2025 Maine Sustainability & Water Conference

Thursday, March 27, 2025
Augusta Civic Center
Augusta, Maine

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Session E – Marshes for Maine’s Future

All Day Session
Presenters are indicated in bold font.

Session Co-chairs:
Tatia Bauer, Maine Coast Heritage Trust
Helena Tatgenhorst, The Nature Conservancy 
Chris Feurt, Wells National Estuarine Research Reserve

Salt marshes in Maine may not be as iconic as the rugged rocky coast, but their value as places that support fish, shellfish and migrating and resident birds makes them one of the most ecologically productive of Maine’s coastal habitats. In the Gulf of Maine, estuaries and coastal wetlands are used by two-thirds of commercially valuable fish, shellfish, baitworms and other forage organisms at some point in their life cycles. Coastal communities benefit from marshes’ ability to buffer storms and filter pollution from water. Salt marshes naturally capture and store carbon, reducing the impacts of fossil fuel emissions. Sustainability of salt marshes is threatened by sea level rise, development, and erosion. A legacy of agricultural practices designed to “reclaim” tidal marshes for farming continues to threaten marsh sustainability by hindering the ability of marshes to keep up with increasing rates of sea level rise. Maine’s Climate Action Plan, the newly funded Resilient Maine project and the newly formed Maine Tidal Marsh Restoration Network are increasing the pace of marsh restoration in Maine. This session highlights the work of organizations using innovative practices to restore hydrology, conserve pathways for marsh migration, protect critical habitat and build marsh resilience for ecosystem service provision.

Part of the afternoon session will be used to hold a meeting of the Maine Tidal Marsh Restoration Network, a collaborative group convening practitioners, scientists, resource managers, policy experts, and others to create a space to exchange information about initiatives, research, and projects. Time will be used to share updates of the nine sub-committees and workshop pressing topics within the group.

Session Schedule

Morning Session

Afternoon Session

8:30AM – 8:50AM
Restoration and building resilience with the 4-Tier method begins with surface hydrology

David Burdick, Jackson Estuarine Lab, UNH, dburdick@usnh.edu
Geoff Wilson, Northeast Wetland Restoration, s2ary@comcast.net
Susan Adamowicz, US Fish and Wildlife Service, susan_adamowicz@fws.gov
J. Grant McKown, Jackson Estuarine Lab, UNH, James.McKown@unh.edu

Maine’s salt marshes are facing an existential crisis. Agricultural infrastructure is combining with rising sea levels to result in large scale loss of elevation from subsidence.  While some subsidence is associated with dense ditching, most of the losses stem from extreme soil waterlogging and flooding as embankments hold excess water on the marsh surface.  Salt Marsh Adaptation and Resilience Teams (SMARTeams) is working with land trusts and agencies responsible for management of marsh resources to identify agricultural impairments, design new hydrologic systems, and implement restoration within a holistic, adaptive management context that is based on a 4-tier approach: Halts further subsidence;  Optimizes plant productivity and marsh building processes; Tunes the hydrology and elevation to promote wildlife concerns (e.g., salt marsh sparrows); and Tends to the functional hydrology through long-term adaptive management.  Our experience over the last decade has shown that the majority of tidal marshes would benefit from analysis of impairments and hydrologic re-design using a light touch that minimizes further human impacts to the marsh. By recognizing the new paradigm of salt marsh development following agricultural abandonment, we can re-set our expectations and begin a new chapter of restoring surface and channel hydrology to stimulate marsh elevation growth and resilience.

8:50AM – 9:10AM
Linking Plants and Groundwater in Midcoast Maine Tidal Marshes

Ruth Indrick, Kennebec Estuary Land Trust (KELT), rindrick@kennebecestuary.org

Salt and brackish tidal wetlands are a mosaic of different plant types. This mosaic can reveal important information about the underlying movement of water. Because these wetlands are stressful places to grow, with flooding, salt, and full sun, they support a limited set of plant species.  Of those plants, each does best in a slightly different combination of flooding and salt.  The mosaic of plants on the surface is shaped by small scale variability within a marsh that provides specific conditions for species to excel and outcompete others.  

Understanding the unique habitat requirements of different plants can reveal locations where water is causing problems. The flow of water within Maine’s salt marshes has been highly modified. Extensive networks of ditches and embankments were built between the 1700s and early 1900s for agriculture in tidal marshes.  Although in many places, the ditches and embankments themselves are no longer clearly visible, the arrangement of plants on the marsh surface into networks of squares and grids provides clues to areas where groundwater is trapped, draining normally, or draining too fast due to hidden agricultural infrastructure.

To learn more about the connections between plant species and the underlying groundwater in Kennebec Estuary marshes that are being evaluated for restoration projects, KELT has monitored groundwater levels using simple shallow wells at five marshes in a variety of different plant communities.  The presentation will share the observed differences between groundwater movement in relation to the overlying vegetation and the additional monitoring helpful for the future.

9:10AM – 9:30AM
High Hopes: Boosting Marsh Elevation and Understanding through Thin Layer Sediment Placement

Bri Benvenuti, Ducks Unlimited, bbenvenuti@ducks.org 
Lauren Lenderman, P.E., Ducks Unlimited 
Kate O’Brien, U. S. Fish and Wildlife Service, Northeast Region
Karl Stromayer,  Rachel Carson National Wildlife Refuge
Adrienne Kovach, University of New Hampshire
Gregg Moore, University of New Hampshire
Marjorie Mednikova, University of New Hampshire

Recent analysis of elevation and tidal data indicates many southern Maine tidal marshes are not building elevation at a rate that is necessary to keep pace with current sea-level rise and the signatures of degradation are already present. Restoration of these systems for ecological integrity and community resilience is urgent before they decline to a point where restoration would be more costly and less effective. This requires a combination of techniques at multiple spatial scales and a phased restoration approach. Our project knits together interdisciplinary research and evidence-based conservation to address elevation deficits due to historic marsh agriculture. Through active collaboration between conservation partners, municipalities, policymakers, scientists, and community members, we will implement the first beneficial use of sediment project in northern New England by placing ~1,000 cubic yards of dredged sediment on the marsh surface in winter 2025. Upon completion, we anticipate this project will serve as a template that can build the knowledge base and acceptance of this restoration practice within the regulatory, restoration, and natural resource community in Maine.

9:30AM – 9:50AM
CoastWise: Maine’s Guidance for addressing road\tidal habitat projects

Robert Van Riper, Maine Coastal Program, Maine Department of Marine Resources, robert.vanriper@maine.gov
Michael Burke, P.E., Interfluve, Inc, mburke@interfluve.com

Historical installations of tidal road crossings has resulted in modification of tidal exchange to upstream habitats, particularly salt marshes. The net effect is disruption of the amount and duration of flooding and the subsequent deposition of marine-derived sediment, which alter marsh composition, productivity and functions. Without regular flooding and sediment deposition, the salt marsh cannot maintain surface elevations to support plant growth, and it ‘drowns’. CoastWise was developed to provide background knowledge and project development procedures for a wide-variety of potential users to assist in retrofit of crossing structures and associated salt marsh rehabilitation. Information in the document was assembled by Government Agencies, Educational Institutions, Non-governmental organizations and consultants. A pilot 2-day training was completed in May 2024. Attitudes on the validity and appropriateness of the training were surveyed and the training revised to reflect areas of improvement. Portions of CoastWise are currently being partitioned into self-paced computerized subject-directed blocks to allow a reduction in in-person training to a single field-oriented day. This discussion will introduce CoastWise to the conference audience and provide a forum to answer questions regarding the process and future training.

9:50AM – 10:10AM
Tidal reintroduction at a system scale: 20 years of collaborative efforts in the WBPR marsh

Kirstin Underwood, Inter-Fluve Inc., kunderwood@interfluve.com
Ellie Mason, Downeast Salmon Federation, ellie@mainesalmonrivers.org
Mike Burke, Inter-Fluve Inc., mburke@interfluve.com
Jamie Carter, NOAA, jamie.carter@noaa.gov
Matthew Bernie, NOAA, matthew.bernier@noaa.gov
Jacob van de Sande, Maine Coast Heritage Trust, jvandesande@mcht.org
Jeremy Gabrielson, Maine Coast Heritage Trust, jgabrielson@mcht.org
Robert VanRiper, Maine Coastal Program, robert.vanriper@maine.gov
Casey Clark, Maine Department of Marine Resources, casey.clark@maine.gov
Helena Tatgenhorst, The Nature Conservancy, h.tatgenhorst@tnc.org

At over 450 acres, the historic tidal wetlands of the West Branch Pleasant River (WBPR) are among the most significant tidally-restricted wetlands in the Gulf of Maine. Tide gates at the mouth of the WBPR have restricted tidal flow to the marsh since 1940. Five additional road-stream crossing structures are present throughout the marsh, most of which currently experience regular flooding. All are within the range of Highest Astronomical Tide and are not currently sized to accommodate tidal flow. The WBPR estuary and surrounding communities are in Washington county, which has some of the highest poverty rates in Maine and faces increasing pressure to adapt to rising sea levels. With this vulnerability comes an opportunity to address critical infrastructure needs while restoring the natural flood protection and ecological benefits of a historic salt marsh ecosystem.

