From: Andy Soos, ENN
Published June 21, 2012 04:29 PM
2012 Gulf of Mexico Dead Zone
Dead zones are hypoxic (low-oxygen) areas in the world's oceans, the
observed incidences of which have been increasing since oceanographers
began noting them in the 1970s. These occur near inhabited coastlines,
where aquatic life is most concentrated A team of NOAA-supported
scientists is predicting that this year's Gulf of Mexico hypoxic zone
could range from a low of approximately 1,197 square miles to as much as
6,213 square miles. The wide range is the result of using two different
forecast models. The forecast is based on Mississippi River nutrient
inputs compiled annually by the U.S. Geological Survey (USGS). The Gulf
of Mexico dead zone is typically about 8,000 square miles and is located
where the Mississippi River dumps high-nutrient runoff from its vast
drainage basin, which includes the heart of U.S. agribusiness, the
Midwest. This is equivalent to a dead zone the size of New Jersey.
The smaller dead zone forecast, covering an area slightly larger than
the state of Rhode Island, comes from researchers from the University of
Michigan. Their predicted size is based solely on the current year's
spring nutrient inputs from the Mississippi River which are
significantly lower than average due to drought conditions throughout
much of the river watershed.
The larger dead zone forecast, the equivalent of an area the size of the
state of Connecticut, is from Louisiana Universities Marine Consortium
and Louisiana State University scientists. The Louisiana forecast model
includes prior year's nutrient inputs which can remain in bottom
sediments and be recycled the following year. Last year's flood,
followed by this year's low flows, increased the influence of this
"carryover effect" on the second model's prediction.
Hypoxia is caused by excessive nutrient pollution from human activities
coupled with other factors that deplete the oxygen required to support
most marine life in bottom and near-bottom water.
During May 2012 stream-flow rates in the Mississippi and Atchafalaya
Rivers were nearly half that of normal conditions. This resulted in a
decrease in the amount of nitrogen transported by the rivers into the
Gulf. According to USGS estimates, 58,100 metric tons of nitrogen (in
the form of nitrite plus nitrate) were transported in May 2012 by the
Mississippi and Atchafalaya Rivers to the northern Gulf. The amount of
nitrogen transported to the Gulf in May 2012 was 56 percent lower than
average May nitrogen loads estimated in the last 33 years.
The two smallest recorded dead zones to date are in 2000 when it
measured 1,696 square miles and a 15 square miles dead zone in 1988.
Last year's dead zone measured 6,765 square miles. The largest hypoxic
zone measured to date occurred in 2002 encompassing more than 8,400
square miles.
The actual size of the 2012 hypoxic zone will be released following a
NOAA-supported monitoring survey led by the Louisiana Universities
Marine Consortium between July 27 and August 3. Collecting these data is
an annual requirement of the Mississippi River/Gulf of Mexico Watershed
Nutrient Task Force Action Plan. Additional NOAA-supported surveys led
by the National Marine Fisheries Service and Texas A&M University will
also provide an indication of the progression of the dead zone during
the year.
The average of impacted waters over the past five years is approximately
6,000 square miles, much larger than the 1,900 square miles which is the
target goal set by the Gulf of Mexico/Mississippi River Watershed
Nutrient Task Force.
The hypoxic zone, that form each spring and summer off the coast of
Louisiana and Texas, threaten valuable commercial and recreational Gulf
fisheries. In 2009, the dockside value of commercial fisheries in the
Gulf was $629 million. Nearly three million recreational fishers further
contributed about $10 billion to the Gulf economy, taking 22 million
fishing trips.
Other known notable dead zones in the United States include the northern
Gulf of Mexico region, surrounding the outfall of the Mississippi River,
and the coastal regions of the Pacific Northwest, and the Elizabeth
River in Virginia Beach, all of which have been shown to be recurring
events over the last several years.
For further information see
NOAA.
Dead Zone image via Wikipedia/NOAA.
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