SALT POOLS IN THE STRATIGRAPHIC RECORD AND THEIR ROLE IN GOVERNING SURFICIAL CHANGE IN FIVE MAINE SALT MARSHES

Salt pools are shallow, water-filled depressions common to many north-temperate salt marshes. Studies from the Mid-Atlantic and Gulf Coast observe an increase in pool size and number in response to relative sea-level rise, resulting in rapid conversion of once-vegetated surfaces to open water over short time periods. Little work characterizes Maine salt pools, despite their abundance and apparently important role governing surficial salt marsh processes. This study examines pools from five salt marshes distributed S-N along Maine's coast (Ogunquit, Brunswick, Gouldsboro, Addison, and Lubec), combining field surveys with spatial analyses and Dutch coring. Our work indicates that most pools in Maine are secondary and dynamic features (84% of cored pools; n = 19), rather than primary, relict landforms. In the stratigraphic record, pool sediment is characterized by dark gray muddy material with high water content, unique micro- and macro-fossils (e.g., Ruppia maritima drupes, Quercus leaf fragments, and Hydrobia totteni gastropods), and low C:N ratios. Time-series of aerial photographs indicate that many pools alter their shape and size over decades. The dynamic exchange between pools and tidal creeks is one geographically universal mechanism for substantial surficial transformations. Isotope analyses (²¹⁰Pb and ¹³⁷Cs) of paired cores in high-marsh and re-vegetated pools indicate that pools may drain, rapidly in-fill, and re-vegetate. This process may be one by which north-temperate salt marshes may achieve a surficial, dynamic equilibrium. These results demonstrate the important morphological role of pools in surficial salt-marsh processes in response to relative sea-level rise. Recognition of this dynamic pool cycle raises doubts about published reports of rapid sea-level fluctuations derived from salt marsh peat records. Better understanding of dynamic modern pools may expand the context for management of these critical coastal environments.