Scarborough Marsh Report

Introduction
	The Study
	Study Site Characteristics
Human Impacts
Current Conditions
	Maine Tidal Marsh Guide Assessment Method
	Hydrology and Tidal Flow:
	Pannes:
	Birds:
	Fish Species:
	Sediment Characteristics:
	Comparison of Relative Elevations:
	Invasive Species
Recommendations
	Invasive Plant Control
	Public Education
	Solutions to Problems Created by Route 1
	Addressing Noise Levels
Literature Cited

Invasive Vegetation Map with Ditches and Pannes	Map Available
Scarborough Marsh Watershed Map	Map Available

It is estimated that estuarine wetlands comprise only approximately 5 percent of the total shoreline zone in Maine. Scarborough Marsh by itself comprises approximately 20 percent of Maine’s total salt marsh area (Deis 1985).

Salt marshes are ecologically rich environments, with relatively high numbers of individual organisms per square meter. The diversity of resident species is only moderate, however, salt marshes act as important habitat for many transient species of fish, birds, and mammals which use the marsh as feeding, nesting, or nursery habitats. Common resident species include amphipods, snails, ribbed mussels, soft-shelled clams, crabs, and fish of various species which frequently live in the tidal streams running through salt marshes. As Deis (1985) describes in Maine’s Intertidal Habitats, "salt marshes once viewed as useless, mosquito-breeding wastelands, are now generally considered one of our most valuable intertidal habitats" (35). These habitats are now widely recognized as having both anthropocentric and biocentric values.

The rich organic detritus and substrate material flushed from the Scarborough Marsh via tidal circulation provide important nutrients for oceanic food chains. The species involved in these food chains are extremely important to Maine’s commercial fisheries. Beyond their ecological and habitat functions, salt marsh systems temporarily store floodwaters, thus reducing the severity of coastal flooding. In addition, the dense peat and vegetation of salt marshes often capture and retain pollutants and sediments that could otherwise run off into shellfish beds and navigational channels. However, salt marshes are also sensitive to human activity. We hope that this report will articulate some of the existing human impacts to the Upper Dunstan River marshes, and more importantly present reasons for the area’s restoration.

The Study

This study focuses on the portion of the Scarborough Marsh ecosystem adjacent to the Dunstan River, especially that portion located upstream from the Route 1 causeway (northwest of the road). Just driving across the causeway, one immediately notices the contrasts between the condition of the upstream and downstream portions of the marsh. The upstream portion has extensive areas of both Phragmites australis (common reedgrass) and Typha angustifolia (narrow-leaved cattail). Pannes are few, and ditches, abundant. In contrast, the downstream portion of the site is dominated by high marsh vegetation, especially Spartina patens. One can see abundant pannes located near the road, and utilization of these habitats by birds, especially ducks, willets, snowy egrets, and glossy ibis, gives the appearance of a much healthier marsh. In this study, we have focused on human impacts to and current conditions of the marsh in hopes that a more complete understanding of the current status of the marsh will help provide guidance on potential restoration activities at the site.

This report was completed in conjunction with Bates College as part of the short term unit, Environmental Studies s11, Ecological Restoration. The project ran from April 20 to May 22, 1998. The study was initiated under the direction of Professor Curtis Bohlen in response to suggestions from Rob Bryan of the Maine Audubon Society. Student researchers were Shauna Accongiagioco, Marco Donadio, Josh Evans, Dave Levin, Julie Macias, Erin Migausky, Greg Shyloski, Eliza Sprecher, and Heidi Vogel.

Study Objectives

The goal of this study was to assess human impacts to Scarborough Marsh, especially the effects of the presence of Route 1, and to develop ideas for the restoration of the marsh system, particularly the portion of the marsh upstream of Route 1.

Primary objectives included the following:

• Map invasive species populations,
• Compare the upstream and downstream sides of the marsh in regards to wildlife, ditching, pannes, and sediments,
• Complete the Salt Marsh Assessments from the Maine Citizens Tidal Marsh Guide for the portions of the marsh upstream and downstream from Route 1,
• Examine tidal restrictions,
• Provide restoration recommendations.

Wetland Characteristics

The study site segments on either side of Route 1 are both classified as salt marsh habitats (estuarine emergent wetlands, according to the National Wetlands Inventory). The site is dominated by marsh grasses, such as saltwater cordgrass (Spartina alterniflora) and salt meadow cordgrass (Spartina patens), typical vegetation for an estuarine wetland. Portions of the Dunstan River wetland ecosystem, especially upstream from Route 1 are less influenced by salt water. These include areas of palustrine emergent wetlands (mostly dominated by broad-leaved cattails, Typha latifolia), areas of palustrine scrub-shrub wetland, and a substantial area of palustrine forested wetland.

