U.S. Department of the Interior

U.S. Geological Survey

Fact Sheet 2011–3015

February 2011

Inventory and Protection of Salt Marshes from Risks 

of Sea-Level Rise at Acadia National Park, Maine

Background

Salt marshes are an important part 

of the landscape of Acadia National Park. 

In addition to their aesthetic beauty, 

they provide significant ecological value 

to Maine’s coastal zone (fig. 1). Their 

ecological functions include habitat for 

many fish and wildlife species; tremendous organic matter production that 

fuels coastal food webs, including many 

commercially and recreationally valuable species; storm and flood protection; 

and filtration of nutrients, sediments, and 

contaminants from waters entering the 

coastal zone. 

Salt marshes form and grow close 

to sea level under special conditions that 

provide intermittent exposure to saltwater and vertical development through 

the supply and accumulation of mineral 

sediment and plant organic matter. As 

the plants grow, the roots and rhizomes, 

along with sediment and organic matter, 

form peat, the foundation of the marsh. 

To keep up with rises in sea level, the 

elevation of salt marsh surfaces must 

increase through a combination of 

sediment accumulation and peat growth 

(Cahoon and others, 1999).

Historically, sea level has risen in 

New England at rates ranging from 0.6 

to 2.5 millimeters per year (mm/yr) (0.02 

to 0.10 inches per year (in/yr)) over the 

last 100 years (Woodworth and Player, 

2003; Kirshen and others, 2008), whereas 

Maine salt marshes have been found to 

accrete surface sediment at rates of up 

to 4.2 mm/yr (0.17 in/yr) (Goodman 

and others, 2007). Many New England 

marshes have been able to adapt to 

historical changes in sea level by accretion of new sediment and organic matter 

and through subsurface peat growth 

(Cahoon and others, 2009; Goodman and 

others, 2007).

The rate of sea-level rise, however, 

is expected to accelerate significantly 

in the next century; this acceleration 

is a projected global effect of climate 

warming caused by melting polar ice 

and expansion of the ocean because 

of warming waters (NECIA, 2006). 

Projected rates of sea-level rise are as 

high as 8.4 mm/yr (0.33 in/yr) (Kirshen 

and others, 2008). This rate of sea-level 

rise could be greater than the rates of 

vertical elevation gain in salt marshes, 

putting them at risk of frequent flooding 

by saltwater, changes in sediment 

supply, changes in salinity, and changes 

in storm intensity and wave action 

(Cahoon and others, 2009). Projections 

of total sea-level rise range from 200 

to 1,000 mm (0.7 to 3.3 feet (ft)) by the 

year 2100 (NECIA, 2006; IPCC, 2007). 

Figure 1. Salt marsh on Deer Isle, Maine. (Photograph by Robert Dudley, U.S. Geological Survey, July 13, 2010). 

Recent U.S. Geological Survey (USGS) climate studies in the northeastern 

United States have shown substantial evidence of climate-related changes during the 

last 100 years, including earlier snowmelt runoff, decreasing occurrence of river ice, 

and decreasing winter snowpack. These studies related to climate change are being 

expanded to include investigation of coastal wetlands that might be at risk from sealevel rise. Coastal wetlands, particularly salt marshes, are important ecosystems that 

provide wildlife nursery and breeding habitat, migratory bird habitat, water quality 

enhancement, and shoreline erosion control. The USGS is investigating salt marshes 

in Acadia National Park with the goal of determining which salt marshes may be 

threatened by sea-level rise and which salt marshes may be able to adapt to sea-level 

rise by migrating into adjacent low-lying lands.
Although there is great uncertainty in 

the precise amount of sea-level rise, a 

rise of 600 mm (2.0 ft) by 2100 has been 

projected for Maine (see, for example, 

Slovinsky and Dickson, 2006). 

If the rates of accretion of existing salt marshes cannot equal those of 

sea-level rise in some areas, the primary 

mechanism for salt marshes and the 

important habitat they offer to survive in 

the long term will be horizontal migration involving the formation of new salt 

marshes on newly flooded lands. The 

identification and protection of adjacent 

low-lying lands available for marsh 

migration are therefore important tasks to 

help ensure future salt marsh survival. 

Equally important is the identification of barriers to the movement of 

salt marshes such as roads, dikes, and 

seawalls. In 2010, the USGS began a 

study with the National Park Service 

to identify the availability of low-lying 

areas near salt marshes in and around 

Acadia National Park and on islands 

from Penobscot Bay to the Schoodic 

Peninsula (fig. 2) and to evaluate the 

marshes for their potential to migrate into 

these adjacent areas under a projected 

600-mm (2.0 ft) rise in sea level.

Study Approach

Several approaches have been used 

in predicting the effect of sea-level rise 

68°40' 68°20'

44°20'

44°00'

EXPLANATION

Acadia salt marshes

Acadia National Park

Atlantic Ocean

Penobscot Bay

Schoodic 

Peninsula

0 5 10 MILES

MAINE

Mount Desert 

Island

MAINE

QUEBEC

Atlantic Ocean

NEW 

BRUNSWICK

VERMONT

NEW 

HAMPSHIRE

MASSACHUSETTS

NOVA 

SCOTIA

Study area

0 5 10 KILOMETERS

Base map from USGS 1:24,000 Digital Line Graphs. Acadia National Park

Boundary from National Park Service, 1:24,000

Figure 2. Distribution of salt marshes near Acadia National Park, Maine.

on coastal habitats. Inundation models, 

also called static models, show where 

low-lying land adjacent to salt marshes 

will be submerged and where engineered 

structures may be threatened for an 

assumed amount of sea-level rise (see, for 

example, Slovinsky and Dickson, 2006). 

