STRATIGRAPHIC ANALYSIS AND RATES OF MAINE'S COASTAL WETLAND TRANSGRESSION DUE TO RISING SEA LEVEL

Sea level in Maine rises at about 2.0 mm/yr and is predicted to accelerate its rate of rise over the next century. Even slight sea-level rise may have dramatic impacts on low-lying areas, including salt marshes and adjacent freshwater wetlands, by driving ecological changes, shoreline erosion, or in-situ drowning. Maine's many freshwater wetlands extend to the coast where they are fronted by eroding bluffs, transgressing barriers, or interface with salt marshes. Published studies of peatlands in the UK suggest that they can collapse when they encounter the sea, but there exist few direct observations or stratigraphic data on this topic. Four freshwater wetland settings were selected for study where rising sea level is interacting with the peat deposits along the Downeast Maine coast. Grand Marsh in Gouldsboro consists of a broad, high salt marsh gradually transitioning into a brackish-to-fresh marsh at the inflow of a minor stream. Hay Creek in Jonesport shows an unusually abrupt transition of a tidal creek and salt marsh intersecting a raised bog, representing an ecological succession driven by salinity and frequency of flooding. Carrying Place Cove in Lubec exposes both a transgressing beach on its seaward side and a rapidly eroding peat bluff on its northern tidal-flat margin. At each site, ground-penetrating radar (GPR) and hand gouge auger (Dutch) cores were used to define the stratigraphic transgression. Time-series of aerial photographs allow measurement of differing transgression rates and predict future land losses. GPR provides information about the contact layers and the relationship of salt water to the freshwater peat. Transects and cores combined yield data that enables the determination of the long-term transgression rates, the processes operating during the change from freshwater bog to salt marsh, and the potential for stratigraphic preservation of freshwater bog sediments below marsh or barrier sediments during transgression. These data help explain earlier collected samples at the base of some Maine marshes with freshwater affinity and dates >10 ka cal, much earlier than the established salt-marsh peat based sea-level curve would predict.