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Botany professor and students prove sewage and fertilizer nutrients are destroying northeastern salt marshes

Clara Chaisson '12 measures slumped areas of marsh
Clara Chaisson '12 measures slumped areas of marsh

Tidal marshes across the world and in the northeastern United States are being lost at alarming rates. Now, scientists have a much better understanding of why at least some of these valuable resources are disappearing, thanks in large part to nine years of research by emeritus professor R. Scott Warren and a dozen Connecticut College students.

An article published this week in Nature, one of the most prestigious scientific journals, details the results of this ecosystem-scale study of the impact of excess nutrients on a salt marsh within the Plum Island Estuary of Massachusetts. Conducted by a multi-disciplinary national research group, including Warren and lead author Linda Deegan of the Marine Biological Laboratory Ecosystem Center, the study found excess nutrients, such as nitrogen and phosphorus from sewer and septic systems and lawn fertilizer runoff, can drive significant salt marsh loss.

"None of us anticipated the marsh would fall apart," said Warren, the Jean C. Tempel '65 Professor Emeritus of Botany at Connecticut College. "But that is exactly what happened."

Warren said previous studies suggested that marshes have an amazing ability to soak up excess nutrients, thus protecting bays and coastlines from pollution. Small sample areas and short time frames, however, didn't allow scientists to witness the full effect on the marshes, which protect coastal cities from storms and provide a critical habitat for fish, birds and shellfish.

Deegan, Warren and a large team of researchers - including faculty from research universities, graduate students and Connecticut College undergraduates - created a very realistic study, pumping nutrients directly into flooding tidal water and monitoring the marsh over nine years. Over time, they found marsh grasses below high tide levels grew fewer roots, and decomposition of the marsh peat accelerated. This caused the banks of the tidal creeks to collapse, converting the low marsh into mudflats, which don't provide the same environmental benefits as grass-covered marshland.

Warren and his revolving team of undergraduates were responsible for following plant communities throughout the duration of the experiment, a labor-intensive process he says wouldn't have been possible without the critical work of the student researchers. With funding from the National Science Foundation, he was able to bring two to four student researchers to Plum Island each summer to take direct field measurements and conduct initial data analysis.

"It was an unbelievable amount of work," Warren said. "But it was a genuine team effort. The students were incredible - responsible and hard working. All of them really learned what field ecology is like, in a way you never do just from reading a book about it."

Warren said nearly all of the Nature article's graphs and more than half of table data stem from the work of the Connecticut College student researchers - a point he makes with great pride. And, with funding from his position as the Jean C. Tempel '65 Endowed Chair, Warren was able to take several students to major regional and national conferences to present initial findings from the research. Many of these students have gone on to graduate programs in marine ecology.

"This is world-class research with significant contributions by undergraduate students," he said.

One of those students was Clara Chaisson '12. She said she loved the collaborative atmosphere on Plum Island, where everyone from the high school intern to the principle investigator was encouraged to contribute ideas. And working with Warren was especially rewarding, she said.

"He is the type of teacher who makes you want to achieve your personal best," she said. "His enthusiasm for his research is contagious, he is a veritable reservoir - or maybe I should say a veritable estuary - of knowledge on coastal ecology, and, last but not least, he's just an incredibly nice, down-to-earth person."

Christopher Haight '11, who worked on various aspects of the study over four summers, agrees.

"To me, Dr. Warren is the quintessential field scientist - dirt on his hands, cord grass between his teeth and a smile on his face," he said. "I feel very fortunate to have him as a role model," added Haight, an environmental studies major who is now pursuing a master's degree at Columbia University in the Department of Ecology, Evolution and Environmental Biology.

Chaisson, a botany major at Connecticut College who is now working on sustainable agriculture, said she is excited by the attention the study's findings are getting, but not surprised. "Salt marshes along the eastern seaboard are falling apart, and this study presents evidence that human activity can drive that disintegration," she said. "This information deserves attention, and should make us seriously reconsider how we treat our waterways."

Warren agrees the study demonstrates that there is a limit to the amount of nutrients marshes can absorb, and that this limit is far lower than conventional scientific wisdom would have anticipated. While marshes are also at risk because of sea-level rise and development, among other factors, limiting nutrients from sewage and septic systems and fertilizer use must become a priority if these critical ecosystems are to be saved, he said. And he is proud that Connecticut College students had a hand - or a muddy foot, as the case may be - in this important discovery.

"Connecticut College is a great place for science," he said. "The active scholars on the Connecticut College faculty provide our students with the opportunity to do real, meaningful research. And that is the very best kind of science education."

October 22, 2012