Front cover: view from Great Brewster Island (©Sherman Morss, Jr.); smaller images (R. 

Tiner photos) 

Back cover: view of Boston Skyline from Thompson Island salt marsh (©Sherman 

Morss, Jr.) 
Wetlands of the Boston Harbor Islands National Recreation Area 

by 

Ralph W. Tiner, John Q. Swords, and Herbert C. Bergquist 

U.S. Fish & Wildlife Service 

National Wetlands Inventory Program 

Northeast Region 

300 Westgate Center Drive 

Hadley, MA 01035 

Prepared for the U.S. Department of Interior, National Park Service 

February 2003 
This report should be cited as: 

Tiner, R.W., J.Q. Swords, and H.C. Bergquist. 2003. Wetlands of the Boston Harbor 

Islands National Recreation Area. U.S. Fish and Wildlife Service, National Wetlands 

Inventory Program, Hadley, MA. NWI technical report. 26 pp. plus appendices. 
Table of Contents

 Page No.

Introduction 1 

Methods 4 

Results 9 

 Digital Inventory Data 9 

 Wetland Status in the Boston Harbor Islands NRA 9 

 Wetland Communities 18 

 Preliminary Assessment of Wetland Functions 23 

Summary 24 

Acknowledgments 25 

References 26 

Appendices 

A: Legend for wetland and deepwater habitat classification following Cowardin et al. 

1979. 

B: Extent of wetlands and deepwater habitats in and around the Boston Harbor Islands 

NRA based on an update of seven NWI maps in this locale. 
 1 

Introduction 

The National Park Service (NPS) needs current information on the distribution and types 

of wetlands occurring within the Boston Harbor Islands National Recreation Area 

(Boston Harbor Islands NRA) to aid its efforts to improve management of Park resources. 

Such information includes maps and digital data for computer analysis using Geographic 

Information System (GIS) technology. 

The U.S. Fish and Wildlife Service (FWS) is mapping wetlands across the country as part 

of its National Wetlands Inventory (NWI) Program. The NWI employs aerial 

photointerpretation techniques to identify, delineate, and classify wetlands on aerial 

photography (see website at: http://wetlands.fws.gov). NWI products include large-scale 

maps (1:24,000/1:25,000) and accompanying digital data. The NWI has prepared 

wetland maps for numerous Federal and state agencies, including the NPS. 

Given the national scope of the NWI, mid- to high-altitude aerial photography (1:40,000 

and smaller) is typically used for wetland mapping. At the outset of the NWI in the late 

1970s, 1:80,000 black and white aerial photography was used. This quad-centered 

photography was acquired by the U.S. Geological Survey (USGS) to produce updates of 

large-scale topographic maps and orthophotoquads in some areas. With this imagery, the 

NWI mapped wetlands 3-5 acres and larger. In the 1980s, this photography was replaced 

by 1:58,000 color infrared photography derived the USGS’s National High-Altitude 

Aerial Photography Program. The NWI used this photography to map wetlands 1-3 acres 

in size or more. In the late 1980s, the USGS began acquiring 1:40,000 color infrared 

and/or black and white aerial photography through its National Aerial Photography 

Program. With this imagery, NWI’s target mapping unit was about one acre in size or 

more. Tiner (1990, 1999) described limitations of aerial photography for wetland 

mapping. 

For the Boston Harbor area, the original NWI maps were produced over 20 years ago 

based on late 1970s 1:80,000 aerial photography. These maps were updated about ten 

years ago with mid-1980s 1:58,000 photography (the most recent photography available 

at that time). The most current mid-altitude aerial photography available for this area is 

1995 1:40,000 color infrared photography. 

In 2001, the National Park Service provided funds to the FWS to do the following: 

• Update NWI maps and digital data for the Boston Harbor Islands NRA 

• Enhance the digital database to include hydrogeomorphic-type descriptors for 

landscape position, landform, and water flow path 

• Prepare a wetlands inventory report for the Boston Harbor Islands NRA 

• Produce a color-coded map showing the wetlands by type within the Boston 

Harbor Islands NRA 
 2 

This work would provide the NPS with needed wetland information for resource planning 

and management. 

The purpose of this report is to summarize the results of this effort, with emphasis on the 

wetlands associated with the islands in the designated Boston Harbor Islands NRA. 

Generalized wetland maps are included in this publication. More detailed map 

information can be obtained from the NWI website (http://wetlands.fws.gov) where NWI 

digital map data can be downloaded for GIS applications or data can be directly viewed 

through the "interactive mapper tool." 

