The Delaware Estuary harbors some of the largest expanses of tidal marsh in northeastern North America with nearly 165,000 acres of intertidal marsh and creeks. However, historically more than half of the tidal marshes were subject to impoundment for salt hay farming from the early colonial period through the early 20th century. When tidal marshes are impounded, tidal flow to the marsh is prevented and drainage systems within the impounded area further dry the marsh to allow for farming activity. Changing the marsh hydrology exposes marsh soils to the air, allowing underlying peat soils to break down resulting in a loss of surface elevation. After the 20th century, when salt hay farming became less profitable, many farmers abandoned their farms, allowing the diked impoundments to fall leaving the marshes behind these dikes at elevations 2-4ft below normal levels. With a large acreage of the bay’s marshes subject to this past management, most of the bay is at high risk of becoming open water in the face of sea level rise.
Salt hay farming in Delaware Bay prevented the natural process of marsh accretion, leading impounded marshes to become lower in elevation under time. These impounded marshes are vulnerable to flooding and inundation from sea level rise.
Most beaches in the Delaware Bay rest on the shoreward edge of broad salt marshes. In the presence of low elevation marshes, the process of inland shoreline realignment (i.e., transgression) with sea level rise causes degradation of beaches and ultimately causes accelerated retreat and erosion of the shoreline when beach barriers disintegrate and expose marshes to full wave action. Over time, the beach becomes fragmented and plays a diminished role in protection of the marsh from erosion and the marsh begins to erode more rapidly as it is exposed to increasing wave action. In addition, the quality of the habitat for horseshoe crabs and shorebirds declines.
The process occurring on the Delaware Bay is akin to the phenomenon known as Runaway Barrier Island Transgression, when marsh loss precedes the disintegration of a beach barriers. The first stage of this process is the conversion of high marsh areas to inter-and subtidal conditions comprised of low marsh and tidal flat. In the case of Delaware Bay marshes, this stage emerges as a result of elevation deficits caused by marsh impoundment. The deficits effectively simulate several feet of sea level rise. Sea level rise and storms, in interaction with past and present management actions along the Bayshore, have resulted in habitats highly vulnerable to degradation. Vulnerabilities that reduce the resiliency of beach and marsh ecosystems surrounding the Delaware Bay communities.
Our team works to reverse the damage to the Delaware Bay marshes from salt hay farming with innovative restoration projects throughout the bay. It is our goal to bring the marsh height back to its naturally stable level – marsh vegetation just barely flooded on a normal tide and to improve the productivity of the wetland.
Saltmarsh grasses re-establishing over formerly degraded mudflat at Thompsons Beach, NJ after restoration efforts. Drone photography courtesy of Joseph Smith (smithjam.com)