R/CL-1

Impact/Outcome:

This section describes how this project has advanced scientific knowledge and made a difference for coastal residents, communities, and environments. Maryland Sea Grant has reported these details to the National Oceanic and Atmospheric Administration (NOAA), one of our funding sponsors.

Summary: Researchers completed the first multi-factor field study indicating that elevated levels of nitrogen and carbon dioxide in Chesapeake Bay marshes directly facilitate increased rates of invasion of Phragmites, the common reed. The findings indicate that land use managers may limit future Phragmites expansion by limiting nitrogen availability. In 2015, the researchers presented these results at a four-day Phragmites symposium they organized at the Society of Wetland Scientists meeting.

Relevance: In the Chesapeake Bay, invasions of a non-native type of Phragmites australis have altered native marsh habitat. The researchers studied how rates of Phragmites growth and invasion in intact marsh ecosystems would be affected by likely future increases in atmospheric carbon dioxide (CO2) and elevated levels of nitrogen (N) caused by human activities. In Chesapeake Bay, Phragmites invasions threaten to alter habitat for aquatic species like the mummichog (Fundulus heteroclitis), an abundant fish on Bay marshes and a food source that supports many commercially important fisheries.

Response: Maryland Sea Grant supported research by principal investigators Patrick Megonigal and Melissa McCormick of the Smithsonian Environmental Research Center and Thomas Mozdzer of Bryn Mawr College. In a field study, they exposed tidal marsh plots to combinations of carbon dioxide gas and nitrogen-rich flood water. Each plot straddled a non-native Phragmites plant community and the native plant community it was invading. The primary response variable of interest was the rate at which non-native Phragmites invaded.

Results: The researchers found that N, CO2, and N+CO2 clearly increased Phragmites invasion rates in marsh habitats. This suggests that future increases in N and CO2 may make non-native Phragmites more capable of displacing native marsh habitat. However, the research team also found that in the low nutrient marsh under ambient conditions, Phragmites density and biomass did not change significantly. This suggests that altering management practices to limit N and/or CO2 may slow future Phragmites invasions. These data can also be used to help prioritize which marshes can and should be managed. The scientists have advised the U.S. Fish and Wildlife Service's (USFWS) Region 5 (Northeast) about applying these findings to improve management of Phragmites in National Wildlife Refuge marshes managed by USFWS. The researchers’ data also indicate that ecosystems dominated by Phragmites may gain surface elevation more quickly than those dominated by native plants, which may make the Phragmites-dominated marshes more resilient to the effects of sea level rise. Dr. Mozdzer organized a four-day Phragmites symposium held during the 2015 Society of Wetland Scientists meeting. About 100 participants, who included land managers, policy makers, federal agencies, and scientists, heard 42 talks, seven of which featured research supported by Maryland Sea Grant.