Study Area 

The Boston Harbor Islands NRA is located within Boston Harbor and neighboring bays 

(Dorchester, Quincy, and Hingham) in eastern Massachusetts. It contains 34 islands: 

Bumpkin, Button, Calf, Deer, Gallops, Georges, Grape, Great Brewster, Green, 

Hangman, Langlee, Little Brewster, Little Calf, Long, Lovells, Middle Brewster, Moon, 

Nixes Mate, Nut, Outer Brewster, Peddocks, Raccoon, Ragged, Rainsford, Sarah, Shag 

Rocks, Sheep, Slate, Snake, Spectacle, The Graves, Thompson, Webb Memorial, and 

Worlds End (Figure 1). 
 3 

Figure 1. Location of Boston Harbor Islands National Recreation Area, with major 

islands highlighted. 

(Click here for image) 
 4 

Methods 

The FWS used conventional photointerpretation techniques to identify and classify 

wetlands and deepwater habitats in the Boston Harbor Islands NRA.1 Color infrared, 

mid-altitude aerial photography (1:40,000) acquired in 1995 was used for this project. 

Wetlands were initially classified according to the FWS’s “Classification of Wetlands 

and Deepwater Habitats of the United States” (Cowardin et al. 1979) – the federal data 

standard established by the Federal Geographic Data Committee. Figure 2 shows the 

boundary between the marine and estuarine systems - the dominant ecosystems of the 

Boston Harbor Islands NRA. Baseline digital wetland data for this inventory came from 

the NWI wetland database derived from 1980s-era aerial photographs. These data were 

revised through interpretation of the 1995 aerial photography. Photointerpretation was 

performed on a digital transfer scope that permitted simultaneous viewing of aerial 

photos and existing digital data. Edits were made directly to the digital database. 

Collateral data sources used during this updated inventory included data on intertidal 

wetlands compiled by Rich Bell of the New England Aquarium (results now published in 

Bell et al. 2002), NWI maps/digital data, eelgrass distribution data from the State’s 

geographic information system (MassGIS at: http://www.state.ma.us/mgis), and U.S. 

Geological Survey topographic maps and accompanying digital raster graphics and 

digital line graphs for hydrology (e.g., rivers, streams, lakes, and ponds). Computergenerated maps were produced and statistics on wetland acreages were tabulated using 

Arcview 3.1 GIS software. 

A field trip was conducted in the study area on October 23, 2001. Visits were made to 

the following islands: Thompson, Peddocks, and Grape. 

After revising the wetlands digital data, hydrogeomorphic-type attributes were added to 

the database to provide a more complete characterization of each wetland and deepwater 

habitat. These attributes included descriptors for landscape position (the relationship 

between a wetland and a waterbody), landform (the physical shape of a wetland), water 

flow path (the directional flow of surface water), and waterbody types following Tiner 

(2000). The addition of these attributes allowed the FWS to perform a preliminary 

assessment of wetland functions for the Boston Harbor Islands NRA. The following 

functions were evaluated: surface water detention, nutrient transformation, sediment 

retention, coastal storm surge detention and shoreline stabilization, fish and shellfish 

habitat, waterfowl and waterbird habitat, and other wildlife habitat.2

 Table 1 summarizes 

the correlations between functions and various wetland types for Northeast wetlands. 

Note that since the study area is characterized by relatively small islands surrounded by 

marine and estuarine waters, most of wetland types listed in Table 1 are not present. The 

rationale for these correlations is reported elsewhere (e.g., Tiner et al. 1999, 2000). 

 

1

 The intertidal zone around most islands was relatively discrete, except for three islands (Button, Sarah, 

and Ragged) in Hingham Harbor that were connected with tidal flats extending to the mainland; a 75m 

boundary was placed around them for calculating wetland acreage associated with these islands. 

2

 Given the lack of perennial streams on the islands, one function listed in Table 1 - streamflow 

maintenance - was not evaluated. 
 5 

Figure 2. Boundary between the marine and estuarine systems in the Boston Harbor 

Islands NRA. 

(Click here for image)
 6 

Table 1. Correlations between wetland functions and types for Northeast wetlands. An asterisk (*) 

indicates a wetland type restricted to coastal waters. Note: Most of the wetland types do not occur in the 

Boston Harbor Islands NRA, since it is comprised on relatively small islands. See an NWI map legend for 

coding (Appendix A). 

 Predicted Level 

Function of Significance Wetland Types 

Surface Water Detention High Estuarine Fringe*, Estuarine Basin*, Estuarine Island*, Lentic 

Basin, Lentic Fringe, Lentic Flat associated with reservoirs 

and flood control dams, Lotic Basin, Lotic Floodplain, Lotic 

Fringe, Lotic Island associated with Floodplain region, Lotic 

Island basin, Marine Fringe*, Marine Island*, Ponds 

Throughflow (in-stream) and associated Fringe and Basin 

wetlands, Ponds Bidirectional and associated wetlands, Ponds 

Bidirectional Tidal and associated wetlands*, Terrene 

Throughflow Basin 

Moderate Lotic Flat, Lotic Island flat, Terrene Interfluve, Other Terrene 

Basins, Other Ponds and associated wetlands 

Streamflow Maintenance High Headwater Wetlands (Terrene, Lotic, and Lentic), Headwater 

