A Characterization of Salt Pools and Their Role in Significant Coastal Change Over the Past 50 Years in Maine

Salt pools are shallow, water-filled depressions common to many north-temperate salt marshes. Studies from the Mid-Atlantic and Gulf Coast observe increases in size and number of pools in response to relative sea-level rise, resulting in a conversion of a once-vegetated surface to open water. Little work characterizes Maine salt pools, despite their important role governing surficial salt-marsh processes. Previous work from Maine, however, indicates that most salt pools are secondary and dynamic features, rather than primary, relict landforms. This study examines 458 pools from five salt marshes distributed S-N along Maine's coast (Ogunquit, Brunswick, Gouldsboro, Addison, and Lubec) and combines field surveys with spatial analyses to describe salt-pool characteristics. Pool depth did not vary significantly by site (19 ± 3 cm), while deeper pools tended to experience greater undercutting of their banks. More than half of pools surveyed were surrounded by low-marsh vegetation (predominantly Spartina alterniflora); only Gouldsboro and Addison pools were more frequently surrounded by high-marsh (predominantly Spartina patens) than low-marsh vegetation. Relatively few pools had obvious surficial drainages (16-28%) or distinct elongate extensions that often contribute to pool state change (14-33%). Finally, many pools contained Ruppia maritima, a submerged aquatic plant and consistent marker of salt pools in the sedimentary record (23, 20, 42, 72, 54% of pools respectively). In addition, preliminary analyses of time-series of aerial photographs indicate that many pools alter their shape and size over decades. The dynamic exchange between salt pools and tidal creeks is one geographically universal mechanism by which substantial surficial transformations occur. These results demonstrate the important morphological role of salt pools in surficial salt marsh processes and may expand the context for management of these critical coastal environments.