Geology

The Scarborough estuary system is classified as a coarse-grained estuary and wetland system. This means that the geology of the Scarborough estuary is shaped primarily by sediment infilling via tidal transport from the mouth of the system rather than from sediment flow from the surrounding uplands (Harvey 1977). Nevertheless, in the upper portions of the marsh such as the area near Route 1 on which this study focuses other forces are important in shaping sediments. Thick stands of vegetation, along with the ebb and flow of relatively low energy tidal currents, produce a nutrient-rich soil composed of plant roots peat, clay and silt. The Route 1 causeway and extensive ditching particularly affected the study area. Sedimentary, hydrologic and erosional factors have been significantly altered by human activity.

Route 1

The 6.2 mile stretch of Route 1 in Scarborough is considered by the town of Scarborough to be the "Town’s major arterial carrying the highest daily volume of traffic" (Martin et al. 1994). The stretch located at our site is a four-lane undivided roadway. As detailed in the 1994 Scarborough Comprehensive Plan, the average annual daily traffic volume along Route 1 in Scarborough ranged in 1990 from a low of 8,200 vehicles per day to a high of 30,120 (Martin et al. 1994). Historically, traffic data have shown peak volumes during the summer months with traffic during August typically being the highest. While doing research in the field, the effects of the traffic on Route 1 on the marsh were particularly noticeable. The large numbers of automobiles and trucks as well as the excessive speeds they travel pose a direct physical threat to wildlife. Persistent noise and widespread litter may disrupt fish and animal populations as well.

Town of Scarborough Wetlands Policy

As the town of Scarborough recognizes "the first step in managing the community’s wetlands is to understand the systems, their existing quality, and the factors that influence their quality" (Martin et al. 1994). In relation to natural systems generally, the Town "conscientiously uses its inventory of natural resources as a guide to land use pattern" (Martin et al. 1994). In Part III of the Scarborough Comprehensive Plan, (Policies and Future Land Use Plan), the Town recognizes that in regards to the Scarborough Marsh the combination of local shoreland zoning and public ownership, with Maine and Federal regulations, provides significant protection. However, the town of Scarborough has proposed that they should further increase the quality of their wetlands by:

(a) encouraging the Maine Department of Inland Fisheries and Wildlife to evaluate wetlands known to exist, but not yet rated with respect to their value for wildlife;

(b) Continuing to propose mandates on landowners to subdivide or develop their properties to inventory the properties for wetlands, so that boundaries of the wetland can be accurately recorded;

(c) Searching for outside resources to assist in mapping wetlands and establishing their values for wildlife habitat, flood storage, recharge of groundwater, and other functions;

(e) Identifying sources of water pollution and working toward eliminating them.

Scarborough Marsh has been significantly affected by human impacts. While actions that have altered the marsh are often regarded individually as insignificant, the cumulative impact of these actions has contributed to the degradation of the salt marsh ecosystem.

One of the major impacts on the marsh is Route 1, which divides the marsh at the Dunstan River into upstream (north of Route 1) and downstream (south of Route 1) sections. The presence of Route 1 prevents the free flow of tidal waters across the surface of the marsh. The two culverts that go underneath the road are undersized and restrict water flow through the main channel (see Hydrology and Tidal Flow section). At high tides the culverts are completely submerged. The restriction of tidal flow in the marsh, as well as the detention of freshwater upstream of the culvert, can cause changes in salinity that in turn affect the plant and animal communities. The tidal restriction present at Route 1 is likely to be a main contributor to the degradation of the marsh. Undersized culverts are often associated with invasive species in salt marshes (e.g. Linnell 1994). At Scarborough Marsh there is a significant level of invasive species on the upstream side of Route 1. More than forty percent of the estuarine marsh upstream of the highway contains either Typha or Phragmites. Less than one percent of the downstream side of Route 1 contains invasive plant species.

Route 1 affects Scarborough Marsh in more than one way. Though the culvert under the road is the main problem, the road also brings trash and debris as well as increased noise from passing cars and trucks. Noise from the road is detrimental to the wildlife habitat of the marsh. The area of the marsh in the immediate vicinity of Route 1 contains heavy amounts of litter. Runoff from the road surface may also introduce pollutants to the marsh, from heavy metals to oil and grease. Maintenance of the road may also introduce salts and other chemicals with a detrimental effect on the marsh.

Scarborough Marsh is extensively ditched, another cause of marsh degradation. On the upstream side of Route 1, the area west of the channel is heavily ditched while the area east of the river contains fewer ditches. Ditches are also widely found on the downstream side although the ditches appear to have existed for a longer time there, as many of them have formed meanders. There are no pannes near the ditched area on the upstream, west side of the channel which seems to indicate an effect on the hydrology of the marsh. Ditching allows the high marsh to drain more quickly following spring tides. Ditches also trap tidal waters and freshwater drainage from the surrounding upland on the marsh surface. This leads to the dieback of natural tidal marsh plant communities, degradation of the marsh peat, and changes in water and soil chemistry.

