Natural and Anthropogenic Influences on the Mount Hope Bay Ecosystem 2006 Northeastern Naturalist 13(Special Issue 4):31–46 The Mount Hope Bay Tidal Restriction Atlas: Identifying Man-made Structures which Potentially Degrade Coastal Habitats in Mount Hope Bay, Massachusetts Stephen B. Barrett1,*, Brian C. Graves2, and Barbara Blumeris3 Abstract - For nearly a decade, Massachusetts resource managers have been systematically inventorying, assessing and restoring coastal wetlands degraded by infrastructure crossings such as bridges and culverts, which, unless properly designed and constructed, restrict tidal flow to upstream areas. These crossings—known as tidal restrictions—alter the natural flooding and flushing dynamics of coastal estuarine and wetland habitats, causing damage to salt marshes, eelgrass beds, and other important shellfish and finfish habitats. The Mount Hope Bay Tidal Restriction Atlas, undertaken by the Massachusetts Wetlands Restoration Program and the US Army Corps of Engineers, is the most recent addition to the statewide inventory effort. The Atlas lists a total of 74 potential tidal restrictions that were initially identified on maps and aerial photographs, of which 25 sites were documented using rapid field assessment techniques. Each field-visited site was assessed for severity of restriction and habitat impacts, potential environmental benefits of restoration, and logistical feasibility for implementing restoration. Using these factors, sites were prioritized using a high/medium/low scale. A three-page Site Assessment Report, which includes data, maps, and photographs, was generated for each field-visited site. The final Atlas was presented in an interactive digital format to allow users to query its database and readily move between data fields, maps, and photographs. The Atlas was distributed to stakeholders as a tool for use in restoration planning and implementation. Introduction The Massachusetts Wetlands Restoration Program (MWRP) and the US Army Corps of Engineers (USACE), New England Division, formed a state/ federal partnership to complete an inventory of tidal restrictions in the Mount Hope Bay area of Massachusetts under the Corps Planning Assistance to States Program. Tidal restrictions are manmade structures (e.g., roads, bridges, dikes/dams, and other barriers) that constrain the natural flood and ebb flow of salt water through upstream marsh habitats that were historically inundated by the tide (Massachusetts Wetlands Restoration Program 1999). The purpose of the inventory was to identify a broad spectrum of tidal restrictions in the study area that affect coastal habitats, and to investigate a subgroup of sites with a high potential for ecosystem restoration. It was 1Epsilon Associates, Inc., 3 Clock Tower Place, Suite 250, Maynard, MA 01754. 2Boston Globe, 135 Morrissey Boulevard, Boston, MA 02108. 3US Army Corps of Engineers, New England District, 696 Virginia Avenue, Concord, MA 01742-2751. *Corresponding author - sbarrett@epsilonassociates.com. 32 Northeastern Naturalist Vol. 13, Special Issue 4 envisioned that this information would then be used by stakeholders in the watershed to prioritize and implement restoration projects. The MWRP established a study area encompassing approximately 64 kilometers of the Mount Hope Bay coastline, including tidally influenced portions of the Cole, Lee, Palmer, Runnins, and Taunton Rivers. Eight Massachusetts towns were included in the project area: Berkley, Dighton, Fall River, Freetown, Rehoboth, Seekonk, Somerset, and Swansea (Fig. 1). The hydrologic effects of tidal restrictions have caused significant damage to salt marshes (Burdick et al. 1997). The hydrologic alteration impacts salt marsh vegetation and the physical and chemical characteristics of marsh sediments (Portnoy 1999), as well as aquatic organisms and water quality. Restricted tidal flow: (1) encourages colonization by plant species less tolerant of salt water than native species (Roman et al. 1984); (2) reduces utilization of salt marsh by fish species for refuge, forage, nursery, and spawning habitat (Raposa and Roman 2003, Weinstein et al. 1997); (3) traps nutrient-enriched waters causing cultural eutrophication (Costa et al. 1999); and (4) increases peat aeration, leading to subsidence (Portnoy 1999). Figure 1. Comprehensive inventory of sites. 