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Smith, S.M., 2020. Salt marsh migration potential at Cape Cod National Seashore (Massachusetts, U.S.A.) in response to sea-level rise. Journal of Coastal Research, 36(4), 771–779. Coconut Creek (Florida), ISSN 0749-0208.Salt marshes can adjust to sea-level rise (SLR) through vertical elevation gain and horizontal expansion into terrestrial environments. The latter depends on the topography of adjacent uplands and the availability of suitable substrate for halophyte colonization. Within Cape Cod National Seashore (CCNS), calculations of marsh migration potential in response to 1-m of SLR were completed using ArcGIS (version 10.4) based on real-time kinematic GPS marsh elevations, local tide data, land-use, and upland topography derived from 2011 LIDAR scans of CCNS. These estimates were combined with marsh-loss predictions from a previous study within their present-day footprint under the same SLR scenario. The results suggest that individual marshes will respond quite disparately, as dictated by their position in the tidal frame, adjacent terrestrial slopes, land-use, and barrier-beach losses. Most sites are expected to gain or lose relatively small amounts of marsh area under few or no migration constraints. However, there could be a large increase (∼144–240 ha) at one site and an almost a complete loss at another (∼260–290 ha). Where migration was constrained to slopes ≤1%, opportunities for marsh expansion diminished the most—even more so when barrier-beach losses are simulated. Overall, losses at five marsh sites were offset by gains at Hatches Harbor and Pleasant Bay, Massachusetts, such that the total area of salt marsh actually increases with 1-m of SLR, except under the strictest slope constraints. Changes in the spatial distribution and total extent of salt marsh within the CCNS will influence both the quality and quantity of ecosystem services they provide. For coastal land managers, understanding the potential for overland marsh migration is critical for the kind of land-use planning that accommodates these transitioning salt marshes.

Smith, S. and Medeiros, K., 2013. Manipulation of water levels to facilitate vegetation change in a coastal lagoon undergoing partial tidal restoration (Cape Cod, Massachusetts) East Harbor is a back-barrier coastal lagoon and salt marsh within Cape Cod National Seashore (Massachusetts), which has been undergoing partial tidal restoration since 2002. The current tidal exchange has been sufficient to elevate salinities in the open lagoon but is still too constrained by the present infrastructure to create high tides sufficient to flood the peripheral marsh areas. Consequently, an adaptive management strategy using a one-way tide gate was implemented in 2011 that let high tides into the system while blocking their escape. The increased flooding of the marsh, above and beyond what the current engineering of the system could provide by opening the restrictive culvert, raised porewater salinities in many areas and resulted in decreases in the cover of freshwater and brackish-water plant taxa—a necessa...

SMITH, S.M.; MEDEIROS, K.C., and TYRRELL, M.C., 2012. Hydrology, herbivory, and the decline of Spartina patens (Aiton) Muhl. in outer Cape Cod salt marshes (Massachusetts, U.S.A.). Salt marsh dieback in different regions of the United States exhibits considerable variability in symptoms, processes, and theoretical or proven causes. On Cape Cod (Massachusetts), where losses within the low-marsh zone (elevations below mean high tide, dominated by smooth cordgrass [Spartina alterniflora Loisel.]) have been particularly severe, recent studies suggest that intense grazing pressure from increased abundances of a native, herbivorous, purple marsh crab (Sesarma reticulatum) is to blame. Low-marsh dieback is spatially heterogeneous because it is closely related to the distribution of the crabs' preferred substrate (peat vs. sand or mud). However, vegetation losses have also occurred in the high marsh, which is comprised of mainly saltmeadow cordgrass (Spartina patens [Aiton] Muhl). In contrast to the low ...

The structure and function of intertidal communities are intimately linked with hydrologic regime, which itself is defined by elevation gradients relative to sea level. Water surfaces have long been used as a reference plane for determining topographic profiles of the underlying ground surface. Although relatively straightforward in static systems such as lakes or ponds, this method is more complicated in the intertidal zone where the water surface is in vertical motion. Here we evaluate a technique using water marks to indicate maximum tide heights from which ground elevations relative to a tidal datum can be calculated. Comparisons of data using this technique to optical-leveling surveys in several salt marshes of Connecticut and Massachusetts showed that the water surface conformed to a horizontal plane at high, slack tide and that watermarks could be used as a reliable reference plane for determining ground elevations from flooding depth.

Smith, S.M.; Tyrrell, M.; Medeiros, K.; Bayley, H.; Fox, S.; Adams, M.; Mejia, C.; Dijkstra, A.; Janson, S., and Tanis, M., 2017. Hypsometry of Cape Cod salt marshes (Massachusetts, U.S.A.) and predictions of marsh vegetation responses to sea-level rise. The structure and functioning of salt marsh ecosystems are being impacted by sea-level rise, and a major determinant of their vulnerability to this aspect of climate change is their ground surface elevation relative to tide heights (hypsometry). In this study, a comprehensive real-time kinematic (RTK) global positioning system (GPS) survey was conducted within four salt marshes at Cape Cod National Seashore (CCNS) to create digital elevation models, and in situ water-level loggers were used to collect tidal data within each system. From these data, marsh surface elevations were calculated relative to mean high tide elevations for 2013 and projected elevation change rates with 50 cm and 100 cm of sea-level rise. Vegetation responses to these scena...

Smith, S.M. and Green, C., 2015. Sediment suspension and elevation loss triggered by Atlantic mud fiddler crab (Uca pugnax) bioturbation in salt marsh dieback areas of southern New England. The effects of bioturbation on sediment suspension and elevation loss by the Atlantic mud fiddler crab, Uca pugnax (Smith), were investigated in this study. High densities of U. pugnax occur in unvegetated areas of Cape Cod salt marshes that have been denuded by the herbivorous Sesarma reticulatum (purple marsh crab). The hypothesis addressed in this study is that U. pugnax then causes sediment suspension and subsequent erosion. Anecdotal evidence suggests that unlike vegetated zones sediments are rapidly eroding from dieback areas, but the various mechanisms by which this is occurring are unclear. In this study, we focused on the role that U. pugnax might play in this process through experiments that assessed sediment suspension during rainfall events and flooding tides, as well as elevation changes. The resu...

Timm, B.C.; Smith, S.M., and Greenspan, S.E., 2014. Remotely sensed mapping of Ammophila spp. distribution and density at Cape Cod National Seashore. Ammophila breviligulata and Ammophila arenaria are pioneer grass species that have been planted within and outside their natural ranges in efforts to stabilize mobile dune fields. While the presence of Ammophila spp. may be considered beneficial in some situations (e.g., for dune stabilization and storm surge protection), there are other cases where Ammophila spp. introductions have had negative ecological consequences (e.g., reduction in native plant and animal diversity, altered dune dynamics). Thus, it is important to be able to effectively map and monitor the distribution and density of these species. In this study, we constructed and assessed the accuracy of a fine-resolution (i.e. 1.0-m-pixel resolution) remote-sensing-based distribution and density map of Ammophila spp. throughout an extensive coastal dune ecosystem at Cape Cod National Seash...