Squeezed between rising seas and landward development, many of our nation’s tidal marshes are in danger of disappearing. Deciding how to protect them requires the ability to conduct “apples to apples’’ comparisons of marsh condition across broad landscapes. This innovative assessment marsh ranks resilience according to metrics of current marsh conditions, vulnerability to sea level rise, and potential for adaptation—critical information for efforts to conserve, restore, or study these habitats around the country.
The big picture of marsh resilience.
Squeezed between rising seas and landward development, many of our nation’s tidal marshes are in danger of disappearing. Deciding how to protect them requires the ability to conduct “apples to apples’’ comparisons of marsh condition across broad landscapes. Led by the National Estuarine Research Reserve System (NERRS) and the National Oceanic and Atmospheric Administration’s (NOAA) Office for Coastal Management, this study compares tidal marsh resilience at the landscape scale.
This study can help inform marsh restoration and conservation planning, identify marshes with particular characteristics across large areas, target fieldwork, and strengthen experimental design. It also can be used as a screening tool for national and regional work or be replicated with finer scale data to create higher resolution products.
Southeast marshes (top) are the most resilient, while Rhode Island marshes (bottom) are among the least resilient nationwide. Photos courtesy of Tara Rudo & the Narragansett Bay Reserve.
The study’s analysis offers standardized comparisons of resilience across “marsh units’’ within and beyond the NERRS. The team calculated tidal marsh resilience to sea level rise at the landscape scale, using 13 GIS-based metrics of current marsh conditions, vulnerability to sea level rise, and adaptive capacity in coastal areas of the lower 48 United States, not including the Great Lakes.
They combined these metrics to rank marsh units from the least (red) to the most (green) resilient at four geographic scales: National Estuarine Research Reserve site, state, regional, and national. Data to support these rankings can be found here.
The study found that overall marsh resilience varies by region, with the Southeast having the most resilient marshes, and the Northeast having the least. Marshes were most resilient in Georgia and least resilient in New York. Different factors, explored in the study report, contributed to the resilience of each region’s marshes.
Marsh resilience by Reserve
The tables below (click to enlarge) show scores for each of the 13 metrics of tidal marsh resilience at each National Estuarine Research Reserve. Green represents higher relative resilience and red represents lower. Reserve sites often have several marsh units within their boundaries, so scores represent an average of all units within a Reserve. Data for each Reserve can be found here.
Applying the data
This map (bottom) shows overall resilience scores for Maine’s tidal marshes, including those at the Wells Reserve (top). Photo courtesy Sue Bickford.
This analysis and its findings can be used to advance understanding of the forces that drive tidal marsh resilience and support a range of efforts to manage and protect these precious resources for the future. Wetland managers can use data from this analysis to determine which marshes need help and what kind of help they may need.
Maps such as the one below could, for example, help a decision maker consider the transferability of marsh science from the Reserve to another region on the coast. Or, it could serve as a screening tool to select a new Reserve in the northern part of the state, a biogeographic area that is underrepresented in the NERRS.
Data for conservation
This assessment underscored that high condition marshes that are likely to persist are the best candidates for conservation and migration. To find areas with the best marsh conservation opportunities, the team first identified which marsh units had high current condition, low vulnerability, and high adaptation potential. Within those units, the team identified the highest quality undeveloped lands with the capacity to support healthy tidal marshes in the future. As demonstrated in the map at left, there are tremendous opportunities to protect marshes in every region, but particularly in the Southeast and Gulf of Mexico.
Data for research & restoration
When explored at the Reserve scale, this analysis can help target and enhance the impact of fieldwork and monitoring. For example, in this theoretical deployment of Sediment Elevation Tables (SETs) in Central California (top), the stations would only monitor low condition marshes. A balanced perspective of the system would require deploying SETs in marshes with mid and high current conditions as well.
Comparing categories and individual metrics of resilience also can help scientists and practitioners identify the appropriate techniques to use for restoration. For example, marshes with high vulnerability to sea level rise and strong potential for migration (such as those indicated in the maps of Washington at left) may be good candidates for experimental restoration techniques like thin layer placement (TLP).