Ponds and Lakes (classified as PUB...on NWI) 

Moderate Lotic (Nontidal) Floodplain, Throughflow Ponds and Lakes 

(classified as PUB on NWI) and their associated wetlands, 

Terrene Outflow wetlands (associated with streams not major 

rivers), Outflow Ponds and Lakes (classified as PUB... on 

NWI), “Natural” Throughflow Ponds and Lakes (classified as 

PUB...on NWI) 

Nutrient Transformation High Vegetated wetlands with C, E, F, and H water regimes, Mixed 

unconsolidated bottom-vegetated wetlands with C, E, F, and H 

water regimes (this includes Lotic, Terrene, and Lentic 

wetlands - mostly floodplain, basin, interfluve-basin, and 

fringe types), Vegetated tidal wetlands (and mixes with 

nonvegetated classes) with N, P, R, and T water regimes* 

 Moderate Vegetated wetlands with A water regime, Lotic tidal vegetated 

 wetlands with S water regime* 

Retention of 

Sediments High Estuarine Basin*, Estuarine Fringe (excluding rocky shore)*, 

Estuarine Island (excluding rocky shore)*, Lentic 

Basin, Lentic Fringe (vegetated only), Lentic Island 

(vegetated), Lotic Basin, Lotic Floodplain,Lotic Fringe 

(vegetated only), Lotic Island, Throughflow Pond (in-stream) 

and associated vegetated wetlands, Bidirectional Ponds and 

associated wetlands, Bidirectional Tidal Ponds and associated 

wetlands*, Terrene Throughflow Basin 

 Moderate Lotic Flat, Lotic Tidal Fringe nonvegetated)*, Marine Fringe 

 (excluding rocky shore)*, Marine Island (excluding rocky 

 shore)*, Other Terrene Basins, Terrene Interfluve Basin, 

 Terrene wetlands associated with ponds, Other Ponds and 

 associated wetlands (excluding slope wetlands) 
 7 

Table 1 (continued). 

Predicted Level 

Function of Significance Wetland Types 

Coastal Storm Surge 

Detention and Shoreline 

Stabilization High Estuarine Basin*, Estuarine Fringe*, Lotic Tidal Fringe*, 

 Marine Fringe* 

Provision of Fish 

and Shellfish Habitat High Estuarine Emergent wetland* (including mixtures with other 

types), Estuarine Unconsolidated Shore*, Estuarine Intertidal 

Reef*, Estuarine Aquatic Bed*, Estuarine Intertidal Rocky 

Shore*, Lacustrine Semipermanently Flooded (excluding 

wetlands along intermittent streams), Lacustrine Littoral 

Aquatic Bed, Lacustrine Littoral Unconsolidated 

Bottom/Vegetated wetland, Lacustrine Littoral Vegetated 

wetland with a Permanently Flooded water regime, Marine 

Aquatic Bed*, Marine Intertidal Rocky Shore*, Marine 

Intertidal Unconsolidated Shore*, Marine Intertidal Reef*, 

Palustrine Semipermanently Flooded (excluding wetlands 

along intermittent streams; must be associated with a 

permanent waterbody such as PUBH, L1UBH, or 

R2/R3UBH), Palustrine Aquatic Bed, Palustrine 

Unconsolidated Bottom/Vegetated wetland, Palustrine 

Vegetated wetland with a Permanently Flooded water regime, 

Palustrine Tidal Emergent wetlands with N, R, or T water 

regimes (excluding “R” wetlands where EM5 is only 

dominant)*, Ponds (PUBH.. on NWI; not PUBF) associated 

with Semipermanently Flooded vegetated wetlands, Riverine 

Tidal Emergent wetland*, Riverine Tidal Unconsolidated 

Shore wetlands (excluding those with an “S” water regime)* 

 Moderate Lentic wetlands that are PEM1E, Lotic River or Stream 

 wetlands that are PEM1E (including mixtures with Scrub- 

 Shrub or Forested wetlands), Semipermanently flooded 

 Phragmites wetlands (PEM5F) where associated with a 

 permanent waterbody, Other Ponds and associated Fringe 

 wetlands (i.e., Terrene Fringe-pond) (excluding 

 industrial, stormwater treatment/detention, and similar ponds 

 in highly disturbed landscapes) 

Important for 

Stream Shading Lotic Stream wetlands that are Palustrine Forested wetlands 

(includes mixes where forested wetland predominates; 

excluding those along intermittent streams) (Note that 

although forested wetlands are designated as important for 

stream shading, forested uplands provide similar functions) 
 8 

Table 1 (continued). 

