NOAA warns: ‘Dead zone’ for fish will be as big as Connecticut this year

A so-called “dead zone” the size of Connecticut will wreak havoc in the Gulf of Mexico this summer, the National Oceanic and Atmospheric Administration (NOAA) predicted.

The larger-than-average summer dead zone could cover an area of ​​about 5,827 square miles and pose a major threat to marine life in the area, NOAA said in a statement.

Dead zones, also called hypoxic areas, are areas where there is a severe lack of oxygen in the water. This can lead to mass fish mortality and also poses a threat to other marine life.

This dead zone occurs every summer, but this year it is expected to be particularly large. These dead zones are caused by an excess of nutrients in the water due to human activities throughout the Mississippi and Atchafalaya river basins.

In May, the U.S. Geological Survey (USGS) reported that the discharge of the Mississippi and Atchafalaya rivers for the period between 1980 and 2023 was about five percent above the long-term average.

USGS data, which includes measurements of nutrient loading, show that nitrate loading is about 7 percent below the long-term average, while phosphorus loading is 22 percent above the long-term average.

These measurements of runoff and nutrient uptake are important for NOAA models that predict the size of the Gulf of Mexico dead zone during the summer.

“Reducing the impacts of hypoxic events and reducing the occurrence and intensity of future dead zones remains a priority for NOAA,” NOAA Administrator Nicole LeBoeuf said in a statement. “These forecasts are intended to provide important data to scientists, coastal managers and communities and to guide the development of planning actions.”

Excess nutrients lead to excessive algae growth. When this algae dies and decomposes, oxygen is removed from the water, resulting in low oxygen levels.

This hypoxic environment forces animals such as fish and shrimp to leave the area. Studies have shown that exposure to hypoxic water can alter fish diet, growth and reproduction, as well as affect habitat use and the availability of commercially important species such as shrimp.

This year marks the seventh time NOAA has predicted the dead zone using models from partners including the University of Michigan, Louisiana State University, the Virginia Institute of Marine Science of William & Mary, North Carolina State University and Dalhousie University. NOAA combines the results of these individual models into an aggregated “ensemble” forecast, providing a comprehensive prediction of the size of the dead zone.

The USGS measures river discharge and nutrient levels using an extensive network of approximately 3,000 real-time gages, 73 real-time nitrate sensors, and 37 long-term monitoring stations spread throughout the Mississippi and Atchafalaya River basins. These data points are important for tracking long-term changes in nutrient inputs to the Gulf and for creating models that identify nutrient sources and hotspots within the basin.

“The USGS has been monitoring rivers and groundwater in the Mississippi and Atchafalaya basins for decades to better understand the causes and impacts of water quality problems,” said Joshua Joseph, USGS deputy director for water resources. “A recent USGS study found that in the Illinois River – a major tributary of the Mississippi – algae initially grow in the upper reaches of the river and are then transported downstream, potentially causing algal toxins and reduced dissolved oxygen in the lower reaches of the river.”

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