Data for marsh management
Resilience rankings can inform where and how to invest in marsh management. In the figure at right, marsh units in the Gulf of Mexico and the Southeast are classified into eight management options, each informed by how well the unit’s marshes ranked in the categories. Using graphics like these, one can identify which marshes to protect, as they are likely to persist in place, which ones might be good candidates for restoration, and which ones require significant investment to save.
The table below summarizes management options based on a marsh’s current conditions, vulnerability to relative sea level rise, and adaptive capacity. Options are considered from an ecological, rather than socioeconomic, perspective. Green text indicates a positive condition, red reflects a negative one. (Click the chart below to enlarge, or click here for a more detailed version of this chart.)
Weighing management options
At the Reserve scale, the overall resilience score for different components can inform where it makes sense to invest in restoration or land protection to maintain marsh health. For example, Maryland’s Chesapeake Reserve has three component sites (see figure below). The marshes in component 1 are less resilient and those in component 2 are moderately resilient, making these areas good places to consider restoration and adaptation. The marshes in component 3, however, are highly resilient and surrounded by other areas with resilient marshes. As a result, this area might be prioritized for land conservation and may serve as a useful reference site for mitigation projects in other areas.
Relative resilience of marshes in Maryland’s Chesapeake Bay Reserve
A case study for in-depth assessment
Along New Hampshire’s shoreline, marshes are a precious resource. Yet local land managers often lack the data to decide where and how best to apply finite resources for marsh conservation and restoration.
In response, the project team developed scaled tools to make this national analysis actionable for New Hampshire decision makers. The team was able to use high-resolution land cover data from NOAA’s Coastal Change Analysis Program (C-CAP) to analyze the current conditions, vulnerability, and adaptation potential of marsh units by parcel—the scale at which land managers make decisions. They found the most relevant management options for each unit and synthesized these for local resource managers and restoration professionals. With these tools, New Hampshire land managers can compare the feasibility and potential return-on-investment of different restoration and conservation strategies.
With the relevant high resolution data, this case study can be emulated in other areas.
High-resolution data from NOAA’s C-CAP program makes it possible to assess marsh resilience at the parcel scale.
NERRS toolkit for marsh resilience.
The NERRS maintains programs and creates tools to assess marsh resilience and vulnerability at multiple scales, from landscape-based tools to detailed field assessments at the plot scale. Used in tandem with other NERRS-based marsh assessment tools, this landscape scale assessment provides an integrated continuum of assessment to inform efforts to study, restore, or protect tidal marshes at the local, state, regional, and national scales.
- Sentinel Site Application Module (SSAM-1)
This monitoring protocol was designed to help understand how climate change, manifested by changing water levels, is impacting coastal habitats.
Using data from the NERRS System-wide Monitoring Program, 16 Reserves conducted the first, national-scale comparison of tidal marsh resilience to sea level rise. Anyone with relevant data can use this approach—from national networks of refuges to managers of individual marshes.
Designed to inform marsh management decisions, this approach provides site-scale information on marsh integrity, vulnerability to inundation stress, human disturbances, and migration potential to local decision makers.
NERRS: A national platform for comparative research on marsh resilience
The NERRS collects and shares timely environmental data on how estuaries respond to a changing climate. This long-term national monitoring allows Reserves to function as sentinel sites, providing front-line information on climate change adaptation and other management strategies.
The NERRS also offers a rare national platform to conduct coordinated restoration experiments and analyses across diverse sites and over extended monitoring periods. This capacity is critical to understanding trends in coastal and environmental conditions, and is extremely rare in the field of wetland restoration science.
This research was made possible by sustained congressional investment in the NERRS approach to collaborative science. By engaging local communities in the research process, NERRS collaborative research projects directly address their needs while advancing estuarine science. Through a national network dedicated to sharing tools and knowledge, local research conducted at one Reserve strengthens all 29 sites and the communities they serve.
More information about the NERRS approach to collaborative science is available from the project sponsor, the NERRS Science Collaborative, which is funded by NOAA and managed by the University of Michigan Water Center. Learn more.