Predicted Level 

Function of Significance Wetland Types 

Provision of Waterfowl 

and Waterbird Habitat High Estuarine Aquatic Bed*, Estuarine Emergent wetlands*, 

Estuarine Unconsolidated Shore* (except S water regime), 

Estuarine Intertidal Reef*, Lacustrine Semipermanently 

Flooded, Lacustrine Littoral Aquatic Bed, Lacustrine Littoral 

Vegetated wetlands with an H water regime, Lacustrine 

Unconsolidated Shores (F, E, or C water regimes; mudflats), 

Marine Aquatic Bed*, Marine Intertidal Reef*, Marine 

Unconsolidated Shore*, Palustrine Semipermanently Flooded 

(excluding PEM5F, but including mixtures containing EM5), 

Palustrine Aquatic Bed, Palustrine Vegetated wetlands with an 

H water regime, Palustrine Unconsolidated Shores (F, E, or C 

water regimes; mudflats), Seasonally Flooded/Saturated 

Palustrine wetlands impounded or beaver-influenced (all 

vegetation types [except PEM5Eh and PEM5Eb] and 

associated PUB waters, Palustrine Unconsolidated Shores (F, 

E, and C water regimes; mudflats), Lotic River or Stream 

wetlands that are PEM1E (including mixtures with ScrubShrub or Forested wetlands; excluding PEM5E), Ponds 

associated with Semipermanently Flooded Vegetated 

wetlands, Palustrine Tidal Emergent wetlands (PEM1R and 

PEM1T and mixes with other EM and with SS and FO; 

excluding wetlands where EM5 is the only EM), Riverine 

Tidal Emergent wetlands, Riverine Tidal Unconsolidated 

Shores (except with S water regime) 

 Moderate Phragmites wetlands that are Seasonally Flooded/Saturated 

 and wetter (PEM5E; PEM5F; PEM5H, and PEM5R) and 

 associated with a waterbody, Other Lacustrine Littoral 

 Unconsolidated Bottom, Other Palustrine Unconsolidated 

 Bottom (excluding industrial, commercial, stormwater 

 detention, wastewater treatment, and similar ponds), Palustrine 

 Emergent wetlands (including mixtures with Scrub-shrub) that 

 are Seasonally Flooded and associated with permanently 

 flooded waterbodies 

Significant for 

 Wood Duck Lotic wetlands (excluding those along intermittent streams) 

 that are Forested or Scrub-shrub or mixtures of these types, 

 Lotic wetlands that are mixed Forested/Emergent or 

 Unconsolidated Bottom/Forested with a E, F, or R water 

 regime 

Provision of Other 

Wildlife Habitat High Large vegetated wetlands (>20 acres, excluding open water 

and nonvegetated areas), small diverse wetlands (10-20 acres 

with 2 or more covertypes; excluding EM5 as one of the 

covertypes), areas with large numbers of small isolated 

wetlands (within an upland forest matrix), interconnected 

wetlands (with corridor vegetation mostly intact) 

 Moderate Other vegetated wetlands (including Phragmites wetlands but 

 excluding aquatic beds) 
 9 

Results 

Digital Inventory Data 

Digital data for seven NWI maps were updated as part of this project: 1) East Half of 

Boston North, 2) West Half of Lynn, 3) East Half of Boston South, 4) West Half of Hull, 

5) East Half of Hull, 6) West Half of Weymouth, and 7) East Half of Weymouth. 

Standard NWI digital data (i.e., Cowardin et al. classifications) for these quads are posted 

on the NWI website at: http://wetlands.fws.gov. Enhanced digital NWI data including 

attributes for describing wetlands by landscape position, landform, and water flow path 

and waterbodies by additional properties have been forwarded to the National Park 

Service for inclusion in the Boston Harbor Islands NRA database. In the future, such 

data will likely be added to geospatial data posted on the NWI website. 

Wetland Status in the Boston Harbor Islands NRA 

A total of 1,276 acres of wetlands were inventoried in the Boston Harbor Islands NRA 

(Table 2; Figure 3). The estuarine and marine systems dominated this area (Figure 2). 

Consequently, most (or 76%) of the wetlands were estuarine types, with marine wetlands 

making up most of the remainder (22%). Only two percent of the wetlands were 

freshwater types (palustrine wetlands). 

Tidal flats (estuarine and marine unconsolidated shore wetlands) predominated. They 

covered 873 acres of intertidal habitat and represented 68 percent of the wetlands. Reefs 

formed by blue mussel (Mytilus edulis) and intertidal rocky shores were present in equal 

amounts, with 87 and 83 acres, respectively. Nearly 82 acres of estuarine emergent 

wetland (i.e., salt/brackish marsh) were inventoried. Only 31 acres of palustrine wetlands 

were mapped and 75 percent was represented by freshwater ponds (palustrine 

unconsolidated bottom and shore). Vegetated wetlands accounted for only 7.7 acres or 

25 percent of the palustrine wetlands. 

Wetlands were most abundant in association with six islands (Table 3). Four islands had 

nearly 100 or more acres: Thompson Island (211 acres), Peddocks (118), Long (116) and 

Worlds End (99). 

