Salt marshes are vegetated coastal wetlands that are the subject of regular tidal inundation (Mitsch and Gosselink, 2000). They are typically found in low energy areas within embayments or along protected coasts. The protected nature of salt marsh systems allow for the trapping and accumulation of sediment by salt marsh vegetation. Sources of sediment include upstream runoff and coastal erosion. Salt marsh vegetation is organized along a gradient depending on species tolerance for saline and anoxic conditions (Mitsch and Gosselink, 2000). The low marsh, which receives tidal flow twice daily, is generally dominated by salt marsh cord grass (Spartina alterniflora). The high marsh, which receives less regular tidal influence, is comprised of a variety of species including salt marsh hay (Spartina patens), black grass (Juncus gerardii), and spike grass (Distichlis spicata) (Nixon, 1982; Bertness, 1991). Salt pannes, pools and tidal creeks may also characterize salt marsh habitats. Salt pannes are bare, exposed, or water-filled depressions in a salt marsh (Mitsch and Gosselink, 2000).
|Figure 1: Salt marsh on Thompson Island|
Salt marshes are one of the most productive ecosystems on earth. As such, they provide real and measurable environmental, social, and economic benefits. Salt marshes act as nurseries for commercially and recreationally important shell and fin fisheries (Cruz, 1973); provide habitat and food sources for birds and other wildlife; protect coastal areas from flooding and storm surges; and provide educational and recreational opportunities. Salt marshes also play a role in estuarine health by aiding in nutrient attenuation and cycling (Welsh, 1980); water quality improvement; shoreline stabilization; and mitigation for climate change and sea level rise (Gulf of Maine Council, 2008). Especially in urban areas where stormwater runoff can have high concentrations of pollutants and nutrients, salt marshes, like those found in the Boston Harbor region, absorb nutrients as they enter the estuary. These urban oases also offer critical refuges for humans and animals.
Salt marsh habitats may play a critical role in protecting coastal areas from the potential impacts of sea level rise. If able to migrate and adapt unimpeded, salt marshes may lessen the adverse impacts associated with sea level rise including increases in coastal flooding, storm surges, and erosion. As sea levels rise, a healthy salt marsh is more likely to capture sediment and keep pace with sea level rise. However, salt marshes that are degraded either with invasive species, a history of ditching, or have been cut off from sediment sources and natural tidal flows, may not be able to effectively respond to sea level rise (Kennish, 2001). Additionally, where hardened structures are built to the salt marsh edge, the salt marsh does not have the space available to migrate inland as sea levels rise. In situations where salt marshes are degraded or lack the space to migrate landward, the ecosystem functions they provide including protection against sea level rise can be greatly diminished or lost (Gulf of Maine Council, 2008).
Salt marshes are found in low energy waters along coasts, embayments, and rivers where tidal influence is present. Because salt marsh species require tidal inundation but cannot survive if constantly submerged, the seaward edge of salt marshes is marked by the low tide line and on the landward edge by the highest high tide line. Salt marsh habitats are found in highly specific ecological locations, thus their geographical extent can be diminished by coastal development, changes in sediment transport, poor water quality, and sea level rise.
Historically, salt marshes ringed the Boston Harbor region and extended well into the Saugus, Mystic, Charles, and Neponset Rivers (Carlisle et al., 2005). Now only a fraction of those historic marshes remain. It is estimated that salt marsh loss in the Boston Harbor region is close to 81% since pre-colonial times. This loss is largely due to placement of fill but is also a result of salt marsh ditching and the restriction of adequate tidal inundation (Reiner, 2011).
Figure 2: Historic USGS topographic map (c. 1900) overlayed with the current extent
of salt marsh in Rumney Marshes (MassDEP wetlands datalayer)(2009)
In 2006, the Office of Coastal Zone Management (CZM) with the US Fish and Wildlife Service and the University of Massachusetts described the changes in estuarine marsh over time by comparing maps and aerial photography of Boston Harbor from four time periods (1893, 1952, 1971, and 1995). The study showed great loss in estuarine marsh between 1893 and 1952 and between 1952 and 1971 (Carlisle et al., 2005). The periods of salt marsh loss coincide with population booms and city expansion. Estuarine marsh acreage has continued to decrease since 1971 but at a slower rate. The EPA performed a similar analysis of salt marsh loss focusing on the Rumney Marshes in Revere and Saugus. The EPA study showed a 40% loss in the Rumney Marshes salt marsh extent since 1800 (Carlisle et al., 2005).
