GEOMORPHIC ANALYSIS OF DELAWARE BAY SALT MARSH POOLS

Using field surveys and analysis of historical aerial photography and drone imagery, we have documented changes of salt marsh geomorphology between 2002 and 2017 at Slaughter Beach, DE. The Delaware salt marshes are vegetated by Sp. Alterniflora, Sp. Patens, Distichlis Spicata species of salt marsh plants and are dissected by tidal creeks, man-made channels and mosquito ditches. We have documented that the surface of the Slaughter Beach salt marsh (~ 5.5 km²) has been decreased due to salt pond development and have identified the areas of most recent changes due to salt marsh degradation, channel in-fill, and the conversion of mosquito ditches to pools. Over 400 salt-marsh pools ranging in size from 0.5 m² to 0.11 km² have been recorded and monitored. We have identified different styles of salt pool evolution and dynamics from spontaneous appearance, to merging, splitting, and disappearance.

We have found that the number of pools has changed from 443 to 372 between 2001-2007, followed by an increase to 426 pools by 2012, and then a decrease to 313 pools by 2017, while the overall inundated surface area increased from ~0.2 to 0.3 km². The stratigraphic signature of most pools indicates that they are of secondary origin. We propose that driving mechanisms of changes in the number and size of salt pools are sea level rise, impact by severe storms (e.g. Irene and Sandy), and alteration of tidal flow and sediment supply due to human activities (jetty construction and channel dredging). However, the relationship between the Slaughter Beach salt marsh pool dynamics and hydrology remains poorly understood.