A recent study of the WBPR complex, led by Downeast Salmon Federation and supported by a range of governmental and non-governmental partners, has built upon previous baseline assessments and feasibility-oriented studies of the marsh since the early 2000’s. In support of a stakeholder-based initiative to restore the historic salt marsh and reduce community vulnerability to sea-level rise, the study identifies challenges and opportunities of restoring tidal flow to the WBPR marsh, and provides recommendations for restoration at a system scale. Indications of change since the first assessments suggest habitat and evolution patterns that respond to the unique legacy of disturbance of this system, showing promise for full recovery of the coastal wetlands.

10:10AM – 10:30AM
Engaged Property Owners: Potential Partners for Maine’s Salt Marsh Future

Caroline Noblet, University of Maine, caroline.noblet@maine.edu
Melissa Godin (student), University of Maine 
Kent Messer, University of Delaware, 
Will Allen, Innovation Resources Group; 
Jamie Christensen, Innovation Resource Group. 

Maine’s salt marshes offer an important local resource in addressing climate change impacts on Maine’s shorelines, therefore understanding the preferences of coastal landowners regarding marsh on their property helps to accelerate and scale key preservation and restoration efforts. We use data collected in fall 2024 via mixed methods (postal mail invitation to an online survey) distributed to coastal property owners of Maine (n= 857; response rate = 18%) to examine landowner knowledge/perceptions of salt marsh on their properties, gauge interest in a series of conservation interventions and examine the efficacy of informational messages surrounding the benefits of salt marshes. More than half of respondents (53%) expect increased flooding and erosion on their property within the next 5 years, 31% expect no change and 16% are unsure. We see impacts of information messages as participants were more likely to state that ‘flood protection’ was an important benefit of salt marshes when exposed to information about the role of marshes in preventing damage from future coastal storms. Importantly, participants expressed interest in learning more about coastal land use management, with 68% of respondents interested in educational workshops. Further, owners of larger parcels (>3 acres) and with salt marsh views from their home expressed greater interest in conservation efforts and collaborating with conservation organizations/university scientists regarding coastal management. Our results expand the understanding of the preferences for action and engagement among coastal property owners, which help shape effective policy and planning around the preservation and restoration of salt marshes.

1:30PM – 1:50PM
Carbon dynamics in three tidally restricted salt marshes in Maine, USA

Beverly Johnson, Department of Earth and Climate Sciences, Bates College, bjohnso3@bates.edu
Claire Enterline, Gulf of Maine Research Institute, centerline@gmri.org
Jamie Hollander, Department of Earth and Climate Sciences, Bates College, jholland@bates.edu
Kate Dickson, Department of Earth and Climate Sciences, Bates College, kdickson@bates.edu
Anna Sarrazin, Department of Earth and Climate Sciences, Bates College, asarrazi@bates.edu
Slade Moore, Little Heron Media, slade@littleheronmedia.com
Kristen Puryear, Maine Natural Areas Program, kristen.puryear@maine.gov

The state of Maine has the second largest area of salt marsh habitat in the Northeast US, thus representing a significant coastal carbon sink in the region. Many of these marshes experience restricted tidal inundation which can result in decreased efficiency of carbon sequestration and storage. Little is known about the carbon dynamics associated with tidal restrictions in Maine salt marshes. This study examines carbon dynamics upstream and downstream of tidal restrictions in three Maine salt marshes: the Spurwink Marsh, in Cape Elizabeth; the Drakes Island Marsh, in Wells; and, the Jones Creek Marsh, in Scarborough. In summer of 2023, carbon dynamics were assessed by measuring monthly greenhouse gas fluxes and pore water salinity, and by analyzing the soil core carbon density and longterm carbon sequestration rates.  Each site behaved differently, due, in part, to the degree to which the tidal restriction appears to impact the hydrology of the site. The Spurwink Marsh has excellent hydrologic connectivity upstream and downstream of the restriction with similar soil carbon densities and sequestration in both areas of the marsh. Upstream of the restriction at Drakes Island, soil salinities are lower and CH4 emissions and carbon sequestration rates are higher. The Jones Creek Marsh is the most degraded site we studied, with the highest rates of peat compaction and largest areas of pool habitat upstream of the restriction. These data provide important baseline information for predicting the carbon benefits that can be accrued with salt marsh restoration via tidal restoration.

