NOAA announces largest-ever Gulf of Mexico ‘dead zone’

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Scientists from the National Oceanic and Atmospheric Administration (NOAA) announced the largest-ever recorded low-oxygen “dead zone” in the Gulf of Mexico. At 22,730 square kilometers (8,776 square miles) the area is the size of the U.S. state of New Jersey.

NOAA announces largest-ever Gulf of Mexico ‘dead zone

At 22,730 square kilometers (8,776 square miles), this year’s dead zone in the Gulf of Mexico is the largest ever measured.
Image courtesy of N. Rabalais, LSU/LUMCON

The dead zone is primarily the result of nutrient pollution that stimulates massive blooms of algae. When this algae decomposes, oxygen levels drop below levels needed by many Gulf species to survive or develop normally; scientists refer to low-oxygen conditions as hypoxia.

“The dead zone adversely affects organisms in a number of ways,” said Robert Magnien, director of NOAA’s Center for Sponsored Coastal Ocean Research. “It reduces available habitat for fish and shrimp and reduces their food supply. Exposure to hypoxia can also directly reduce growth and reproduction.”

This can have knock-on effects for local economies if hypoxia kills off or changes commercially important populations.

“The fear is that if the size of the dead zone remains at its current level or increases in the future, there will likely be further reductions in the abundance of key commercial and recreational species,” Magnien told Mongabay.

A study by Duke University found shrimp grow more slowly in the dead zone. This led to a deficit in large shrimp, lower prices for small ones and consequential economic changes to the Gulf brown shrimp fishery.

Midwest ag driving Gulf dead zone

NOAA announces largest-ever Gulf of Mexico ‘dead zone’ - Midwest ag driving Gulf dead zone

Scientists from Louisiana Universities Marine Consortium deploy a water sensor called a CTD sonde rosette to collect water samples to test for oxygen levels during the 2015 R/V Pelican’s shelf wide hypoxia cruise.
Photo courtesy of LUMCON

NOAA scientists are pinning the blame for the increasing size of the dead zone – indeed, its existence at all – primarily on nutrients like nitrate that are washed off agricultural fields in the Mississippi watershed. The Mississippi River carries these nutrients as far as 2,000 miles before they’re released into the Gulf of Mexico.

The U.S. Geological Survey (USGS) found about 1.15 million metric tons of nitrogen pollution was released into the Gulf of Mexico in 2016; preliminary data from May 2017 indicate pollution this year is set to eclipse that number, with levels well above the 1980-1996 baseline average.

“We expected one of the largest zones ever recorded because the Mississippi River discharge levels, and the May data indicated a high delivery of nutrients during this critical month which stimulates the mid-summer dead zone,” said research professor Nancy Rabalais in a statement. Rabalais is a research professor at Louisiana State University (LSU) and Louisiana Universities Marine Consortium, and led the survey mission that measured the extent of the dead zone.

In addition to creating and exacerbating the dead zone, nitrate runoff can contaminate drinking water. A 2015 Health Department report found agriculture-related nitrate pollution is a “growing chemical threat” to the drinking water of the U.S. state of Minnesota.

The race to reduce

NOAA announces largest-ever Gulf of Mexico ‘dead zone’ - The race to reduce

“Dead zones” or areas with low oxygen levels are mainly on the coasts.
Map of the “Water Resources Institute”

The data are clear, nutrient pollution is creating a big problem in the Gulf of Mexico. And scientists worry it is getting even bigger.

“Our models show a strong correlation between the size of the dead zone and the amount of nutrient pollution entering the Gulf of Mexico during the spring,” said NOAA’s Robert Magnien “With expected increases in runoff-producing storms and increasing temperatures in the future, the size of the dead zone may well increase even if current practices remain the same.”

A number of initiatives are working to limit the growth of the dead zone, such as the interagency Mississippi River/Gulf of Mexico Hypoxia Task Force (HTF). A consortium of federal, state, and tribal members, the goal of the HTF is to shrink the dead zone through state and federal nutrient reduction strategies.

But industry participation is also crucial, according to Magnien.

“The raising of animals, along with many other human activities that produce nutrient pollution, contribute to dead zone formation,” Magnien said. “Reduction of nutrient pollution requires a multi-sector management strategy. The cooperation of industries and municipalities to significantly reduce nutrient runoff from land and wastewater will be needed not only for restoration of impacted areas of the Gulf, but also to protect drinking water supplies and freshwater lakes and reservoir in the watershed.”

From: Morgan Erickson-Davis | Mongabay

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