Dead Zone: Mixed Views
Photograph by NASA-GSFC, Science Faction/Corbis
Each September, a giant low-oxygen "dead zone"
forms in the Gulf of Mexico as nutrients from agricultural runoff into the
Mississippi River support the growth of oxygen-hungry algae, which can choke
out other sea life. It can be seen here as the teal blue area along the
Louisiana coastline.
A major question was whether this hypoxic area would be
worsened by the assault of crude oil from the BP spill.
Researchers from Louisiana State University and the
Louisiana Universities Marine Consortium concluded in a study published in
February in Marine Pollution Bulletin that the net effect of the spill on the
dead zone's size appeared to be "negligible." The hypoxic area was 20,000 square kilometers
in 2010, close to the size predicted in a new model the researchers developed.
(The dead zone has ranged between 40 square kilometers and 22,000 square
kilometers from 1985 through 2010, and has averaged 13,600 square kilometers,
or 5,200 square miles.)
But the Louisiana researchers cautioned that Tropical Storm
Bonnie, which crossed the Gulf during July 2010, may have had a great enough
impact to disguise the impact of the crude oil on the Gulf dead zone.
When oil spilled into the Gulf from the Macondo well, that
zone expanded, leading scientists to study the situation and offer a number of
explanations.
Other scientists have noted impact from the BP spill on
Gulf oxygen levels. A study from the
University of California, Santa Barbara, which appeared in the January 2012
issue of the journal Science indicated that abnormally large blooms of
methane-consuming bacteria had reduced the Gulf of Mexico's methane and oxygen
levels.
Barbara Mulligan