The combination of press ( long-term ) and pulse ( short-term ) events introducing seawater landward significantly impacts groundwater resources on coastal barrier islands . Over time the freshwater lens on barrier islands will become shallow and saline . This change in groundwater will affect the native upland vegetation and facilitate major changes to coastal habitats .
Marsh Sediment Dynamics
There are also unique challenges to the physical habitats of the marsh as well , mainly through changes influenced by the movement of marsh sediments . The elevations of marshes are maintained by vegetation which increases surface elevation by accumulating organic matter and trapping the external supply of upstream sediments ( Ganju , 2019 ). A major contributor of organic matter in the system is the dominant smooth cordgrass , which is an annual grass that dies back every year following the growing season . Salt marshes are known to have maintained an elevation in equilibrium with sea level as tidal creeks erode banks and creek beds accumulate sediments .
“ The long‐term stability of these ecosystems is explained by interactions among sea level , land elevation , primary production , and sediment accretion that regulate the elevation of the sediment surface toward an equilibrium with mean sea level ” ( Morris , 2002 ).
However , there is concern that the rate at which marshes vertically accrete sediment is outpaced by the present rate of sea level rise . If salt marshes cannot accrete sediment quickly enough along their stream banks , or if the marshes ’ migration landward is blocked by physical barriers , rising water elevations will cause marsh vegetation to drown and convert to areas of exposed marsh sediments . Common hardened coastal infrastructure that is used as erosion control devices ( e . g ., bulkheads and seawalls ) can also negatively impact the marshland by acting as the physical barriers that disrupt the migration of marshland onto higher ground and exacerbate erosion on adjacent areas of the upland .
These changes would lead to cascading impacts affecting the ecosystem services salt marshes provide . Because of these considerations and similarities to coastal sediment processes , there has been a paradigm shift in viewing marsh sediments in the same manner as beach sediments ( Ganju , 2019 ). This also brings into consideration how marsh sediments reach equilibrium following restoration projects .
MARSH VULNERABILITY PROJECT
Beginning in January 2020 , the Kiawah Conservancy and the College of Charleston , through Dr . Norm Levine at the Santee Cooper GIS Laboratory and Lowcountry Hazards Center , embarked on a project to map the historical progression of marshland vegetation and current geological features . The primary goals of this study were to identify areas where we are experiencing losses of marsh vegetation and to understand the current status of marshland habitat .
Historical Shoreline Changes
SCDHEC-OCRM completed a study in 2017 using AMBUR ( Analyzing Moving Boundaries Using R ) which modeled historical shoreline changes in the marsh and beachfront for the entire coast of South Carolina ( Jackson , 2017 ). The first stages of the project built off of the AMBUR dataset by capturing shoreline changes in finer detail while also filling in data gaps with additional datasets . The project used ESRI geospatial software to create a digitized map of these natural and built structures . Shoreline data was obtained by manually digitizing marsh shorelines within the mapping software from imagery from different years during the peak of the respective growing seasons . The
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NATURE-BASED SOLUTIONS MANUAL FOR KIAWAH ISLAND