A "dead zone" in the Gulf of Mexico is smaller than predicted this year. The region covers around 5,000 square miles in 2014, smaller than average for the last five years.

The region is low in oxygen, preventing both microscopic and larger lifeforms from living in the affected area. It is located off the coasts of Texas and Louisiana.

The dead zone was examined over a five-day period, by researchers from the Louisiana Universities Marine Consortium (LUMCON). This was the 30th cruise for the group, as they study changes in the oxygen-poor water.

Gene Turner, a researcher at Louisiana State University, predicted the dead zone would extend for over 5,700 square miles this season. This estimate was based on the concentration of nitrogen dissolved in the Mississippi River.

The Gulf of Mexico dead zone is created from nitrogen-rich fertilizers and other chemicals, fed by runoff from farms along the giant waterway. These substances feed the growth of algae, which sinks and perishes. The decomposing organisms take in much of the dissolved oxygen in water, killing off marine life in the region. Fish, crustaceans and other creatures that are not killed by the introduction of large volumes of oxygen-poor water leave the area.

"Sometimes the size of the zone is influenced by other factors, such as droughts or hurricanes that can reduce the size of the zone, or floods that can increase the size," the Mississippi River Gulf of Mexico Watershed Nutrient Task Force stated on their website.

Hypoxic areas, or dead zones, were first recorded in the 1970's, and have become more common since that time. The area off the Louisiana and Texas coasts are the second-largest region of this type in the world.

The task force assigned to reduce the extent of the dead zone had hoped the feature would be down to around 2,500 square miles by now.

"The July distribution of hypoxic waters is most often a single continuous zone along the Louisiana and adjacent Texas shelf, but this year was located in two separate areas. The largest area was off central to southeastern Louisiana between the deltas of the Mississippi and Atchafalaya rivers, and the smaller was off southwestern Louisiana," Louisiana University researchers wrote [pdf].

More than 111,000 tons of nitrates ran down the Mississippi River this year, according to conservationists.

Marine dead zones are a phenomenon which is well-understood, but environmentalists have, so far, been unable to slow or stop the process from occurring.

The Environmental Protection Agency (EPA) and National Oceanic and Atmospheric Administration (NOAA) are tracking the size and appearance of this dead zone, along with similar features around the globe.

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