2006 S.B. Barrett, B.C. Graves, and B. Blumeris 33 Of these impacts, the most visible indicator of salt marsh degradation from restricted tidal flow is the extensive colonization of salt marsh by invasive plant species (Tiner 1998). These invasive species, including common reed (Phragmites australis (Cav.) Trin. Ex Steud) and purple loosestrife (Lythrum salicaria L.), thrive in disturbed fresh and brackish areas where they can out-compete the native plant community. Woody plants, native and exotic, are also able to move onto the marsh where restrictions can cause the marsh edge to recede or retain freshwater (Buzzards Bay Project 2002). Other visible signs of restricted tidal flow may include: back-up or impoundment of water on the upstream side of the structure, referred to herein as “ponding” (Costa 2000, Montague et al. 1987); increased flow velocity through the restriction opening; and scouring and slumping of the marsh downstream of the restricting structure caused by increased flow velocity (Warren 1993). Tidal restrictions can also exacerbate water quality problems upstream of the structure due to reduced flushing and mixing. Sources of estuarine pollution include septic systems, roadways and parking lots, agricultural fields, and residential lawns. Some pollutants such as excess nutrient loading (nitrogen and phosphorous) may produce nuisance aquatic plant growth. Elevated bacterial levels may occur or be more persistent where a bacteria source exists. Where polluted waters are subject to full tidal flushing, the diurnal flood and ebb can rapidly dilute contaminants before habitat impacts are sustained (Kim et al. 2003). Tidal restrictions, however, trap nutrients upstream and exacerbate eutrophication (Costa et al. 1999). Dense growth and decomposition of algae deplete oxygen required by marine organisms, reduce light available to aquatic plants such as eelgrass, and smother benthic surfaces used by fish for spawning (Valiela et al. 1992). The removal of tidal restrictions can restore degraded salt marsh and estuarine habitats by: (1) re-establishing salinity levels that impede encroaching woody and invasive plants species (Roman et al. 1984, Sinicrope et al. 1990); (2) flushing stagnant, brackish backwater areas and replenishing them with low-nutrient marine waters that inhibit the growth of algae and support healthy aquatic vegetation such as eelgrass (Zostera marina L.) and fish-spawning habitat utilized by species like winter flounder (Pseudopleuronectes americanus L.); and (3) improving access to estuarine habitats used for spawning and foraging by marine fishes. Mount Hope Bay Study Area Mount Hope Bay, including the lower Taunton River, is located in the northeastern section of Narragansett Bay (Fig. 1). Like other estuarine systems in the northeastern US, Narragansett Bay is a drowned river valley (Roman et al. 2000). The Taunton River watershed, the second largest watershed in Massachusetts with an area of 1372.7 square kilometers (Williams and Wiley 1970), provides the largest contribution of freshwater to the estuary and regulates seasonal salinity variations. The other rivers in the 34 Northeastern Naturalist Vol. 13, Special Issue 4 project area—Cole, Lee, Palmer, and Runnins—drain a comparatively smaller area (290 square kilometers) of the Mount Hope Bay watershed (Wiley et al. 1983). Salt marsh in Mount Hope Bay Salt marsh occupies the coastal and estuarine intertidal zone (Nixon 1982) and is generally defined by a low marsh dominated by smooth cordgrass (Spartina alterniflora Loisel) and a high marsh dominated by salt marsh hay (Spartina patens (Ait.) Muhl.) (Niering and Warren 1980, Nixon and Oviatt 1973). The New England-type salt marsh ranging from Maine to Long Island is distinct from those to the north (Fundy-type) and to the south (Coastal Plain-type), differing in substrate and vegetation (Johnson 1925). The distribution and abundance of salt marsh in Mount Hope Bay, as elsewhere, is primarily governed by salinity, tidal elevation, substrate characteristics, and bathymetry. Salt marsh habitat extends upstream in the Taunton River to about the Berkley Bridge (Massachusetts Department of Environmental Protection 2003). While salinity in this area is often below one part per thousand (ppt), particularly during low tides and seasonally high river flow, the combination of tidal influence and periodically high salinity (during high tides and low river flows) impedes competition by salt-intolerant species and thereby supports the salt marsh community. Naturally low salinity is characteristic of the study area due to its location in the Upper Narragansett Bay. Substrate suitability is also important for salt marsh distribution. Salt marsh colonizes the intertidal zone where it is regularly inundated by tides (low marsh is flooded daily, high marsh less frequently). Shorelines with gentle topography, broad areas exposed at low tide, and shelter from wave energy provide suitable conditions for extensive salt marsh growth. An example in Massachusetts is Essex Bay, which has 939.3 hectares of salt marsh and 95.4 kilometers of coastline, a