URI graduate researcher discovers benefits of invasive marsh grass

Having powered through her doctoral work in three years, newly minted University of Rhode Island Ph.D. Rose Martin credits her Rhode Island EPSCoR graduate fellowship as the most productive year of her research.

Phragmites australis, an invasive grass that often inundates salt marshes, is the target of costly and difficult eradication efforts. However, the research work of a Rhode Island EPSCoR graduate fellow finds that we may be better off leaving the grass alone.

“I think it’s fair to say that the take home message is that the presence of the plant may contribute to the marsh’s function of greenhouse gas uptake,” said Rose Martin, a University of Rhode Island doctoral student who recently gave her dissertation on the Phragmites role in carbon dioxide and methane emission and uptake in coastal marshes.

“Often times, diminishing the cover of Phragmites is one of the goals of marsh restoration because it has a negative impact on biodiversity and wildlife in marshes,” Martin explained. “But, this dissertation joins the growing body of literature that says the plants’ presence might support other functions of the marsh ecosystem.

“The results suggest that perhaps Phragmites is not the absolute worst thing that could be happening to a marsh.”

For her dissertation — Coastal Marshes of the Anthropocene: A potential role for an invasive species in maintaining ecosystem function — Martin said she wanted to know whether the carbon dioxide uptake of Phragmites was great enough to offset removal benefits. What she found, she said, was that a marsh dominated by Phragmites took up more carbon dioxide and at a higher rate than native vegetation marshes.

With plots in three Rhode Island locations — Round Marsh, Fox Hill Marsh, and Sage Lot Pond — Martin also found that projected temperature hikes from climate change would not alter the Phragmites invasion of salt marshes.

In pursuit of science

Introducing Martin to the audience gathered to hear her presentation one recent morning in the URI Coastal Institute auditorium, Assistant Professor Serena Moseman-Valtierra reeled off a list of accomplishments:

• Best Graduate Oral Presentation, 2014 New England Estuarine Research Society (NEERS) fall meeting, “From a Spartina patens meadow to a Phragmites jungle: a biological invasion may change coastal carbon cycling”
• Four manuscripts from her thesis chapters in various stages of the publication process, and contributing author on three more papers
• Rhode Island NSF EPSCoR graduate fellow, 2013-14; research support 2014-15
• At least five presentations at national and regional conferences
• Mentor to undergraduates and outreach volunteer for RI EPSCoR

Most impressively, perhaps, Martin achieved all of this while earning her Ph.D. in a blistering, three-year pace.

And, true to form, she went straight from her dissertation to a post-doctoral post at the Environmental Protection Agency (EPA) in Narragansett. Oak Ridge Institute for Science and Education (ORISE) administers the position through an interagency agreement between the Department of Energy (DOE) and the EPA.

Martin arrived in Moseman-Valtierra’s lab in the summer of 2012, with a master’s in natural resources and the environment from the University of Connecticut and a bachelor’s in environmental science from URI. On September 28, 2015, she presented her dissertation.

“I am extraordinarily honored to be a mentor for Rose Martin,” Moseman-Valtierra said, before leading into Martin’s achievements. “She has set a dangerous precedent for future students.”

Grasses and greenhouse gases

The term anthropocene denotes the era in the earth’s history when humankind has dominated the function of ecosystems, bringing on climate change, influencing nutrient cycling and introducing invasive species.

Coastal ecosystems, which encompass the sub-tidal part of an estuary and the fresh and brackish marshes further upstream, serve as a critical buffer between land and saltwater. The salt marshes also play a vital role in the ecosystem by sequestering carbon dioxide — actually, at a higher rate than tropical rain forests.

Yet, for centuries, these intertidal zones have weathered the brunt of human activity, filled in and built over to pave the way for development.

Martin said she wanted to gain a better understanding of how coastal systems functioned under human dominance of the ecosystem, specifically looking at the potential for enhancement of greenhouse gas uptake in marshes dominated by Phragmites. The species, which can be found in old herbarium records dating back to the early 1900s, spreads easily, starting in the upland area and spreading into the salt marsh.

Phragmites is known to drive changes in carbon cycling of salt marshes, moving gases from the atmosphere through its above ground plant structure and root system below the soil. The grass also has the ability to change the soil it invades.

“One of the services coastal marshes provide is that they store or sequester abundant carbon dioxide,” explained Martin. “If carbon dioxide is stored in the soil of the marsh, it’s not entering the atmosphere in forms of greenhouse gases that cause climate change.”

Salt marshes, in particular, are extremely efficient in carbon dioxide uptake, according to Martin. When marsh plants die, they decompose slowly and the material becomes part of the soil that builds up, trapping the carbon.

In the final experiment of her research, Martin simulated climate change under projections for the year 2100, with elevated temperatures and the levels of carbon dioxide in the atmosphere. She measured the greenhouse gas fluxes that would result from both Phragmites and native vegetation, and found that with the amount of carbon dioxide Phragmites could take up, there was a good chance the grass could balance out the increased amount of methane emitted.

“It’s interesting to think about the idea, that the effect could be a mixed bag,” said Martin. “The results of my dissertation show that although Phragmites is associated with negative consequences, there is potential for its presence in marshes to maintain or even enhance the service of GHG (greenhouse gas) uptake.”

The path taken

Martin’s extraordinarily high level of academic achievement and scientific discovery seems unlikely at first glance for a youngster who saw the field as inaccessible. Conducting outreach with Rhode Island EPSCoR, Martin has recounted her journey for audiences of middle and high school students:

“Everyone else in my family sells tile and my parents are teachers, so I’m kind of the odd one out.”

She said that when she was growing up in Rhode Island, she didn’t know any scientists and the picture in her mind was “an old man in a white coat.” Still her parents reinforced the mindset that education was power; that no one could take away her education.

She initially enrolled at URI with microbiology as her intended major, but hit a roadblock. Her grades were lackluster and she couldn’t figure out her direction.

But, she wound up in a soil science class and the subject matter resonated. The professor suggested she switch her major to environmental science. He and other mentors along the way helped her steer a new course and she embraced the possibilities offered by a graduate degree and research.

After that turning point, Martin said, she had the good fortune to meet Moseman-Valtierra and benefit from her mentoring: “Serena is the first female advisor and first female mentor I’ve had. It’s nice to have someone who has gone through the same struggles as a young female scientist. We’ve seen a lot of progress, but there is a long way to go for the representation of women and women of color.”

Martin said her EPSCoR fellowship also played a crucial role, freeing her from the obligation of teaching or working as a research assistant and allowing her to devote her time to research and collaboration.

“That was my most productive year in terms of research and manuscripts,” said Martin. “Also, EPSCoR funding for research supplies was used to purchase materials to build the tall gas flux chambers I used for Phragmites measurements. They made my research possible, and will continue to be used by Serena’s lab.”

Next, looking ahead to her post-doctoral position, Martin said her work would take her to an urban ecosystem in Puerto Rico, the resulting environmental degradation and the impact on the health of people in communities using the watershed. The research will focus on the interface between environmental degradation and human health.

“I’m very excited,” Martin said. “It will broaden my understanding of how people work with the environment. My Ph.D. focused on how people affect the environment. Now, I will be on the other side of the relationship.”

By Amy Dunkle