Fill may be another contributor to the degradation of the Dunstan River Marsh. The upstream side is more than five percent filled. The fill includes Route 1 (~5%), and several house lots on the western side of the marsh that have lawns that appear to be partially constructed on fill. Fill is not significant immediately downstream of Route 1. Fill results in direct loss of marsh area and ecological function, and is often associated with expansion of invasive plant species, especially Phragmites.

An additional human impact on the Dunstan River Marsh system is the development surrounding the marsh. There are several types of land use within the Dunstan River watershed and within the one half mile Zone of Influence surrounding Scarborough Marsh. These uses range from forests to residential to commercial areas. While the forested areas of the marsh are likely to contribute to the health of the marsh, the residential and commercial areas may have detrimental effects on it. The extent of development surrounding a tidal marsh can affect the wildlife habitat, water quality, recreational potential, and aesthetics of the marsh. In particular the proportions of developed land within the one half mile zone of influences, and within the watershed of the marsh serve as indicators of nutrient enrichment and influence by other pollutants. Buildings in the immediate area and throughout the watershed produce increased runoff, nutrient loading from the use of fertilizers and increased activity in and around the marsh system. High levels of human activity in the Zone of Influence may also disturb marsh wildlife.

Maine Tidal Marsh Guide Assessment Method

One of the tools used to organize and compile data for this project was the Tidal Marsh Evaluation method found in the Maine Citizens Tidal Marsh Guide (Bryan et al. 1997). This consisted of groups of evaluation sheets aimed at assessing the ecological integrity and societal values associated with various components of the marsh. Subjects covered in these sheets include the following: Ecological Integrity of the Marsh System, Ecological Integrity of the Zone of Influence, Wildlife, Finfish, & Shellfish Habitat, Recreational and Commercial Potential, Acetic Quality, Educational Potential, and Noteworthiness.

We carried out separate evaluations of the condition of the marsh areas upstream and immediately downstream of Route 1. The results of these evaluations are included as an appendix to this report. In general, the marsh upstream of Route 1 shows many signs of deterioration due to human activity. Nevertheless, it has significant potential for recreational and other values because of its accessibility to the local community. The downstream portion of the marsh has a higher degree of ecological integrity, and is perhaps even more valuable as a recreational resource because noise and trash from Route 1 do not as severely degrade the experience of being on the marsh.

Hydrology and Tidal Flow

In order to determine the effects of the Route 1 culvert restrictions on tidal flow, it was important to observe a tidal cycle to determine the amount of water flowing through the culvert. The cross-sectional area of the culvert was measured and six sub-areas of the culvert cross section were selected for measurement of water velocities. Our goal was to determine the velocity of the water in each of the six segments as well as the depth of the water in order to estimate the amount of water flowing through the culvert throughout a tidal cycle. We measured current velocity and water depth at thirty minute intervals. From general observation during our time in the field, it was obvious that the culverts did restrict tidal flow. Several times we saw that the culverts were completely submerged and our data supports this conclusion.

Our original plan was to collect data at the western culvert under Route 1 on tidal elevation, current velocity, discharge, salinity, and total suspended solids every 30 minutes for a full tidal cycle. Because of logistical difficulties, we did not collect data for the full tidal cycle, yet the data we were able to collect provides a preliminary profile of flow conditions during normal tides. After we collected our data, we compared the elevation data we collected to predictions of the tidal cycle at Old Orchard Beach. When the data were plotted on a graph, they showed us that the tidal flow on the Dunstan River is between 30 minutes and a hour later than the tides at Old Orchard Beach. Although our data are incomplete, it appears that the tidal amplitude at the culverts under Route 1 is somewhat reduced compared to amplitude at Old Orchard Beach. A linear regression of tidal height on the Dunstan River versus predicted height at Old Orchard shows tidal amplitude at the culverts to be approximately 75% of amplitude on the ocean. Nevertheless, the culverts at Route 1 were completely submerged at all high tides that we witnessed, not just at spring tides.

Salinity, total suspended solids, and current velocity also showed strong relationships to the tides. Both salinity and total suspended solids increased as the tide rose. They then peaked an hour or so after high tide, and declined steadily until the end of our observation period. Current velocity shows a more complex sinusoidal pattern with tidal height, since the direction of the current reverses at high and low tides (see figure).

