initially believed nitrogen was the major culprit,  
the assessment team for the Science Advisory Board of the  
Environmental Protection Agency realized that phosphorus also plays a  
significant role. The team is recommending a 45 percent reduction in  
phosphorus and nitrogen from the 1980-1996 average flux during the  
spring (April, May and June) on a five-year running average.

The assessment team found that the most significant opportunities for  
nitrogen and phosphorus reduction in the Mississippi Basin are  
promotion of the production of environmentally sustainable biofuel and  
other perennial crops, improved infield management of nutrients,  
construction and restoration of wetlands, tighter nitrogen and  
phosphorus limits on municipal and industrial sources and improved  
targeting of riparian buffers.

Other recommendations include using cellulosic biofuels such as  
switchgrass and poplar hybrids, but the assessment team acknowledged  
that field implementation of cellulosic biofuel crops is under  
development. In the meantime, cellulosic ethanol is being produced  
from corn stover -- the cobs, leaves and stalks left in a field after  
harvest.

Dale is proposing research to establish landscape design that will  
help farmers and land management agencies determine where and how  
biofuel feedstocks can be grown with minimal environmental impacts.

"In our report to the EPA, we're recommending planting perennials,  
promoting environmentally sustainable biofuel production and using no- 
till farming as key land management strategies," Dale said. "Reducing  
the amount of nutrients on fields and restoring wetlands are other  
important parts of the panel's land management recommendations."

At a recent Department of Energy conference, "Biomass 2008: Fueling  
our Future," researchers discussed multiple aspects of bioenergy crops.

"Choices about what crops are grown and how they are planted,  
fertilized and harvested influence the effects of biofuels on native  
plant diversity, competition with food crops and effects on water and  
air quality," Dale said.

Decisions in this area also affect economic viability because the  
distance that biofuels must be transported has a large effect on the  
market cost of biofuels as well as the quality of life for those who  
live in communities through which the bulky fuel is transported, Dale  
said.

Dale and colleagues at ORNL are now focusing on watershed studies to  
determine what is happening between fields and the Gulf using models  
at different scales to interpret the data.

"Understanding these intermediate layers is crucial to filtering out  
the noise and figuring out how to shrink the hypoxic zone," Dale said.  
"The approach we're developing considers aspects of the landscape,  
including environmental and socioeconomic conditions, the bioenergy  
features and ecological and biological feedbacks."

While water availability and quality emerges as one of the most  
limiting factors, the linkage between water and bioenergy choices on  
medium and large scales is poorly qualified, according to Dale. An  
approach that considers environmental and socioeconomic changes in  
land use and landscape dynamics provides a way to quantify the  
influence of alternative bioenergy choices on water quality and other  
components of the environment.

This assessment was supported by EPA while the landscape research was  
funded by ORNL's Laboratory Directed Research and Development program.  
UT-Battelle manages Oak Ridge National Laboratory for the Department  
of Energy.

Adapted from materials provided by DOE/Oak Ridge National Laboratory.