U.S. Department of the Interior
U.S. Geological Survey
Scientific Investigations Report 2012–5290
Prepared in cooperation with the National Park Service
Estimates of Future Inundation of Salt Marshes in
Response to Sea-Level Rise in and Around Acadia
National Park, Maine
Cover. View of salt marsh (looking east) on Great Cranberry Island. Photograph taken by Robert Dudley.
Estimates of Future Inundation of Salt
Marshes in Response to Sea-Level Rise in
and Around Acadia National Park, Maine
By Martha G. Nielsen and Robert W. Dudley
Prepared in cooperation with the National Park Service
Scientific Investigations Report 2012–5290
U.S. Department of the Interior
U.S. Geological Survey
U.S. Department of the Interior
KEN SALAZAR, Secretary
U.S. Geological Survey
Suzette M. Kimball, Acting Director
U.S. Geological Survey, Reston, Virginia: 2013
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Suggested citation:
Nielsen, M.G., and Dudley, R.W., 2013, Estimates of future inundation of salt marshes in response to sea-level rise in
and around Acadia National Park, Maine: U.S. Geological Survey Scientific Investigations Report 2012–5290, 20 p.,
http://pubs.usgs.gov/sir/2012/5290/.
iii
Acknowledgements
This study was funded through the National Park Service Natural Resource Stewardship and
Science Climate Change Response Program. The authors thank the staff at Acadia National Park,
The Nature Conservancy, and especially the Maine Coast Heritage Trust for their assistance in
obtaining permissions for access to privately held salt marshes for the surveying phase of the
project. We also thank the numerous private landowners who allowed access to their property.
Luke P. Sturtevant of the U.S. Geological Survey, Maine Water Science Center, provided valuable
assistance with the mapping and geodatabase. National Park Service staff who reviewed the
initial proposal provided very helpful suggestions for the project.
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v
Contents
Acknowledgments ........................................................................................................................................iii
Introduction.....................................................................................................................................................1
Coastal Inundation from Sea-level Rise and Migration of Salt Marshes ....................................2
Approaches and Datum Characteristics for Assessing Potential Effects of Inundation ..........4
Purpose and Scope ..............................................................................................................................5
Land-Surface Elevation Data .......................................................................................................................5
Land Surveying ......................................................................................................................................5
Vertical Accuracy Assessment for Land-Surface Elevation Data ................................................8
Salt-Marsh Inventory ...........................................................................................................................8
Estimated Future Inundation Resulting from Sea-Level Rise at Salt Marshes ....................................9
Inundation Potential and Barriers to Migration .............................................................................10
Summary and Conclusions .........................................................................................................................16
References Cited..........................................................................................................................................17
Appendix 1. Geospatial data of salt marshes, inundation contours, and surveying data in
and near Acadia National Park, Maine. .....................................................................................19
Figures
1. Photograph showing Mitchell Marsh near Bass Harbor, Maine ..........................................2
2. Map showing location of study area in and around Acadia National Park, Maine ..........3
3. Photographs showing A, a lag bolt anchored in bedrock that serves as an elevation
reference mark, B, a global-positioning system (GPS) receiver placed on an
elevation reference mark, and C, a wooden stake flush with the marsh surface that
serves as a control point .............................................................................................................6
4. Graph showing cumulative distribution of salt marsh areas, in hectares ..........................9
5. Map showing the distribution of salt marshes within the coastal towns in the
study area ....................................................................................................................................10
6. Diagram showing relation of local elevation datum to the inundation contours,
95-percent confidence interval contours, and the inundation uncertainty zone for
salt marshes in the study area .................................................................................................11
7. Histogram showing the estimated area of upland adjacent to salt marshes that will
be inundated with 60 centimeters of sea-level rise, shown as a percentage of
adjacent salt marsh area ...........................................................................................................12
8. Histogram showing the average distance of the 60-centimeter inundation contours
inland from salt marsh edges ...................................................................................................12
9. Static inundation map for 60 centimeters (cm) of sea-level rise and upper and lower
95-percent confidence interval contours for the Somesville area, Mount Desert,
Maine, using A, shaded relief image of light detection and ranging (LiDAR) data and
B, orthophoto base .....................................................................................................................13
10. Static inundation map for 60 centimeters (cm) of sea-level rise and upper and lower
95-percent confidence interval contours for the Northeast Creek area, Bar Harbor,
Maine, using A, shaded relief image of light detection and ranging (LiDAR) data and
B, orthophoto base .....................................................................................................................14
11. Static inundation map showing potential barriers to marsh migration for the Thomas
Bay area, Bar Harbor, Maine ....................................................................................................15
vi
Tables
1. Inventory of salt marshes in towns within the study area, including number of
marshes and total marsh areas for areas with Acadia National Park ................................9
2. Inventory of potential barriers to marsh migration in towns within the study area ........16
Conversion Factors and Datum
Multiply By To obtain
Length
centimeter (cm) 0.3937 inch (in.)
millimeter (mm) 0.03937 inch (in.)
meter (m) 3.281 foot (ft)
kilometer (km) 0.6214 miles (mi)
Area
hectare (ha) 2.471 acre
Vertical coordinate information is referenced to the North American Vertical Datum of 1988
(NAVD 88).
Horizontal coordinate information is referenced to the North American Datum of 1983 (NAD 83).
Elevation, as used in this report, refers to distance above the North American Vertical Datum
(NAVD 88).
vii
Abbreviations
ALS Airborne laser surveying
ANP Acadia National Park
CO-OPS Center for Operational Oceanographic Products and Services
CORS Continuously operating reference stations
DEM digital elevation model
DSC Denver Service Center
ERM elevation reference mark
GPS global-positioning system
HAT highest astronomical tide
HME highest marsh elevation
LGO Leica GeoOffice
LiDAR light detection and ranging
MDI Mount Desert Island
MHW mean high water
MRSA Maine Revised Statutes Annotated
MSL mean sea level
NGS National Geodetic Survey
NMAS National Map Accuracy Standard
NOAA National Oceanic and Atmospheric Administration
NOS National Ocean Services
NPS National Park Service
NRPA Natural Resources Protection Act
NTDE National Tidal Datum Epoch
ODI ortho-rectified digital images
OPUS Online Positioning User Service
RMSE Root mean square errors
SLR Sea-level rise
TS Total Station
USGS U.S. Geological Survey
USEPA U.S. Environmental Protection Agency
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Estimates of Future Inundation of Salt Marshes in
Response to Sea-Level Rise in and Around Acadia
National Park, Maine
By Martha G. Nielsen and Robert W. Dudley
Abstract
Salt marshes are ecosystems that provide many
important ecological functions in the Gulf of Maine. The U.S.
Geological Survey investigated salt marshes in and around
Acadia National Park from Penobscot Bay to the Schoodic
Peninsula to map the potential for landward migration
of marshes using a static inundation model of a sea-level
rise scenario of 60 centimeters (cm; 2 feet). The resulting
inundation contours can be used by resource managers
to proactively adapt to sea-level rise by identifying and
targeting low-lying coastal areas adjacent to salt marshes for
conservation or further investigation, and to identify risks to
infrastructure in the coastal zone. For this study, the mapping
of static inundation was based on digital elevation models
derived from light detection and ranging (LiDAR) topographic
data collected in October 2010. Land-surveyed control points
were used to evaluate the accuracy of the LiDAR data in the
study area, yielding a root mean square error of 11.3 cm. An
independent accuracy assessment of the LiDAR data specic
to salt-marsh land surfaces indicated a root mean square error
of 13.3 cm and 95-percent condence interval of ± 26.0 cm.
