Based on streamflow and nutrient runoff from the Midwest and Plains, federal scientists forecast a “dead zone” of 5,827 square miles in the Gulf of Mexico this summer, 50 percent larger than last year and three times bigger than the 2035 target for reducing nutrient pollution. This year’s dead zone would be the equivalent of 3.7 million acres, or 14 percent of the farmland in Illinois.
Low oxygen levels in the dead zone, the result of waterborne nutrients that stimulate an overgrowth of algae, drive away fish and shrimp, and can affect commercial fishing. The dead zone appears each summer as the result of nutrient runoff from cities and farmland in the Mississippi and Atchafalaya river basin.
“Reducing the impact of hypoxic events and lessening the occurrence and intensity of future dead zones continues to be a NOAA priority,” said Nicole LeBoeuf, a National Oceanic and Atmospheric Administration official. NOAA will report in early August on the results of tests this summer of Gulf of Mexico waters.
The measurements assist the work of the interagency Hypoxia Task Force, created in 1997 with federal, state, and tribal members, with the goal of mitigating the size, severity, and duration of the dead zone. “Activities include coordinating and supporting nutrient management activities from all sources, restoring habitats to trap and assimilate nutrients, and supporting other hypoxia-related activities in the Mississippi River and Gulf of Mexico watersheds,” says the EPA.
Since monitoring began in 1985, the dead zone has averaged 5,205 square miles in size. The record is 8,776 square miles in 2017. Last year, the dead zone covered 3,058 square miles. The task force goal is to reduce the dead zone to 1,900 square miles by 2035 through steps such as state-written nutrient reduction strategies.
Snowmelt and springtime rainfall are annual factors affecting the size of the dead zone by washing nutrients from farms, lawns, sewage treatment plants, and other sources into waterways that drain into the Gulf of Mexico. A rainy spring slowed field work in the Farm Belt this year.
NOAA said discharge into the Mississippi and Atchafalaya rivers during May was 5 percent higher and phosphorus content of the water was 22 percent higher than the 1980-2023 average. Nitrate runoff was 7 percent below the longterm average. The data were drawn from U.S. Geological Service stream gauges and nutrient sensors.
“Exposure to hypoxic waters has been found to alter fish diets, growth rates, reproduction, habitat use and the availability of commercially harvested species like shrimp,” said NOAA.