Sewanee: The University of the South

David Johnson part of research team showing impact of nutrients on coastal ecosystems

October 31, 2012

Sewanee’s David Johnson, visiting assistant professor of biology, is part of a multi-disciplinary national research group that recently discovered the impact of nutrient enrichment on salt marshes. The group’s work was the first to demonstrate that nutrient enrichment (nitrogen and phosphorus) results in loss of salt marshes. Salt marshes are important both for storm protection for coastal cities and as habitat for commercially important species such as crabs, shrimp, and fish.

Salt marshes have been disintegrating and dying over the past two decades along the U.S. Eastern seaboard and other highly developed coastlines, without anyone fully understanding why. Last week in the journal Nature, Johnson and colleagues reported that nutrients—such as nitrogen and phosphorus from septic and sewer systems and lawn fertilizers—can cause salt-marsh loss.

Until this study, it seemed that salt marshes had unlimited capacity for nutrient removal, with no harmful effects on the marshes themselves. In the next phase of research, the scientists will study the recovery of the nutrient-enriched marsh. This information will be important in reclaiming the health of salt marshes that are currently suffering from nutrient enrichment. (See the journal article )

“People living far from coastal areas may think that there's no connection between them and our coastlines,” says Johnson. “But we are all connected to the ocean by rivers and streams. Thirty-one states drain into the Mississippi River, and nine of those states (including Tennessee) are greatest contributors of the nutrient pollution.

“Two common sources of nutrient pollution are agricultural run-off and wastewater. Sewanee, which sits at the top of its watershed, treats its wastewater biologically using lagoons and forests to remove nutrients and prevent sending nutrient pollution downstream to its neighbors. Responsible stewardship such as this helps protect our waters and coastlines.”

Researchers on the team include lead scientist Linda Deegan of the Ecosystem Center at the Marine Biological Laboratory at Woods Hole; Johnson; Bruce J. Peterson of the MBL; R. Scott Warren of Connecticut College; John W. Fleeger of Louisiana State University; Sergio Fagherazzi of Boston University; and Wilfred M. Wolheim of The University of New Hampshire.

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