LiDAR-derived digital elevation 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 land surface at each salt marsh
in the study area. Inundation contours for 60-cm of sea-level
rise were delineated above the highest marsh elevation
for each marsh. Condence interval contours (95-percent,
± 26.0 cm) were delineated above and below the 60-cm
inundation contours, and articial 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) to 52 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 inundated with 60 cm of sea-level
rise. Many of these areas are currently freshwater wetlands.
There are potential barriers to marsh migration at 27 of the
1
14 marshes.
Although only 23 percent of the salt marshes in
the study are on
ANP property, about half of the upland areas
that will be inundated 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 the salt marshes analyzed do not have a signicant
amount of upland area available for migration. Seventy-ve
percent of the salt marshes have 20 meters or less of adjacent
upland that would be inundated along most of their edges. All
inundation contours, salt marsh locations, potential barriers,
and survey data are stored in geospatial les for use in a
geographic information system and are a part of this report.
Introduction
Salt marshes provide signicant ecological value and
aesthetic beauty to Maine’s coasts (g. 1). Their ecological
functions include nursery and breeding habitat for many
sh, migratory birds, and other wildlife species; organic-
matter production that maintains coastal food webs for many
commercially and recreationally valuable species; storm,
ood, and erosion protection; carbon sequestration; and
ltration 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 ne-grained mineral
sediment and plant organic matter (Cahoon and others, 2009).
As salt-marsh plants grow, their roots and rhizomes, along
with sediment and organic matter, form peat—the foundation
of the marsh.
A recent vegetation inventory of the Acadia National
Park (ANP) and its associated lands (conservation easements)
identied 47 salt-marsh areas on numerous islands and other
parcels in and near ANP land holdings in the Gulf of Maine
(Lubinski and others, 2003). Many additional salt marshes
along the hundreds of kilometers of coastline exist within the
area encompassed by the ANP vegetation survey (from eastern
Penobscot Bay to the Schoodic Peninsula), but were not
2 Estimates of Future Inundation of Salt Marshes in Response to Sea-Level Rise in and Around Acadia National Park, Maine
Figure 1. Mitchell Marsh near Bass Harbor, Maine.
mapped for that study. These salt marshes are highly valued
for their wildlife viewing and aesthetic landscape, and are
enjoyed by the 2.5 million visitors to ANP annually as well
as by local residents. Salt marshes are afforded legislative
protection under Federal and State statutes because of their
well-documented ecological importance (for example, the
Natural Resources Protection Act (NRPA; Maine Legislature,
undated a). The ANP Water Resources Management Plan
documents the importance of maintaining the functional
quality of the coastal wetlands of ANP (Kahl and others, 2000;
Vaux and others, 2008).
In 2010, the U.S. Geological Survey (USGS), in
cooperation with the National Park Service (NPS), began a
study to map potential static landward inundation around salt
marshes in ANP and its associated lands (g. 2). The goals
of the project were to map the additional salt marshes not
covered by the earlier ANP vegetation survey, to map the
areal extent of static landward inundation around salt marshes
expected from sea-level rise (SLR) by 2100 and identify
adjacent low-lying land that may provide area into which salt
marshes may migrate, and to map potential articial barriers
to migration.
Coastal Inundation from Sea-Level Rise and
Migration of Salt Marshes
Sea level has been rising globally for the last
20,000 years largely because of melting continental ice
sheets that had accumulated during the last ice age (Poore
and others, 2000). During the last 100 years, measured rates
of SLR in New England ranged from 0.6 to 2.5 millimeters
per year (mm/yr; Goodman and others, 2007; Kirshen and
others, 2008). Historically, many New England marshes have
been able to keep pace with observed rates of SLR by the
accretion of sediment and organic matter (Roman and others,
1997; Goodman and others, 2007; Cahoon and others, 2009).
Accretion is a complex process involving sediment supply
and organic-matter accumulation. Sediment supply must
be sufcient to maintain the marsh surface, and the relative
importance of inorganic sediment and organic matter varies
depending on local factors (Cahoon and others, 2009). Salt
marshes in Maine have been found to be capable of accreting
up to 4.2 mm/yr (Goodman and others, 2007). Although
maximum possible accretion rates are unknown, the rates of
accretion have been found to correlate positively with tidal
range (Morris, 2007). The large tidal ranges in the Gulf of
Introduction 3
Hog Bay
Deer
Isle
Bar Harbor
Somesville
Bass Harbor
Grand
Marsh
Somes Sound
Swans
Island
Penobscot Bay
Atlantic Ocean
Northeast Creek
Schoodic Peninsula
Mount Desert IslandMount Desert Island
Blue Hill Peninsula
ACADIA
NATIONAL
PARK
ACADIA
NATIONAL
PARK
68°00'68°15'68°30'68°45'
44°30'
44°15'
Bass
Harbor
area
3
Northern Mount
Desert Island area
EXPLANATION
Salt marshes with high-precision
surveying
Published benchmarks used for surveying
Salt marshes in the study area
Acadia National Park
Inset 1
Inset 1
Inset 2
Base from U. S. Geological Survey digital line graphs
1:24,000. Universe Transverse Mercator, zone 19N, NAD83.
Thomas Bay
Inset 2
!
!
!
MAINE
Bangor
Augusta
Portland
Bass Harbor Marsh
Area of study
0 5 10 MILES
0 5 10 KILOMETERS
G
u
l
f
o
f
M
a
i
n
e
Figure 2. Location of study area in and around Acadia National Park, Maine.
4 Estimates of Future Inundation of Salt Marshes in Response to Sea-Level Rise in and Around Acadia National Park, Maine
Maine and Bay of Fundy (not shown in gures) may provide
conditions favorable to faster accretion for salt marshes in
Maine than for salt marshes farther south on the Atlantic coast.
One of the projected effects of climate warming is a
continued rise in sea level caused by a combination of melting
glaciers and polar ice and thermal expansion of the ocean
(Frumhoff and others, 2007). Whereas SLR rates historically
have been about 0.6 to 2.5 mm/yr, future rates may go as
high as 8.4 mm/yr (Frumhoff and others, 2007; Day and
others, 2008; Kirshen and others, 2008). Although there is
great uncertainty in the precise amount, a 60-centimeter (cm;
2-foot) rise is cited as a 100-year planning target by the State
of Maine (Maine Department of Environmental Protection,
1993). Slovinsky and Dickson (2006) used the 100-year
projected rise of 60 cm (2 feet) for a demonstration project
mapping static inundation for an area of the Rachel Carson
National Wildlife Refuge in coastal Maine.
Vertical accretion can be accompanied by horizontal
transgression, or migration, of salt marshes into adjacent
lowlands, provided there are no articial barriers to prevent
migration (Goodman and others, 2007; Kirwan and Murray,
2008; Cahoon and others, 2009). Articial structures, such as
roads, dikes, and seawalls, can act as barriers to salt-marsh
migration in two ways: the elevated land area occupied
by the structures decreases the land area available for salt-
marsh formation, and barriers can act as dams and prohibit
the colonization of adjacent lands by salt-marsh vegetation
and restrict the vegetative transition zone at the upper marsh
border (Bozek and Burdick, 2005). Some barriers may allow
water passage through a culvert or bridge, but water and
sediment movement may be so restricted that healthy marsh
growth is not possible.
The migration of marsh surfaces onto adjacent low-lying
land will be important in the overall survival of salt marshes
by the year 2100, even if accretion of current (2012) marsh
surfaces cannot occur fast enough to keep pace with SLR.