The best static models use the most accurate elevation data available, such as light 

detection and ranging (LiDAR) data, to 

delineate the areas that would be submerged under a given sea-level rise scenario (Gesch and others, 2009). LiDAR 

data are collected by flying over the area 

of interest and scanning the ground with 

pulsed laser light to accurately detect the 

elevation of the ground beneath (fig. 3).
The average accuracy of groundelevation data collected by using LiDAR 

for this project is expected to be about 

92.5 mm (3.64 in.). USGS scientists will 

assess the accuracy of LiDAR data specifically in the salt marshes of the study 

area (fig. 4). The USGS is working with 

the National Park Service and conservation partners such as the Maine Coast 

Heritage Trust to select salt marshes that 

will be used for the LiDAR data accuracy 

assessment. The elevations of 20 marshes 

will be determined by surveying marsh 

elevations in relation to independent 

stable control points for which precise 

elevations will be established by using 

high-accuracy Global Positioning System 

(GPS) equipment. Surveyed marsh elevaFigure 3. Example of LiDAR (light detection and ranging) data for Kennebec County, Maine. Note the accuracy of the 

LiDAR data such that roadbeds and driveways are visible.

tions will be used as a check against the 

LiDAR-derived elevations.

LiDAR elevation data were collected in the fall of 2010. Once the final 

processing of the LiDAR data has been 

done, a detailed map of all salt marshes 

in the study area will be overlain onto 

the LiDAR-derived land surface. Using 

this land-surface dataset, low-lying areas 

adjacent to existing salt marshes that 

could be expected to flood as a result of a 

600-mm (2.0 ft) rise in sea level and that 

could be suitable for salt marsh habitat 

(that is, not developed) will be identified. In addition, areas along the coastline 

that currently do not have salt marsh but 

would be protected and sheltered enough 

to sustain salt marsh ecosystems if they 

became flooded also will be identified. 

roadbed

driveways

0 500 1,000 FEET

0 100 200 METERS

Threecornered Pond

69°39' 69°38'40" 69°38'20"

44°21'

44°20'40"

USGS scientists also will identify any 

potential physical barriers (roads, berms, 

and bridges) to inland migration of salt 

marshes. The results of the accuracy 

assessment of the LiDAR data will be 

used to estimate confidence intervals for 

the prediction of areas with a potential to 

flood and possibly form new salt marsh. 

Benefits

This project will inform the National 

Park Service and its conservation partners 

about which salt marshes in and around 

Acadia National Park might migrate into 

adjacent low-lying lands given future sealevel rise projections. Using this information, park managers can plan for additional land conservation into the future. 
For more information, please contact:

Director

USGS Maine Water Science Center

196 Whitten Road

Augusta, Maine 04330

Telephone: (207) 622-8201

E-mail: dc_me@usgs.gov

Web site: http://me.water.usgs.gov

References

Cahoon, D.R., Day, J.W. Jr., and Reed, D.J., 1999, The influence of surface and shallow subsurface soil processes on wetland 

elevation—A synthesis: Current Topics in Wetland Biogeochemistry, v. 3, p. 72–88.

Cahoon, D.R., Reed, D.J., Kolker, A.S., Brinson, M.M., Stevenson, J.C., Riggs, S., Christian, R., Reyes, E., Voss, C., and Kunz, 

D., 2009, Coastal wetland sustainability, chap. 4 in Titus, J.G., coordinator, Coastal sensitivity to sea-level rise—A focus on the 

Mid-Atlantic region: A report by the U.S. Climate Change Science Program and the Subcommittee on Global Change Research, 

Washington, D.C., U.S. Environmental Protection Agency.

Gesch, D.B., Gutierrez, B.T., and Gill, S.K., 2009, Coastal elevations, chap. 2 in Titus, J.G., coordinator, Coastal sensitivity to sealevel rise—A focus on the Mid-Atlantic region: A report by the U.S. Climate Change Science Program and the Subcommittee on 

Global Change Research, Washington, D.C., U.S. Environmental Protection Agency.

Goodman, J.E., Wood, M.E., and Gehrels, W.R., 2007, A 17-year record of sediment accretion in the salt marshes of Maine (USA): 

Marine Geology, v. 242, p. 109–121.

IPCC (Intergovernmental Panel on Climate Change), 2007, Climate change 2007—The science basis, contribution of Working Group 

1 to the Fourth Assessment Report: Cambridge, U.K., Cambridge University Press.

Kirshen, P., Watson, C., Douglas, E., Gontz, A., Lee, J., and Tian, Y., 2008, Coastal flooding in the Northeastern United States due to 

climate change: Mitigation and Adaptation Strategies for Global Change, v. 13, p. 437–451.

NEICA (Northeast Climate Impacts Assessment), 2006, Climate change in the U.S. Northeast: Cambridge, Mass., Union of 

Concerned Scientists, 35 p.

Slovinsky, P.A., and Dickson, S.M., 2006, Impacts of future sea level rise on the coastal floodplain: Maine Geological Survey OpenFile Report 06–14, 25 p.

Woodworth, P.L., and Player, R., 2003, The permanent service for mean sea level—An update to the 21st century: Journal of Coastal 

Research, v. 19, p. 287–295.

Figure 4. USGS scientists surveying a salt marsh (top) and 

collecting high-accuracy elevation data with Global Positioning 

System equipment (bottom). (Photographs by Robert Dudley, 

U.S. Geological Survey, July 13, 2010 (top), and Martha Nielsen, 

U.S. Geological Survey, July 12, 2010 (bottom).)

By Robert W. Dudley and Martha G. Nielsen