We were unable to measure current velocities throughout the tidal cycle, and thus we can only estimate total flows through the culvert on a daily or tidal basis. It appears from our data that in the neighborhood of 4000 to 5000 m3 of water passes through the culverts at Route 1 during a normal flood tide. Outflow is somewhat larger. As a result, there is a net outflow during a tidal cycle in the neighborhood of 3000 m3.

Ditches and Drainage Network

On the western side of the channel upstream from Route 1, ditching is present at a density (in meters of channel per hectare of marsh surface) of 90 meters per hectare. On the eastern side of the main stream channel, it is present at a frequency of 48 meters per hectare. In the study area downstream of Route 1, ditching is present at a rate of 50 meters per hectare on the eastern side, and 35 meters per hectare on the western side. Overall, ditching is more prevalent on the upstream side of Route 1, contributing to the poorer quality of the upstream marsh environment.

Through the development of GIS maps of the study area, we were able to approximately determine the total drainage density (including both ditches and natural streams) for the area. On the western side of the marsh upstream from Route 1, the total drainage density is 187 meters per hectare, while on the eastern side, it is only 95 meters per hectare. Downstream, the total drainage network on the eastern side is 322 meters per hectare; on the western side, it is 123 meters per hectare. The drainage network is significantly smaller on the upstream segment of our study area. It is possible that increasing Phragmites growth is restricting the marsh drainage network. In effect, the tidal restriction created by Route 1 is causing a vicious cycle. The Route 1 culvert restricts the amount of water from the tidal cycle that reaches the upper marsh. This, in turn, allows further invasion of Phragmites, which further restricts the natural marsh drainage network. Ditching may also have to paradoxical effect of decreasing the drainage density as measured in this way. Drainage via straight channels is likely to involve shorter networks than drainage via meandering streams.

	Ditching (m/hectare)	Total drainage network (m/hectare)
Upstream Western Side	90	187
Upstream Eastern Side	48	95
Downstream Western Side	50	123
Downstream Eastern Side	35	322

Runoff From Developed Land

Observations of widespread algal mats both on the marsh surface and within the pannes suggest that the Upper Dunstan River Marsh may be influenced by high nutrient loading. The most likely source of nutrient influx is runoff from the adjacent, developed landscape. Runoff from urban environments is generally enriched with a variety of pollutants, including fecal coliforms, oil and grease, heavy metals, and nutrients. To assess the degree to which the Upper Dunstan River may be affected by urban runoff, we examined the percentage of the watershed that is in either residential or commercial use. Nearly half of the watershed is in developed land, mostly in low density residential use. That is a sufficiently high degree of land development to suggest that nutrient influxes from urban runoff may be adversely affecting the marsh system.

Type of Zone in Upper Watershed	Percentage of watershed occupied by zone
Low density residential	28
High density residential	2.7
Commercial	15
Other (Agriculture, forest, and wetlands)	54.3

Pannes

Pannes are a distinctive feature of salt marshes. They are usually described as bare or water-filled depressions in the marsh. During high tides, and especially during spring tides, the pannes are flooded with tidal waters containing variable amounts of salt. Then, when the tide drains, the water level in the pannes is significantly lowered. The pannes often are not flooded again until the next spring tides, several weeks to a month later. During hot, dry weather, much of the water in the pannes may evaporate, increasing the salinity of the water. If salinities rise sufficiently high, they will kill off the vegetation in the panne, although even high salinity pannes will often be covered with a film blue-green algae (cyanophytes).

Salinity of pannes varies both in time and space. Patterns of variation are determined by a combination of the elevation of the panne inlet/outlet, (which determines how frequently they are flooded by tidal action), degree of groundwater influence from adjacent uplands, depth, times since last inundation, and weather.

Mud pannes are pannes which retain water during both high and low tides. Submerged or floating vegetation can usually be found in this sort of panne. Since the mud barren is continually flooded, the vegetation that occurs within it is usually tolerant of salt. One example of this is Widgeon Grass (Ruppia maritima) which is frequently found in the pannes at Scarborough Marsh. In some marshes, relatively permanent ponds may form which are shallow in depth and rarely flooded. This makes them ideal for supporting submerged vegetation.

The pannes in Scarborough Marsh have continuous standing water and are flooded at high tide. They support various species of fish, amongst which the most frequently recorded were mummichogs (Fundulus heteroclitus) and three and four spine sticklebacks (Gasterosteus aculeatus, Apeltes quadracus) . The panne environment also supports a number of plant species. Spartina alterniflora is commonly found around the pannes and on the stream banks. Some pannes also support submerged aquatic vegetation, especially Ruppia maritima, widgeongrass. Others support extensive mats of filamentous green algae. The salinity of the pannes varies considerably, depending on the time of day when the samples were taken (low tide or high tide) and on the proximity to tidal channels. Within our study area, however, these differences in salinity do not seem to affect the fish or plant species present in the pannes.