If seaward erosion of the salt-marsh surface occurs and (or)
accretion cannot keep pace with SLR, the presence of adjacent
low-lying land for inland migration and the mitigation of
articial barriers to migration will be critical for maintaining
salt-marsh areas (Cahoon and others, 2009). Therefore, the
identication and protection of low-lying lands adjacent
to existing salt marshes and the identication of migration
barriers are important parts of any proactive adaptation
strategy for salt-marsh persistence.
Approaches and Datum Characteristics for
Assessing Potential Effects of Inundation
Several methods have been used in predicting the effect
of SLR on coastal habitats, and generally can be categorized
as either process-driven or static. Process-driven methods
attempt to address the complex relations between SLR and
natural and anthropogenic environmental drivers, accretionary
processes, and geomorphic settings of salt marshes (for
example, Morris, 2007; Kirwan and Murray, 2008; Craft and
others, 2009). Consequently, process-driven methods are more
data intensive than static inundation methods, and the need for
highly intensive data collection makes process-driven methods
impractical for predicting high-resolution effects at regional
scales (Cahoon and others, 2009).
Static methods indicate where uplands will be submerged
and where articial structures may be threatened (for example,
Slovinsky and Dickson, 2006) but do not quantify effects of
erosion or accretion on coastal environments. Static methods
delineate areas of inundation below a specied elevation and,
therefore, rely on accurate topographic data for modeling and
mapping exactly the areas that would be submerged under a
given amount of SLR, absent accretion (Gesch and others,
2009). For static inundation mapping, Gesch (2009) proposes
a guideline that the elevation data to be used are at least
twice as accurate (as measured by the 95-percent condence
interval) as the amount of SLR being mapped. Thus, for a
60-cm SLR scenario, the topographic data used for mapping
should have an accuracy of ±30 cm or better at the 95-percent
condence level.
The present study used a static mapping approach to
evaluate the potential for inundation of salt marshes and
adjacent uplands; accretion and erosion rates of marsh surfaces
were not estimated. The resulting inundation delineations
will help the NPS to adapt proactively to SLR by identifying,
and targeting for conservation or further study, low-lying
coastal wetlands that are not presently (2012) protected. In
addition, the NPS will be able use the inundation delineations
to propose where further study of factors affecting marsh
accretion, such as sediment characteristics of salt marshes
in the study area, sedimentation rates, sources of sediment
transport, and hydrodynamic modeling of currents carrying
sediment to and from salt marshes would be most warranted.
The identication of potential migration barriers provides
the means for identifying potential risks to some NPS
infrastructure (such as roads or bridges) in the coastal zone,
and where mitigation of those barriers may be considered.
Salt marshes exist in a narrow elevation range relative to
sea level and local tides; the elevation range favorable to salt
marshes can be most directly described using tidal datums.
A tidal datum is a base elevation, computed on the basis of a
particular phase of the tide, from which relative heights and
depths are measured. Tidal datums are determined by the
National Oceanic and Atmospheric Administration (NOAA)
National Ocean Service’s (NOS) Center for Operational
Oceanographic Products and Services (CO-OPS) on the basis
of a 19-year observation cycle referred to as the National
Tidal Datum Epoch (NTDE). Tidal datums include, but are
not limited to, mean high water (MHW), highest astronomical
tide (HAT), and mean sea level (MSL). MHW is the arithmetic
mean of all high water heights, HAT is the elevation of
the highest predicted astronomical tide, and MSL is the
arithmetic average of all hourly water height observations
during a NTDE (National Oceanic and Atmospheric
Administration, 2000).
Land-Surface Elevation Data 5
In general, high marsh vegetation, typically dominated
by salt-meadow grass (Spartina patens) grows best between
the local MHW and the HAT; low marsh vegetation, typically
dominated by smooth cord grass (Spartina alterniora),
grows optimally between MSL and MHW (Provost, 1976;
Slovinsky and Dickinson, 2006). These tidal elevation ranges
in which high and low marshes are thought to grow are not
dened by distinct boundaries, as the growth of high and low
marsh vegetation can vary depending on local conditions such
as salinity, nutrient availability, tidal range, and landscape
disturbances (McKee and Patrick, 1988). The Maine
Department of Environmental Protection (2012) uses the HAT
to locate the upland edge of coastal wetlands for regulatory
purposes (http://www.maine.gov/dep/land/slz/predictions.pdf,
accessed July 11, 2012), under the NRPA and the Mandatory
Shoreland Zoning Act (Maine Legislature, undated b). For
this study, high and low marshes were considered together
during the mapping of areas considered to be salt marsh and
a different method was used to dene the upland edge of the
salt marshes.
As tidal datums vary from location to location because
of differing hydrographic characteristics, in the interest of
transferability of results it is most useful to present the data
in terms of global datums that do not depend on mean sea
level (a tidal datum). In this study area, the tidal datum of
local mean sea level is 5 to 10 cm lower than 0 m North
American Vertical Datum of 1988 (NAVD88; according to
local conversions done using the VDatum datum converter
(National Oceanic and Atmospheric Administration, 2012c)).
Therefore, all elevations for this study were computed relative
to the global NAVD 88, and horizontal coordinates were
located relative to North American Datum of 1983 (NAD 83)
(Continuously Operating Reference Stations (CORS) 96,
Epoch 2002).
Purpose and Scope
This report describes the mapping of contour lines
adjacent to salt marshes that show areas that would be
inundated in a SLR scenario of 60 cm (2 feet) in and around
ANP and includes the identication of potential barriers to
future salt-marsh migration. The report includes descriptions
of the data and methodology used to conduct the mapping
and to conduct an independent evaluation of the elevation-
data accuracy and the derivation of 95-percent condence
intervals for the inundation contours. The inundation contours
indicate which lowlands adjacent to existing salt marshes
may provide potential areas for migration of salt-marsh
habitat. The mapped inundation contours are accompanied
by 95-percent condence interval contours determined on
the basis of an independent accuracy assessment of the salt-
marsh-specic topographic data used for mapping. This report
presents example maps showing the inundation contours and
the 95-percent condence interval contours around those
contours. A geodatabase accompanying this report presents
all the inundation contours produced by this study, along with
the surveying data and locations of all the salt marshes used in
the study. The geodatabase is a data management framework
used to store and easily access geospatial data for a variety
of applications.
Land-Surface Elevation Data
The elevation range that denes the physical bounds of
marsh ecology is relatively small; it is, therefore, important to
use accurate regional land-surface elevation data (topographic
data) to delineate the extant marsh boundaries and adjacent
regions estimated to be inundated by SLR (Gesch, 2009).
This study made use of topographic data collected by use
of a remote sensing technique generally referred to as “light
detection and ranging” (LiDAR). Airborne laser surveying
(ALS) is a type of LiDAR data collection done from an
aircraft. ALS serves as a rapid and relatively accurate
method for collecting topographic data over large areas
(Brock and Sallenger, 2001). LiDAR data routinely achieve
vertical accuracy on the order of a 15-cm RMSE, have been
successfully used in ood modeling applications, and are well
suited for mapping inundation of low-relief areas, such as
coastal wetlands (Gesch, 2009; Gesch and others, 2009).
LiDAR topographic data were collected in October 2010
by Photo Science, Inc. for the Atlantic shoreline from Long
Island, New York, to the border of Canada and Maine using
ALS methods. Photo Science, Inc. derived digital elevation
models (DEMs) from the LiDAR data with a 2-meter (m)
horizontal resolution. The DEMs were used in this study to
help map present marsh boundaries, estimate SLR inundation
boundaries, and dene articial structures that may present
barriers to the migration of salt marshes.
Land Surveying
USGS staff established land-surveyed control points in
the ANP study area as part of an independent evaluation of the
accuracy of the LiDAR data specic to salt-marsh land-cover
types. Five control points were surveyed at each of 20 selected
marshes across the study area (g. 2) for a total of 100 points.
