?.4.'. Dissolverl Oxygen 



Diurnal and seasonal variations of 

 dissolved oxygen (Figure 1"^) reflect 

 biological and physical processes in the 

 svstem. Maximum levels usually occur 

 during winter and spring months because of 

 low water temperature and, to a lesser 

 degree, low salinity. During summer and 

 fall periods, vertical stratification of 

 dissolved oxygen is evident in various 

 parts of the estuarv. Spatial 

 distribution of mean dissolved oxvgen 

 values (Figure 13) is not uniform; the 

 highest values occur in the upper reaches 

 of East Bav (i.e.. Round Bay), iust off 

 St. George Island (i.e., Nick's Hole), and 

 alona the eastern side of St. Vincent 

 Island. Concentrations of dissolved 

 oxygen in most of the estuary during the 

 10-vr period of observation are sufficient 

 to support most forms of estuarine biota 

 (Figure 1'^) . No sign of cultural 



eutrophication is evident. The long-term 

 pattern of dissolved oxyqen maxima 

 followed the long-term temperature trends, 

 with dissolved oxygen peaking during the 

 cold winters from \^''6 to 1'378. Such 

 changes represent an indirect effect of 

 temperature on long-term habitat variation 

 in the estuary. 



?.4.3. _pH 



From 1^7? to I'^S?, the pH throughout 

 most of the bay system ranged between fi 

 and P (Livingston lQ?^3c, unpublished- 

 data). However, relatively low pH levels 

 (4-5) were observed in upper portions of 

 East Bay during periods of heavy local 

 rainfall and runoff from newly cleared 

 lands in Tate's Hell Swamp (Livingston 

 19 78). Such changes were temporary and, 

 overall, the pH of the Apalachicola Bay 

 system remains within a range that is not 

 limiting to most life forms. 



"^ . ^ . ^ . Water Color and Turbidit y 



Light transmission, as determined by 

 color (measured in platinum-cobalt units) 

 and turbidity (in .lackson Turbidity 

 Units), is a key variable in the timinq 

 and distribution of orimary and secondary 

 productivity in the estuarv. The spatial 

 and temporal distributions of water color 

 and turbiiHity (Figures 13, 16, 17) are 

 related to patterns of fresh-water flow 



into the bav system. The highest levels 

 of both factors are found at the mouth of 

 the river and throughout upper East Bay 

 with clear-cut gulfward gradients. Both 

 color and turbidity reach seasonal hiqh 

 levels during winter and early spring 

 periods of hiqh river flow and overland 

 runoff. During the major flooding in the 

 winter of 197?-73, turbidity and color in 

 the estuary reached a 10-yr high point at 

 most stations. While the general pattern 

 of color in the estuary follows river flow 

 fluctuations, the highest levels occurred 

 in eastern East Bay. The color was 

 directly associated with forestry 

 activities and runoff from the Tate's Hell 

 Swamp (Livingston 1"578). Various 



compounds such as tannins, lignins, and 



E 

 a. 



a. 125 



> 



o 



Q 

 Ul 



o 



</} 



a 



1972 1973 1974 1975 1976 1977 1978 1979 1960 1981 1962 



YEAR and MONTH 



Figure 15. Surface dissolved oxygen 

 (5-month moving averages) at stations 1 

 and 5 in the Apalachicola estuary taken 

 monthly from 1972 through 1982. 



18 



