The Impact of the 2008 Midwest Flood on the Gulf of Mexico “Dead Zone”

Aaron Gwinnup collecting samples in the Gulf of Mexico

Project Personnel (University of Iowa):

• Dr. Jerry Schnoor (Professor)
• Dr. Craig Just (Associate Research Scientist)
• Aaron Gwinnup (Graduate Student)
• Nancy Rabalais and Eugene Turner of the Louisiana Universities Marine Consortium

Nutrients and sediment from the Mississippi River watershed cause a seasonal hypoxic plume in the Gulf of Mexico (often called the “Dead Zone”). This is the result of agricultural runoff and urban discharges, which introduce nitrogen and phosphorus into streams and rivers. The nutrients promote massive algal blooms (phytoplankton) in the Gulf, which then sink and decompose, consuming vital oxygen. The state of Iowa contains 42 of the top 150 watersheds that contribute the majority of the nutrients responsible for forming the Dead Zone.

University of Iowa researchers monitored the Iowa flood waters as they moved down the Mississippi River during the summer of 2008. When floodwaters entering the Gulf were at their peak in late July 2008, researchers on board the R/V Pelican traversed the Dead Zone assessing water chemistry and “mapping” the extent of the hypoxic plume. The hypoxic zone covered more than 8,000 square miles off the coast of Louisiana and Texas, the second largest zone recorded to date.

The data analysis for this research is still underway. The “baseline” nutrient load from Midwestern streams and rivers will be subtracted from the total load observed during the flood event to yield the quantified impact of this extreme event. High frequency data (sampling every 15 minutes) will be used, where available, to help improve the accuracy of existing “nutrient flux” models.

MODIS Satellite image showing the sediment and phytoplankton plume emanating from the Louisiana coastline

Funding Source: