ebb tide, the result of solar heating in 

 the marsh during the tidal excursion over 

 dark sediments with low albedo (reflec- 

 tance). 



Dissolved oxygen concentrations gen- 

 erally increase from the upper, riverine- 

 dominated portion of the estuary to the 

 lower sound and inlet. This pattern close- 

 ly parallels that of salinity. Howard 

 et al. (1975) found that during the summer 

 dissolved oxygen values ranged from 4 to 6 

 microliters/liter for a portion of the 

 Ossabaw Sound, Georgia. These relatively 

 low values may reflect the consumption of 

 oxygen during the oxidation of organic de- 

 tritus in suspension in the upper section 

 of the estuary. Frankenberg and Wester- 

 field (1968) reported that the dissolved 

 oxygen levels in estuarine waters in 

 coastal Georgia were extremely sensitive 

 to sediment disturbance; during the summer 

 the oxygen demand of a single milliliter 

 of disturbed sediment could deplete the 

 dissolved oxygen contained within 986 ml 

 of water. 



Oertel (1976) described large tempo- 

 ral and spatial variations in turbidity in 

 estuarine waters. These variations relate 

 to riverine input, local resuspension of 

 bottom sediments by tidal scour and waves, 

 and trapping of fine-grained sediments in 

 the lower portions of estuaries (Schubel 

 1971). Turbidity is greater in the upper 

 reaches of the estuarine system than 

 either farther upstream in the source 

 river or farther seaward. This zone has 

 been termed the "turbidity maximum" by 

 Schubel (1968). Oertel (1976) found sus- 

 pended sediment concentrations in the up- 

 per Wassaw ranging from 9.6 mg/liter to 

 585.6 mg/liter, averaging 46.6 ng/liter. 

 Higher levels of turbidity were measured 

 during spring tides. In tidal creeks, tur- 

 bidity increases significantly during per- 

 iods of local rainfall when the marshes 

 are exposed at low tide (Settlemyre and 

 Gardner 1975). Oertel (1976) found a con- 

 sistent inorganic-organic ratio in sus- 

 pended sediments in the upper estuary, 

 averaging 70% inorganic material and 30% 

 combustible organic detritus. 



1.3 ESTUARINE PRODUCERS 



The estuary is perhaps best known 

 ecologically for its typically high net 



primary productivity. The productivity of 

 estuarine systems relative to other eco- 

 systems is illustrated in Figure 3. A de- 

 tailed explanation of the high annual net 

 productivity in southeastern estuaries was 

 presented by Schelske and Odum (1962). 

 They listed five essential factors: (1) 

 tidal currents; (2) abundant nutrients; 

 (3) rapid turnover and conservation of 

 nutrients; (4) three separate groups of 

 producers; and (5) year-round productiv- 

 ity. Factors 4 and 5 ensure that primary 

 production occurs throughout the year; 

 therefore, energy and nutrient sources are 

 optimally exploited and net production is 

 maximized. The three primary producers 

 discussed by Schelske and Odum (1962) are 

 emergent macrophytes, phytoplankton, and 

 benthic algae. Another group recently has 

 received scientific attention: chemosyn- 

 thetic bacteria (Howarth and Teal 1979). 

 Each group is briefly discussed below. 



Emergent Macrophytes 



The marsh-estuarine complexes within 

 the study area are characterized by broad 

 expanses of salt marshes dominated by two 

 marsh grass species which compose a major 

 portion of the annual primary production 

 of these systems. These are the saltmarsh 

 cordgrass (Spartina alterniflora ) and the 

 black needlerush (Juncus roemerianus ). 

 Spartina is dominant overall, and large 

 continuous stands of this plant occur be- 

 hind the barrier islands (Pomieroy and 

 Wiegert 1980). The annual production cycle 

 of these marshes peaks in late summer, 

 followed by a long period of decay and 

 gradual export of dead vegetation (detri- 

 tus) into waterbodies or incorporation 

 into peat deposits within the marsh. 



In terms of overall primary produc- 

 tion, the emergent macrophytes are consid- 

 ered to contribute a major portion of par- 

 ticulate carbon to the estuarine ecosys- 

 tem. Pomeroy and Wiegert (1980) reported 

 that Spartina production makes up 79% of 

 the particulate organic matter annually 

 produced by the entire marsh estuarine 

 ecosystem. Spartina also produces dis- 

 solved organic matter that leaches into 

 the water column during each tidal inunda- 

 tion. This leachate is thought to contri- 

 bute significantly to the total carbon 

 budget of the estuarine ecosystem (Turner 

 1978). 