The extent of wetlands classified by hydrogeomorphic descriptors (i.e., landscape 

position, landform, and water flow path) is summarized in Table 4 and illustrated in 

Figure 4. Of the estuarine wetlands, nearly all were fringe types located along the 

margins of the islands. Only 12.4 acres of estuarine wetlands were classified as islands. 

These island wetlands were tidal flats that are exposed at low tide. Nearly 15 acres of 

intertidal rocky islands were inventoried in the marine system, while most marine 

wetlands fringed upland islands. Almost 31 acres of freshwater wetlands (including 

ponds) were associated with the Boston Harbor islands; most were isolated ponds. 
 10 

While the islands are surrounded by marine and estuarine waters, deepwater habitats 

were scarce on the islands themselves. Only 4.5 acres of estuarine waters were located 

on the islands. Nearly 85,000 acres of these waters were identified in the broader survey 

area which included seven NWI maps (see Appendix B). 
 11 

Table 2. Extent of wetlands associated with islands in the Boston Harbor Islands 

National Recreation Area based on an update of National Wetlands Inventory maps. 

Ecological System Aquatic Habitat Acreage 

Estuarine Aquatic Bed 33.8 

Emergent Wetland 81.9 

---------------------------------- ------- 

Vegetated Wetland 115.7 

Mussel Reef 60.4 

Rocky Shore 48.1 

Unconsolidated Shore 741.6 

---------------------------------- ---------- 

Nonvegetated Wetland 850.1 

Total Estuarine Wetland 965.8

Marine Aquatic Bed 86.7 

 ---------------------------------- -------- 

 Vegetated Wetland 86.7 

 Mussel Reef 26.4 

 Rocky Shore 35.1 

 Unconsolidated Shore 131.0 

 --------------------------------- --------- 

 Nonvegetated Wetland 192.5 

 Total Marine Wetland 279.2

Palustrine Emergent Wetland 5.9 

 Forested Wetland 1.0 

 Scrub-Shrub Wetland 0.8 

 --------------------------------- ------- 

 Vegetated Wetland 7.7 

 Unconsolidated Bottom 13.2 

 Unconsolidated Shore 9.9 

 --------------------------------- ------- 

 Nonvegetated Wetland 23.1 

 Total Palustrine Wetland 30.8

All Wetlands 1,275.8 
 12 

Figure 3. Wetlands classified by Cowardin et al. (1979) (simplified for this figure). 

(Click here for image)
 13 

Table 3. Wetland acreage summaries by island following Cowardin et al. (1979). 

Island System Wetland Type Acreage (total/island)

Bumpkin Estuarine Unconsolidated Shore 20.6 

 (20.6) 

Button Estuarine Emergent 1.5 

 Unconsolidated Shore 4.9 

 (6.4) 

Calf Estuarine Emergent 1.6 

 Marine Aquatic Bed 18.3 

 Rocky Shore 5.1 

 Unconsolidated Shore 2.1 

 (27.1) 

Deer Estuarine Unconsolidated Shore 26.8 

 Marine Aquatic Bed 5.6 

 Rocky Shore 3.6 

 Unconsolidated Shore 47.6 

 (83.6) 

Gallops Estuarine Aquatic Bed 1.3 

 Rocky Shore 2.1 

 Unconsolidated Shore 19.3 

 (22.7) 

Georges Estuarine Reef 3.1 

 Unconsolidated Shore 8.1 

 Marine Reef 9.5 

 (20.7) 

Grape Estuarine Emergent 9.9 

 Reef 15.8 

 Unconsolidated Shore 22.3 

 (48.0) 

Great Brewster Marine Aquatic Bed 5.9 

 Rocky Shore 4.6 

 Unconsolidated Shore 49.6 

 Palustrine Emergent 0.4 

 (60.5) 

Green Marine Aquatic Bed 13.7 

 Rocky Shore 2.9 

 (16.6) 

Hangman Estuarine Aquatic Bed 2.1 

 Emergent 0.4 

 Unconsolidated Shore 1.6 

 (4.1) 

Langlee Estuarine Rocky Shore 2.2 

 Unconsolidated Shore 4.9 

 (7.1) 

Little Brewster Marine Reef 7.5 

 Rocky Shore 3.0 

 Unconsolidated Shore 0.9 

 (11.4) 

Little Calf Marine Aquatic Bed 4.7 

 (4.7) 
 14 

Table 3 (continued). 

