SALT POOLS AS INDICATORS OF SURFACE DYNAMISM IN NORTH-TEMPERATE SALT MARSH ENVIRONMENTS

Salt pools are shallow, continuously flooded depressions common to many north-temperate salt marshes. Previous studies suggest that pools may either be primary or secondary features of these environments. In some regions, pools presage the fragmentation and erosion of marshes. Recent analyses of a time series of aerial photographs from the Webhannet Estuary, Wells, ME, reveal that pools are dynamic, some drastically altering their shape and size over relatively short time periods. Many pools were observed to drain and re-vegetate during the 41 years of available aerial photography, while other, once-vegetated surfaces converted to pools during the same time period. Dutch cores confirm this dynamism and that pools in the Webhannet Estuary, and similar areas, form via secondary mechanisms. Pool environments are recognized in the stratigraphic record by largely inorganic sediments containing high water content, macrofossils of the submerged aquatic plants Ruppia maritima and Zostera marina, and potentially unique foraminiferal or diatom assemblages. We are currently examining pools in a transect from SW to NE coastal Maine, involving a gradient in tidal ranges from 3 m to 6 m and a climatic gradient that is reflected in the ecology of the salt marshes. Preliminary analyses of cores from Lubec, ME suggest that pools there may be of primary origin. This very youthful barrier spit (< 200 years old), may provide a glimpse of how marshes begin their evolution. These results may force us to re-examine the role of salt pool processes in our interpretation of the stratigraphic record and in governing salt marsh evolution.