THE DYNAMIC ECOGEOMORPHOLOGIC ROLE OF SALT POOLS IN SALT MARSH EVOLUTION: WELLS, MAINE, U.S.A

Salt pools are shallow, continuously flooded depressions common to many north-temperate salt marshes. Previous work suggests that pools form as either primary or secondary features of salt marshes and that pools may serve as indicators of marsh break-up and wetland loss. This study combined field observations, sediment cores, and geographic information system (GIS) analyses of a time-series of aerial photographs to characterize salt pools of the Webhannet Estuary, Wells, Maine. In 2004/2005, we sampled 119 pools, recording presence/absence of a surficial drainage, Ruppia maritima, Spartina alterniflora pool invasion, average bank thickness and undercut measurements, and adjacent vegetative percent cover. A Principal Components Analysis of these data reveals three distinct pool types, though subsequent spatial analyses revealed no strongly associated trends in marsh location or pool shape with pool type. Spatial analyses of pools from aerial photographs from 1962, 1977, 1991, and 2003, show that pools were highly dynamic in both size and shape over the 41-year time period. Dutch cores support the aerial photograph analyses and reveal that most pools are secondary and ephemeral features of this salt marsh. High marsh, low marsh and pool facies in cores record largely pool formation, drainage, re-vegetation and new pool formation over time, and contain no signal of sea-level variation. Pools change shape and size by several modes, including channelized groundwater flow, narrow bay elongation and waterlogging/flooding of adjacent marsh. Preliminary observations in higher tidal regimes (4 – 6 m range) suggest that pools may ultimately transform to tidal channels in the process of draining. The results of this study show that pools are integral, and possibly the principal contributors to the dynamic salt marsh surface and the resulting stratigraphic record of north-temperate marshes.