Spring floods across the Midwest are expected to contribute to a very large and potentially record-setting 2013 Gulf of Mexico “dead zone,” according to a U-M ecologist and colleagues who released their annual forecast last week, along with one for the Chesapeake Bay.
The Gulf forecast, one of two announced by the National Oceanic and Atmospheric Administration, calls for an oxygen-depleted, or hypoxic, region of between 7,286 and 8,561 square miles, which would place it among the 10 largest on record.
The low end of the forecast range is well above the long-term average and would be roughly equivalent to the size of Connecticut, Rhode Island and the District of Columbia combined. The upper end would exceed the largest ever reported (8,481 square miles in 2002) and would be comparable in size to New Jersey.
Farmland runoff containing fertilizers and livestock waste, some of it from as far away as the Corn Belt, is the main source of the nitrogen and phosphorus that cause the annual Gulf of Mexico hypoxic zone. In its 2001 and 2008 action plans, the Mississippi River/Gulf of Mexico Watershed Nutrient Task Force, a coalition of federal, state and tribal agencies, set the goal of reducing the five-year running average areal extent of the Gulf hypoxic zone to 5,000 square kilometers (1,950 square miles) by 2015.
Little progress has been made toward that goal. Since 1995, the Gulf dead zone has averaged 5,960 square miles, an area roughly the size of Connecticut.
“The size of the Gulf dead zone goes up and down depending on that particular year’s weather patterns. But the bottom line is that we will never reach the action plan’s goal of 1,950 square miles until more serious actions are taken to reduce the loss of Midwest fertilizers to the Mississippi River system, regardless of the weather,” said U-M aquatic ecologist Donald Scavia, director of the Graham Sustainability Institute, who contributes to both the Gulf and Chesapeake Bay forecasts.
This year’s Chesapeake Bay forecast calls for a smaller-than-average dead zone in the nation’s biggest estuary. The forecast from Scavia and University of Maryland researchers has 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 forecast calls 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 dead zones. Last year, the mid-summer hypoxic zone was 1.45 cubic miles. Because of the shallow nature of large parts of the estuary, the forecast focuses on water volume expressed in cubic miles instead of surface area in square miles.
The annual Gulf forecast is prepared by researchers at U-M, Louisiana State University and the Louisiana Universities Marine Consortium. The Bay forecast is provided by U-M and the University of Maryland’s Center for Environmental Science. Both studies are funded by NOAA.
The forecasts are based on nutrient runoff and river-and-stream data from the U.S. Geological Survey, which are then fed into computer models developed with funding from NOAA’s National Centers for Coastal Ocean Science.
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