SALT POOLS DRIVE SURFICIAL TRANSFORMATIONS OF MAINE SALT MARSHES

Salt pools are shallow, water-filled depressions that are common features of north-temperate salt marshes. In other regions, like the Gulf of Mexico and the Mid-Atlantic, vegetated marsh platforms convert to open water through the expansion of pools over decadal time periods and in response to rising sea level. These changes are a concern because they signify ongoing loss of marsh ecosystem area, associated resources, and may represent an irreversible, ecological tipping point in these environments. 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 geologic 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 pool types and that pool type may relate to observed patterns of surficial change. Our results demonstrate that many pools in north-temperate marsh systems are dynamic and that they are important drivers of surficial change as these marshes respond to sea-level rise.