Sentinel Monitoring of Salt Marshes in the Narragansett Bay National Estuarine Research Reserve
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Posted byRachel Gregg
The Narragansett Bay National Estuarine Research Reserve (NBNERR), along with several other National Estuarine Research Reserves, acts as a sentinel site to monitor climate change impacts. The reserve is engaged in several long-term ecological monitoring programs to determine the effects of sea level rise, saltwater intrusion, warmer temperatures, and coastal storms on species and habitats.
The NBNERR is located over 2,400 acres of upland habitat and 1,730 acres of estuarine water across four islands in the bay—Prudence, Patience, Hope, and Dyer. Habitats within the reserve include salt marshes, maritime forests, and rocky and cobble shores. The reserve’s salt marshes provide valuable habitat for fish, crabs, and other wildlife, and important ecosystem services by filtering water and protecting the shoreline during strong coastal storms. About 50% of the original salt marshes in NBNERR have either been altered or destroyed by human activities (e.g., roads, dikes, development); invasive species and pollution have also caused problems. Restoration efforts are underway at many marshes. These habitats are also threatened by climate change; impacts of concern include sea level rise, warmer temperatures, and coastal storms. Sea level rise may cause saltwater intrusion, which in turn may affect the groundwater supply of Prudence Island. The island gets a large percentage of its water supply from community wells. Volunteer monitoring and public workshops educating the island population on water conservation efforts are used to inform efforts that protect these water supplies from saltwater contamination.
The NBNERR was part of a national effort, created in 2007, to establish salt marshes as long-term reference sites at five reserves (Narragansett; Wells, Maine; Chesapeake Bay, Virginia; North Carolina; South Slough, Oregon) to compare marsh restoration success. Additionally, the reserve, along with other NERRs, participates in the System Wide Monitoring Program (SWMP), tracking changes in water quality, plants, animals, and habitats within the reserve over time. SWMP provides real-time NERR data and allows users to compare variables between reserves over different time periods.
The NERR System and NOAA Restoration Center partnered on a project—created in 2007—to establish salt marshes as long-term reference sites at five reserves (Narragansett; Wells, Maine; Chesapeake Bay, Virginia; North Carolina; South Slough, Oregon). The project was funded through the National Oceanic and Atmospheric Association to 1) use natural marshes as references to understand what is happening at restored marshes, and 2) use these natural reference sites to understand how marshes across the United States are responding to the impacts of climate change. The project required the reserves to conduct effectiveness monitoring of 17 Estuary Restoration Act-funded projects at paired restoration and reference sites. The study used a restoration performance index (RPI) to compare different salt marsh characteristics (e.g., salinity, vegetation cover, flow patterns, peat soils) at natural marsh reference sites and recently restored marsh sites over a two-year period (2008–2010) to track water levels and marsh height in order to determine if and how salt marshes can respond to environmental changes, including sea level rise. The NBNERR compared results between three reference sites (Nag Marsh, Coggeshall Marsh, Jacob’s Point) and five restoration sites (Potter Pond, Walker Farm, Silver Creek, Gooseneck Cove, Jacob’s Point).
The study determined that the restoration of hydrologic processes across the five NERRs were quite high while biological processes (e.g., species density, vegetation composition) varied as coastal marsh plant community development may lag in recovery (see Evaluating Tidal Wetland Restoration Performance Using National Estuarine Research Reserve System Reference Sites and the Restoration Performance Index).
The NBNERR is primarily funded through the National Oceanic and Atmospheric Association. The reserve also receives assistance from the Rhode Island Department of Environmental Management and Audubon Society of Rhode Island. Since reserve monitoring efforts began in 2000, collected data reveals that Narragansett Bay’s salt marshes are shrinking and that sea level rise plays a significant role in their disappearance. Inundation drowns out existing salt meadow vegetation, primarily Spartina patens, which is replaced by either barren patches or monocultures of flood-tolerant low marsh plants such as Spartina alterniflora.
The NBNERR has conducted a variety of studies based on SWMP Sentinel Site data. Estuarine research projects include studying the effectiveness of alleviating marsh waterlogging by digging drainage channels, and examining the impacts of growing crab populations on Narragansett marshes. Another central focus of Narragansett Bay studies is using the Sea Level Affecting Marshes Model (SLAMM) to map the effects of sea level rise. In addition to the 50% of the Bay’s salt marshes already damaged or lost, the NBNERR 2017 technical report determined that 13–87% of the remaining marsh will be permanently submerged based on one to five-foot sea level rise scenarios, respectively. SLAMM is also able to indicate areas where marsh migration is likely to occur, highlighting upland low-grade slopes free of obstructions, though the NBNERR acknowledges that the rate of sea level rise may further impede the process of natural marsh migration.
Outcomes and Conclusions
In general, NERRs can be particularly useful as long-term reference sites in a changing climate as they are protected areas that undergo regular long-term monitoring of environmental changes. The data collected may be used to inform other restoration efforts and coastal management.
Evaluating Tidal Wetland Restoration Performance Using National Estuarine Research Reserve System Reference Sites and the Restoration Performance Index (RPI)
The State of Narragansett Bay and Its Watershed Technical Report (2017)
National Estuarine Research Reserve System-Wide Monitoring Program (SWMP) Data
Gregg, R. M. and J. Sheldon. (2021). Sentinel Monitoring of Salt Marshes in the Narragansett Bay National Estuarine Research Reserve[Case study on a project of the Narragansett Bay National Estuarine Research Reserve]. Version 2.0. Product of EcoAdapt’s State of Adaptation Program. (Last updated June 2021)