The final phase of the project was to conduct an overall assessment of the Scarborough Marsh system using methods described in the Maine Citizens Guide to Evaluating, Restoring, and Managing Tidal Marshes (Bryan et. al. 1997). The Maine Citizens Tidal Marsh Guide includes seven assessments that can be undertaken by local citizen groups with an interest in marsh conservation and restoration. Two assessments that focus on threats to the marsh and potential for restoration were used in this project: Ecological Integrity of the Marsh System (Assessment 1) and Ecological Integrity of the Zone of Influence (Assessment 2). Ecological Integrity is a measure of the state of an ecosystem as compared to an undisturbed ecosystem of the same type and in the same region. In evaluating the Ecological Integrity of the Marsh System we looked at conditions within the marsh that affect the health of the ecosystem; when evaluating the Ecological Integrity of the Zone of Influence we looked at surrounding land uses that impact the marsh.

To identify local differences within the marsh system, the marsh is broken down into a series of Evaluation Units (EUs) based on tidal restrictions. The evaluation units used in this analysis are shown in Figure 5. The Maine Citizens Tidal Marsh Guide then asks the user to answer a series of predictor questions about the marsh. For example, in evaluating the Ecological Integrity of the Marsh System, the user must identify the number and severity of tidal restrictions affecting the evaluation unit, the area of fill, the area affected by ditching, and the area dominated by invasive plants. In evaluating the Ecological Integrity of the Zone of Influence, the user records the dominant land use surrounding the marsh, the number of buildings within the 250 foot shoreland zone around the marsh perimeter, and the percentage of natural vegetation buffer surrounding the marsh perimeter. A complete list of the questions used in the analysis is included in Appendix D.

For each question, the evaluation unit is assigned a Functional Index score ranging from 1.0 (most natural) to 0.1 (least natural). For example, an evaluation unit with less than 5% of its area dominated by Phragmites would receive a score of 1.0, whereas one with more than 20% dominance by invasive species would receive a score of 0.1. An Average Functional Index (AFI) is then calculated for the evaluation unit. Average Functional Index is a relative indicator of the ecological health of the system. After the individual evaluation unit scores have been calculated, an overall AFI score can then be calculated for the entire marsh system. The size of each evaluation unit is considered when calculating the overall AFI score for the entire marsh.

The results of the analysis are summarized in Table 8 and 9. The Average Functional Index (AFI) scores ranged from 0.27 for EU 8 to 0.90 for EU 1. The low score for EU 8 (the area on the inland side of Route 1) is primarily due to the number of tidal restrictions affecting this unit, the amount of ditching, and the large amount of Phragmites growing in the unit. EU 10, a small branch of the Route 1 marsh cut off by Payne Road, also received a low AFI score due to the number of restrictions, amount of ditching, and fill placed for the roadbed. (Because the fill for a road is assigned to the EU on the inland side of the road, small marsh fingers cut off by roads tend to have a low Functional Index for fill.). EU 2, the Jones Creek Marsh west of Pine Point Road and EU 14, small finger of marsh cut off by the Eastern Road, also had relatively low AFI scores. EU 1, the most seaward of the evaluation units, had a very high AFI due to the lack of tidal restrictions, evidence of only small isolated patches of Phragmites, and little fill or ditching. Because this evaluation unit comprises about one third of the total marsh system area, it makes a significant contribution to the ecological health of the entire marsh system as measured by the Overall Average Functional Integrity.

Restoration Potential. The AFI scores can be used as a preliminary indicator of restoration potential; evaluation units with the lowest scores may be more likely to need restoration. Based on this approach, the evaluation units with the greatest restoration potential, ranked from lowest to highest AFI scores, are EUs 8, 10, 2 and 14. However, in evaluating restoration potential, the results of these evaluations must be balanced with the analysis of tidal restrictions and extent of Phragmites or other invasive species, as well as the area that could be restored in an evaluation unit. Restoring tidal flows and controlling invasive species can be expensive, so it is important to focus restoration efforts on evaluation units where restoration will affect the greatest number of acres per dollar spent. In considering the results of Assessment 1 plus the evaluations of tidal restrictions and Phragmites in Sections III, IV, and V, EUs 8 and 2 appear to have high potential for marsh restoration. Although EUs 10 and 14 had low AFI scores, they are located well inland in the transition zone where freshwater influence is strong, so restoration efforts, such as installing larger culverts, might have little effect. Moreover both EUs 10 and 14 are small, so restoration efforts based on actions such as culvert replacement would not be cost effective. EU 5 had a low AFI score, but the major contributing factors are the road itself and the restriction caused by the bridge. Both have been upgraded in the recent past, so any changes at this location in the near future are unlikely. Furthermore, the restriction caused by the bridge is less than that of a culvert of similar width, a fact not integrated into the relatively simple quantitative assessment method used. EU 7 also had a low AFI score, but that is mostly due to the lasting impact of the tide gates described in Section V. Hydrologic modeling would be necessary to determine if placing culverts at intervals under the Eastern Road to improve tidal flow during spring tides would be cost effective. EU 13 might warrant further study. This area has low tidal dam at Black Point Road and comparatively high concentration of Phragmites. Detailed hydrologic studies would be needed to determine the impact of the dam on salinity and Phragmites growth in this evaluation unit.

Despite a relatively high AFI score, EU 3 on the Libby River appears to have restoration potential. This area has the most severe tidal restriction on the marsh and stands of Phragmites are located just upstream of the restriction. Additional culverts under Black Point Road could benefit almost 60 acres of salt marsh.

Ditching affects many of the evaluation units, especially EUs 7, 8 and 10. While plugging ditches can create valuable waterfowl and wading bird habitat, pannes and other shallow water habitats appear to be abundant in the marsh. No studies have been done to show that shallow water habitats are limiting wildlife. In addition, plugging ditches could reduce tidal exchange and might promote the growth of Phragmites in areas of freshwater influence. In some cases (especially EU 8) areas with ditching have natural salt marsh vegetation and less Phragmites than nearby areas. Therefore, top restoration priority should be given to restoring tidal flows and controlling the spread of Phragmites.

The results of this assessment are included in Table 9. The evaluation units with the lowest scores, EUs 10, 11, 12, and 14, are also the smallest units in the marsh system. This is because the Zone of Influence is proportionately larger around a small evaluation unit, so the AFI score is more sensitive to development adjacent small units.

The Overall Average Functional Integrity of the Zone of Influence represents the general condition of the surrounding uplands and freshwater wetlands within \0xBD mile of the entire marsh system. The medium Overall AFI score (0.54) indicates that development pressures around the marsh are significant, but that despite these pressures the marsh is somewhat buffered by its large size. As development pressures continue, however, threats to water quality will increase due to surface runoff, and disturbance of wildlife in the marsh will increase. In addition, the development results in loss and fragmentation of wildlife habitat needed by species that use both the marsh and surrounding uplands, such as red fox or white-tailed deer. Species that utilize upland grasslands, a habitat type that is disappearing from our region but found in the zone of influence, will also benefit from habitat conservation. Upland species such as wood thrush or broad-winged hawk, which require relatively large blocks of forest, will also decline as more land is developed around the marsh.