Figure 3: Current extent of salt marsh in Boston Harbor Region (MassDEP 2009)
The integrity of our nation's coastal ecosystems is exposed to many threats, many of which are associated with their close proximity to population centers and development. In a national study, NOAA reported that 53 percent of the US population lives in coastal counties, but these coastal counties make up only 17 percent of the country's land area (excluding Alaska)(Crossett et al., 2004). Impacts from coastal development on salt marshes include an increase in nutrient runoff and invasive species, a lack of sufficient tidal flow, and the loss of salt marsh due to filling. This national picture is reflected in the Boston Harbor region as much of its salt marsh is degraded.
The degradation of salt marshes by human impacts comes in various forms. Although illegal now, historically, salt marshes were filled to form upland. Filling is largely attributed to the dramatic loss of salt marsh in the Boston Harbor region (Bromberg and Bertness, 2005). Historically, salt marshes were also drained or diked to create farmland. Present day causes of salt marsh loss are most commonly due to indirect impacts of coastal development. Undersized culverts installed beneath roads and railways restrict natural tidal hydrology. The lack of natural tidal hydrology can lead to degraded systems that are more susceptible to colonization by invasive species such as perennial pepperweed (Lepidium latifolium) and common reed (Phragmites australis). Also the encroachment of development abutting salt marshes can cause an unnatural and unsustainable input of freshwater runoff, nutrients, sediments, and toxins degrading the system. Freshwater runoff will lower the salinity of the system allowing for the potential colonization of invasive species while an increase in nutrient inputs can adversely affect the health of wildlife in the marsh (Gulf of Maine, 2008).
As documented by a number of studies, the condition of salt marshes in the Boston Harbor region suffers many of these fates. In the Atlases of Tidal Restrictions for the North and South Shores, CZM identified and prioritized salt marshes which were cut off from tidal flow. These salt marshes do not receive adequate tidal flushing due to under sized or absent culverts. The Atlases identify a total of 72 salt marshes in the Boston Harbor region, which are degraded due to lack of sufficient tidal flow. The University of Massachusetts also assessed salt marsh condition through an ecosystem based approach that assessed the ecological integrity of lands and waters in the state under the Conservation and Assessment Prioritization System (CAPS) project. CAPS developed an Index of Ecological Integrity (IEI) to identify and prioritize areas for land and habitat conservation efforts. Ecological integrity is defined as the ability of an area to support biodiversity and the ecosystem processes necessary to sustain biodiversity over the long term (UMass Amherst CAPS website). Maps depicting the IEI for the Boston Harbor region show areas of relatively higher ecological integrity associated with some of the Boston Harbor Islands, at the mouth of the Neponset, Fore, and Back Rivers and in portions of Rumney and Belle Isle Marshes. However, as a whole the Boston region has a lower IEI than many other coastal areas of the state including the Upper North Shore, Cape Ann and much of Cape Cod. Maps depicting IEI by town may be found at the bottom of the CAPS website. It is no surprise that these assessments depict salt marsh habitat within the Boston Harbor region as degraded and with a relatively low ecological value.
Protection and Restoration Potential
The dramatic loss of salt marsh in the Boston Harbor region is an indicator of restoration potential. Some of the historically filled marshes may be candidates for fill removal restoration projects. Other restoration opportunities lie in the replacement of undersized culverts and water conduits where development crisscrosses marshes without providing adequate hydrologic connections to the ocean. The presence of invasive species also creates an opportunity for salt marsh restoration since invasive plants such as perennial pepperweed and common reed significantly alter the functional value of salt marsh habitat. There also may be the opportunity to protect upland buffers between coastal development and salt marshes so that these systems may migrate landward with sea level rise (Gulf of Maine, 2008).
