This summer’s Gulf of Mexico “dead zone” – an area with depleted oxygen – could be a near-record size. Models differ, but show the affected area growing.
Nutrients like nitrogen and phosphorous travel down the Mississippi River into the Gulf. They trigger algae blooms that take oxygen from the water, threatening fish and shrimp.
Researchers from Louisiana State University forecast this “dead zone” in the Gulf in late July will cover almost 8,720 square miles near Louisiana and Texas. The area is about the size of the state of New Jersey, or the land area of New Hampshire, according to researchers.
Eugene Turner, a Louisiana State University professor and one of the co-authors of the annual forecast, said the actual “dead zone” could vary because of storms in the Gulf. Last year, researchers projected the “dead zone” would measure 6,570 square miles, but the actual “dead zone” measured in July spanned less than half of that, at 2,720 square miles.
“What it continues to say every year is that we’re not making any progress on improving water quality in the Mississippi River, which means all the states that are contributing to it also don’t have really any improvements in their water quality,” Turner said.
According to a University of Iowa study published in April 2018, Iowa has contributed an average of 29 percent of the total nitrogen to the Gulf over the last 18 years. Chris Jones, a research engineer with University of Iowa, said there’s been some progress in cutting phosphorous runoff from Iowa, but a lot remains to be done to curb nitrogen.
“We need more cover crops on our farm fields, for example, we need more edge of field treatment practices to be implemented, things like wetlands,” Jones said. “And we need to very carefully manage our manure.”
Jones is waiting to see what the actual measurements are for the “dead zone”, because “sometimes they’re wrong,” he said, of the predictions.
“Trying to predict a response of an ecosystem to these various drivers like weather and nutrient loading…is sometimes tricky business,” he said.
If the 2019 “dead zone” is as high as LSU researchers predict, it would be the second-highest on record since scientists started mapping it in 1985. The largest “dead zone” ever recorded was almost 8,780 square miles in 2017.
The National Oceanic and Atmospheric Administration predicts the area will be smaller than LSU researchers project, taking up almost 7,830 square miles. This is still larger than the “dead zone’s” 5-year average of 5,770 square miles. The agency says a higher-than-usual amount of spring rainfall and record river flows in the watershed are to blame for more nutrients going into the Gulf.
“This past May, discharge in the Mississippi and Atchafalaya rivers was about 67% above the long-term average between 1980 and 2018,” NOAA said in a news release.
According to NOAA, the U.S. Geological Survey estimates more than 150,000 metric tons of nitrates went into the Gulf in May.
Louisiana State University researchers plan to measure where the zone is by boat in late July. A survey for NOAA will be done in early August.