Estimates of future inundation of salt marshes in response to sea-level rise in and around Acadia National Park, Maine

Nielsen, Martha; Dudley, Robert

From Official Abstract:"Salt marshes are ecosystems that provide many important ecological functions in the Gulf ofMaine. The U.S. Geological Survey investigated salt marshes in and around Acadia National Parkfrom Penobscot Bay to the Schoodic Peninsula to map the potential for landward migration ofmarshes using a static inundation model of a sea-level rise scenario of 60 centimeters (cm; 2feet). The resulting inundation contours can be used by resource managers to proactivelyadapt to sea-level rise by identifying and targeting low-lying coastal areas adjacent to saltmarshes for conservation or further investigation, and to identify risks to infrastructure in thecoastal zone. For this study, the mapping of static inundation was based on digital elevationmodels derived from light detection and ranging (LiDAR) topographic data collected in October2010. Land-surveyed control points were used to evaluate the accuracy of the LiDAR data inthe study area, yielding a root mean square error of 11.3 cm. An independent accuracyassessment of the LiDAR data specific to salt-marsh land surfaces indicated a root mean squareerror of 13.3 cm and 95-percent confidence interval of ± 26.0 cm. LiDAR-derived digitalelevation models and digital color aerial photography, taken during low tide conditions in 2008,with a pixel resolution of 0.5 meters, were used to identify the highest elevation of the landsurface at each salt marsh in the study area. Inundation contours for 60-cm of sea-level risewere delineated above the highest marsh elevation for each marsh. Confidence intervalcontours (95-percent, ± 26.0 cm) were delineated above and below the 60-cm inundationcontours, and artificial structures, such as roads and bridges, that may present barriers to salt-marsh migration were mapped. This study delineated 114 salt marshes totaling 340 hectares (ha), ranging in size from 0.11 ha(marshes less than 0.2 ha were mapped only if they were on Acadia National Park property) to52 ha, with a median size of 1.0 ha. Inundation contours were mapped at 110 salt marshes.Approximately 350 ha of low-lying upland areas adjacent to these marshes will be inundatedwith 60 cm of sea-level rise. Many of these areas are currently freshwater wetlands. There arepotential barriers to marsh migration at 27 of the 114 marshes. Although only 23 percent ofthe salt marshes in the study are on ANP property, about half of the upland areas that will beinundated are within ANP; most of the predicted inundated uplands (approximately 170 ha)include freshwater wetlands in the Northeast Creek and Bass Harbor Marsh areas. Most of thesalt marshes analyzed do not have a significant amount of upland area available for migration.Seventy-five percent of the salt marshes have 20 meters or less of adjacent upland that wouldbe inundated along most of their edges. All inundation contours, salt marsh locations, potentialbarriers, and survey data are stored in geospatial files for use in a geographic information systemand are a part of this report."