U.S. Water News Online
BATON ROUGE, La. -- A Louisiana State University scientist says his accurate predictions for the large low-oxygen "dead zone" in the Gulf of Mexico prove that nitrogen is a main factor in its creation.
Eugene Turner, a professor with LSU's Coastal Ecology Institute, several years ago designed a method using the Mississippi River's nitrogen level in May at St. Francisville to calculate the likely size of the Gulf of Mexico's summer dead zone.
Turner said the model is not 100 percent accurate -- that's very difficult to achieve with predictive models -- but that it has been very close in the last three years, he said.
He said he was 99.2 percent accurate in predicting the dead zone's size this year, which came in at about 6,662 square miles -- or about the size of Connecticut and Rhode Island combined.
Every summer, a sea bottom area with too little oxygen to support aquatic life forms along Louisiana's coast. That phenomenon, known as hypoxia, occurs when fertilizer, urban runoff, sewage and other substances feed the growth of microscopic organisms, which then die and fall to the Gulf floor. The decomposition uses up oxygen in the lower layer of water.
Fish, shrimp and other marine life move out of the low-oxygen water -- that led scientists to name it the dead zone. Winter storms dispel the dead zone by mixing the low-oxygen water with oxygen-rich surface water.
There is a national effort to reduce the size of the dead zone in the Gulf, but there is still discussion about how that should be done.
Doug Daigle of the Mississippi River Basin Alliance said Turner's model underscores what many scientific reports have said in the past.
"The model certainly strengthens the body of evidence that nitrogen drives the dead zone," Daigle said.
Turner's prediction is based on the pioneering work his wife, Nancy Rabalais, has done in dead zone research -- and on her crew's annual game.
Every summer, a team of scientists led by Rabalais, director of the Louisiana Universities Marine Consortium's center in Cocodrie, measures the dead zone. before each trip, crew members would make their best guesses of the dead zone's size. After the trip, the sealed envelopes would be opened. Whoever's guess was closest to the actual size would win.
It was just for fun, but it got Turner thinking about creating a predictive model.
He said the model isn't a substitute for the survey trips -- it can predict the dead zone's size, but not its location.
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