ratio of 9.8 hectares of salt marsh for each kilometer of shoreline (Chesmore et al. 1973). In comparison, Mount Hope Bay has little salt marsh relative to the length of its shoreline, primarily due to the steep topography of the landscape. Mount Hope Bay has 165.9 hectares of salt marsh and 64.4 kilometers of shoreline, a ratio of 2.6 to 1. Approximately 60 percent of the salt marsh in Mount Hope Bay is located in Broad Cove, the Segreganset River, and Assonet Bay (Curley et al. 1974). Table 1 lists salt marsh area and shoreline length in representative estuaries in Massachusetts and demonstrates that salt marsh area is relatively small in Mount Hope Bay. Water Quality in Mount Hope Bay Water quality in Mount Hope Bay is impacted by wastewater treatment plants and combined sewer overflow discharges in the watershed, highdensity development in coastal communities, and industrial development including power generating stations (Curley et al. 1974). Mount Hope Bay 2006 S.B. Barrett, B.C. Graves, and B. Blumeris 35 and its primary tributary rivers (Cole, Lee, Palmer, Runnins, and Taunton) do not meet state water quality standards for nutrients, organics, and pathogens (Massachusetts Department of Environmental Protection 2004). Water quality impairment has degraded estuarine habitats and culturally important fisheries in Mount Hope Bay as highlighted by commercially important shellfish species and winter flounder. Harvesting of shellfish, such as northern quahog (Mercenaria mercenaria L.), soft-shelled clam (Mya arenaria L.), and eastern oyster (Crassostrea virginica Gmelin), is restricted due to high bacteria (Germano 1997). Populations of winter flounder, a commercially important groundfish, have decreased significantly since the 1970s (Rountree et al. 2003) probably due to over-fishing, effects from Brayton Point Power Station, and degraded water quality . It is also possible that high nutrient loading from upstream sources is causing an over-abundance of green algae (Ulva spp.) which may cover spawning areas for winter flounder in the lower Lee River (M. Scherer, Marine Research, Inc., Falmouth, MA, pers. comm.). Green macroalgae have been found to be dominant in shallow, nutrient-enriched estuaries in southern Connecticut (Harlin 1995). Some fish species, such as tautog (Tautoga onitis L.), however, benefit from increased macroalgae in bottom waters (Dorf and Powell 1997). Cultural eutrophicaton can also degrade eelgrass. Eelgrass beds, an important habitat for a variety of marine organisms (Heck and Thoman 1984), are absent from Mount Hope Bay, due in part to eutrophication (Kopp et al. 1995). The Mount Hope Bay Tidal Restriction Atlas focused on the potential impacts of tidal restrictions to salt marsh, intertidal and subtidal flats, and submerged vegetation such as eelgrass. While the scope of the project did not allow for a full exploration of the effects of tidal restrictions on water quality and estuarine habitats, reduced tidal flushing and the documented water quality impairment of Mount Hope Bay suggest that restrictions have exacerbated water quality problems. Table 1. Salt marsh area in Massachusetts estuaries. Area Shoreline length Ratio of area to Estuary (hectares) (kilometers) shoreline length Mount Hope Bay1 165.9 64.4 2.6:1 Plum Island Sound2 3294.1 262.0 12.6:1 Essex Bay3 939.3 95.4 9.8:1 Herring River4 405.9 49.7 8.2:1 Pleasant Bay5 445.6 105.7 4.2:1 Westport River6 405.9 82.6 4.9:1 1Curley et al. 1974 2Buchsbaum and Purinton 2000 3Chesmore et al. 1973 4Curley et al. 1972 5Pleasant Bay Resource Management Alliance 2003 6Fiske et al. 1968 36 Northeastern Naturalist Vol. 13, Special Issue 4 Methods The geographic scope of the project was limited to the portion of Mount Hope Bay coastline located within Massachusetts. In addition, the MWRP established criteria for assessing the landward extent of the survey. For the Taunton River, the upstream extent of the study area was identified as the Berkley Bridge, based on known distribution of salt marsh. For other tributary streams, the upriver extent was established either by a dam, which prevents further upstream tidal flow (e.g., Cole, Runnins Rivers) or by an abrupt change in topography and vegetation (e.g., Lee, Palmer Rivers). The upland boundary of the study area was identified as the area subject to the one-year storm tidal flood elevation based on mapping by the Federal Emergency Management Agency (FEMA). Wetland vegetation types illustrated on Massachusetts Geographic Information System (MassGIS) provided additional information to verify the upland boundary. The five steps for developing The Mount Hope Bay Tidal Restriction Atlas were: (1) initial site identification using a geographic information system (GIS), (2) stakeholder review of initial site list, (3) field investigations of a subset of sites, (4) desktop GIS analysis to complete data collection of field visited sites, and (5) categorization of results. Initial site identification using GIS ArcGIS v.8.2 was used as the supporting program for initial site identification. Existing data, including true color orthophotography, USGS topographic maps, and 1:5000 scale wetlands and streams maps produced by MassGIS, were used to complete the analysis. Data layers were assembled into a single project file and viewed simultaneously as overlapping layers. Potential restriction sites were initially identified on orthophotographs and USGS topographical maps where manmade obstructions were located downstream of the FEMA one-year storm elevation. Wetland data layers were then overlain to assess wetland types upstream and downstream of potential restriction sites. A point shapefile was created in GIS to show the location of all potential tidal restriction sites in the study area. For each site, a unique site number was assigned and the following information recorded in a corresponding data table: town; name of waterbody; proximity to other restriction sites when “hydrologically connected” (i.e., sites in a series); cumulative area of affected wetlands; and area of adjacent affected wetlands for sites in a series. Cumulative affected wetlands are defined as all tidally influenced wetlands located upstream of the restriction site, including those affected by other restrictions. Adjacent affected wetlands are defined as only the wetlands directly upstream of the restriction site. Once the site information was compiled, an area shapefile was created to illustrate the spatial extent of wetlands potentially affected by suspected restriction sites. Wetlands and waterbodies were determined to be tidally influenced based on hydrologic connection to tidal waterways, topographic 2006 S.B. Barrett, B.C. Graves, and B. Blumeris 37 position relative to adjacent wetlands, and proximity to salt marsh. The following upgradient wetland types (as defined in the wetlands datalayer) were determined to be potentially affected by a restriction: open water, salt marsh, deep marsh, shallow marsh, and shrub swamp. Wooded swamp was included only in cases where site-specific characteristics (e.g., proximity to marsh, tidal creeks, and topography) provided compelling evidence that the wetland was affected by an identified restriction. Stakeholder review and selection of sites for field investigation The list of sites identified using GIS was forwarded to local stakeholders for comment. Stakeholders, including representatives from municipal conservation commissions, non-profit organizations, and state and federal agencies, were selected based on their knowledge of the study area and interest in wetlands restoration. Stakeholders were provided with a summary cover letter and a series of maps illustrating identified sites, and asked to provide detailed comments. Follow-up phone calls were made to actively collect information. Stakeholders provided both confirmatory information on wetland vegetation, including presence of salt marsh and invasive species, as well as specific descriptions of the tidal restriction sites, including relative size and type of restricting structure. Stakeholder comments were used along with information collected during the initial identification stage to prioritize sites based on potential restoration benefits. Factors considered in prioritizing the sites included restricting structure type, proximity to salt marsh, proximity to tidal waters, and supporting details provided during stakeholder review. The project team selected 37 sites as the maximum number that could be investigated in the field based on project funding. Field investigations The purpose of the field investigations was to verify the restriction of tidal flow and to collect information on the restriction site. Criteria used to evaluate tidal influence included tidal elevation, flow through the restriction, and presence of salt marsh upstream and downstream of the restriction. Sites determined to be tidally influenced and potentially restrictive were further investigated using a rapid assessment technique. A four-page field inspection form was developed to ensure consistent data collection for each site. Collected site information included restriction-feature type (e.g., roadway culvert, bridge, dam) and dimensions, condition of the restriction and its components, wetland vegetation, waterbody characteristics, tide level, salinity level and tidal stage, adjacent land uses, and hydrologic evidence (e.g., ponding water, flow velocity, scouring). Tide level was measured immediately upstream and downstream of the restriction opening. Salinity was measured in the waterway approximately 1.5 m to the side of the structure opening and 1 m below the surface immediately upstream and downstream of the restriction using field meter YSI Model 85. Tidal stage was also recorded at the time of the salinity reading. Digital photographs were taken of the restriction and adjacent wetlands. 