Pannes are significantly more abundant downstream from Route 1 than they are upstream. During the period of our study, submerged vegetation was just beginning to get established within the pannes following winter dormancy. Accordingly, we made no effort to quantify the abundance of submerged plants on either side of the road, except to note that it was present in some pannes both upstream and downstream of the road.

Birds

Birds are generally considered to be a good indicator of the overall health of a salt marsh ecosystem. The common belief that more is better holds true in this category. It is important, however, that one remember that more does not simply refer to the total amount of birds but also to the amount of species represented in a specific area. This study has observed the population of birds in the upstream and downstream marsh regions with these ideas in mind.

Our examination of the local bird community consisted of collecting data on all birds observed over a 15 minute period. Several such walks were carried out in both the upper and lower marsh areas. Two researchers would work together on each bird walk, with one researcher observing through binoculars and the other recording the number and species of all birds observed. An effort was made to cover the widest possible total area by observing a different section of both the upper and lower areas with each walk.

Although the total number of species was similar upstream and downstream of route 1, the data recorded from the walks showed differences in species composition between the upper and lower areas. For instance, in the upper marsh, a total of 36 red-winged black birds were recorded, as opposed to 4 in the lower marsh; or an average of 12 per walk versus 2. This points to a marsh system that contains a higher amount of habitat suitable for redwing blackbirds, especially areas dominated by Phragmites and cattail. This pattern may be contrasted with the number of snowy egrets recorded in each area. The upstream portion of the marsh had no snowy egrets while 16 were recorded in the downstream section. The downstream portion of our study area contained more abundant pannes than did the upstream portion of the marsh, providing these waders with more of their preferred habitat. It is worth noting that these contrasting bird communities were observed in areas within 200 meters of one another. This shows the dramatic difference in the bird populations and overall marsh condition on either side of Route 1.

Fish Species

Seven minnow traps were set in the Scarborough Salt Marsh as part of a fish survey of the marsh. In all, four fish species were found, mummichog (Fundulus heteroclitus), three-spine stickleback (Gasterosteus aculeatus), four-spine stickleback (Apeltes quadracus), and American eel (Anguilla rostrata). The minnow traps were set in a variety of locations in order to determine the relative distribution of species in the marsh. Trap locations included pannes and the tidal creek. Moreover, to assess the effects of Route 1 on fish populations, traps were set on both the upstream and downstream side of the road. Distance away from the tidal creek was also taken into consideration.

From this one-day observation, we were able to determine that the greatest densities of fish occurred in the pannes as opposed to the tidal creek. This pattern held on both the upstream and downstream sides of the culvert. The most prominent fish species found in all the pannes was the mummichog. Distance away from the creek did not seem to have much effect on fish densities. This suggests that these fish species are very tolerant of changes in salinity and temperature. Four-spine sticklebacks were found exclusively within the tidal creeks while the other species were found within the pannes. Route 1 does not appear to have affected the distribution of fish species in the marsh.

Sediment Characteristics

The sediments associated with salt marshes may come from river silt, organic productivity from the marsh itself, or marine deposits reworked over time. The general pattern of sediment deposition is initiated as the tidal creek rises out of its banks. Water carrying sediments is slowed by the vegetation and allows for the coarser grained sediments to fall out by the stream edge. This in turn results in a slightly elevated streamside levee. The finer sediments are carried away from the creek banks and dropped further inland. This pattern is called the "streamside" effect, which is characterized by higher productivity of grasses along the tidal creek banks as opposed to inland. This effect is made possible by the slightly larger nutrient input, higher elevation, and better drainage associated with the deposition of sediments. Therefore, when looking at sediment deposition in a salt marsh, it is more valuable to look at elevation, drainage, and organic content than the source of sediments itself (Mitsch and Gosselink 1993).

To examine the deposition of sediments in the marsh, as well as the possibility of interference created by Route 1 on the natural distribution of sediments, sediment analyses were performed. In total, 24 core samples were collected, taken with a Russian peat corer, to a depth of 60 cm below the marsh surface (12 samples on the upstream and 12 samples on the downstream side of the Route 1 culvert respectively). The samples were spaced away from the tidal creek bank at measured distances (see map). At the time of collection, each core was described and photographed and each distinct horizon was sampled. Soil textures ranged from a distinct organic layer consisting of old and new marsh grass near the surface to a rich root-filled peat, and finally a fine silt-clay soil. There is more fine-grained silt-clay soils present downstream of the culvert.

