west Florida and the semidiurnal tides on 

 the Gulf peninsula. Tides at Aoalachicola 

 are diurnal to semidiurnal, with 

 "uncertainties" concerninq the selection 

 of a "typical" tide pattern for each month 

 (Conner et al. I'^Sl). Tides in the 

 Apalachicola estuary are influenced by the 

 main entrances and smaller passes. Tidal 

 ranqes vary from 0.13 m (0.^3 ft) at Doq 

 Island near the eastern end of the estuary 

 to 0.?3 m (0.75 ft) at East Pass. 

 Gorsline (1963) classified this estuary as 

 "unsymmetrical and semidiurnal except 

 durinq periods of stronq wind effect." 

 While currents in the Apalachicola estuary 

 are tide-dominated, they are also 

 dependent on local physioqraphic 

 conditions and wind soeed and direction 

 (Livinqston 1<578). River discharqe has 

 little influence on the hydrodynamics of 

 the partially stratified estuary (Conner 

 et al. 1°81). Shallow estuaries such as 

 the Apalachicola are wind dominated in 

 terms of flushing and current movement. 

 The wind can be up to three times more 

 important than the tidal input in the 

 determination of current strength and 

 direction (Conner et al. 1981). 



Net flows tend to move to the west 

 from St. George Sound; East Ray water 

 merqes with the westward flow (Fiqure 11). 

 West Pass appears to be a maior outlet for 

 the discharge of estuarine water to the 

 Gulf, especially when influenced by long- 

 term or high velocity winds from the east. 

 Water movement through Indian Pass also 

 occurs in a net westward direction, 

 although the Picoline Bar may retard 

 passage (Dawson 1955). Estuarine currents 



Figure 11. Net water current patterns in 

 the Apalachicola estuary as indicated by 

 flow models developed by B. A. Christensen 

 and colleagues. (A detailed analysis of 

 such currents can be found in Conner et 

 al. (1981).) 



may be affected by excessive land runoff 

 or high velocity winds from the east or 

 west. Strong north to northeast winds 

 deflect water downwind and to the west. 



Gorsline (1963) estimated a tidal 

 prism equal to about ?0^ of the bay water 

 volume, and he suggested that the 

 residence time of river water in the 

 estuary ranges from a few days to a month. 

 The two western passes account for over 

 669$ of the total bay discharqe, even 

 though they account for only 10°4 of the 

 inlet area (Gorsline 1'563). The bulk of 

 river flow exits through these passes, and 

 the effects of river flow on salinity can 

 be felt ?65 km (165 miles) offshore in the 

 gulf. Tidal deltas extend seaward from 

 Indian Pass, West Pass, and East Pass, 

 indicating appreciable sediment transport 

 through these areas. Current velocities 

 in the bay rarely exceed 0.5 m sec"^, 

 while velocities in the passes may reach 

 2-3 m sec"l. 



?.4. PHYSICAL/CHEMICAL HARITAT 



Important habitat features of the 

 Apalachicola Bay system include physio- 

 • graphic, climatic, and river-flow 

 conditions. While marshes (emergent 

 vegetation), oyster beds, and qrassbeds 

 (submerqent veqetation) represent 

 important biological habitats of the 

 estuary. the primary physical habitat in 

 terms of areal extent is the shallow, 

 unvegetated soft sediment bottom (Table 

 1). Within the myriad of rapidly changing 

 gradients of physical and chemical 

 features of the estuary, there are certain 

 recurrent patterns and general trends that 

 remain more or less constant in soace and 

 over time. Such water-quality features 

 and nutrient distributions are important 

 determinants of the habitat conditions in 

 the Apalachicola Bay system. 



?.^.\. Temperature and Salinity 



Because of the shallowness of the bay 

 system and wind-mixing of the water 

 column, there is little thermal 

 stratification in the estuary. Water 

 temperature is hiqhlv correlated (r = 

 O.QO, p < 0.00001) with air temperature 

 (Livinqston 1983c), which indicates rapid 

 mixing. Summer temperature peaks are 

 similar from year to year, with seasonal 

 highs usually in August. Water 



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