because both the animals and plants ut bcntliic 

 soft sediments are extremely sensitive to grain 

 size differences and the asscjciatcd chemical and 

 biochemical differences between sands and muds. 

 For instance, Brett (1963) documents how the 

 molluscan fauna changes as a function ol sedi- 

 ment type in a North Carolina sound. 



Superimposed upon the pattern of gradual 

 change in grain sizes along a gradient away from 

 inlets are other patterns created in part by the 

 second major energy source, wind-driven waves. 

 Waves moving across a body of water have their 

 greatest effect upon the bottom when they reach 

 the shoreline. At the shoreline, even small waves 

 can cause enough water turbulence to resuspend 

 fine sediment particles in the water column. 

 These particles are then transported into quieter 

 areas of deposition, retained in suspension until 

 the winds become calmer, or flushed out of the 

 estuarine or lagoonal system into the ocean. This 

 process, whereby waves expend their energy by 

 breaking at the shoreline, produces the familiar 

 gradient of increasing median particle diameters 

 along a transect from subtidal to intertidal flats. 

 The higher levels of the intertidal shoreline ex- 

 perience most of the wave action and are depleted 

 of the silt-clay fraction. Lower levels of the shore- 

 line less often feel the impact of wave action and 

 are therefore able to retain a muddier sediment 

 character. Most flats in coastal North Carolina, 

 where sounds tend to be large and wave action 

 significant, illustrate this change from sandy sed- 

 iments in the high intertidal to muds in the shallow 

 subtidal (Tenore 1972). 



Wave action within enclosed embayments 

 such as lagoons and estuaries varies with the size 

 of the body of water. In relatively large bodies of 

 water, the fetch is sufficient for substantial wave 

 devel(ipment, while the same wind speed would 

 fail to produce appreciable wave action in a small 

 tidal creek. The coastline along the North Caro- 

 lina Outer Banks is characterized by relatively 

 large sounds lying behind long barrier islands with 

 comparatively few inlets to the ocean (Figure 3). 

 Such coastal morphology is typical of a coastline 

 where tidal range is small to moderate, with tides 

 of approximately 1 m creating a so-called "micro- 

 tidal coast" (Davies 1964, Hayes 1975). Further 

 south in North Carolina (Figure 3), and especially 

 along the coasts of South Carolina and Gecjrgia, 

 the coastal morphology is radically different 

 (Williams et a!. 1966, Schwartz and Chestnut 



1973). The tidal range becomes larger (2 to 4 m), 

 producing a "mesotidal" coast and, as a conse- 

 cjuencc, barrier islands are short, inlets numerous, 

 marshes well-develcjped, and sounds and estuaries 

 quite small (Davies 1964, Hayes 1975). In areas 

 away frcjm the inlets, most intertidal flats in 

 South Carolina and Georgia are very muddy, 

 whereas the intertidal flats along the North Caro- 

 lina Outer Banks, even including those of Bogue, 

 Back, and Core Sounds tend to be true sand flats 

 (Figiue 3). This geographical pattern in sediment 

 size on intertidal flats is produced largely by the 

 varying importance of wind-driven waves, which 

 have a greater impact in larger bodies of water 

 because the fetch is greater. In smaller estuaries 

 and tidal channels, where waves are insignificant, 

 the slowing of tidal currents in the shallows is of 

 overriding importance and produces abundant 

 sedimentation of fine particles on the tidal flats. 



Although muddy areas are indicative of low- 

 energy environments where sediment deposition 

 is common, even mud-flat sediments are mobile. 

 Because they are finer, less energy is needed to 

 suspend and transport silts and clays than is re- 

 quired to move sand grains. Either tidal currents 

 or wave energy can be sufficient to transport 

 sediments on mud flats, as well as on sand flats. 

 The activities of burrowing benthic animals also 

 contribute to destabilization of soft sediments. 

 Although sediment mobility is greater in high- 

 energy sand environments, the mobility of uncon- 

 solidated, uncemented soft sediments is a univer- 

 sal characteristic of soft-sediment habitats. 



The largest of the North Carolina sounds, the 

 Pamlico, Albemarle, and Currituck, have negli- 

 gible contact with the .Atlantic Ocean (Figure 3). 

 This feature produces very brackish waters and 

 isolates these embayments from the influence of 

 lunar tides (Riggs and O'Connor 1974). Except in 

 the immediate vicinity of the few inlets (Ocra- 

 coke, Hatteras, etc.) where tid;il influence is felt, 

 there are few true intertidal flats or salt marshes 

 along the shorelines of these major bodies of 

 water. Persistently strong winds, operating over 

 large ex[)anses of water in these brackish sounds, 

 create occasional wind tides which expose portions 

 of the shorelines (Riggs and O'Connor 1974). 

 These exposed shorelines are not true inlertidal 

 flats in that they are not regularly exposed and 

 covered by lunar tides. Instead, they are usually 

 covered by water and are only exposed at irregu- 



