GEOLOGIC AND HUMAN-FACTORS IN THE DECLINE OF THE TIDAL SALT-MARSH LITHOSOME - THE DELAWARE ESTUARY AND ATLANTIC COASTAL ZONE

Two to three thousand years ago, the fringing tidal salt marsh wetlands (including brackish and freshwater marsh) of the Delaware coastal zone were three to four times wider than at present. Observed variations in rates of marsh surface aggradation suggest that some areas are undergoing inundation whereas many other areas are undergoing aggradation at rates greater than sea-level rise as measured by a local tidal gauge (average 33 cm/century based on a 70-year record) and may be undergoing floral succession. Accompanying these sedimentary processes are coastal erosion rates up to 6.9 m/yr along the Delaware estuary, up to 2.8 m/yr along the Delaware Atlantic coast, and ranging from 0.1 m/yr to 0.6 m/yr along the Delaware Atlantic coastal lagoons. Human development has destroyed nearly 9% of Delaware's fringing salt marshes between 1938 and 1975. The rapidly growing trend toward hardening the edge of the adjacent landward uplands leads us to the conclusion that much of the fringing salt marsh of Delaware will disappear over the next two to three centuries with only small remnants declining to extinction ca. 1500-1700 years into the future. Impacts on the State of Delaware, comprised of 13% fringing salt marshes 1/4 century ago, will be profound in terms of destruction of a large segment of the Atlantic coastal or eastern North American migratory bird flyway, and an eventual forced accommodation of the inhabitants of Delaware to these naturally ongoing geological processes.