Scarborough Marsh, approximately 3,000 acres in size, is Maine’s largest and best known salt marsh. It is owned and managed by the Maine Department of Inland Fisheries and Wildlife. This report summarizes the results of a study of the Scarborough Marsh ecosystem conducted in 1998 and managed by the Maine Audubon Society. The goals of the study were to raise citizen awareness of threats facing tidal marshes and increase local grassroots support for tidal marsh conservation and restoration; collect baseline data on tidal restrictions and invasive plants in Scarborough Marsh for use by cooperating agencies and organizations; and prioritize restoration opportunities within the Scarborough Marsh estuary. Maine Audubon trained a group of volunteers to gather field data on tidal restrictions, tidal elevations, salinity, and invasive plants, provided the technical expertise and logistical support for the project, and prepared this final report.

Scarborough Marsh is a back-barrier salt marsh, formed behind the protective barrier beach at Pine Point and the more stable Prouts Neck. These barriers provide the sheltered conditions necessary for fine sediments to be deposited and salt marsh plants to become established in the intertidal zone. The salinity ranges from that of seawater in sections of the marsh near the mouth of the Scarborough River to brackish and fresh water at the most inland reaches of the marsh. Salt Marsh Hay and other typical salt marsh plants are found throughout most of the marsh, with species that are more adapted to the brackish conditions such as Narrow-leaf Cattail found well away from the river mouth where freshwater influence is stronger. As salt marshes develop over time, they build up a thick layer of peat (15 feet is not uncommon) as dead marsh vegetation and sediments brought in by the tides are deposited in a process known as accretion. In this fashion, tidal marshes have been able to keep pace with the gradual rise in sea level over the last 5,000 years. Scarborough Marsh provides unique wildlife habitat for a great variety of plants and animals, offers important opportunities for hunting, fishing, boating and nature study, and surrounds tidal flats with commercially-important shellfish beds.

Human activities have significantly altered Scarborough Marsh and other tidal marshes in the Gulf of Maine. The most significant threat continues to be roads and railroads that cross the marsh and form barriers to the free flow of tidal water. These barriers limit the amount of water reaching the inner marsh, and hence the salinity and amount of sediment available for marsh accretion. The worst type of tidal restriction is the tide gate, which is designed to prevent salt water from reaching sections of the marsh. This type of restriction will cause the marsh to decompose as it becomes less saline, resulting in a lower surface elevation on the inland side of the restriction. If the marsh surface subsides more than a few inches it becomes impossible to fully restore the native plant community that existed prior to the restriction. The spread of invasive plants such as Common Reed (Phragmites australis), often abetted by tidal restrictions, also is a threat to the ecological integrity of the marsh. Past ditching for agriculture or mosquito control and direct fill of the marsh also add to the cumulative impacts to the marsh, while ongoing development in the surrounding uplands affects water quality and wildlife habitat. All these factors have adversely affected Scarborough Marsh.

Fourteen tidal restrictions were evaluated during the study (Figure 3 and Table 1). An initial assessment and additional field studies found that five restrictions currently have or have had a significant impact on sections of the marsh system. These include Pine Point Road where it crosses Jones Creek, the Eastern Road, a low steel dam where Blue Point Road crosses Cascade Brook, Route 1, and the Black Point Road where it crosses the Libby River.

Jones Creek. Most of the drainage from the east-coastal section of Old Orchard Beach has been diverted into Jones Creek and hence into the Scarborough River. A tide gate located on Jones Creek was removed approximately 10-15 years ago, but a significant restriction still exists at this point. Some of the Jones Creek marsh has since reverted to salt-tolerant vegetation, but tidal flushing is poor and freshwater plants continue to occupy a significant portion of the marsh. Two large Phragmites stands totaling approximately 8 acres are found in this marsh.

