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Wednesday, July 17, 2019

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Dead zone off Louisiana about at 5-year average

Dead zone off Louisiana about at 5-year average

NEW ORLEANS (AP) — This dead zone — an area off Louisiana where there's too little oxygen in the Gulf of Mexico to keep sea creatures alive — is about average this year and currently the size of Connecticut, a veteran scientist reported Monday.

The dead zone covered about 5,050 square miles as of Aug. 1, triple the 2015 target set by a task force led by the U.S. Environmental Protection Agency, said Nancy Rabalais of Louisiana Universities Marine Consortium.

The scientist has spent decades researching the phenomenon. She said she could not tell whether this year's dead zone was likely to become larger than average, but conditions on the surface make an increase in size likely in coming weeks.

The dead zone forms when nitrogen and other nutrients carried in fresh water from the Mississippi River enter the Gulf and feed huge numbers of plankton at the surface. The plankton then die and fall to the seabed where their decomposition uses up oxygen — a condition called hypoxia.

Surface conditions, including less salty water with higher than usual levels of chlorophyll and oxygen from plankton, indicated that the dead zone was likely to increase, Rabalais said. The fresher water comes from the Mississippi River, which carries runoff from 40 percent of the continental United States, and the Atchafalaya River, which branches off from it.

The microscopic water plants called phytoplankton contain chlorophyll and produce oxygen through photosynthesis, the same process found in leaves and grasses. Oxygen levels in water at the surface along the research vessel Pelican's route ranged from 130 to 150 percent of those in the atmosphere above it and once hit 245 percent, Rabalais said.

"Which means the phytoplankton community was just really — I don't want to use the word 'cooking.' But it was almost as if the water was bubbling in places, there was so much photosynthesis going on," she said. Much of that plankton will end up on the bottom, she said.

In 2001, the Mississippi River Gulf of Mexico Watershed Nutrient Task Force set a goal to reduce the annual size of the dead zone to less than 1,930 square miles. The fact that it's nowhere near that target shows that too little is being done to clean up the Mississippi River, said an official for the Gulf Restoration Network, made up of environmental, social justice, and citizens' groups.

"We see most of the Mississippi River states dragging their feet, claiming that voluntary actions alone can clean up the Dead Zone. If the past decade of 'Action Plans' and 'reduction strategies' is any indication, this simply isn't working," said Matt Rota, senior policy director. "It is obvious that if the states don't want to address this issue, EPA must act, and regretfully we aren't seeing significant action from EPA either."

The annual survey is paid for by the EPA and National Oceanic and Atmospheric Administration.


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Photo courtesy of Microbial Life Educational Resources.