Hypoxia

New Model for Mississippi Nutrient Pollution

By Marguerite Huber

Landsat image of the mouth of the Mississippi River

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)

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.

Editor's Note: The opinions expressed here are those of the author. They do not reflect EPA policy, endorsement, or action.

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Researching and Restoring the Gulf

By Marguerite Huber

Hypoxia sounds like some sort of deadly disease. While it is not a disease, it is in fact deadly. Also referred to as dead zones, hypoxic water kills bottom-dwelling marine life such as crabs and mussels. (To learn more, see the video at the end of this blog.)

Dead zones lack dissolved oxygen and are caused primarily by excess nutrients such as nitrogen and phosphorous. Too many nutrients cause algae and plankton to grow in large numbers, and as the algae die and decompose, oxygen is consumed.

Excess nutrients are especially a problem in the Gulf of Mexico. Every summer, nutrient-rich freshwater from the Mississippi River flows into the Gulf, resulting in a dead zone of about 7,772 sq. mi. that causes massive fish kills and chases other creatures further out to sea.

In an effort to understand this annual occurrence, EPA researchers have developed a modeling framework for predicting how nutrient management decisions and future climate change scenarios will impact the size, frequency, and duration of hypoxic conditions that form in the Gulf of Mexico every summer.

Providing 17% of the Nation’s gross domestic product, the natural resources of the Gulf’s coastal and marine habitats and their ecosystem services are critical to both the regional and national economy. That’s a major reason why EPA researchers are exploring ways to improve and restore Gulf water quality and aquatic habitats.

Since the 1990’s, the Agency and its partners from coastal states have been monitoring estuaries and most recently, wetlands. This baseline came in handy in the aftermath of Hurricane Katrina and the BP oil spill, and it will continue to help researchers track the degree of recovery resulting from ongoing and future restoration actions in the Gulf.

Monitoring in the future will also help inform environmental management decisions by addressing linkages between ecosystem condition and the goods and services provided. Agency researchers have several methodologies in development for examining these linkages, including spatial analysis tools, and human well-being indices.

About the AuthorMarguerite Huber is a Student Contractor with EPA’s Science Communications Team.

Editor's Note: The opinions expressed here are those of the author. They do not reflect EPA policy, endorsement, or action.

Please share this post. However, please don't change the title or the content. If you do make changes, don't attribute the edited title or content to EPA or the author.