Long Estuarine Rocky Shore 23.2 

 Unconsolidated Shore 88.8 

 Palustrine Emergent 3.0 

 Unconsolidated Bottom 0.7 

 (115.7) 

Lovells Estuarine Emergent 1.1 

 Reef 20.5 

 Unconsolidated Shore 8.7 

 Marine Aquatic Bed 9.4 

 Reef 9.4 

 Unconsolidated Shore 30.9 

 Palustrine Emergent 0.2 

 (80.2) 

Middle Brewster Marine Aquatic Bed 6.3 

 Rocky Shore 7.0 

 Palustrine Emergent 0.1 

 (13.4) 

Moon Estuarine Aquatic Bed 1.6 

 Unconsolidated Shore 24.6 

 Palustrine Unconsolidated Shore 9.9 

 (36.1) 

Nixes Mate Estuarine Unconsolidated Shore 11.5 

 (11.5) 

Nut Estuarine Rocky Shore 5.3 

 Unconsolidated Shore 13.2 

 (18.5) 

Outer Brewster Marine Aquatic Bed 11.0 

Rocky Shore 8.8 

 (19.8) 

Peddocks Estuarine Emergent 19.1 

Reef 16.3 

Rocky Shore 6.7 

Unconsolidated Shore 75.4 

(117.5) 

Raccoon Estuarine Aquatic Bed 2.9 

Emergent 2.4 

Unconsolidated Shore 1.2 

(6.5) 

Ragged Estuarine Aquatic Bed 0.6 

Unconsolidated Shore 7.9 

(8.5) 

Rainsford Estuarine Aquatic Bed 2.3 

Rocky Shore 4.9 

Unconsolidated Shore 20.5 

(27.7) 

Sarah Estuarine Aquatic Bed 8.1 

 (8.1) 

Shag Rocks Marine Aquatic Bed 8.2 

 (8.2) 

Sheep Estuarine Aquatic Bed 4.1 

Emergent 1.1 

Unconsolidated Shore 6.7 

(11.9) 
 15 

Table 3 (continued). 

Slate Estuarine Aquatic Bed 13.9 

Reef 4.9 

Unconsolidated Shore 6.0 

(24.8) 

Snake Estuarine Aquatic Bed 5.1 

Emergent 13.4 

Unconsolidated Shore 62.4 

(80.9) 

Spectacle Estuarine Rocky Shore 0.8 

 Unconsolidated Shore 39.8 

 (40.6) 

The Graves Marine Aquatic Bed 3.7 

 (3.7) 

Thompson Estuarine Emergent 19.4 

 Rocky Shore 2.9 

 Unconsolidated Shore 187.2 

 Palustrine Emergent 1.0 

 (210.5) 

Worlds End Estuarine Emergent 12.2 

 Unconsolidated Shore 71.2 

 Palustrine Emergent 1.2 

 Forested 1.0 

 Scrub-shrub 0.8 

 Unconsolidated Bottom 12.5 

 (98.9) 
 16 

Table 4. Wetlands of the Boston Harbor Islands NRA classified by landscape position, 

landform, and water flow path according to Tiner (2000). 

Landscape Position Landform Water Flow Path Acreage

Estuarine Fringe Bidirectional-tidal 951.8 

 Island Bidirectional-tidal 12.4 

Marine Fringe Bidirectional-tidal 266.0 

 Island Bidirectional-tidal 14.9 

Terrene Basin* Isolated 30.7 

------------------- 

*Includes 23.0 acres of ponds. 

 
 17 

Figure 4. Wetlands classified by landscape position and landform (Tiner 2000). 

(Click here for image) 
 18 

Wetland Communities 

As mentioned earlier, most of the wetlands are intertidal flats (including narrow beaches) 

composed of unconsolidated substrates exposed at low and extreme low tide (Figure 5). 

Mussel reefs dominated by blue mussel (Mytilus edulis) are also prominent in the lower 

intertidal zone (Figures 6 and 7). Rocky shores may be devoid of vegetation or covered 

by brown macroalgae (Ascophyllum nodosum and Fucus spp.) (Figure 8). 

Most of the vegetated wetlands are estuarine emergent wetlands (Figures 9-13). These 

wetlands are dominated by halophytes (salt-tolerant plants). Smooth cordgrass (Spartina

alterniflora) forms nearly pure stands in the low marsh (the regularly flooded zone - 

subject to daily tidal inundation). A short form of this species along with other 

halophytes typify the high marsh (the irregularly flooded zone - flooding less often than 

daily). The more abundant high marsh species include low-growing plants such as salt 

hay grass (Spartina patens) and salt grass (Distichlis spicata), while a tall grass, common 

reed (Phragmites australis) is also common, especially along the upland border and in 

more brackish conditions. See Tiner (1987) for descriptions and illustrations of tidal 

wetland flora common to the northeastern United States. One freshwater marsh observed 

on Thompson Island was dominated by a millet grass (Echinochloa sp.) with several 

other species present including two invasive plants - purple loosestrife (Lythrum

salicaria) and common reed (Figure 14). 

Table 5 presents a few examples of Boston Harbor Islands NRA wetland plant 

communities based on our limited field work. See Bell et al. (2002) for detailed 

descriptions of intertidal communities and their biota. 

