Map showing the hypoxia area on the Louisiana Gulf of Mexico shelf in 2013. (Photo Credit: LUMCON - Rabalais)
Dead zone in the Gulf of Mexico is not as large as expected
Thursday, August 01, 2013, 04:40 (GMT + 9)
National Oceanic and Atmospheric Administration (NOAA)-backed scientists have recently discovered a hypoxic or oxygen-deprived zone in the Gulf of Mexico, which despite being large is smaller than expected.
One of the researchers who led the 21-28 July survey cruise, Nancy Rabalais, PhD Executive director of the Louisiana Universities Marine Consortium (LUMCON), commented: “A near-record area was expected because of wet spring conditions in the Mississippi watershed and the resultant high river flows which deliver large amounts of nutrients.”
Anyway she stressed that "the alarming news is that it continues to be large year after year after year."
This scientist, who has been measuring the dead zone since 1985, also pointed out: “But nature’s wind-mixing events and winds forcing the mass of low oxygen water towards the east resulted in a slightly above average bottom footprint.”
Due to this, nutrients from the Mississippi River watershed are still affecting the nation’s recreational and marine resources in the Gulf.
Hypoxia is caused by excess nutrients from human-related activities such as agriculture into the watershed. These surplus nutrients cause particular algae to overgrow and these in turn sink, rot and take up most of the oxygen that is otherwise needed for marine life. In normal conditions, the oxygen-deprived area is closer to the Gulf bottom as the decomposing algae sinks to the ocean’s floor.
During the survey cruise, scientists discovered that many animals which normally swim along the seabed were instead swimming near the ocean’s surface and there were many areas in the Gulf where the oxygen was extremely low.
However, a similar inspection cruise conducted last year showed that drought conditions yielded the fourth smallest dead zones ever recorded, encompassing 2,889 square miles. The biggest oxygen-free zone previously recorded was in 2002 measuring 8,481 square miles. The smallest hypoxic zone, recorded in 1988, encompassed 15 square miles.
In the past 5 years, the average hypoxic zone has had a size of 5,176 square miles, over double the size targeted in 2001 by the Gulf of Mexico / Mississippi River Watershed Nutrient Task Force with 1,900 square miles.
On 18 June, NOAA predicted the Gulf dead zone would have grown between 7,286 and 8,561 square miles with the help of forecast models built for that purpose.
Since 2008 the Gulf task force has been working on implementation actions which will come under review this coming summer as the results of the findings concluded that deficient nutrient pollution management was responsible for this situation.
The dead zone occurs each year off the coast of Texas and Louisiana and severely endangers the marine ecosystems of the area where fish kills of massive proportions are a direct consequence of hypoxia. It normally lasts until the end of the summer or early autumn.
The Gulf task force 2008 report indicates that "hypoxia has negative impacts on marine resources." It further states that research on living resources in the Gulf show long term ecological changes in species diversity and a large scale, often rapid change, in the ecosystem's food-web that is both "difficult and impossible to reverse."
The negative commercial impact of this ecological disaster will also be felt in commercial and recreational fishing activities, a sector that in this area of the gulf generates about USD 2,000 million per year.
By Gabriela Raffaele