Once the samples had been collected, a loss on ignition (LOI) analysis was performed in order to determine the organic content of the sample. Using a muffle furnace, the dried samples were heated to 450C for two hours and the loss of mass (assumed to primarily consist of organic matter) was determined. Analyses were carried out on samples from surface horizons and the deepest (60 cm) horizons. An analysis of variance was carried out to determine whether there were any significant patterns in soil organic matter based on depth or location (See table). Our results indicate a significant difference in LOI with distance from the tidal creek. The LOI was higher for samples further away from the stream. Furthermore, a significant interaction indicates that the effect of the distance from the stream is stronger upstream (P<<.001, refer to table). We conclude from this, and from visual examination of sediment cores that the Route 1 causeway is affecting migration of sediments in the system. The primary effect appears to be to decrease the flow of silts and sands into the upstream portion of our study area.

Relationship between Location and Sediment LOI

Location	Mean LOI (Percent)
Downstream Near Culvert	33.80
Downstream Away from Tidal Creek	86.06
Upstream Near Culvert	19.02
Upstream Away from Tidal Creek	86.13

Comparison of Relative Elevations

Determining relative elevations in the marsh can help decide if Route 1 has affected the Dunstan River Marsh, and if so, how. Differences in elevation may also provide mechanistic explanations for some of the ecological and geological differences between the upstream and downstream sides of Route 1.

All elevation measurements were taken using a sight level and stadia rod. To determine the relative height of the culverts, we sighted from the upstream culvert to the downstream culvert and then arbitrarily set the elevation of the top of the western, downstream culvert equal to zero. We then sighted 19 points around the main channel on the downstream side. 4 of those 19 points were tied to upstream elevation as well, in order to be able to better compare upstream and downstream elevation. 12 points were sighted around the upstream side of the channel, and 4 of those 12 were tied to downstream elevations. To compare the relative elevations away from the main channel, 10 points were surveyed extending to the edges of the marsh downstream, and the same was done for 11 points on the upstream side. Again, upstream-downstream relative elevations were taken for comparison purposes. Elevations were taken at the same locations from which soil cores were collected, as well as from several other locations. All elevations were taken within 50 meters of Route 1. They thus provide a cross section of the marsh immediately upstream and downstream of the road.

On average, the upstream portion of the marsh is somewhat higher in elevation than is the marsh on the downstream side of the causeway (see table). The elevation profile, both upstream and downstream of the road shows a characteristic stream-side levy. Downstream of the Culvert, elevations on the marsh remain low behind the levy. Upstream, however, elevations climb within 100 meters of the stream channel (see figure).

Comparison of average elevations near the Dunstan River and Route 1 culverts

		Downstream	Upstream
Near Creek
	Mean Elevation	-0.91	-1.32
	Std Dev.	0.2323	0.3780
Farther From Creek
	Mean Elevation	-0.96	-0.71182
	Std Dev.	0.2140	0.1622

Elevations are measured relative to an arbitrary datum located on top of the
western culvert under Route 1.

As documented by Linnell (1994), the area of a marsh upstream from a tidal restriction is often lower than the downstream areas, presumably because of peat wasting and changes in sediment inputs. This pattern is not evident in Scarborough Marsh; if anything, elevations appear higher on the upstream portion of the marsh. Linnell (1994) points out that when elevations upstream of a tidal restriction are lower than downstream from the restriction, the effects of restoring tidal influence may be detrimental. In particular, re-establishment of tidal influence may simply convert the marsh to open water. The high elevations observed upstream of Route 1 at the Dunstan River suggest that restoration of tidal influence would not lead to such an undesirable outcome.

Invasive Species

The Phragmites Problem Of The Upper Marsh

As described by Holm et al. (1977) Phragmites australis (common reedgrass) is believed by some to be the most widely distributed of all angiosperms. It is a perennial reed with broad, flat, leaf blades and large terminal panicles. It reproduces primarily from vegetative propagules and has a vigorous, branched, rhizome system that spreads quickly to new areas. Rhizome fragments are readily transported by water, and provide an efficient means of long-distance dispersal. These vegetative propagules are the most important means by which the species propagates and spreads. For Phragmites and many other hydrophytes the range of suitable habitats for successful seed germination is significantly narrower than the range of habitats for successful establishment by vegetative means. As articulated by Holm et al. (1977) "there was doubt for a time that seeds of some types of Phragmites could supply new individuals in natural sites. Even in the laboratory there were few reports of germination."

The Phragmites of our study area covers approximately 25% percent of the upstream portion of the study area. Moreover, comparing our maps of invasive vegetation with recent aerial photographs of the area, it appears that Phragmites is expanding within the marsh system, and is continuing to encroach on the forested wetland east of the marsh.