Figure 5. Tidal flat and beach (estuarine unconsolidated shore) exposed at low tide on 

Langlee Island. (photo: Sherman Morss, Jr.) 
 19 

Figure 6. Mussel reef in Boston Harbor. (R. Tiner photo) 

Figure 7. Close-up of mussel reef. (R. Tiner photo) 

Figure 8. Vegetated rocky shore at Calf Island. (photo: Sherman Morss, Jr.) 
 20 

Figure 9. Salt marsh on Thompson Island. (R. Tiner photo) 

Figure 10. Salt marsh on Grape Island with mussel reef in foreground. (R. Tiner photo) 

Figure 11. Salt marsh on Peddocks Island. (photo: Sherman Morss, Jr.) 
 21 

Figure 12. Salt marsh on Ragged Island. (photo: Sherman Morss, Jr.) 

Figure 13. Oligohaline marsh on Grape Island. (R. Tiner photo) 

Figure 14. Freshwater marsh (palustrine emergent wetland) on Thompson Island. 

(R. Tiner photo) 
 22 

Table 5. Examples of wetland plant communities in the Boston Harbor Islands NRA. 

Wetland Type 

(Location) Dominant Species Associated Species

Estuarine Emergent Spartina patens- Limonium sp., Suaeda sp., Salicornia sp., 

(Thompson Island) S. alterniflora S. alterniflora (tall form), Solidago 

 (short form) sempervirens, Atriplex patula 

Estuarine Emergent S. alterniflora Distichlis spicata, S. patens, P. australis, 

(Thompson Island) Salicornia europaea, S. sempervirens, A. patula, 

Limonium sp. 

Estuarine Emergent S. alterniflora D. spicata, P. australis, S. sempervirens, 

(Peddocks Island) A. patula, Iva frutescens, Limonium sp., 

Typha angustifolia, Juncus gerardii, Scirpus 

robustus, Calystegia sepium, Scirpus pungens, 

Puccinellia sp., Agropyron repens, S. patens

Estuarine Emergent S. patens-D. spicata (on edge) P. australis, Epilobium sp., Galium sp., 

(Grape Island) S. sempervirens, Eupatorium serotinum, Circium 

canadense, Lythrum salicaria, Agrostis sp., Rubus sp. 

Estuarine Emergent P. australis S. pungens, Lythrum salicaria, S. robustus, Verbena

Oligohaline hastata, Galium sp., S. patens, Scirpus cyperinus, 

(Grape Island) Epilobium sp., Agrostis palustris, Onoclea sensibilis, 

C. canadense Note: This slightly brackish 

(oligohaline) wetland is inundated by salt water 

during overwash events. 

Palustrine Emergent Echinochloa sp. L. salicaria, Eleocharis sp., Panicum rigidulum, 

Seasonally Flooded P. australis, S. robustus, Polygonum pensylvanicum, 

(Thompson Island) V. hastata, Erechtites hieracifolia, Cyperus sp., 

C. sepium, T. angustifolia 
 23 

Preliminary Assessment of Wetland Functions 

Since most of the wetlands are estuarine wetlands, the preliminary assessment of wetland 

functions is not as interesting as it would be if the wetland diversity was greater. Table 6 

summarizes the results by function. Given that the Boston Harbor Islands NRA wetlands 

are mostly estuarine and marine intertidal marshes, rocky shores, and tidal flats 

(including intertidal mussel reefs), it is not surprising that most of the wetlands in this 

area are significant for surface water detention, retention of sediments, coastal storm 

surge detention and shoreline stabilization, provision of fish and shellfish habitat, and 

provision of waterfowl and waterbird habitat. Vegetated wetlands represented only a two 

percent of the wetlands, hence the low percent of wetlands that was identified as 

significant for nutrient transformation and other wildlife habitat. 

Table 6. Wetlands of potential significance for performing various functions in the 

Boston Harbor Islands NRA. Note: None of the islands had any streams, therefore no 

wetlands were significant for this streamflow maintenance. 

 Predicted Level Wetland Percent of Wetland 

Function of Significance Acres Acreage in BHINRA 

Surface Water Detention High 1,245.1 98% 

 Moderate 30.7 2% 

Nutrient Transformation High 210.1 16% 

Retention of Sediments High 881.0 69% 

 Moderate 311.6 22% 

Coastal Storm Surge 

 Detention/Shoreline 

 Stabilization High 1,217.8 95% 

Provision of Fish and 

 Shellfish Habitat High 1,245.1 98% 

 Moderate 13.2 1% 

Provision of Waterfowl 

 and Waterbird Habitat High 1,075.1 84% 

 Moderate 14.4 1% 

Provision of Other 

 Wildlife Habitat High 0 0% 

 Moderate 89.6 7% 

 
 24 

Summary

A total of 1,276 acres of wetlands were inventoried for the Boston Harbor Islands NRA. 

