NOAA forecasts average ‘dead zone’ in Gulf this summer

Low oxygen levels, fish kills expected in hypoxic Gulf waters

The summer “dead zone” in the Gulf of Mexico will be approximately 5,364 mi2 (13,893 km2), average based on 35 years of seasonal measurements and integrated results of multiple models into an aggregate forecast.

Now in its fifth year, NOAA has produced a dead zone forecast using a suite of models jointly developed with a spate of researchers and U.S. Geological Survey (USGS), which provided the Mississippi River nutrient loading dataset.

Every summer NOAA supports a water quality monitoring survey to confirm the size of the hypoxic zone and refine the forecast models. The forecast assumes typical coastal weather conditions, but the actual hypoxic area could be impacted by major weather events. such as tropical storms and hurricanes.

The dead zone primarily results from excess nutrient pollution from human activities in urban and ag areas throughout the Mississippi River watershed.

Excess nutrients that reach Gulf waters stimulate an overgrowth and decay of algae. Less oxygen is left for fish and other aquatic life, especially near the bottom of the body of water. Larger, mobile wildlife like fish, shrimp and crabs can migrate to find more oxygen. Unfortunately, smaller wildlife will experience stress and mortality.

“The Gulf dead zone remains the largest hypoxic zone in U.S. waters, (so) we want to gain insights into its causes and impacts,” said Nicole LeBoeuf, Asst. Administrator of NOAA’s National Ocean Service. “(This) modeling is important … to protect, restore… coastal and ocean resources through ecosystem-based management.

Enhanced nutrient runoff map shows impact of human activities on water quality and annual summer dead zone in the Gulf of Mexico; image credit NOAA
Nutrient runoff map shows impact of human activities on water quality and the annual summer dead zone in the Gulf of Mexico | image source: NOAA

USGS measures nutrient levels using more than 3,500 real-time stream gages, 68 real-time nitrate sensors, and 38 long-term monitoring sites in rivers throughout the Mississippi-Atchafalaya watershed. This information helps track long-term nutrient sources and hotspots within the watershed.

A USGS study based on data collected from 1975 to 2017 indicates that nutrient inputs like fertilizer, agricultural management practices, and accumulated nutrients like phosphorus are factors.

The Interagency Mississippi River and Gulf of Mexico Hypoxia Task Force has set a long-term goal to reduce the size of the dead zone to 1,900 mi2 (4921 km2). Partnering agencies share data to inform nutrient reduction targets with states across the Mississippi River watershed.

NOAA releases the dead zone forecast in coordination with the following research partners; some of which develop independent forecasts: