Monday, July 30, 2012

NOAA Scientists Measure Small Gulf Hypoxic Zone; Link Size Reduction to Drought Conditions

(Click this link to a graphical representation
of dead zone size changes over time)
The National Oceanic and Atmospheric Administration's ("NOAA's") National Centers for Coastal Ocean Science (or NCCOS) announced on July 27 that its scientists had observed the fourth smallest hypoxic or oxygen-free zone in the northern Gulf of Mexico since record-keeping began in 1985. Drought conditions in the country's midsection are largely believed to have directly resulted in the "dead zone's" smaller than average size (2,889 square miles), since both lower amounts of water and accompanying plant nutrients (nitrogen and phosphorus) flowed down the Mississippi River system this spring and summer into the Gulf of Mexico. The dead zone is widely acknowledged to be caused by the decrease in dissolved oxygen caused when enormous algal blooms die off and decay (the algal growth being spurred largely by nutrient-laden runoff from agricultural sources upstream in the Mississippi River watershed) (see this USGS Gulf hypoxia study for additional information).

In June 2012 scientists from the NCCOS-funded Northern Gulf of Mexico Ecosystems and Hypoxia Assessment (NGOMEX) program had issued two contrasting predictions of the expected size of this summer's Gulf dead zone. A University of Michigan model had predicted a size of 1,197 square miles, which contrasted with the findings of a Louisiana State University model predicting an hypoxic zone size of 6,213 square miles.

The smallest dead zone obeserved to date was 15 square miles in 1988, which was another drought year. The largest was measured in 2002 at slightly more than 8,400 square miles (see the above graph or follow this link to a graphical representation of dead zone size changes over time).

The NCCOS Mid-Summer Survey Result's press release noted that "The hypoxic zone that forms each spring and summer off the coast of Louisiana and Texas, threatens (sic) 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."

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