SALT MARSH: Background

Emergent wetlands are very diverse and widespread within the mid-Atlantic Coastal Plain. These wetlands vary according to salinity, soils, and position within the coastal landscape. The salt marsh is a common term for the wetland type classified as estuarine, intertidal, emergent. Salt marshes are abundant within this physiographic region and occur primarily within lagoon systems behind barrier islands, and along the shorelines of major bays and estuaries. This marsh type also extends up the lower reaches of major tributaries but ultimately gives way to brackish and

tidal fresh wetlands within lower salinity waters.

Within the mid-Atlantic region, a substantial number of salt marshes have been lost over the past 200 years. Between 1954 and 1978, loss rates were extremely high primarily due to urban and industrial development. However, since the passage of protective legislation, loss rates have declined dramatically. For example, before the passage of the Wetlands Act in 1972, Delaware was losing nearly 450 acres of estuarine wetlands annually. After implementation of protective legislation, losses have declined to just 20 acres per year. Other mid-Atlantic states have experienced similar trends.

Elevation within the saltmarsh determines inundation frequency and the associated vegetation. These vegetation zones have distinctive breeding-bird communities and conservation concerns. The low marsh is inundated daily by normal high tides and within the mid-Atlantic is dominated by smooth cordgrass (Spartina alterniflora) and black needlerush (Juncus roemerianus). The high marsh is inundated irregularly by spring tides and has a savannah-like structure. The high marsh zone is dominated by salt grass (Distichlis spicata) and salt meadow hay (Spartina patens) but also contains scattered shrubs (typically Iva frutescens or Baccharis hamilifolia).

One of the greatest future threats to salt marshes within the region is sea-level rise. If marshes are unable to accrete sediment at a rate that exceeds the rate of sea-level rise, vast areas of marsh may be lost to erosion and subsidence over the next century. Sea-level rise may be particularly detrimental to high marsh habitats because plants within this zone are very sensitive to inundation frequency. These habitats are already very limited within the region.

Another factor that threatens salt marshes is invasion by exotic species. Common reed (Phragmites spp.) is rapidly spreading throughout the planning unit and has already rendered vast areas of marsh unsuitable for many obligate species. Common reed is particularly detrimental to species such as Henslow's Sparrows and Sedge Wrens because it invades along the marsh-upland ecotone where these species occur. It is conceivable that this sensitive and very limited habitat could be lost entirely over the next few decades due to Phragmites alone.