Scientists are expecting a very large "dead zone" in the Gulf of Mexico and a smaller than average hypoxic level in the Chesapeake Bay this year, based on several NOAA-supported forecast models.
NOAA-supported modelers at the University of Michigan, Louisiana State University, and the Louisiana Universities Marine Consortium are forecasting that this year's Gulf of Mexico hypoxic "dead" zone will be between 7,286 and 8,561 square miles which could place it among the ten largest recorded. That would range from an area the size of Connecticut, Rhode Island and the District of Columbia combined on the low end to the New Jersey on the upper end. The high estimate would exceed the largest ever reported, 8,481 square miles in 2002, US Geological Survey (USGS) said in a press release.
Hypoxia, or low oxygen, is an environmental phenomenon where the concentration of dissolved oxygen in the water column decreases to a level that can no longer support living aquatic organisms. Hypoxic areas, or "Dead Zones," have increased in duration and frequency across the world's oceans since first being noted in the 1970s.
Hypoxic (very low oxygen) and anoxic (no oxygen) zones are caused by excessive nutrient pollution, often from human activities such as agriculture, which results in insufficient oxygen to support most marine life in near-bottom waters. Aspects of weather, including wind speed, wind direction, precipitation and temperature, also impact the size of dead zones.
The largest hypoxic zone currently affecting the United States, and the second largest hypoxic zone worldwide, is the northern Gulf of Mexico adjacent to the Mississippi River.
The Gulf estimate is based on the assumption of no significant tropical storms in the two weeks preceding or during the official measurement survey cruise scheduled from July 25-August 3. If a storm does occur the size estimate could drop to a low of 5344 square miles, slightly smaller than the size of Connecticut.
This year's prediction for the Gulf reflects flood conditions in the Midwest that caused large amounts of nutrients to be transported from the Mississippi watershed to the Gulf.
A second NOAA-funded forecast, for the Chesapeake Bay, calls for a smaller than average dead zone in the nation's largest estuary.
The forecasts call for a mid-summer hypoxic zone of 1.46 cubic miles, a mid-summer anoxic zone of 0.26 to 0.38 cubic miles, and a summer average hypoxia of 1.108 cubic miles, all at the low end of previously recorded zones.
Both forecasts are based on nutrient run-off and river stream data from the U.S. Geological Survey.
"Monitoring the health and vitality of our nation's oceans, waterways, and watersheds is critical as we work to preserve and protect coastal ecosystems," said Kathryn D. Sullivan, Ph.D., acting under secretary of commerce for oceans and atmosphere and acting NOAA administrator.
The dead zone in the Gulf of Mexico affects nationally important commercial and recreational fisheries, and threatens the region's economy. The Chesapeake dead zones, which have been highly variable in recent years, threaten a multi-year effort to restore the Bay's water quality and enhance its production of crabs, oysters, and other important fisheries.
During May, stream flows in the Mississippi and Atchafalaya rivers were above normal resulting in more nutrients flowing into the Gulf. According to USGS estimates, 153,000 metric tons of nutrients flowed down the rivers to the northern Gulf of Mexico in May, an increase of 94,900 metric tons over last year's 58,100 metric tons, when the region was suffering through drought. The 2013 input is an increase of 16 percent above the average nutrient load estimated over the past 34 years.
For the Chesapeake Bay, USGS estimates 36,600 metric tons of nutrients entered the estuary from the Susquehanna and Potomac rivers between January and May, which is 30 percent below the average loads estimated from 1990 to 2013.
"Coastal hypoxia is proliferating around the world," said Donald Boesch, Ph.D., president of the University of Maryland Center for Environmental Science.
The confirmed size of the 2013 Gulf hypoxic zone will be released in August, following a monitoring survey led by the Louisiana Universities Marine Consortium beginning in late July, and the result will be used to improve future forecasts. The final measurement in the Chesapeake will come in October following surveys by the Chesapeake Bay Program's partners from the Maryland Department of Natural Resources and the Virginia Department of Environmental Quality.
Despite the Mississippi River/Gulf of Mexico Nutrient Task Force's goal to reduce the dead zone to less than 2,000 square miles, it has averaged 5,600 square miles over the last five years. Demonstrating the link between the dead zone and nutrients from the Mississippi River, this annual forecast continues to provide guidance to federal and state agencies as they work on the 11 implementation actions outlined by the Task Force in 2008 for mitigating nutrient pollution.
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