US EPA

Coastal salt marshes--which provide valued ecosystem services such as flood control, water purification and critical habitat--are vulnerable to ongoing sea level rise, which is interacting with physical and biological attributes of the system to induce complex changes in salt marsh habitats. For salt marshes such as those in the Delaware Bay, management techniques need to be adapted to account for these effects when carrying out activities to preserve priority salt marsh areas.

This report presents future projections of change for seven salt marsh areas of the Delaware Bay, using the Sea Level Affecting Marshes Model (SLAMM). SLAMM simulates the dominant processes involved in determining distributions of wetlands across space and time under conditions of accelerated sea level rise. Our methods differ from other SLAMM reports in that we derive results for specific marsh habitat types (high marsh, low marsh, total marsh) that correspond to different ecosystem services of interest. This allows consideration of vulnerability from the perspective of different management objectives.

The intended audiences for this report are wetland managers, scientists and decision makers of the Delaware Bay region. The salt marsh areas of focus were chosen because they are of key management concern to the Partnership for the Delaware Estuary (PDE) and its regional partners. The projections in this report not only fulfill immediate information needs of these partners, but also serve as inputs to larger studies on how to interpret and use this type of vulnerability information for robust analysis and design of effective adaptation practices for protecting, restoring and/or enabling migration of valued salt marsh ecosystems under changing environmental conditions.

This report was produced by the Air and Energy (A-E) Research Program of the EPA Office of Research and Development, with support from Tetra Tech, Inc., and in collaboration with PDE. The A-E research program provides scientific information and tools to support EPA’s commitment to clean air, clean water and sustainable natural resources, even as environmental conditions change. A key component of this is the development of sound science to support adaptation. Adaptation involves preparing for and adjusting to the effects of expected future environmental changes.

This report presents results from the Sea-Level Affecting Marshes Model (SLAMM), which was used to generate spatially explicit projections for sea level rise (SLR)-induced changes in acreage for seven salt marshes in the Lower Delaware Bay. Four of the marshes are located in New Jersey (Dividing, Lower Maurice, Dennis, Reeds Beach) and three are located in Delaware (Broadkill/Canary, Mispillion, Lower St. Jones). SLAMM is widely recognized as an effective model to study and predict wetland response to long-term SLR (Park et al. 1991) and has been applied in every coastal U.S. state. Prior SLAMM work has been performed in the Delaware Bay (Kassakian et al. 2017), but our methods differ in that we derive results for specific marsh areas and utilize more recent, higher resolution elevation data, the most recent SLR projections, and site-specific accretion data. These SLAMM simulations were performed as part of a larger project by the USEPA on frameworks and methods for characterizing relative wetland vulnerabilities (Wardrop et al. in press, Stamp et al. in prep).

We ran SLAMM simulations for early to late century time periods under three SLR scenarios (low, intermediate and high), based on projections in Sweet et al. (2017). We also generated results for three different model protection scenarios, ranging from no protection (where all cells are subject to inundation) to protection of all dry land (where all cells designated as dry land are protected from inundation). In addition, we ran a sensitivity analysis to better understand the influence of each input variable on the projected changes in salt marsh acreage.

U.S. EPA. Application of the Sea-Level Affecting Marshes Model (SLAMM) to the Lower Delaware Bay, with a Focus on Salt Marsh Habitat. U.S. Environmental Protection Agency, Washington, DC, EPA/600/R-18/385, 2019.