The marshes used in the USGS control-point land surveys
were chosen to represent the size range and geographic
distribution of all marshes in the study area.
An elevation reference mark (ERM) was established in
the vicinity of each of the 20 salt marshes to maintain vertical
control near the marshes (g. 3A). The ERMs also will serve
as stable datum points to support future salt-marsh research.
ERMs established for this study were documented with
latitude and longitude coordinates, location descriptions, and
photographs. These data were uploaded to the NPS Denver
Service Center (DSC) survey monuments database (Benjamin
Zank, National Park Service Denver Service Center, written
commun., July 14, 2011). The NPS DSC survey monuments
6 Estimates of Future Inundation of Salt Marshes in Response to Sea-Level Rise in and Around Acadia National Park, Maine
database stores these spatial data for all National parks and
enables convenient access by ArcGIS clients.
The
A
elevations of the ERMs were determined using
Leica high-precision (millimeter accuracy) dual-frequency
global-positioning system (GPS) receivers (g. 3B). This
technique (referred to as “high-precision surveying”) uses a
GPS receiver (base) set on (occupying) a survey monument
or published benchmark (g. 2) that has a known elevation;
base-unit occupy times ranged from 5 hours (hr) to 10 hr 53
minutes (min); the average occupy time was 7 hr 33 min.
The base units received GPS signals from United States GPS
satellites, computed a positional error, and broadcast the error
to a second GPS receiver (rover) that occupied an ERM.
Rover
-unit-occupy times ranged from 15 to 48 min with an
average occupy time of 30 min.
Base-receiver data were submitted to the National
Geodetic Survey (NGS; National Oceanic and Atmospheric
Administration, 2012c) using the Online Positioning User
Service (OPUS) precise processing service (http://www.ngs.
noaa.gov/OPUS/about.jsp, accessed June 25, 2012). Base-
point elevations were solved by OPUS using the network
of Continuously Operating Reference Stations (CORS;
National Oceanic and Atmospheric Administration, 2012a).
Root mean square errors (RMSE) for OPUS base-point
elevation solutions ranged from 1.5 to 1.8 cm, with a mean
of 1.6 cm. Rover receiver data were used in conjunction with
base-point elevation solutions to compute ERM elevations.
ERM elevations were solved using Leica GeoOfce (LGO)
2.0 software. GEOID09 is the geoid model used to convert
ellipsoid heights to orthometric heights above NAVD
88. Elevation solutions between base points and ERMs
had standard deviations that ranged from 0.05 to 0.51 cm
(average 0.14 cm).
Five control points were established on each marsh
using wooden stakes that were set ush with the bare ground
level (g. 3C). The marsh control points were located on at
terrain within each marsh with a minimum spacing of 10 m
between points. Control-point elevations were then surveyed
relative to nearby ERMs using a Sokkia Set 4B Total Station
(TS) infrared laser transit and survey rods with retro-reectors
(prisms). The Sokkia TS provided 5-second angular precision
and millimeter-scale precision in both distance and elevation
with shots up to 1 kilometer (km) distant, depending on
atmospheric conditions. Potential errors were controlled by
resurveying if survey loops did not close to less than 2.0 cm.
A
Figure 3. A, a lag bolt anchored in bedrock that serves as an elevation reference mark, B, a global-positioning system (GPS) receiver
placed on an elevation reference mark, and C, a wooden stake flush with the marsh surface that serves as a control point.
Land-Surface Elevation Data 7
B
C
Figure 3. A, a lag bolt anchored in
bedrock that serves as an elevation
reference mark, B, a global-
positioning system (GPS) receiver
placed on an elevation reference
mark, and C, a wooden stake flush
with the marsh surface that serves
as a control point.—Continued
8 Estimates of Future Inundation of Salt Marshes in Response to Sea-Level Rise in and Around Acadia National Park, Maine
Vertical Accuracy Assessment for Land-Surface
Elevation Data
Photo Science, Inc. contracted land surveyors James W.
Sewall Company (Co.) to locate control points throughout
coastal Maine on relatively at terrain that generally consisted
of grass, gravel, or bare earth for evaluating the accuracy of
the collected LiDAR data. The reported overall accuracy the
LiDAR data was assessed using 44 control points subsampled
from control points established by James W. Sewall Co.
and the USGS. Vertical errors between LiDAR data and
the 44 control points ranged from -24.2 to 18.7 cm, with
a mean of -2.8 cm and RMSE of 11.3 cm. A RMSE of no
greater than 9.25 cm is equivalent to the accuracy required
for 1-foot contour-interval mapping, and an RMSE of no
greater than 18.5 cm is equivalent to the accuracy required for
2-foot contour-interval mapping (National Digital Elevation
Program, 2004).
The independent accuracy assessment of LiDAR
topographic data in comparison to land-surveyed control
points was conducted by the USGS in selected salt marshes
in the study area quantify the uncertainty of inundation
contours for a 60-cm projected SLR. This accuracy assessment
was done using LP360, a plug-in for ArcGIS. Because of
limitations on LiDAR data availability during this study, only
57 of the 100 USGS-surveyed control points were used for
the independent accuracy assessment. Vertical errors between
LiDAR data and 57 USGS land-surveyed control points at
salt-marsh surfaces ranged from -20.2 to 41.8 cm, with a mean
of 5.9 cm and RMSE of 13.3 cm. A small observed positive
bias (+5.9 cm) was not unexpected because the presence of
dense marsh grass overlying the ground likely prevented
penetration of many LiDAR signals to the marsh surface.
The RMSE of the LiDAR data were used to calculate
the 95-percent condence interval of the elevation data. The
95th percentile method may be used regardless of whether
the errors follow a normal distribution or qualify as outliers
(National Digital Elevation Program, 2004). From the
57 marsh-surface control points used, the LiDAR data had a
95-percent condence interval of ±26.0 cm, which falls within
the accuracy threshold of ±30 cm recommended by Gesch
(2009) for modeling static inundation of a 60-cm SLR.
Salt-Marsh Inventory
Digital color aerial photography was used to verify and
update boundaries identied in the 1997 vegetation survey
produced for the Acadia National Park Vegetation Mapping
Project, USGS–NPS Vegetation Mapping Program for Mount
Desert Island (MDI), Schoodic Peninsula, and ANP holdings
and easements on outlying islands (g. 2; Lubinski and
others, 2003) and to identify additional signicant (larger
than 1 ha) salt marshes in all the coastal areas from eastern
Penobscot Bay to Grand Marsh. Conservation partners,
especially the Maine Coast Heritage Trust, were consulted
to help identify additional salt marshes for inclusion in the
study. Salt marshes were located and veried with the aid of
various sets of high-resolution aerial photos, taken at different
seasons and in different years, provided by several online
mapping services (Google Maps
TM
, Bing!
TM
) and digital color
aerial photography from eastern Penobscot Bay to Schoodic
Point, consisting of high-resolution 24-bit color orthorectied
digital images (ODIs) with a pixel resolution of 0.5 meters,
which was used as the primary source. The photographs
were taken by J.W. Sewall Co. during August 2008 at and
near low-tide conditions. These digital 2008 low-tide photos
are geo-referenced and suitable for applications requiring
a 1:2400 National Map Accuracy Standard (NMAS). The
aerial photography was accessed using the Maine Geolibrary
(2011) Web mapping services application, which serves the
photography as a seamless mosaic.