Federal, state, local, and non-profit organizations are actively involved in salt marsh restoration in Massachusetts. Consequently, there is a great wealth of restoration plans from which to draw for assessing restoration opportunities. Salt marsh restoration planning in the Boston Harbor region includes the development of site-specific restoration plans, the identification of tidally restricted marshes, and the assessment of ecosystems for restoration opportunities. Salt marsh restoration projects identified include the removal of fill, the reintroduction or increase of tidal flow, or the removal of invasive species. Examples of agencies or planning documents that identify salt marsh areas restoration opportunities in the Boston Harbor Region are listed below. These reports can also be viewed in the Boston Harbor Habitat Atlas map viewer.
- North Shore Atlas of Tidally Restricted Marshes (1996)
This Atlas identifies salt marshes on the North Shore that do not receive adequate tidal flow due to the undersizing or absence of culverts. The North Shore Atlas was the first of the Tidal Restriction Atlases created for the Massachusetts coast. The methodology was improved upon for the other Atlases.
- Restoring Wetlands of the Neponset River Watershed – A Watershed Wetlands Restoration Plan (2000)
This restoration plan is one of the oldest in the Boston Harbor region and is the only one that focuses on the Neponset River ACEC. The document serves as a good starting point for selecting restoration opportunities in this watershed.
- South Shore Atlas of Tidally Restricted Marshes (2001)
This Atlas identifies 30 salt marshes on the South Shore and within the Boston Harbor region, which do not receive adequate tidal hydrology due to the undersizing or absence of culverts.
- Rumney Marshes Area of Critical Environmental Concern Restoration Plan (2002)
This restoration plan identifies and provides basic information on approximately 30 restoration projects within the Rumney and Belle Isle Marshes. The projects are not prioritized or ranked.
- EPA's Rumney Marshes identified restoration areas
This geospatial compilation by EPA Region 1's Wetland Division identifies salt marsh restoration opportunities within the Rumney Marsh system. The data calls out fill removal areas and poorly functioning tide gates as well as areas of historic fill, completed projects, and completed projects which need additional attention. The data serves as the most current restoration information available for the Rumney Marsh ecosystem. The data will be available in the Atlas map viewer soon.
- NOAA's Restoration Atlas
The NOAA Restoration Atlas identifies seven projects within the Boston Harbor region. The Atlas displays information relating to project status, acreage, partners, funding and timeline.
- Division of Ecological Restoration's Active Habitat Restoration Priority Projects list
DER's Priority Project list currently includes six projects in the Boston Harbor region. This list of projects is the result of a peer reviewed process. Project proponents submit proposals which are evaluated based on a series of criteria including the project's public and ecological benefit, clarity of goals, level of support, cost, and size, among others.
- Logan Airport Runway Safety Area Improvement Project FEIR (2011)
The process of selecting salt marsh mitigation for the Logan Airport Runway improvements serves as the most recent survey of salt marsh restoration opportunities in the region. However, criteria such as size and land ownership used to choose the final mitigation may have eliminated viable restoration opportunities.
|Figure 4: Salt marsh restoration sites selected for Logan Runway Safety Area Improvement Project|
The most recent review of salt marsh restoration opportunities in the Boston Harbor region was associated with the mitigation study for the Logan Runway Safety Area Improvement Project. Restoration opportunities were sought because this project required mitigation for impacts to salt marsh. The initiative surveyed existing restoration plans, including those listed here, to find sites that matched the mitigation criteria (i.e., sites must be greater than 1 acre). The project identified 40 sites in the Boston Harbor Region that fit the specific criteria. Two sites were ultimately chosen as mitigation for the Logan Airport project, the other potential mitigation sites identified represent opportunities for restoration that have gone through some vetting by the salt marsh restoration community.
Protection and restoration opportunities in the Boston Harbor region include a range project types. For a habitat which already boasts a long list of restoration partners in the Boston Harbor region, the protection and restoration opportunities identified here seek to support and coordinate with the existing initiatives by others.
- Review existing restoration plans. As noted above there are many planning documents which identify salt marsh restoration opportunities for the Boston Harbor region. However, these plans were created across many years, for different entities and with differing purposes. A formal and systematic review of these plans would allow for a true comparison of the opportunities. A proposal will be developed for a comprehensive survey of the restoration opportunities. The survey will evaluate restoration projects based on criteria including restoration acreage, complexity, and cost. Rapid site assessments performed on a subset of the sites will provide the basis for a prioritization of restoration opportunities in the region.