These wetlands were dominated by marine and estuarine intertidal types, mostly 

nonvegetated unconsolidated shores (i.e., tidal flats). Only 82 acres of estuarine 

vegetated wetlands (i.e., salt/brackish marshes) were inventoried, while 87 acres of 

intertidal blue mussel reefs were surveyed. Freshwater wetlands were extremely limited 

on the islands, with only 31 acres mapped. Most of these wetlands were small ponds. 

The Boston Harbor Islands NRA wetlands were predicted to perform numerous 

functions, with most of the wetlands designated as potentially significant for surface 

water detention, sediment retention, coastal storm surge detention and shoreline 

stabilization, fish and shellfish habitat, and waterfowl and waterbird habitat. 
 25 

Acknowledgments 

Funding for this project was provided by the National Park Service (NPS). Norm Farris 

served as project officer for the NPS. Ralph Tiner was principal investigator for the U.S. 

Fish and Wildlife Service (FWS) and was responsible for study design, data analysis, and 

report preparation. Wetland photointerpretation was performed by John Swords (FWS). 

The National Wetlands Inventory Center (St. Petersburg, FL) provided quality control of 

draft inventory products to insure national consistency. Herb Bergquist (FWS) classified 

wetlands according to hydrogeomorphic properties, performed GIS analyses, generated 

statistics for tables, and created figures for this report. Charles Roman and Norm Farris 

(NPS) assisted in field work along with Rick Bell (New England Aquarium) who also 

provided data from his field investigations of intertidal wetlands. Sherman Morss Jr. 

gratuitously permitted use of his photographs for this report. Deb DiQuinzio and Mary 

Raczko (NPS) provided information on official park boundaries and island names. 

 
 26 

References 

Bell, R. M. Chandler, R. Buchsbaum, and C. Roman. 2002. Boston Harbor Islands 

Intertidal Biotic Overview and Assessment. National Park Service, Boston, MA. 

Cowardin, L.M., V. Carter, F.C. Golet, and E.T. LaRoe. 1979. Classification of 

Wetlands and Deepwater Habitats of the United States. U.S. Fish and Widlife Service, 

Washington, DC. FWS/OBS-79/31. 

Tiner, R.W. 2000. Keys to Waterbody Type and Hydrogeomorphic-type Wetland 

Descriptors for U.S. Waters and Wetlands (Operational Draft). U.S. Fish and Wildlife 

Service, Region 5, Hadley, MA. 

Tiner, R.W. 1999. Wetland Indicators: A Guide to Wetland Identification, Delineation, 

Classification, and Mapping. Lewis Publishers, CRC Press, Boca Raton, FL. 

Tiner, R.W. 1990. Use of high-altitude aerial photography for inventorying forested 

wetlands in the United States. For. Ecol. Manage. 33/34: 593-604. 

Tiner, R.W. 1987. A Field Guide to Coastal Wetland Plants of the Northeastern United 

States. University of Massachusetts Press, Amherst, MA. 

Tiner, R., M. Starr, H. Bergquist, and J. Swords. 2000. Watershed-based Wetland 

Characterization for Maryland's Nanticoke River and Coastal Bays Watersheds: A 

Preliminary Assessment Report. U.S. Fish and Wildlife Service, National Wetlands 

Inventory (NWI) Program, Northeast Region, Hadley, MA. NWI technical report (posted 

on the web at: http://wetlands.fws.gov). 

Tiner, R. S. Schaller, D. Petersen, K. Snider, K. Ruhlman, and J. Swords. 1999. Wetland 

Characterization Study and Preliminary Assessment of Wetland Functions for the Casco 

Bay Watershed, Southern Maine. U.S. Fish and Wildlife Service, National Wetlands 

Inventory (NWI) Program, Northeast Region, Hadley, MA. NWI technical report. 
 

Appendices 
 

Appendix A. Legend for wetland and deepwater habitat classification following Cowardin et al. 1979. 

(Click here for image) 
 

Appendix B. Extent of wetlands and deepwater habitats in and around the Boston Harbor 

Islands NRA based on an update of seven NWI maps in this locale. 

Ecological System Aquatic Habitat Acreage 

Estuarine Deepwater Habitat 24,771.0 

Aquatic Bed 433.2 

Emergent Wetland 3,868.0 

Mussel Reef 62.2 

Rocky Shore 53.8 

Scrub-Shrub Wetland 6.9 

Unconsolidated Shore 4,656.2 

Lacustrine Deepwater Habitat 2,747.8 

 Unconsolidated Shore 0.2 

Marine Aquatic Bed 1,155.0 

 Deepwater Habitat 59,852.0 

 Mussel Reef 26.4 

 Rocky Shore 121.2 

 Unconsolidated Shore 1,791.0 

Palustrine Aquatic Bed 0.4 

Emergent Wetland 919.3 

 Forested Wetland 8,203.5 

 Scrub-Shrub Wetland 1,032.1 

 Unconsolidated Bottom 764.0 

 Unconsolidated Shore 10.1 

Riverine Perennial Deepwater Habitat 755.4 

 Intermittent Streambed 59.9