The 1997 ANP vegetation survey identied 47 salt
marshes in and near the park. This survey veried those
salt marshes and identied an additional 67 salt marshes
within the study area. A total of 114 salt-marsh areas were
identied. Large salt-marsh complexes were split into several
marshes on the basis of physical proximity and congruity,
and the locations of major water bodies separating different
parts of the marsh complexes. Very small fringing salt
marshes (<0.2 ha, or having widths of 3 m or less) are not
well represented in the survey, particularly outside the ANP
boundary. They are difcult to distinguish even on good-
quality aerial photos, and there were no existing maps of their
locations outside the earlier ANP vegetation study.
The marshes in the study area encompass a total area of
340 ha and range in size from 0.11 ha to 52 ha (Grand Marsh,
which is located northeast of the Schoodic Peninsula; g 2).
The median salt marsh size was 1.0 ha (g. 4). Only a very
few marshes are larger than 10 ha—the marshes associated
with the Northeast Creek estuary and Bass Harbor Marsh,
both of which are represented by several different marshes in
the database, and large series of marshes at the end of Hog
Bay, north of Mount Desert Island. Most of the marshes in the
database are fairly small, isolated marshes. Marshes within
ANP boundaries and easements held by ANP accounted for 26
of the marshes (23 percent), and the State of Maine accounted
for 1 of the 114 marshes.
The towns of Gouldsboro, Bar Harbor, Franklin, and
Tremont had the greatest area of salt marshes in the study
area (table 1, g.5), many of which were in large salt marshes
and salt marsh complexes. Deer Isle and Trenton each have a
relatively large number of small salt marshes. Ten of the 22
towns in the study area are host to salt marshes on ANP lands;
Bar Harbor, Frenchboro, Tremont, Trenton, and Southwest
Harbor all have more than 5 ha in salt marsh habitat within the
ANP landholdings (table 1).
Estimated Future Inundation Resulting from Sea-Level Rise at Salt Marshes 9
Estimated Future Inundation Resulting
from Sea-Level Rise at Salt Marshes
The delineation of inundation contours from any given
amount of SLR assumes a common datum for all the salt
marshes involved in the study. Because of the ecological
niche occupied by salt marshes, the HAT could be used as
a common datum. However, there is no available spatial
dataset representing HAT in the study area and the numerous
islands and tidal restrictions in many bays and estuaries
create great spatial variability in the HAT datum. This study,
therefore, used the highest marsh elevation (HME) at each
salt marsh as a proxy for the local HAT. The inundation
mapping was done relative to the highest elevation of each
marsh surface, derived from the LiDAR data. The HME was
determined in an iterative fashion. After the marsh extent was
mapped using the high-resolution aerial photos available for
the marsh, as described above, the LiDAR DEM data were
used to nd the highest elevation of the marsh at the upland
edge, where the marsh transitioned into other ecosystems (in
many locations this was a very abrupt transition, whereas in
others the transition was more gradual) . Next, a contour was
drawn at that elevation and compared to the marsh upland
boundary as mapped using the aerial photos. The process
was repeated until a contour elevation was found that best
delineated the marsh–upland boundary, and that elevation
was dened as the HME (g. 6).
Inundation contours were delineated at each salt marsh
using an elevation of the HME +60 cm to indicate adjacent
lowlands that are expected to be inundated from 60 cm of
SLR and would be available for the potential migration
of the marsh. The 95-percent condence interval on the
LiDAR elevation data (±26.0 cm) was mapped relative to
the estimated HME +60-cm SLR elevation line by dening
an upper and lower 95-percent condence interval contour
on either side of the 60-cm inundation contour (g. 6).
The differences in inundated areas between the upper and
lower 95-percent condence interval contours are the spatial
0
0.1
0.2
0.3
0.4
0.5
0.6
0.7
0.8
0.9
1
0.10 1.00 10.00 100.00
Percentile of total marshes
Area, in hectares
Median size of study
area saltmarshes
Figure 4. Cumulative distribution of salt marsh areas, in hectares.
Table 1. Inventory of salt marshes in towns within the study area,
including number of marshes and total marsh areas for areas with
Acadia National Park.
[ha, hectares; ANP, Acadia National Park; --, none; Note: some of the salt
marshes are located on the border between towns and appear more than once
on the list]
Town
Total
salt marsh
area,
in ha
Number
of
salt
marshes
Total
salt marsh
area
in ANP
Number
of salt
marshes
in ANP
Bar Harbor 46.8 14 18.2 7
Brooklin 8.8 5 0.3 1
Brooksville 11.1 5 -- --
Cranberry Isles 15.7 4 0.8 2
Deer Isle 11.1 17 3.6 1
Franklin 37.1 4 -- --
Frenchboro 10.5 2 6.5 1
Gouldsboro 52.8 2 -- --
Hancock 20.5 8 -- --
Lamoine 18.0 6 -- --
Mount Desert 13.4 6 -- --
North Haven 0.1 1 -- --
Penobscot 4.1 2 -- --
Sedgwick 6.0 3 -- --
Sorrento 0.3 1 -- --
Southwest Harbor 14.9 6 14.9 6
Stonington 5.1 4 -- --
Surry 0.2 1 -- --
Swans Island 10.4 5 5.4 4
Tremont 33.1 8 18.1 5
Trenton 11.9 10 5.8 7
Winter Harbor 2.6 4 1.6 3
10 Estimates of Future Inundation of Salt Marshes in Response to Sea-Level Rise in and Around Acadia National Park, Maine
Deer Isle
Blue Hill
Surry
Gouldsboro
Orland
Ellsworth
Frenchboro
Tremont
Bar Harbor
Winter Harbor
Brooklin
Swans Island
Penobscot
Brooksville
Hancock
Mount
Desert
Trenton
Sullivan
T7 SD
Stonington
Sedgwick
Franklin
Cranberry Isles
Lamoine
Castine
North Haven
Prospect
T10 SD
Sorrento
T8 SD
Vinalhaven
Bucksport
Isle Au Haut
Islesboro
Steuben
Stockton
Springs
Southwest Harbor
Verona
Searsport
T9 SD
68°15'68°45'
44°30'
44°15'
Base from U. S. Geological Survey digital line graphs
1:24,000. Universe Transverse Mercator, zone 19N, NAD83.
EXPLANATION
Town boundaries
Salt marsh
Acadia National Park
0 5 10 MILES
0 5 10 KILOMETERS
Figure 5. Distribution of salt marshes within the coastal towns in the study area.
representations of uncertainty associated with the topographic
data used to produce the inundation maps and can be thought
of as an uncertainty zone (g. 6). For marshes in a low-relief
setting, such as in Northeast Creek or Bass Harbor Marsh, the
uncertainty zone can cover 100 to 300 m of distance on the
ground. In areas where relief is higher, such as in Somesville
at the head of Somes Sound, the uncertainty zone covers a
distance of only 10 m or less.
Articial structures, such as roads or bridge abutments,
that could act as potential barriers to salt-marsh migration
were identied and mapped. The geodatabase identies
which of the potential barriers are associated with one of the
26 salt-marsh areas of ANP and its conservation partners.
These potential barriers represent ANP infrastructure that
could be affected by SLR in the future, some of which
could be mitigated to improve the availability of uplands for
marsh migration.
