(0-6.5 ft). Tides at ^lasonboro Inlet on 

 the southern coast of North Carolina range 

 from 1.2 m (4 ft) to 1.4 m (4.5 ft) for 

 mean and spring conditions, respectively 

 (Vallianos 1975). Wind and wave processes 

 are the principal forces dictating coastal 

 morphology in microtidal coastal systems 

 (Hayes 1975). Barrier islands in North 

 Carolina tend to be long and narrow, and 

 they contain relatively few tidal inlets. 

 Lagoon-marsh systems are usually narrow 

 (1.5 km or 0.6 mi), shallow, and densely 

 vegetated (Cleary et al. 1979). 



Farther south in South Carolina and 

 Georgia, the coastal system has been clas- 

 sified as mesotidal (Davies 1964), having 

 a tidal range between 2 and 4 m (6.5 and 

 13 ft). This coastline is characterized 

 by short (20 to 30 km or 12 to 19 mi) bar- 

 rier islands, with a wider central portion 

 and narrow ends broken by numerous tidal 

 inlets. In response to the higher tidal 

 range, larger areas of lagoon-marsh are 

 broken by extensive and complex networks 

 of tidal drainage channels. Tidal inlets 

 between barrier islands tend to be rela- 

 tively deep (>10 m or 34 ft) and are 

 flanked by extensive bars and spits. 



Estuaries and lagoons with associated 

 marsh, mudflat, and tidal drainage net- 

 works compose the dominant habitat of the 

 American oyster, £. virginica , in the 

 Southeastern United States. The term estu- 

 ary from the Latin aestus , meaning tide 

 (Schubel 1971), has been defined in vari- 

 ous ways. Geologists tend to accept the 

 strictly physical interpretation of Prit- 

 chard (1967), who defined an estuary as "a 

 semi-enclosed coastal body of water which 

 has a free connection with the open sea 

 and within which sea water is measurably 

 diluted with fresh water from land drain- 

 age." A broader, more ecological defini- 

 tion proposed by Cowardin et al. (1979) is 

 "deep-water tidal habitats and adjacent 

 tidal wetlands which are usually semi- 

 enclosed by land, but have open, partially 

 obstructed, or sporadic access to the open 

 ocean and in which ocean water is at least 

 occasionally diluted by fresh water runoff 

 from the land." In this paper we define 

 estuaries even more broadly to include all 

 the ecological subsystems that interact to 

 form the coastal marsh-estuarine ecosys- 

 tem. In other words, to quote Odum et al. 

 (1974), "It is the ecosystems rather than 



the estuarine waterbodies that are dis- 

 cussed ...here. 



Pr. 

 waterbod 

 types 



'itchard (1967) subdivided estuarine 

 )dies into four geomorphological 



„^ , (1) drowned river valleys; (2) 



fjord-type estuaries; (3) bar-built estu- 

 aries; and (4) estuaries produced by tec- 

 tonic processes. All southeastern coastal 

 plain estuaries fall into either the bar- 

 built or the drowned river valley estua- 

 rine types. 



General Estuarine Hydrography 



Water circulation patterns are of 

 primary significance in determining the 

 physical and chemical conditions of the 

 estuarine ecosystem. Water circulation 

 strongly influences salinity, but it also 

 directly influences sedimentation pat- 

 terns, turbidity, temperature, and nutri- 

 ent conditions. Estuaries with signifi- 

 cant riverine sources of low salinity 

 water are distinctly different in form and 

 hydrographic character from those without 

 such sources (Oertel 1974). 



Classifications of estuarine water 

 circulation patterns are based largely on 

 the relative magnitude of either riverine 

 or tidal influence (Ketchum 1951; Stommel 

 1951; Pritchard 1955, 1967, 1971; Bowden 

 1967) in conjunction with the geomorphol- 

 ogy of the estuarine basin (Schubel 1971). 

 Estuaries with large riverine sources of 

 fresh water show a well-defined vertical 

 salinity stratification. Fresh water over- 

 rides higher density salt water and forms 

 an upper, freshwater layer. The entrain- 

 ment of salt water from the lower layer 

 into the upper, freshwater layer through 

 eddy diffusion results in the mass move- 

 ment of the saline bottom layer into the 

 estuarine basin (Schubel 1971). This 

 mechanism creates the salt-wedge type es- 

 tuary as described by Pritchard (1971). A 

 partially mixed estuary occurs when the 

 tidal flow is sufficiently strong to pre- 

 vent the river from dominating the circu- 

 lation pattern (Schubel 1971). Turbulence 

 generated by the movement of the saline 

 bottom layer results in increased vertical 

 mixing and moderate salinity stratifica- 

 tion (Pritchard 1967). Many southeastern 

 estuaries with relatively large freshwater 

 sources (e.g., Altamaha and Ossabaw Sounds 

 in Georgia and Charleston Harbor in South 



