ARE MAINE'S SALT MARSHES DROWNING? SALT POOLS AS DYNAMIC DRIVERS OF SURFICIAL CHANGE FOR SIX MAINE SALT MARSHES

Salt marshes are critical components of coastal systems and are vulnerable to rising sea-level in response to climate change. Studies in the Gulf of Mexico and Mid-Atlantic regions indicate that one response to sea-level rise is an expansion of salt pools in interior marsh sections, leading to the rapid conversion of once-vegetated surfaces to open water over short time periods. These changes are a concern because they signify ongoing loss of ecosystem area and associated natural systems and resources. This may represent an irreversible ecological tipping point (or state change) within these environments. In Maine, previous work demonstrates that the dynamic exchange between pools and tidal creeks is one mechanism for substantial transformations of the marsh surface. This study examines surficial dynamics of six salt marshes distributed S-N along Maine’s coast (Ogunquit, Wells, Brunswick, Gouldsboro, Addison, and Lubec), combining field surveys of pool ecophysical properties with geological coring and spatio-temporal analyses. Time-series of aerial photographs starting in the 1960s indicate that many pools alter their shape and size and that new pools form over decadal time periods. Dating sediments with ²¹⁰Pb and ¹³⁷Cs in high-marsh and re-vegetated pools indicate that pools can drain, rapidly fill in, and re-vegetate at 2-3 times the rate of the adjacent high-marsh surface. By this process, some north-temperate salt marshes may mitigate or circumvent potential drowning. Preliminary results of the ecophysical data (area, location, elevation, pool depth, and surrounding vegetation type) from 458 pools suggest that there are several distinct types and that pool type may relate to observed patterns of surficial change. Our results demonstrate that many pools are dynamic and that they are important drivers of surficial change as these marshes respond to sea-level rise.