Inundation Potential and Barriers to Migration
A set of four contour lines were delineated for each salt
marsh in the study area (g. 6):
• a contour line representing the HME
• the inundation contour line for 60 cm of SLR
• the contour line of the upper 95-percent condence
interval above the 60-cm SLR line (SLR + 26 cm)
• the contour line of the lower 95-percent condence
interval below the 60-cm SLR line (SLR–26 cm)
Estimated Future Inundation Resulting from Sea-Level Rise at Salt Marshes 11
LMSL
NAVD 88 — 0 meters
HME
HME + 60 cm SLR
95-percent confidence interval (±26 cm)
Upper 95-percent confidence interval contour
Inundation contour for 60 cm SLR
Lower 95-percent confidence interval contour
DRAWING NOT TO SCALE
Upland Salt marsh
Uncertainty zone
for inundation from
60 cm SLR
L
a
n
d
s
u
r
f
a
c
e
Figure 6. Relation of local elevation datum to the inundation contours, 95-percent confidence interval
contours, and the inundation uncertainty zone for salt marshes in the study area. cm, centimeter; HME, high
marsh elevation; LMSL, local meal sea level; NAVD 88, North American Vertical Datum of 1988; SLR, sea-level
rise
These delineations were stored as a polyline data layer in
the geospatial data accompanying this report (appendix 1). The
geospatial data are described in appendix 1 and are available
for download at http://pubs.usgs.gov/sir/2012/5290/.
Inundation contours at 110 marshes were mapped during
this study. Inundation contours were not mapped for the
4 marshes smaller than 0.2 ha on private property. The contour
lines are truncated along the shoreline at the edge of the
salt-marsh areas. The inundation contours are not meant as a
forecast of areas into which salt marshes will migrate. Rather,
they provide a basis for planning management decisions and a
basis for further study of factors such as sediment supply and
current accretion rates for determining site-specic potential
for migration.
Although this study does not attempt to predict whether
any of the salt marshes in the study area will be able to keep
up with sea–level rise, it may be useful to understand how
those salt marshes are situated in the topographic landscape.
Some of the marshes are constrained within fairly steep
topographic boundaries and have little room to expand or
migrate, while others are located in broad lowland areas; many
others are somewhere in between these two extremes. Two
measures of this “room to expand” were evaluated for the
population of salt marshes in the study area—an estimate of
the area that would be inundated adjacent to each salt marsh,
in comparison to the original marsh area, and the average
distance inland that the inundation contour lies from the
marsh edge. Because the mapping of the SLR lines did not
create polygons, a visual estimate of the inundated area was
generated for every marsh in the study. The visual estimates
were calibrated based on polygons were created for a few of
the largest marshes (including the Northeast Creek and Bass
Harbor marsh areas).
In total, the amount of land adjacent to the study marshes
that will be inundated with 60 cm of SLR is estimated to be
approximately 350 ha, which is about the same amount of
area that the salt marshes now occupy (340 ha). But this total
inundation area is not evenly distributed across the study
area. Upland areas expected to be inundated near 19 of the
salt marshes are much smaller than the areas occupied by
those marshes (25 percent of the size (in 2010) or smaller;
g. 7). Only a few of the marshes have relatively large areas
for possible migration (more than 200 percent of their size in
2010). While salt marshes in ANP account for just 23 percent
of all the marshes in the study, two large areas within ANP
(Northeast Creek and Bass Harbor Marsh) account for 170 ha
(50 percent) of the total amount expected to be inundated.
Similarly, the average distance inland from the current marsh
edge to the inundation contour in 83 of the 110 salt marshes
(75 percent) is only 20 meters or less (g. 8). There are only
7 marshes that have an average of over 75 meters of inland
expansion area directly adjacent to their perimeter. Fringing
marshes in general have very little room for migration or
expansion in their adjacent upland areas.
Two examples of marshes with very different landscape
positions are shown in gures 9 and 10. The marsh in
Somesville at the head of Somes Sound (g. 9) has an upland
area inside the 60-cm inundation contour that is less than
25 percent of the current (2012) marsh area and has little room
for expansion or migration. In contrast, the amount of area
expected to be inundated in the Northeast Creek area (g. 10)
is more than 600 percent larger than the current (2012) area
of the marsh (Bass Harbor Marsh has a similarly large area of
12 Estimates of Future Inundation of Salt Marshes in Response to Sea-Level Rise in and Around Acadia National Park, Maine
0
5
10
15
20
25
30
Number of marshes
Area of upland inundated, as a percentage of marsh area
< 15
–
16−25
26−50
51−75
76−100
101−150
151−200
201−250
251−300
>300
Figure 7.
Histogram showing the estimated area of upland adjacent to salt
marshes that will be inundated with 60 centimeters of sea-level rise, shown as a
percentage of adjacent salt marsh area. <, greater than; ≤, less than or equal to.
0
5
10
15
20
25
30
Number of marshes
Distance, in meters
< 5
–
6−10
11−15
16−20
21−25
26−30
31−50
51−75
76−100
>100
Figure 8. Histogram showing the average distance of the 60-centimeter
inundation contours inland from salt marsh edges. <, greater than; ≤, less than or
equal to.
Estimated Future Inundation Resulting from Sea-Level Rise at Salt Marshes 13
68°19'15"68°19'30"68°19'45"
44°22'30"
44°22'15"
EXPLANATION
Somesville area marshes contour lines:
Upper 95-percent confidence interval
contour
60 centimeters of sea level rise
Lower 95-percent confidence interval
contour
Highest marsh surface elevation (2010)
Potential barrier to migration
Salt marshes mapped from aerial photos
Base from U.S. Geological Survey Digital Elevation Data:
LiDAR for the Northeast, USGS Contract G10PC00026,
Photo Science, Inc., 2011.
0 0.1 0.2 MILES
0 0.1 0.2 0.3 KILOMETERS
68°19'15"68°19'30"68°19'45"
44°22'30"
44°22'15"
Base image credit: Maine Coastal Low Tide Ortho-rectified Digital Images, 2008
Maine Office fo Geographic Information Systems (MEGIS).
B
A
EXPLANATION
Somesville area marshes contour lines:
Upper 95-percent confidence interval
contour
60 centimeters of sea level rise
Lower 95-percent confidence interval
contour
Highest marsh surface elevation (2010)
Potential barrier to migration
Salt marshes mapped from aerial photos
0 0.1 0.2 MILES
0 0.1 0.2 0.3 KILOMETERS
Figure 9. Static inundation map for 60 centimeters (cm) of sea-level rise and upper and lower 95-percent confidence interval
contours for the Somesville area, Mount Desert, Maine, using A, shaded relief image of light detection and ranging (LiDAR) data and
B, orthophoto base. The average distance of the 60- cm inundation contour to the current marsh edge is about 15 meters. The area
between the 2010 high marsh elevation and the 60-cm inundation contour is less than 25 percent of the marsh area in 2010.
14 Estimates of Future Inundation of Salt Marshes in Response to Sea-Level Rise in and Around Acadia National Park, Maine
Base from U.S. Geological Survey Digital Elevation Data:
LiDAR for the Northeast, USGS Contract G10PC00026,
Photo Science, Inc., 2011.
Base image credit: USDA Farm Service Agency Aerial Photography Field Office,
NAIP 2009, Maine Office of Geographic Information Systems (MEGIS)
A
B
68°17'30"68°18'68°18'30"68°19'
44°25'30"
44°25'
44°24'30"
68°17'30"68°18'68°18'30"68°19'
44°25'30"
44°25'
44°24'30"
EXPLANATION
Northeast Creek area marshes contour lines:
Upper 95-percent confidence interval
contour
60 centimeters of sea level rise
Lower 95-percent confidence interval
contour
Highest marsh surface elevation (2010)
Potential barrier to migration
Salt marshes mapped from aerial photos
0 0.1 0.2 MILES
0 0.1 0.2 0.3 KILOMETERS
EXPLANATION
Northeast Creek area marshes contour lines:
Upper 95-percent confidence interval
contour
60 centimeters of sea level rise
Lower 95-percent confidence interval
contour
Highest marsh surface elevation (2010)
Potential barrier to migration
Salt marshes mapped from aerial photos
0 0.1 0.2 MILES
0 0.1 0.2 0.3 KILOMETERS
Figure 10. Static inundation map for 60 centimeters (cm) of sea-level rise and upper and lower 95-percent confidence interval
contours for the Northeast Creek area, Bar Harbor, Maine, using A, shaded relief image of light detection and ranging (LiDAR) data and
B, orthophoto base. The area between the 2010 high marsh elevation and the 60-centimeter inundation contour is more than six times
the size of the marsh in 2010.