Phragmites is a particularly harmful invasive species because it can take over the relatively low Spartina-dominated estuarine wetlands by virtue of its 8 to 10 foot tall growth form. As the plant spreads within the marsh, it causes a variety of difficulties within the salt marsh, including loss of wildlife habitat and alterations in sedimentation patterns. Holm et al. (1977) suggest that Phragmites is "an excellent soil binder," and hence traps more sediment than other salt marsh species. Dense stands of Phragmites act to trap suspended particles better than the lower grasses such as Spartina (Vadas 1982), locally increasing sedimentation rates, and potentially altering local elevations.

Cattail Invasion

Typha angustifolia, also known as the narrow-leaved cattail, and Typha latifolia, the broad-leaved cattail, also often invade and colonize large areas of marshland. They are grass-like perennial herbs that grow rapidly and spread aggressively, over a foot a year with the use of rhizomes. Each can grow up to 6 feet tall or taller within 3-4 years, sometimes reaching up to 10 feet in height. Almost any soil will do as long as it is wet enough. Moist, unconsolidated soil allows for the rapid spread of these species, often including invasion of other species’ territories. Mosquito ditches expose more of the soil to water and, therefore, give more space for the vegetation development of both the broad-leaved and the narrow-leaved cattails, depending on the salinity of the water. Once communities dominated by these plants have developed, a drought does not restrain their development or health.

The narrow-leaved cattail can thrive in both fresh and brackish tidal marshes, tolerating moderate salinity measurements, up to about 15 ppt, whereas, the broad-leaved cattail is unable to tolerate salinity. The marsh’s wildlife, such as waterfowl and muskrats, feed on the seeds, rootstocks, and stems, while the marsh wren and the red-winged blackbird, as well as some fish, use the patches as nesting areas and protective cover.

Both species of cattails are sometimes considered invasive species that out-compete the native vegetation. When that happens they may adversely affect the diversity of the natural marsh community. Both narrow-leaved and broad-leaved cattails provide certain environmental values, such as nutrient removal and the stabilization of the soil for erosion control.

Present-day Distribution

Present-day distributions of invasive plant species were mapped in the field using a Trimble Pro XR differential GPS receiver. This GPS receiver provides sub-meter real-time positional accuracy, so the primary limit to the accuracy of these maps was our ability to locate the edge of stands of invasive plants. While the edges of Phragmites stands towards the open marsh were sharp, the edge of the Phragmites located in the forested wetland east of the study area was more diffuse and difficult to determine. Similarly, edges of cattail stands were often difficult to determine accurately, as scattered cattails were observed embedded in other vegetation. We tried to identify major areas of cattail and Phragmites dominance, and we mapped every Phragmites stand we saw, however, it is possible that we overlooked areas of scattered cattails, which were more difficult to discern (see map).

	Percentage Phragmites	Percentage Typha angustifolia
Upstream Side	25	32
Downstream Side	0.38	0.054

From our field observations and maps it is obvious that invasive plant species are highly prevalent in the marsh upstream from Route 1. Phragmites is present in dense stands especially on the eastern side of the stream channel, near the road. Taking soil samples in stands of Phragmites revealed the plant’s extensive root system, which resists the decay that occurs with other salt marsh vegetation. From visual observation, it was obvious that Phragmites limits habitat available to wildlife and is detrimental to biological diversity. Phragmites covered approximately 25% of the marsh area upstream of Route 1 and 0.38% of the downstream area.

Narrow-leaved cattail is also present in large quantities upstream of Route 1, mostly on the western side of the stream channel. Although not as obviously detrimental to the marsh ecosystem as Phragmites, the presence of large quantities of narrow-leaved cattail in the marsh indicates that the system is not functioning as it should. Distribution of Phragmites and narrow-leaved cattail at the perimeter of the marsh indicates that these are the areas that are most affected by the tidal restriction created by Route 1. Areas that would normally be flooded during the spring tide are not being reached, altering the hydrology and salinity of these areas enough to encourage the presence of invasive species.

This report has identified many contributors to the degradation of the Dunstan River Marsh upstream of Route 1, including urban runoff, tidal restrictions caused by inadequate culverts under Route 1, noise and litter stemming from the traffic along the highway, and extensive ditching. We examined a variety of restoration alternatives that might address one or more of the existing impacts to the marsh. The recommendations we offer here include actions that are likely to be important for restoring the ecological integrity of the Dunstan River Marsh, as well as actions that are likely to be relatively inexpensive to implement. These inexpensive options are worth considering even though they are unlikely, by themselves, to restore the Marsh to full ecological health.

Invasive Plant Control

Control of invasive plants should be a central goal of restoring the Dunstan River Marsh, and it is likely to be a primary method of marsh restoration as well. It is important to realize, that invasive plants are a symptom of other ecological changes in the marsh ecosystem that allowed establishment of the invasive species, and that permit their persistence and spread. Accordingly, the best approach to reducing invasive plant populations is to alter the marsh environment through other restoration actions in such a way that populations of invasive plants stabilize or decline. More expensive approaches to control of invasive plants, however, may be necessary.