38 Northeastern Naturalist Vol. 13, Special Issue 4 Desktop analysis Upon completion of the field work, each confirmed tidal restriction site underwent further computer-based analysis. A one-page analysis sheet was created to provide a consistent and organized approach to information gathering. The attributes listed on the sheet and reviewed by GIS included: ownership type; presence of upstream/downstream restrictions; location within a designated fish run; total acreage; acreage by wetland type (e.g., open water, salt marsh); Massachusetts Natural Heritage and Endangered Species Program rare species or priority habitat designation; and associated protected open space. Categorization of results and distribution to end users Using the information collected, confirmed tidal restriction sites were assigned a priority ranking of low, medium, or high in terms of potential for restoration. Criteria used to prioritize sites included observable impact indicators (e.g., invasive species, ponding, scouring), potential benefits of restoration (e.g., reduction in invasive species, increased flushing to water quality-impaired waters), and feasibility based on practical factors such as ownership and present uses. Sites that most fully met the criteria were scored “high” (i.e., high feasibility for restoration), while those that partially met the criteria were scored “medium,” and those that least met the criteria were scored “low.” All data generated for each site were compiled into individual three-page site-assessment reports. Site-assessment reports were formatted in Adobe and linked to a database-supporting searchable data fields with site attributes, aerial photography with superimposed GIS data layers, and representative photographs taken at the site (Figs. 2, 3, and 4). The final Atlas included site-assessment reports for the field-visited sites as well as a spreadsheet of data collected during the initial stage of the project. The Atlas was presented in an interactive digital format to provide users with a practical means for reviewing the data. It was distributed to local stakeholders on a compact disk and made available on internet webpages. Examples of the representative site assessment reports can be viewed at www.epsilonassociates.com. Results and Discussion Seventy-three sites were identified through the initial GIS-based identification step (Fig. 1). A 74th site was added following stakeholder input. Of the 74 sites, 37 were selected for field investigation. Of these 37, twelve were determined in the field not to be tidally influenced, and therefore no further data were collected. For the remaining 25 sites, data were collected in the field and from the desktop, and a site-assessment report was generated. Priority designations for the 25 sites where restrictions were found included 11 low-, 12 medium-, and 2 high-priority sites. 2006 S.B. Barrett, B.C. Graves, and B. Blumeris 39 Tidal restrictions in the Mount Hope Bay study area can be broadly categorized as bridges/fill, undersized culverts, and dams/impoundments (Table 2). These structures support active or abandoned highways, roads, cartpaths, railroad lines, and stonewalls. Other components of restrictions included dikes, berms, tide gates, and fill material. Bridges Fourteen of the tidal restrictions investigated in the field were bridges with adjacent fill and causeways. The majority of these crossings were road bridges, and the remainder were abandoned railroad bridges. In two instances, the railroad bridges have been removed, with the causeway fill left in place, restricting tidal flow. As a group, these restrictions appear to be relatively minor in that they permit sufficient water to pass so that no differences in tidal height and/or salinity were found on either side of the restriction. However, the structures often exhibit hydrologic indicators of restricted flow (such as ponding, increased flow velocity, and scouring). These restrictions, where significant length of fill has been placed in a tidal tributary, also exhibit channel widths much larger than the widths of structure openings. While visible indicators of water quality impairment such as algal blooms were generally not observable during winter field work, blooms have been observed during the growing season, and these barriers likely exacerbate nutrient and