Drought, sluggish Mississippi River make small dead zone
NEW ORLEANS (AP) — Drought made the Mississippi River sluggish and led to a smaller than average dead zone in the Gulf of Mexico — an area where there’s too little oxygen to support marine life, the scientist who’s been measuring it for decades said Wednesday.
Each year, investigators cruise the region to measure the zone. This year, they found it covers 3,275 square miles (8,500 square kilometers), said lead researcher Nancy Rabalais, of the Louisiana Marine Universities Consortium, and Steve Thur of the National Oceanic and Atmospheric Administration.
That’s just under 70% of the average-sized area predicted in early June.
The oxygen-depleted area usually stretches from the Mississippi River into Texas waters but this year stopped at the Atchafalaya River, Rabalais said during a video conference.
However, it’s still well above the goal of a five-year average of 1,900 square miles (4,920 square kilometers) or less set in 2001 by a task force organized to reduce its size.
“We cannot take this smaller Dead Zone as an indication of success of the Hypoxia Task Force,” said Matt Rota, Senior Policy Director for the environmental nonprofit Healthy Gulf. “Much more action must be taken.”
Rabalais, who has been measuring the dead zone since 1985, said the river is usually high from April to September, with a summertime peak. And it was normal for the season in May. But she said drought — possibly an effect of climate change — kept it low in late June and in July.
That reduced runoff, and therefore the amount of nitrogen and phosphorus in the river’s water.
Rabalais said the low flow limited another key component of the dead zone’s creation: a layer of lighter fresh water above the Gulf’s salt water. Nutrients in the fresh water feed algae. The algae die and fall to the bottom, where decomposition uses up oxygen.
The difference between prediction and reality “emphasizes the role that Mississippi River runoff and weather patterns play ... and the inherent uncertainty of predicting” such occurrences, said Thur, director of NOAA’s National Centers for Coastal Ocean Science, which pays for the annual study.
The measured size was within the possible extremes provided by the models on which NOAA based its prediction, he said.
Bruno Pigott of the Environmental Protection Agency noted that an infrastructure bill passed by Congress in November includes a five-year total of $60 million for the 12 task force states. That is the biggest annual infusion of federal money the group has received, he said. He did not know how much the government has provided to date.
Task force co-chairperson Mike Naig, Iowa’s secretary of agriculture, described some state plans to help shrink the dead zone. For example, he said Ohio plans to reduce sewage runoff in nine counties while Indiana recently reported a record number of cover crops, which will help prevent soil erosion.
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