Researchers from U-M, Louisiana State University, and Limnotech Inc, an Ann Arbor-based firm, used three different models to analyze oxygen depletion and to answer two key questions: Is the expanded dead zone human-caused? Will a proposed goal of 30 percent nitrogen load reduction be sufficient to reduce the zone to below 5,000 square kilometers, as agreed to by federal, state and tribal leaders in 2001?
The hypoxic region is an area where water lacks sufficient oxygen to sustain most marine life, and in the Gulf of Mexico it is caused by excess nitrogen---largely runoff from mid-west agriculture, said Donald Scavia, director of the Michigan Sea Grant College Program and professor in the School of Natural Resources and Environment.
Scavia's paper, published in the June edition of the journal Estuaries, found that the 30 percent nitrogen load reduction will not likely shrink the dead zone to the desired 5,000 square kilometers. According to the paper, the nitrogen load must be reduced by 40 percent to 45 percent to achieve that reduction in most years.
Comparing the results of the three models also confirmed anecdotal and sparse historic data indicating that large-scale hypoxia did not occur before the mid-1970s and supports the notion that tripling the nitrogen load over the past 50 years has led to the heightened Gulf of Mexico hypoxia problem.
Confidence in the model analysis was bolstered this year as the operational ecological forecast from the National Oceanic and Atmospheric Administration, based on Scavia's model, predicted this summer's dead zone to be 5,400 square miles. Measurements from the NOAA-supported surveys by the Louisiana Universities Marine Consortiu
Contact: Laura Bailey
University of Michigan