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Delaware River Terraces and Uplands

Ecoregion in Atlantic Coastal Plain in DE, NJ, PA

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The Delaware River Terraces And Uplands ecoregion is a narrow, marshy, nearly level to rolling lowland adjacent to the Delaware River estuary and Delaware Bay that extends from southeastern Pennsylvania to southeastern Delaware. It is characterized by low, nearly level terraces, an ocean modified climate, a long growing season, freshwater intertidal marshes, saltwater marshes, and small, sluggish, meandering streams; physiography is distinct from that of the higher, less level, and much less marshy Delmarva Uplands (63f), Piedmont Uplands (64c), and Northern Rolling Inner Coastal Plain (65n). Low lying areas are commonly saturated during the growing season or flooded. Saline marsh deposits dominate; alluvial and estuarine sand and silt are also widespread. These deposits are underlain by unconsolidated and easily eroded Quaternary gravels, sands, and silts. Elevations are less than 60 feet (18 m), local relief is less than 35 feet (11 m); streams have low gradients and are often tidally influenced. Erosion, dredging, filling, and the construction of embankments and bulkheads has eradicated many wetlands; regulations since the 1970s have reduced annual wetland loss substantially. Ecoregion 63b is universally low in elevation and is characterized by nearly flat terrain, terraces, tidal marshes, ponds, and swampy streams. Brackish wetlands are common and serve as habitat for fish, shellfish, and wildfowl. Elevations range from 0 to 50 feet (0-15 m) and relief is less than 35 feet (11 m); surrounding ecoregions are both higher and better drained. Ecoregion 63b is underlain by unconsolidated lower terrace sediments of Quaternary age. Alluvial sand and silt, estuarine sand and silt, saline marsh deposits, and marine sand, silt, and clay are common; swamp deposits occur (Richmond and others, 1987). Ultisols and Histosols have commonly developed from residuum. They support a potential natural vegetation of Oak-Hickory-Pine Forest (dominants: hickory, longleaf pine, shortleaf pine, loblolly pine, white oak and post oak), Northern Cordgrass Prairie, and Southern Floodplain Forest (Kuchler, 1964). Extensive tidal marshes and salt estuarine bay marshes are found on the poorly drained soils of the silty low terraces of Ecoregion 63b. The tidal marshes are most extensive on the lower Eastern Shore of the Chesapeake Bay; here, the terrain is low and tidal marshes extend farther inland than in other coastal areas (White, 1997). Dominant brackish marsh plant species are: a) big cordgrass along margins of tidal creeks and ponds; b) hightide bush along the higher periphery of marshes; c) saltmeadow cordgrass in marsh meadows; d) saltmarsh cordgrass - saltmeadow cordgrass on well-drained tidal flats; e) olney three-square in extensive, poorly drained, shallow depressions normally covered with surface water; and f) saltgrass. Salt estuarine bay marshes are found in lower Chesapeake Bay waters where salinity is relatively high and tidal fluctuations are narrow (Lippson, 1973).

— EPA

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