Abstract
Coastal salt marshes, which provide valuable ecosystem services such as flood mitigation and carbon sequestration, are threatened by rising sea level. In response, these ecosystems migrate landward, converting available upland into salt marsh. In the coastal-plain surrounding Chesapeake Bay, United States, conversion of coastal forest to salt marsh is well-documented and may offset salt marsh loss due to sea level rise, sediment deficits, and wave erosion. Land slope at the marsh-forest boundary is an important factor determining migration likelihood, however, the standard method of using field measurements to assess slope across the marsh-forest boundary is impractical on the scale of an estuary. Therefore, we developed a general slope quantification method that uses high resolution elevation data and a repurposed shoreline analysis tool to determine slope along the marsh-forest boundary for the entire Chesapeake Bay coastal-plain and find that less than 3% of transects have a slope value less than 1%; these low slope environments offer more favorable conditions for forest to marsh conversion. Then, we combine the bay-wide slope and elevation data with inundation modeling from Hurricane Isabel to determine likelihood of coastal forest conversion to salt marsh. This method can be applied to local and estuary-scale research to support management decisions regarding which upland forested areas are more critical to preserve as available space for marsh migration.
Highlights
Salt marsh survival through the end of this century is threatened as sea level rise (SLR) continues to accelerate at rates unseen for two millennia (IPCC, 2013)
This study considers salt marshes to be estuarine intertidal emergent wetlands as classified by National Wetlands Inventory (NWI) following Cowardin classification (Federal Geographic Data Committee, 2013)
We developed and tested our slope quantification method along the coast of Chesapeake Bay, United States (Figure 1)
Summary
Salt marsh survival through the end of this century is threatened as sea level rise (SLR) continues to accelerate at rates unseen for two millennia (IPCC, 2013). Marshes are vulnerable in the lateral direction from wave erosion and sediment deficits that degrade the marsh at the seaward edge and can lead to marsh loss (Kirwan et al, 2016). Salt marshes can migrate inland where upland is available for conversion to marsh (Williams et al, 1999; Enwright et al, 2016), responding to sea level rise and counteracting marsh loss from those lateral processes. Marsh migration inland is well documented on the Atlantic and Gulf coasts of the United States (Williams et al, 1999; Smith, 2013; Raabe and Stumpf, 2016; Anisfeld et al, 2017; Schieder et al, 2018; Schieder and Kirwan, 2019), the mechanisms that control this process are less firmly established
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