Rates of Mainland Marsh Migration into Uplands and Seaward Edge Erosion are Explained by Geomorphic Type of Salt Marsh i
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MARSH RESILIENCE SUMMIT
Rates of Mainland Marsh Migration into Uplands and Seaward Edge Erosion are Explained by Geomorphic Type of Salt Marsh in Virginia Coastal Lagoons Jessica A. Flester 1
&
Linda K. Blum 1
Received: 14 January 2020 / Accepted: 2 October 2020 # Society of Wetland Scientists 2020
Abstract Complexities of terrestrial boundaries with salt marshes in coastal lagoons affect salt marsh exposure to waves and sediments creating different potentials for marsh migration inland and seaward-edge erosion, and consequently, for marsh persistence. Between 2002 and 2017, migration and edge erosion were measured in three mainland geomorphic marsh types (headland, valley, hammock) and were used to assess the rate and spatial extent of marsh change for a Virginia coastal lagoon system. Treelines, shorelines, and marsh perimeters were delineated in ArcGIS at 1:600 resolution. All marsh types increased in spatial extent; increases were greatest for the valley type (0.58 ha ± 0.31 ha or + 0.32% per annum). Measured rates of migration (headland > valley > hammock) and erosion (headland > hammock > valley) for each geomorphic type were averaged and applied to obtain changes in these same marsh types at the regional scale. At this scale, valley marsh area increased (82.5 ha or 5.5 ha a−1) more than the other two marsh types combined. This analysis demonstrates the critical influence that geomorphic type has on lateral marsh responses to sea-level rise and that efforts to conserve or restore salt marshes are most likely to be successful when focused on valley marshes. Keywords Salt marsh . Marsh migration . Marsh edge erosion . Marsh geomorphology . Transgression . Sea-level rise
Introduction Throughout the mid-Atlantic region of the USA, sea-level is rising at an increasing rate and coastal wetlands are disappearing simultaneously. While the global rate of sea-level rise throughout most of the twentieth century was approximately 1.8 mm yr−1, since the start of the satellite sea-level record in 1993, the average rate of global sea-level rise has been about 3.1 mm yr−1 (Lindsey 2020). Although sea-level rise is occurring globally, there are spatial variations in the rates of sea-level rise (Sallenger et al. 2012). Within the mid-Atlantic region, along the Atlantic seaside of Virginia’s Eastern Shore, relative rates of sea-level rise are more rapid than the global rate; recorded rates at Wachapreague, Virginia are 3.2 ± 0.3 to 5.37 ± 0.69 mm yr−1, recorded from 1930 to 1993 and 1978 to 2019 respectively
* Jessica A. Flester [email protected] 1
Department of Environmental Sciences, University of Virginia, Charlottesville, VA 22904-4123, USA
(Nerem et al. 1998; NOAA 2019). While these rates of relative sea-level rise seem insignificant, they can have highly significant horizontal effects that threaten the persistence of salt marsh ecosystems (Reed et al. 2008). Salt marsh persistence as sea-level rises is dependent on the ability of these wetlands to either keep pace with sea-level rise through vertical growth (or
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