Estimated Future Inundation Resulting from Sea-Level Rise at Salt Marshes 15
low-relief upland that would be inundated). In both cases, the
areas expected to be inundated are largely freshwater wetlands
at present.
After the extent of the inundation contours were
determined, the landscape around the salt marshes and
inundated areas were surveyed for articial structures that
either currently impede water movement or would at a higher
sea level. A total of 41 potential barriers to marsh migration
were identied in and around the 110 salt marshes analyzed
in the study area; examples are shown in gure 11. All but
two of the potential barriers were roadways. The other two
potential barriers are part of an old railroad grade. While
many of the potential barriers identied do not completely
block water movement to and from these marshes (having
some sort of bridge or culvert), they all restrict water and
sediment movement compared to the natural hydrologic
regime of the marsh. Ten of the potential barriers are on or
cross ANP property or ANP conservation easements (table 2).
If mitigation strategies for salt marsh migration are to be
developed in the future, the sediment-supply and water-
supply constrictions of these potential barriers should be taken
into consideration.
68°20'30"68°21'
44°25'20"
44°25'
Base image credit: Maine Coastal Low Tide Ortho-rectified Digital Images, 2008
Maine Office fo Geographic Information Systems (MEGIS).
Thomas Bay
0 0.1 0.2 0.3 MILES
0 0.2 0.4 KILOMETERS0.1
EXPLANATION
Thomas Bay area marshes contour lines:
Upper 95-percent confidence interval
contour
60 centimeters of sea level rise
Lower 95-percent confidence interval
contour
Highest marsh surface elevation (2010)
Potential barrier to migration
Salt marshes mapped from aerial photos
Figure 11. Static inundation map showing potential barriers to marsh migration for the Thomas Bay
area, Bar Harbor, Maine.
16 Estimates of Future Inundation of Salt Marshes in Response to Sea-Level Rise in and Around Acadia National Park, Maine
a 60-centimeter (cm; 2-foot) rise has been cited as the
environmental planning target by the State of Maine.
In response to rising sea levels, the vertical accretion
and horizontal migration of salt-marsh surfaces onto adjacent
low-lying land will be important for the survival of salt
marshes in the future. The U.S. Geological Survey (USGS),
in cooperation with the National Park Service (NPS), began
a study in 2010 to map lowland areas around salt marshes in
and near ANP and its associated lands that would be inundated
with a 60-cm SLR and that could potentially provide areas into
which salt marshes could migrate under favorable conditions.
The goals of the inundation mapping project were to indicate
the areal extent of static landward inundation around salt
marshes expected from 60 cm of SLR, identify adjacent low-
lying land that may provide area into which salt marshes could
migrate, and identify potential articial barriers to migration;
these are critical parts of any proactive adaptation strategy for
salt-marsh persistence.
This study made use of topographic data collected using
aircraft-borne light detection and ranging (LiDAR) during
October 2010 as part of a larger data-collection effort along
the northeastern shoreline from Long Island, New York, to
Eastport, Maine. The overall accuracy of the LiDAR data had
a root mean square error (RMSE) of 11.3 cm. This study also
used digital color aerial photography from Eastern Penobscot
Bay to Schoodic Point, taken during August 2008 at or near
low-tide conditions and consisting of high-resolution 24-bit
color orthorectied digital images with a pixel resolution of
0.5 meters (m); other high-resolution digital images, which are
available online, also were used.
The study marshes consisted of 47 salt marshes
previously mapped on and near ANP-associated lands and
an additional 67 salt marshes identied from high-resolution
aerial photos in an area from western Penobscot Bay east
to Gouldsboro, Maine. The inventory of salt marshes in the
study area indicates that marshes cover a total area of at least
340 ha (many of the very small salt marshes in the study area
were not inventoried); the inventoried marshes range in size
from 0.11 to 52 ha with a median size of about 1 ha. Only a
very few, such as Grand Marsh in Gouldsboro, the marshes
associated with the Northeast Creek estuary, Bass Harbor
Marsh, and large series of marshes at the end of Hog Bay,
north of Mount Desert Island, are larger than 10 ha. Most
of the marshes identied in the inventory are fairly small,
isolated marshes. Twenty-six of the 114 marshes are within
ANP and easements held by the ANP, and one is owned by the
State of Maine.
Elevation reference marks (ERMs) were established for
vertical datum control for control-point surveys done for this
study and to serve as stable datum points to support future
salt-marsh research. The ERMs established for this study were
documented and uploaded to the NPS Denver Service Center
survey monuments database. Control points surveyed by the
U.S. Geological Survey at selected salt marshes indicated
that the LiDAR data used to delineate the marshes and the
inundation contours had a RMSE of 13.3 cm in salt marsh
Table 2. Inventory of potential barriers to marsh migration in
towns within the study area.
[ANP, Acadia National Park; --, none; Note: some of the salt marshes and
potential barriers are located on the border between towns and appear more
than once on the list.]
Town
Number of
potential barriers
Number of
potential barriers in ANP
Bar Harbor 8 2
Brooklin -- --
Brooksville 3 --
Cranberry Isles -- --
Deer Isle 5 --
Franklin 2 --
Frenchboro -- --
Gouldsboro 1 --
Hancock 2 --
Lamoine 4 --
Mount Desert 2 --
North Haven -- --
Penobscot -- --
Sedgwick -- --
Sorrento -- --
Southwest Harbor 2 2
Stonington 2 --
Surry -- --
Swans Island 2 1
Tremont 7 2
Trenton 2 1
Winter Harbor 2 2
Summary and Conclusions
Salt marshes provide signicant ecological functions
that include nursery and breeding habitat for sh, birds, and
other wildlife species; organic-matter production; storm, ood,
and erosion protection; carbon sequestration; and ltration of
nutrients, sediments, and contaminants from waters entering
the coastal zone. Salt marshes exist in a narrow elevation
range relative to sea level; in general, the tidal range favorable
to salt-marsh formation and growth is between mean sea
level (MSL) and the highest annual tide (HAT). For this
reason, rising sea levels threaten the persistence of coastal
salt marshes. Sea level has been rising globally for the last
20,000 years and has risen from 0.6 to 2.5 millimeters per
year (mm/yr) in New England during the last century. Sea
level is expected to continue to rise as a result of melting
glaciers and polar ice and thermal expansion of the ocean; the
estimated rate of sea-level rise (SLR) is as much as 8.4 mm/yr
over the next century. Although there is great uncertainty in
the precise amount of SLR expected over the next century,
References Cited 17
habitats. This was used to calculate the 95-percent condence
interval to be ± 26 cm, which was used to delineate condence
interval contours above and below the SLR contours.
