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Saltwater Systems

Saltwater systems along the North Carolina coast include estuaries, sounds, intertidal flats and tidal salt marshes. Estuaries encompass riverine environments that have increased salinity as they move toward the ocean (Cowardin, 1985/7). There is a point where a freshwater river, as in the Neuse River of NC, becomes an estuary as elevation decreases and salt water intrudes from the ocean. As rivers flow to the ocean and become estuaries they create unique coastal shallow water and wetland habitats both by carving new land forms into the terrain and by depositing sediment. As estuaries enter the ocean they can become sounds, which is just the very large and shallow part of the estuary, and will often result in unique intertidal flats where the depth allows. Sounds dominate much of the NC coast; these dynamic areas are protected by the barrier islands that constitute the Outer Banks, thereby allowing the extensive formation of large sounds like the Albemarle and Pamlico.

Bodie Island Salt Marsh

Often, when most people think about coastal habitats they are thinking about salt marshes, and for good reason! These unique ecosystems are some of the most productive in the world, a characteristic attributed to the influx of nutrients from the constant influence of the tides. Salt marshes along the NC coast are covered by tidal creeks, little saltwater channels that scar the smooth green color created by the dominant plant species, Spartina alterniflora, or marsh cordgrass. Created by the deposition of sediments either by the estuaries or the nearshore marine environment, salt marshes are extremely sensitive both to this rate of accretion and the rate of sea level rise in a particular region (Mitsch & Gosselink, 2000). Over time the long term rise and fall of the sea level has slowly shaped the NC coast, allowing marshes and barrier islands to form. Eustatic, or regional, sea level rise in North Carolina is currently about a foot per century (Riggs & Ames, 2003), a rate that has been extremely variable over geologic time but is currently increasing, alarmingly so in some areas.

Salt Marsh Waterfowl Impoundment

Human impacts on species in saltwater systems of NC are largely ruled by the effects of development and climate change. Development of the outer coastal plain, including the construction of roads, buildings, industry and sewer systems, results in increased pollution, either as a point or non-point source, loss and degradation of habitat and the direct killing of a species as a result of construction. Increased development compounds the impacts of climate change especially in the salt marshes that are so sensitive to the disequilibrium involved in accretion of sediments versus the eustatic sea level rise. As development in these areas occurs salt marsh ecosystems are “starved” of sediments; estuarine sediment inputs are inhibited by dams, dredging and shoreline development and marine sediment inputs are restricted as developments decrease barrier island overwash, a critical process that supplies sediment to NC’s extensive back-barrier marsh systems (see barrier island section for more) and the dredging of inlets (Riggs & Ames, 2003). As the rate of sea level rise increases, the marshes cannot “find” enough sediment from other sources to keep up with the rising waters, and can essentially drown as elevation is lost.