25 Nearshore and Estuarine Research: Dynamics and Future Resiliency in the Coastal Zone II

This session focuses on drivers of change in coastal environments as well as planning for future resiliency in tidal marshes, mudflats, estuaries, and barrier systems, including human activity impacts, sea level rise, & changing sediment supply.

Monday, 23 March 2026
1:30 PM - 5:30 PM
CCC, Room 22/23

Tidal Flat Sediment, Access, and Carbon Storage in the Gulf of Maine

Paper number: 25-8
Program: Technical Sessions
Time: 3:50 PM – 4:10 PM

Authors

Abstract

Tidal flats play a vital role in ecosystem health, cultural history, and commercial shellfish harvesting. In the Gulf of Maine, tidal flats have been harvested for over 9,000 years (Kelly et al., 2010) and currently produce more than 95% of the nation’s soft-shell clams (NOAA FOSS, 2023). However, these environments are impacted by rising sea levels and a changing climate. In addition to threats from invasive species and warming temperatures, tidal flats are vulnerable to changes in Mean Low Water (MLW). Due to their shallow slopes (~1:800), even small increases in water level can lead to substantial reductions in exposed surface area at low tide—decreasing the area and time shellfish harvesters have to work. At Maquoit Bay in Brunswick, ME, a simple “bathtub” model of sea level rise predicts a loss of approximately 140 acres (26%) of exposed area between 2015 and 2025.

In this study, we use satellite imagery to measure sediment accretion and loss in surface area for several flats throughout the Gulf of Maine. We survey all available Sentinel-2 imagery of the sites and isolate cloud- and ice-free scenes from which to extract a series of instantaneous shorelines, mapping the location of the tide across various years and tidal stages. Each shoreline is then assigned a “2022 elevation” based on LiDAR data from the same year. We derive contemporaneous shoreline elevations from the nearest long-term water level logger to each site, accounting for timing differences with deployments of our own water level loggers when necessary.

By approximating tidal flat elevation from the water level in satellite images, we measure changes in elevation and calculate a rate of sediment deposition. We also compare satellite-derived surface area changes to those predicted by a bathtub model of sea level rise, investigating the significance of accretion relative to rising sea levels. These results are interpreted in the context of an anomalously rapid increase in MLW in the Gulf of Maine, which rose by 25 cm over the 10-year study period. Finally, we examine how harvester observations of changing access times align with both measured and modeled changes in tidal flat exposure.

Geological Society of America Abstracts with Programs. Vol. 58, No. 2

doi: 10.1130/abs/2026NE-411447

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