By Marguerite Huber

Landsat image of the mouth of the Mississippi River. (NASA Image by Robert Simmon, based on Landsat data provided by the UMD Global Land Cover Facility.)

EPA scientists are tackling one of the nation’s biggest water quality challenges, and I mean in physical size and importance: nutrient pollution flowing from the Mississippi River watershed into the Gulf of Mexico.

Scientific assessments have concluded that the nutrients from the Mississippi River watershed are the primary cause of the dramatic drop in oxygen levels (“hypoxia”) sparking the Gulf of Mexico’s summer time “dead zone.”

EPA researchers have built the Coastal General Ecosystem Model (CGEM) to help address that challenge.

Mississippi watershed (image courtesy of NASA)

The state-of-the-art Coastal General Ecosystem Model provides a wealth of important information to scientists and stakeholders seeking to better understand the dynamics of nutrient pollution in the Gulf. The model receives nitrogen and phosphorus data collected from the Mississippi River and then predicts how these nutrients trigger eutrophication and hypoxia.

Armed with that information, researchers and others can predict the impacts of reducing nitrogen and phosphorus on water quality in the Gulf, including estimating how much nitrogen and phosphorus reduction would be needed to achieve the Mississippi River Gulf of Mexico Watershed Nutrient Task Force’s goal of reducing the size of the hypoxic area from its current average size of 15,000 km² down to 5,000 km².

John Lehrter, research ecologist developing and working with CGEM notes, “Knowing that the goal is 5,000 km², we can adjust the nitrogen and phosphorus inputs to the model to estimate a range of reductions required to achieve the goal. Water quality managers and policy makers can then use this and other information to determine how to achieve these reductions.”

Additionally, a team of federal and academic scientists are using the model in the Coastal and Ocean Modeling Testbed. The Testbed aims to increase the accuracy and reliability of coastal and ocean forecasting products.

Overall, the model will help the states in the Mississippi River Basin demonstrate to stakeholders the link between nutrient loading and water quality impairment in the Gulf and show how nutrient reductions result in water quality improvement.

About the Author: Marguerite Huber is a Student Contractor with EPA’s Science Communications Team.