Investigate the strategic and prioritized removal of the I-95 berm. The I-95 berm, which crosses Rumney Marsh, represents the largest opportunity for fill removal restoration in the Boston Harbor region in terms of restored acreage and habitat function. The long-term goal is to maximize the removal of the berm thereby allowing for salt marsh restoration. A management plan that addresses the many competing uses of the berm for salt marsh restoration, flood control, passive and active recreation, visual barrier, and source of beach nourishment will be developed.
Identify local projects. Through engaging local planning departments, watershed associations, Departments of Public Works (DPW) and Conservation Commissions, smaller salt marsh restoration projects may be identified. These opportunities could include restoration of smaller salt marshes (i.e. Belle Isle Marsh) or working with DPWs to reduce direct and indirect (i.e., stormwater runoff) impacts when planning for road repairs, culvert replacement, and other maintenance activities.
Protect salt marsh for sea level rise. Recent studies have assessed the potential impacts of sea level rise in the Boston Harbor region (e.g. The Boston Harbor Association). Because salt marsh habitat provides a critical buffer between ocean and upland areas, understanding the ability of salt marsh habitat to migrate as sea level rises would be valuable. Existing sea level rise studies will be compared with mapped salt marsh areas to identify locations where salt marsh migration may be possible. These areas may then be evaluated for conservation, protection from development, and restoration or enhancement opportunities.
Bertness, M.D. 1991. Zonation of Spartina patens and Spartina alterniflora in a New England Salt Marsh. Ecology 72: 138-148.
Carlisle, B.K., R.W. Tiner, M. Carullo, I.K. Huber, T. Nuerminger, C. Polzen, and M. Shaffer. 2005. 100 Years of Estuarine Marsh Trends in Massachusetts (1893 to 1995): Boston Harbor, Cape Cod, Nantucket, Martha's Vineyard, and the Elizabeth Islands. Massachusetts Office of Coastal Zone Management, Boston, MA; U.S. Fish and Wildlife Service, Hadley, MA; and University of Massachusetts, Amherst, MA. Cooperative Report.
Crossett, Kristen, M., Culliton, Thomas, J., Wiley, Peter, C., and Timothy R. Goodspeed. 2004. Population Trends Along the Coastal United States: 1980 - 2008. National Oceanic and Atmospheric Administration.
Cruz, A. A. de la. The role of tidal marshes in the productivity of coastal waters. Bulletin of the Association of Southeast Biology 20: 147-156.
Final Environmental Assessment/Environmental Impact Report for Boston-Logan International Airport Runway Safety Area Improvements Project. Prepared for the Massachusetts Port Authority. Prepared by Vanasse Hangen Brustlin, Inc. January 2011. http://www.massport.com/environment/environmental_reporting/Documents/Environmental%20Filings/
2011_LoganRSA_EAEIR.pdf. Last viewed on 12/30/2011.
Gulf of Maine Council. 2008. Salt marshed in the Gulf of Maine - human impacts, habitat restoration, and long-term change analysis. http://www.gulfofmaine.org/saltmarsh/ Last viewed on 5/9/2012.
Kennish, Michael, J. 2001. Coastal salt marsh systems in the U.S.: A review of anthropogenic impacts. Journal of Coastal Research. Vol.17. No.3. 731-748.
Mitsch, William J. and James G. Gosselink. Wetlands. 3rd ed. New York: John Wiley & Sons, Inc., 2000.
Massachusetts Division of Ecological Restoration Active Habitat Restoration Priority Projects. http://www.mass.gov/dfwele/der/der_maps/pp_map.htm. Last viewed on 12/14/2011.
National Oceanic and Atmospheric Administration Restoration Atlas. http://seahorse2.nmfs.noaa.gov/restoration_atlas/src/html/index.html. Last viewed on 12/30/2011.
Nixon, S. W. 1982. The ecology of New England high salt marshes: A community profile. United States Department of the Interior, Washington, D.C., U.S.A.
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University of Massachusetts Amherst Conservation and Assessment System (CAPS). http://www.umasscaps.org/data_maps/maps.html. Last viewed on 5/24/2012. Welsh, Barbara. 1980 Comparative nutrient dynamics of a marsh-mudflat ecosystem. Estuarine Coastal Marine Science. Vol. 10 Issue 2: 143-164.