This year, scientists are expecting a very large “œdead zone“ in the Gulf of Mexico, according to several NOAA-supported forecast models. Those same models predict a smaller than average hypoxic level in the Chesapeake Bay.
A research team comprised of scientists from the University of Michigan, Louisiana State University, and the Louisiana Universities Marine Consortium used the NOAA-supported models to forecast that this year´s Gulf of Mexico hypoxic “œdead zone” will be between 7,286 and 8,561 square miles, which could place it among the ten largest recorded. To understand the scale of this dead zone, the affected area would range from an area the size of Connecticut, Rhode Island and the District of Columbia combined on the low end to the whole state of New Jersey on the upper end. The largest hypoxic area reported to date was 8,481 square miles in 2002.
Excessive nutrient pollution, often from human activities such as agriculture, causes hypoxic (very low oxygen) and anoxic (no oxygen) zones. The excessive nutrient pollution results in insufficient oxygen to support most marine life in near-bottom waters. The size of the dead zone is also affected by aspects of weather, such as wind speed, wind direction, precipitation and temperature.
The estimate for the Gulf of Mexico is based on the assumption that there will be no significant tropical storms in the two weeks before or during the official measurement survey cruise scheduled for July 25-August 3, 2013. The estimate could drop as low as 5,344 square miles, approximately the size of Connecticut, if such a storm does occur.
Flood conditions in the Midwest caused large amounts of nutrients to be transported from the Mississippi watershed to the Gulf, resulting in this year´s predictions. The Gulf dead zone last year was the fourth smallest due to record drought conditions in 2012, covering an area of approximately 2,889 square miles, an area slightly larger than the state of Delaware. Between 1995 and 2012, the overall average is 5,960 square miles — an area about the size of Connecticut.
Also, the forecast for the Chesapeake Bay calls for a smaller-than-average dead zone in the nation´s largest estuary. Researchers at the University of Maryland Center for Environmental Science and
the University of Michigan developed a forecast with three parts: a prediction for the mid-summer volume of the low-oxygen hypoxic zone, one for the mid-summer oxygen-free anoxic zone, and a third that is an average value for the entire summer season.
The mid-summer hypoxic zone will be approximately 1.46 cubic miles, according to the forecasts. The mid-summer anoxic zone will range between 0.26 to 0.38 cubic miles, with a summer average hypoxia of 1.108 cubic miles — all of which are at the low end of previously recorded zones. The final mid-summer hypoxic zone in the Chesapeake Bay last year was 1.45 cubic miles.
Because of the shallow nature of large areas of the Chesapeake Bay estuary, the Bay outlook focuses on water volume or cubic miles, instead of square miles. This is the seventh year of the Bay outlook report; the history of hypoxia in the Chesapeake Bay since 1985 can be found at the EcoCheck website.
Both the Gulf and Chesapeake Bay forecasts are based on nutrient run-off and river stream data from the US Geological Study (USGS). This data is inserted into models developed by funding from the National Ocean Service’s National Centers for Coastal Ocean Science (NCCOS).
“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, PhD, acting undersecretary of commerce for oceans and atmosphere and acting NOAA administrator. “These ecological forecasts are good examples of the critical environmental intelligence products and tools that help shape a healthier coast, one that is so inextricably linked to the vitality of our communities and our livelihoods.”
Nationally important commercial and recreational fisheries are affected by the dead zone in the Gulf of Mexico, which threatens the region´s economy. The dead zones in the Chesapeake Bay, which have been highly variable in recent years, threaten a long-term program to restore the Bay´s water quality and enhance its production of crabs, oysters, and other important fisheries.
Stream flows in the Mississippi and Atchafalaya rivers were above normal resulting in more nutrients flowing into the Gulf during May 2013. About 168,600 tons of nutrients flowed down the rivers to the northern Gulf of Mexico that same month, according to USGS estimates. This represents an increase of 104,600 tons over last year´s 64,000 tons, when the region suffered an extreme drought. The models predict an increase of 16 percent above the average nutrient load estimate over the last 34 years in 2013.
From January to May, the USGS estimates 40,300 tons of nutrients entered the Chesapeake Bay from the Susquehanna and Potomac rivers. This is 30 percent below the average loads estimated from 1990 to 2013.
“Long-term nutrient monitoring and modeling is key to tracking how nutrient conditions are changing in response to floods and droughts and nutrient management actions,” said Lori Caramanian, deputy assistant secretary of the interior for water and science. “Understanding the sources and transport of nutrients is key to developing effective nutrient management strategies needed to reduce the size of hypoxia zones in the Gulf, Bay and other U.S. waters where hypoxia is an ongoing problem.”
“Coastal hypoxia is proliferating around the world,” said Donald Boesch, PhD, president of the University of Maryland Center for Environmental Science. “It is important that we have excellent abilities to predict and control the largest dead zones in the United States. The whole world is watching.”
In August, the confirmed size of the 2013 Gulf hypoxic zone will be released, following a monitoring survey led by the Louisiana Universities Marine Consortium (LUMCON) beginning in late July. The result of this survey will be used to improve future forecasts. The final size of the Chesapeake Bay dead zone will be reported 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 efforts by the Mississippi River/Gulf of Mexico Nutrient Task Force to reduce the dead zone to less than 2,000 square miles, it continues to average 5,600 square miles over the last five years. This annual forecast demonstrates the link between the dead zone and nutrients from the Mississippi River, providing 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.