pathogen enrichment. The removal or modification of these tidal restrictions for increased tidal flushing would be expected to improve upstream water quality and estuarine habitats. Examples of restoration actions include the addition of culverts or small bridges to open up discrete areas along the filled causeway. The feasibility for removing such restrictions varies widely. Where the restricting structure is no longer in use (e.g., abandoned railroad beds), removal of the structure could be an option. Where the restriction is part of an active roadway, reasonable improvements are dependent on scheduled repairs and extent of work necessary to alleviate the restriction. Table 2. Types of tidal restriction identified in the study area. Restriction type Number identified Bridges 14 Roadway bridges 6 Roadway causeways 3 Railroad bridges 1 Railroad causeways 3 Stone wall 1 Culverts 8 Arched culverts 2 Single conventional culverts 4 Multiple (grouped) conventional culverts 1 Culverts with tide gates 1 Dams 3 Dams 2 Dikes 1 40 Northeastern Naturalist Vol. 13, Special Issue 4 Figure 3. Site assessment report example: site photographs. Figure 2. Site assessment report example: site overview. 2006 S.B. Barrett, B.C. Graves, and B. Blumeris 41 Culverts While bridges were the most common restricting structure in Mount Hope Bay, undersized culverts and their impacts on New England salt marsh have been the focus of past research (Burdick et al. 1997, Sinicrope et al. 1990, Warren et al. 2002) and inventory work (Buzzards Bay Project 2002, Cape Cod Commission 2001, MWRP 1999). Eight such sites were identified in the study area during the field investigations. The culverts observed in the field included a range of configurations from 23-centimeter diameter round culverts to 61-centimeter box culverts. Most restrictions consisted of a single culvert, but in one case a system of six parallel Figure 4. Site assessment report example: site data. 42 Northeastern Naturalist Vol. 13, Special Issue 4 culverts was identified. Varying culvert sizes designed to accommodate different amounts of stream flow also affected the potential for tidal restriction. For example, larger arch culverts located near major tributaries pass significantly more water and therefore are similar in characteristics to bridges rather than the undersized culverts studied elsewhere in New England (Burdick et al. 1997, Sinicrope et al. 1990, Warren et al. 2002). Smaller culverts were identified, and several of these sites included upstream salt marshes extensively colonized by invasive plant species. At some sites, the most noticeable indicators of a tidal restriction—differences in tidal height and salinity between the upstream and downstream openings—were recorded. A tide gate observed at one of the culvert sites provided undisputable evidence of tidal flow restriction. While many factors, such as potential flooding impacts on upstream private property, must be evaluated before enlarging an undersized culvert, these sites are among the most promising to remediate, as the solution requires replacing the existing culvert with a larger one (Roman et al. 1995). Accurately predicting hydraulic design is essential for selecting the appropriately sized replacement culvert (Sinicrope et al. 1990). Dams While restrictions caused by roads and railroads are mostly unintended consequences of development, dams and impoundments have been constructed for the primary purpose of impounding water for various uses. Three such structures were identified in the study area: a farm pond, a former hydroelectric dam (known as the Mobil Dam), and a golf course irrigation pond. Restoration feasibility is dependent, in part, on the utility and value of the structure to its owner. If the structure is no longer serving its intended use, then there is an opportunity to remove or modify it. An example in the study area is the Mobil Dam, which measures 2.5 meters in height, on the Runnins River. Built for hydropower, it is no longer used for its original purpose. However, a thorough evaluation of the value of the existing impounded habitat compared to the restored tidal habitat is needed. Environmental factors also affect feasibility such as the potential impact of mobilizing contaminated sediment that may have collected behind the dam. Where impoundments continue to provide value to the owner, restoration requires the consideration of multiple factors that balance restoration benefits and the current uses. While the two irrigation ponds identified above continue to provide water for their existing owners—a country club and a farmer—creative solutions may be available. Conclusions The Mount Hope Bay Tidal Restriction Atlas is different from other atlases completed