CHAPTER 2 

 ENVIRONMENTAL SETTING 



?.l. ORIRIN AND EVOLUTION OF THE ESTUARY 



?,1.1. Geological Time Frame 



The Dhysiograohic structures of most 

 estuaries are ephemeral in terms of 

 geological time. Climatological forces 

 are continuously at work shaping and 

 reshaping the basin features. 

 Characteristics of the Apalachicola 

 estuary are dependent on the interaction 

 of an upland drainage system wi^h offshore 

 marine conditions. The estuary is, in 

 effect, an extension of the upland river 

 or drainage area, and its origin and 

 evolution are inextricably linked to the 

 dynamic geological history of the land/sea 

 interaction. 



approximately '^?.^ km (14 mi) northeast of 

 Apalachicola, Florida. These islands were 

 located in what is now the Tate's Hell 

 Swamp (Figure 1). The general dimensions 

 of the Apalachicola vallev as we see them 

 today were established in the Pleistocene. 



The maior drainages of the Florida 

 panhandle (which includes the Apalachicola 

 drainage system) are alluvial in that they 

 carry sediment loads that eventually end 

 UD in the coastal estuaries (Figures 1, 

 ^). The geological structure of the 

 Apalachicola River estuary is of Recent 

 and Pleistocene origin. Marine sediments 

 comprise a maior physical feature of the 

 region. The Apalachicola estuary is 

 bounded by well-developed beach-ridge 



The Aoalachicola River is the only 

 drainage area in Florida that has its 

 origin in the Piedmont, which, as will be 

 explained later, is of biological 

 importance to the region. The geological 

 history of this area is well known in 

 general terms. Rv the Cretaceous period 

 (about 135 million years ago), most of the 

 tri -river valley was submerged under 

 ancient seas (Tanner 19fi2). The origin of 

 the Apalachicola River or its antecedents 

 occurred some time in the Miocene epoch 

 about 25 million years ago (W. F. Tanner, 

 Florida State University, pers. comm.). 

 There has been a gradual decline in sea 

 level through Cenozoic time (70 million 

 years ago to present); sea level has 

 dropped an estimated 70-100 m from the 

 middle of the Miocene (Tanner 1968). 

 Olsen (1^68) gives evidence that the uoper 

 Apalachicola River basin (the area around 

 Blountstown, Florida; Figure 1) was a 

 deltaic or coastal environment during the 

 Miocene. By the Pleistocene epoch (1 

 million years ago), there was evidence of 

 an arcuate chain o^ barrier islands 



Figure 5. The Apalachicola estuary with 

 details of upland drainage areas and the 

 placement of permanent sampling sites for 

 the long-term field studies of the Florida 

 State University research team (after 

 Livingston et al. 1974). 