Narrow-leaved Cattails

Vegetation dominated by narrow-leaved cattail is among the most abundant vegetation in the Dunstan River Marsh, covering about a third of the marsh surface. Any effort to reduce or eradicate the plant through direct efforts is likely to be difficult and expensive. Indirect efforts, however, may be effective at reducing the extent of this species. Although in our brief study we were unable to document whether existing distributions are in fact limited by salinity, cattails are found primarily in the upper portion of the marsh where salinity is lowest. Further downstream, the vegetation found at similar relative elevations is dominated by Spartina patens (saltmeadow hay). The narrow-leaved cattail is known to be sensitive to high salinity, and if more vigorous tidal exchange is restored to the upper marsh, the population of this plant may well decline without direct control action being required.

Phragmites

Phragmites control is likely to be more difficult. Phragmites is tolerant of a wide variety of conditions, and while restoration of full tidal exchange to the upper marsh may slow or even halt its spread, the plant is unlikely to recede. Physical and chemical control will probably be needed to reduce the plant's population at this site. Physical control of Phragmites can be accomplished in small areas with hand weeding. Over larger areas, however, control of Phragmites may require either use of heavy machinery to scrape away the undesirable plant, or application of an herbicide such as Round Up. Both of these methods are only partially effective. Typically, effective control of Phragmites requires repeated control efforts over a period of several years, and control can not be considered complete until one or more desirable plant species have become firmly established.

Public Education

Public education on the degradation of the marsh caused by human impacts is an inexpensive and potentially wide reaching approach to addressing a number of the marsh's problems. Efforts to reach visitors, commuters, local citizens and landowners may influence people's behavior, especially with respect to use of fertilizers throughout the watershed, and littering along the Route 1 causeway.

The placement of signs along the area of Route 1 surrounding the marsh ("Take Pride in Scarborough Marsh -- Largest Saltmarsh in the State") could increase public awareness regarding preservation of the marsh system. This may help to reduce littering along Route 1. Marsh clean-up efforts and an "adopt a marsh" program in association with local schools or civic groups might also prove effective at reducing litter near the road.

A public information campaign emphasizing the uniqueness of the marsh, its significance within the state of Maine, and its value as a recreational resource might also be of benefit. This effort might be targeted more specifically on nearby residences and businesses informing them of ways to reduce nutrient loading and other pollutants reaching the marsh through application of urban Best Management Practices (e.g., A.R.T. 1991). Mailings, advertising, signs, editorials and op-ed pieces in the local and regional papers, and similar efforts would make an effective way of reaching a large public audience.

Solutions to Problems Created by Route 1

Undersized Culverts

It is clear that the existing culverts under Route 1 are of a size and elevation that reduces tidal influence upstream of the road. The top of the culvert is submerged during ordinary high tides, and is more than a foot and a half below the water's surface during spring high tides. It has been well documented that such tidal restrictions have a variety of often profound effects on saltmarsh ecosystems (Linnell 1994). Solutions to these problems are obvious, but likely to prove expensive and difficult to implement. Existing culverts need to be substantially enlarged and complemented by installation of smaller culverts that would permit wider tidal exchange across the causeway during spring tides. The elevation of the top of the culverts also needs to be raised so that the culverts offer no restriction to flow even during spring tides. A more expensive solution would be to build a bridge over a portion of the marsh surface, rather than having a road run across the marsh surface as Route 1 currently does.

Addressing Noise Levels

Traffic restrictions on Route 1 in the immediate vicinity of the marsh would be an effective way to reduce some of the current noise levels. Speed limits in the commercial areas on either side of the marsh are substantially lower than they are on the causeway itself. The speed limit across the causeway could be reduced with only a small impact on travel times for local residents and commuters. A reduction in the local speed limit would most likely provide a significant decrease in noise pollution and may also help avoid collisions.

Ditches

The widespread ditching of the marsh has caused significant hydrological alteration of the marsh and reduced desirable habitat features such as salt marsh pannes. Blocking or filling in some or all of these ditches can be carried out relatively inexpensively, and would restore a more natural hydrology to much of the upper marsh. Blocking drainage ditches is also likely to produce additional salt marsh pannes. Creation of artificial pannes and blockage of existing drainage are among the most widespread strategies for salt marsh restoration in use today. Because of their widespread use, they are likely to be among the most frequently recommended strategies for restoration of the Dunstan River marshes. Given the other, more systemic causes of deterioration of this marsh, however, we believe blockage of drainage ditches, should be considered as a part of a larger restoration strategy that addresses tidal restrictions, invasive plant management, and impacts of suburban runoff.