in Massachusetts in two important ways. First, the majority of identified tidal restrictions in the study area are affecting tidal exchange in estuaries rather than in salt marshes. Second, salinity levels in upper Mount 2006 S.B. Barrett, B.C. Graves, and B. Blumeris 43 Hope Bay are naturally low, which has implications for restoring the salt marshes that are restricted. These factors presented challenges for assessing tidal restrictions and the potential benefits of their removal. The unique characteristics of Mount Hope Bay with its relatively small area of salt marsh were first recognized after the project had begun. The initial site identification confirmed a considerable number of bridges and filled causeways, but few marshes. The field program was modeled after other tidal restriction assessments, which focused on rapid field assessment based on visible evidence of impact (e.g., vegetation, tidal height and salinity disparities, ponding, scouring). While at least one of these indicators was present at each of our sites, vegetation and salinity change were often not visually perceptible at bridge/fill sites, the most common restriction type found. Assessments of bridge/fill sites that are based solely on these factors would have resulted in a conclusion that such restriction sites do not cause habitat impacts. However, extensive fill in a natural channel to support causeways and bridges suggests that tidal flow patterns and water exchange upstream of the crossing may be impacted. Water sampling conducted by state agencies and local groups demonstrates that nutrients and pathogen levels in most upstream areas are elevated. Targeted water-quality sampling upstream and downstream of restriction sites could provide evidence of water-quality impacts of restrictions, but this was beyond the scope of the project. Instead, potential impacts of restrictions were inferred based on published pathogen data, past observations of macroalgal growth during the growing season, and known effects of structures on limiting tidal exchange. The initial site identification located many undersized culverts; however, field work showed that many were located above tidal influence, due to steep topography. For undersized culverts that were confirmed, two factors suggest that enlarging these culverts may not have a significant positive effect on upstream marshes in Mount Hope Bay. First, natural salinity is generally lower than 10 ppt due to the location of these sites in the upper estuary. As a consequence, an increase in salinity to 20 ppt (necessary to prevent growth of invasive species such as common reed [Tiner 1998]) will not occur. Second, the marshes upstream of the culverts in Mount Hope Bay are often small (􀂧 0.5 hectare) due to the steep shoreline topography. While the identified culverts appeared to be undersized, they seemed to pass sufficient tidal water to flood the upstream marsh due to the small area which required flooding. Despite the challenges presented by the broadened scope, The Mount Hope Bay Tidal Restriction Atlas attained several fundamental achievements. First, it compiled a comprehensive inventory of potential tidal restriction sites in Mount Hope Bay using GIS and aerial photographs. Second, the project provided the restoration community with a database of useful information about restriction sites in Mount Hope Bay. The Atlas has a user-friendly format with searchable data fields, GIS data layers, and site photographs in digital form. Third, the project has increased the attention of 44 Northeastern Naturalist Vol. 13, Special Issue 4 State restoration planners on other estuarine habitats that may be impacted by tidal restrictions. While additional research is required to demonstrate the extent of water-quality impacts and degradation of other estuarine habitats, the problem of eutrophication is documented in past reports (Massachusetts Department of Environmental Protection 2004), and the Atlas has identified the restriction sites for future investigation. Finally, the Atlas has provided restoration advocates with a baseline tool for future environmental restoration planning in Mount Hope Bay. Acknowledgments We wish to thank Deb Walker of Battelle Ocean Sciences and Hunt Durey of Massachusetts Coastal Zone Management for their technical assistance during the project’s implementation; Lori Parham of the Cobb County (GA) Planning Office (formerly of Epsilon Associates) for GIS support; and Bill Hubbard of the US Army Corps of Engineers New England District and Sam Mygatt and Les Smith of Epsilon Associates for editorial assistance in reviewing this manuscript. Literature Cited Buchsbaum, R., T. Purinton, and B. 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