The highest elevation at each salt marsh was selected as
the common datum from which to delineate the inundation
contours (as a proxy for the highest annual tide). A set of four
contour lines were delineated for each marsh:
• contour lines representing HME
• the inundation contour line for 60 cm of SLR
• the contour line of the upper 95-percent condence
interval above the 60-cm SLR line (SLR +26 cm)
• the contour line of the lower 95-percent condence
interval below the 60-cm SLR line (SLR –26 cm)
In addition, any articial structures presenting potential
barriers to salt-marsh migration were delineated for each salt
marsh in the study area. The differences in inundated areas
between the 60-cm SLR +26 cm and 60-cm SLR –26 cm
contour lines indicate the spatial representation of uncertainty
associated with the topographic data used to produce the
inundation contour lines. Inundation contour lines and HME
contour lines, salt-marsh polygons, barriers to migration,
ERMs, and surveyed control points for 114 salt marshes are
stored in a geodatabase for use in a geographic information
system. The geodatabase accompanies this report and is
available for download at http://pubs.usgs.gov/sir/2012/5290/.
The amount of land that will be inundated with 60-cm
SLR was estimated to be approximately 350 ha in upland
areas adjacent to the inventoried salt marshes, a large portion
of which is currently (2012) freshwater wetland habitat. This
total inundation area, however, is not evenly distributed across
the study area. Only a few of the marshes have relatively
large areas for possible migration (more than 200 percent
of their size in 2010). While salt marshes in ANP account
for 23 percent of all the marshes in the study, two large
areas within ANP (Northeast Creek and Bass Harbor Marsh)
account for 170 ha (50 percent) of the total amount expected
to be inundated. Similarly, the average distance inland from
the current marsh edge to the inundation contour in 75 percent
of the marshes is only 20 meters or less. Fringing marshes in
general have very little room for migration or expansion in
their adjacent upland areas.
A total of 41 potential barriers to marsh migration were
identied in and around the 110 salt marshes analyzed in the
study area. While many of the potential barriers identied
do not completely block water movement to and from these
marshes (having some sort of bridge or culvert), they all
restrict water and sediment movement compared to the natural
hydrologic regime of the marsh. Ten of the potential barriers
are on or cross ANP property or ANP conservation easements.
If mitigation strategies for salt marsh migration are to be
developed in the future, the sediment-supply and water-
supply constrictions of these potential barriers should be taken
into consideration.
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Appendix 1 19
Appendix 1. Geospatial data of salt marshes, inundation contours, and
surveying data in and near Acadia National Park, Maine.
This section describes the geospatial data produced for
this report. These geographic information system (GIS) layers
were developed along with the report for the identication
of areas adjacent to salt marshes that are expected to be
inundated after 60 centimeters (cm) of sea-level rise (SLR)
occurs. The layers document the location and extent of the
salt marshes, the extent of inundation expected around each
marsh (with 95-percent condence interval lines), potential
manmade barriers to marsh migration, and all the surveying
data collected as part of the project.
The layers are delivered in ESRI File Geodatabase format
in the Universal Transverse Mercator, Zone 19, projection (in
meters). Metadata are Federal Geographic Data Committee
(FGDC) compliant and provided in in Extensible Markup
Language (xml) format.
The layers may be viewed in ArcGIS 9.x or ArcView 3.x
or higher. If you do not have any GIS software, you may view
the data via ArcReader, a free mapping application distributed
by ESRI for Windows, Linux, and Unix operating systems at
http://www.esri.com/software/arcgis/arcreader/download.html.
The data are available from the index page of this report
(http://pubs.usgs.gov/sir/2012/5290/) and by searching for
data at “ACAD” on the the National Park Service Integrated
Resource Management Applications (IRMA) Web portal at
https://irma.nps.gov/App/Portal/Home.
Layer Description Thumbnail Metadata
--- Overview of U.S. Geological Survey Scientic
Investigations Report 2012–5290 saltmarsh
spatial data
http://pubs.usgs.gov/sir/2012/5290/
Appendix1/Metadata/
SIR2012_5290_ACAD_
SaltmarshSLR_overview.xml
Saltmarsh
polygons
These polygons of salt marshes in the study
area, in and around Acadia National Park
(ANP), Maine, were used as an inventory
of the population of salt marshes that are at
risk because of expected sea level rise in the
coming decades. Each marsh is represented
by one or more polygons, and contours
representing sea level rise are mapped for
each marsh in this inventory.
http://pubs.usgs.gov/sir/2012/5290/
Appendix1/Metadata/
SIR2012_5290_ACAD_
Saltmarshpolygons.xml
Inundation
lines
The purpose of this data layer is to show
lowland areas surrounding salt marshes
in the study area that would be inundated
after 60 cm of SLR, and would therefore
provide potential areas for salt marshes
to migrate into, if accretionary processes
accompanying SLR permit. The 95-percent
condence intervals on the elevation
data are also shown, to illustrate how
the uncertainty in the light detection and
ranging (LiDAR) data translates into
uncertainty in the land area that would
be inundated.
http://pubs.usgs.gov/sir/2012/5290/
Appendix1/Metadata/
SIR2012_5290_ACAD_
Inundationlines.xml
20 Estimates of Future Inundation of Salt Marshes in Response to Sea-Level Rise in and Around Acadia National Park, Maine
Layer Description Thumbnail Metadata
Potential
barriers to
migration
Landforms that are potential barriers to the
horizontal migration of salt marshes in and
around Acadia National Park are potentially
important in the analysis of the future
viability of saltmarshes. Roads and railroad
grades both may act as potential barriers.
The potential barriers to migration of salt
marshes in and around ANP were developed
using the inundation lines for salt marshes
with 60 cm of sea level rise, and a shaded-
relief image of the LiDAR data on which
the inundation lines were based.
http://pubs.usgs.gov/sir/2012/5290/
Appendix1/Metadata/
SIR2012_5290_ACAD_
Potentialbarriers.xml
Surveyed
benchmarks
Published benchmarks and other base stations
used for differential Global Positioning
System (GPS) surveying of elevation
reference marks (ERMs) and marsh points.
http://pubs.usgs.gov/sir/2012/5290/
Appendix1/Metadata/
SIR2012_5290_ACAD_
SurveyedBMs.xml
Surveyed
ERMs
Vertical control was established using
previously-published benchmarks and
one base station that was not previously
published. ERM points were used as datum
to survey elevations of marsh points.
http://pubs.usgs.gov/sir/2012/5290/
Appendix1/Metadata/
SIR2012_5290_ACAD_
SurveyedERMs.xml
Surveyed
marsh
points
Marsh Points were used as part of independent
accuracy assessment of LiDAR data at
salt marsh surfaces. Five surveyed points
at each of the 20 marshes were used for
LiDAR elevation accuracy assessment.
Each of these points is located at a wooden
stake pounded into the marsh surface
and ush with the marsh surface. These
points were used to determine the root
mean squared error (RMSE) of the LiDAR
data in this study area, and the 95 percent
condence intervals.
http://pubs.usgs.gov/sir/2012/5290/
Appendix1/Metadata/
SIR2012_5290_ACAD_
Surveyedmarshpoints.xml
Although these data have been used by the U.S. Geological Survey, no warranty expressed or implied is made by the
U.S. Geological Survey as to the accuracy of the data. The act of distribution shall not constitute any such warranty, and no
responsibility is assumed by the U.S. Geological Survey in the use of these data, software, or related materials. The use of
rm, trade, or brand names in this report is for identication purposes only and does not constitute endorsement by the U.S.
Geological Survey. The names mentioned in this document may be trademarks or registered trademarks of their respective
trademark owners.
Prepared by the Pembroke Publishing Service Center.
For more information concerning this report, contact:
Office Chief
U.S. Geological Survey
New England Water Science Center
Maine Office
196 Whitten Road
Augusta, ME 04330
or visit our Web site at:
http://me.water.usgs.gov
Nielsen and Dudley—Estimates of Future Inundation of Salt Marshes in and Around Acadia National Park, Maine—Scientific Investigations Report 2012–5290