1:50PM – 2:10PM
High Resolution Mapping of Carbon Stocks and Sequestration and Organic Matter Sources over the last 2000 Years in the Sprague River Marsh, Phippsburg Maine

Adelle Welch, Bates College, awelch@bates.edu
Beverly Johnson, Bates College, bjohnso3@bates.edu
Phil Dostie, Bates College, pdostie@bates.edu
Margo Danahey, Bates College, mdanahy2@bates.edu
Adi Kolf, Bates College, akolff@bates.edu
Izzy Larson, Bates College, ilarson@bates.edu
Hadley Blogett, Bates College, hblodgett@bates.edu
Sam Turtle, Bates College, sturtle@bates.edu
Evelyn Marchand, Bates College, emarchand@bates.edu 
Riley Baker, Bates College, rbaker3@bates.edu

Salt marshes are regarded as key blue carbon stocks with high rates of carbon sequestration due to tidal inundation. However, the impacts that rising sea levels and human development and alterations to salt marshes have on carbon stocks and organic matter deposition have yet to be fully understood. The Sprague River Marsh, in Phippsburg Maine, has been subject to many alterations through the last 400 years (ditching, the building of a tidal restriction and the dredging and redirection of the natural tidal channel). This study analyzes the geochemical records (carbon density and sequestration, d13C, d15N, and C:N ratio) of 43 sediment cores from Sprague Marsh. The geochemical data were parsed into different time intervals (0-50, 50-100, 100-200, 200-300, 300-500, 500-1000, 1000-2000 YRS BP) based on an age model derived from 7 radiocarbon dates. Marsh surfaces were mapped using ArcGIS and kriging to identify areas and times where organic deposition was dominated by high salt marsh, upland plant input, or marine input. These marsh surface reconstructions illuminate shifts in organic matter deposition with changes in relative sea level rise (in agreement with Johnson et al., 2007), the dredging of the tidal channel, marsh evolution and colonization, marsh growth prior to European Colonization, and show significantly higher carbon stocks in the northernmost area of Sprague Marsh. This detailed history of Sprague Marsh can be used to identify areas of high carbon content and the number of cores needed to accurately reconstruct marsh history and analyze and predict carbon stocks.

2:10PM – 2:30PM
Climate Adaptation of US Route 1, US Route 9, and the Scarborough Marsh: A hydraulic modeling study of the upper reach of the Scarborough Marsh

Leila Pike, GEI Consultants, Inc., lpike@geiconsultants.com

This presentation will discuss the findings of a hydraulic modeling study of the Scarborough Marsh which was conducted as part of a climate adaptation study for the US Route 1 Dunstan River crossing and the US Route 9 Cascade Brook crossing. This modeling study was performed as part of a Maine DOT project to adapt the roadway infrastructure to reduce flood risk during extreme tides and for increased sea levels. The study evaluated how the existing crossings, along with proposed design alternatives, such as a box culvert addition and a single-span bridge for US Route 1, would perform under current tidal conditions and a future scenario with four feet of sea level rise.

Using SRH-2D modeling software, the hydraulic study analyzed key performance indicators such as peak hydraulic head difference, upstream water surface elevations, and inundation extents.  Results revealed that increasing the structure’s hydraulic opening reduced flow restrictions. This would promote marsh health, increase terrestrial and aquatic connectivity, and foster tidal transparency. However, increased tidal transparency could lead to increased water surface elevations upstream of the crossings, which may contribute to roadway inundation in upstream reaches of the marsh. 

Multiple state agencies and departments within the agencies, federal agencies, and municipal staff members were part of a technical committee reviewing results of the modeling analysis and providing input on project goals. Adaptation of the US Route 1 and US Route 9 crossings with increased hydraulic openings are a valuable approach to meet both infrastructure and salt marsh climate adaptation goals.

3:00PM – 4:30PM
Maine Tidal Marsh Restoration Network Spring Meeting

Tatia Bauer, Maine Coast Heritage Trust  
Helena Tatgenhorst, The Nature Conservancy 
Julia Kemnitz, Coastal Program, U.S. Fish & Wildlife Service
Bobby Van Riper, Maine Coastal Program, Maine Department of Marine Resources, robert.vanriper@maine.gov

The Maine Tidal Marsh Restoration Network formed from a group of partners in 2023 to achieve the following objectives: 1) Convene practitioners, scientists, resource managers, policy experts, and others to collaborate in restoration of Maine’s tidal marshes; 2) Create a space to exchange information about initiatives, research, and projects; and 3) Identify and begin to address challenges around tidal marsh restoration in Maine.

The draft agenda for the meeting is available here: