GEOMORPHIC CHARACTERIZATION OF SALT PONDS IN SLAUGHTER BEACH, DELAWARE

The purpose of this study is to analyze salt pond geomorphic characteristics in order to assess salt marsh vulnerability and its resilience to disturbances (e.g. storms surges, sea level rise, anthropogenic factors). The typical Delaware salt marshes are dissected by tidal creeks, man-made channels, mosquito ditches, and subject to semidiurnal tidal inundation. Using analysis of historical aerial photos and seasonal drone imagery we documented changes in geomorphology over ~ 5.5 km² of salt marsh between 2002 and 2018 at Slaughter Beach, DE. We documented that the surface of the Slaughter Beach salt marsh has been decreased due to salt pond development and identified the areas of most recent changes due to salt marsh degradation, channel in-fill, and conversion of mosquito ditches to ponds. Over 400 salt-marsh ponds ranging in size from 0.5 m² to 0.11 km² has been identified and monitored. The stratigraphic signature of most ponds indicates they are of secondary origin. We identified different styles of salt pond evolution and dynamics from spontaneous appearance, merging, splitting, to disappearance. The monitoring of permanently inundated marsh area of ~0.1 km² revealed its dynamic changes from 46% increase of its surface area between 2007-2012 to a 36% loss due to splitting and disintegrating into smaller ponds by 2017 and 2018.

Though many marshes in Delaware have been extensively studied, the Slaughter Beach salt marsh platform and hydrology remains poorly understood. Through aerial interpretation, we have found that the number of ponds has changed from 443 to 339 between 2002-2007, followed by an increase to 428 by 2012, and then decrease to 326 ponds by 2017, while the overall inundated surface area decreased from ~0.2 to 0.15 km². We propose that Delaware Bay salt marsh is impacted by rising sea level causing salt marsh degradation and ponds merging, severe storms (e.g. Irene and Sandy), and alteration of tidal flow and sediment supply due to human activities (jetty removal and channel dredging). The purpose of this study is to determine if salt pond characteristics at Slaughter Beach can be used as an indicator that the salt marsh platform is resilient to the aforementioned disturbances.