Eastern Road. A tidal restriction has existed here since a railroad was built in the 1840’s. A tide gate existed here for about 60 years until the 1940’s or 1950’s. Our study found that the tidal marsh peat subsided approximately 6 inches during the period the tide gate was in place. As a result, the vegetation, while consisting of native salt marsh plants, is significantly different from the natural high marsh community immediately seaward of the road. While our measurements indicate that the Eastern Road is a minor impediment to tidal flow, the tide gate made a permanent change in the marsh above this point.

Cascade Brook, Blue Point Road. A low steel dam installed by the Maine Department of Inland Fisheries and Wildlife to provide more freshwater habitat has significantly altered several acres of salt marsh. Salt-tolerant vegetation is limited to a small length of stream channel above this point. Several stands of Phragmites are located just seaward of this restriction.

Dunstan River, Route 1. Almost half the Phragmites in the marsh system is located in this area. Earlier studies have shown that its growth has been very rapid, with the result that open marsh habitat favored by waterfowl and wading birds is being lost. Phragmites is now spreading on the seaward side of Route 1. Our study found a significant difference in marsh elevation, salinity, and plant communities on opposite sides of the highway as one moves away from the immediate vicinity of the Dunstan River and toward the edge of the marsh. While the culverts under Route 1 allow fair tidal exchange, strong freshwater influence and possibly runoff from developed areas may also encourage the rapid spread of Phragmites.

Libby River, Black Point Road. The culvert width where the Libby River crosses under Black Point Road is only 18% of the river width, the lowest percentage of any restriction in the Scarborough Marsh system. An earlier study found significant differences in salinity, vegetation, and marsh elevation between the inland and seaward side of the restriction. One stand of Phragmites is located just upstream of the restriction.

Maine Audubon makes the following recommendations for restoration and further monitoring of Scarborough Marsh.

1. Control Phragmites in the vicinity of Route 1. Our study confirms that this is the highest restoration priority within the marsh system. The study results suggest that a restoration plan encompassing multiple elements, including additional culverts, ditches to improve tidal flushing, and if necessary, control in nitrates entering the watershed may be necessary. The Maine Department of Inland Fisheries and the National Atmospheric and Oceanic Administration have begun to investigate the feasibility of restoring this site.
   
2. Restore Jones Creek Marsh. Tidal flows to this marsh might be significantly improved by cutting a new channel that would cross Pine Point Road about 0.3 miles south of the current culvert. This could result in restoration of about 75 acres of tidal marsh south and east of the Boston and Maine Railroad, including over 30 acres of former salt marsh that is now freshwater wetland and enhancement of approximately 40 acres of existing salt marsh with improved tidal flushing. Additional restoration may be possible beyond the railroad. The Maine Department of Fisheries and Wildlife could partner with the US Fish and Wildlife Service, the Maine Department of Transportation, and other potential cooperators on a restoration effort at this site.
   
3. Improve tidal flow under Black Point Road at the Libby River. Placing additional culverts in the river channel at this point would restore tidal flows, possibly reducing or eliminating Phragmites just inland of the road and allowing salt marsh vegetation to replace brackish-marsh vegetation further inland. The Maine Department of Inland Fisheries and Wildlife, US Fish and Wildlife Service, and the Maine Department of Transportation could coordinate this restoration project.
   
4. Continue to monitor Phragmites growth. Evidence suggests that Phragmites was almost non-existent in the marsh 25 years ago but that it is now spreading rapidly. We recommend a volunteer-based monitoring project that would a) monitor the spread of selected Phragmites stands and b) repeat the marsh-wide Phragmites assessment summarized in Section IV after 5 years (in 2003) to see if new stands have appeared or existing stands have significantly increased in size. A local watershed group (see Recommendation 5) could coordinate the monitoring.
   
5. Establish a Scarborough River Watershed Association. Ultimately, maintaining and restoring the ecological integrity of the marsh will require a broad watershed-based constituency and an organization that can help build on and integrate the work of individuals, committees, and organizations with various interests in marsh conservation. While this study is the first to systematically evaluate the entire marsh system, it is still limited in scope and there is much follow-up work to be done. The future of the state’s largest salt marsh will be best served by a watershed-based organization whose sole focus is conservation of Scarborough Marsh and its estuary system.