General plant distribution in the 

 riverine wetlands is associated with 

 topographic features of the flood plain 

 and surrounding forested lowlands (Clewell 

 1978). H. M. Leitman et al. (1^8?) showed 

 that the height of natural riverbank 

 levees and the size and distribution of 

 levee breaks control floodplain hvdrologic 

 conditions. Vegetative composition is 

 highly correlated with depth of water, 

 duration of inundation and saturation, and 

 water level. Leitman (1978, 1983) and 

 Leitman and Sohm (1981) described in 

 detail the distribution of floodplain 

 trees in the Apalachicola drainage. 

 According to these studies, pine flatwoods 

 and loblolly pine-sweetgum associations 

 are often found on elevated slopes while 

 more mesic hardwoods inhabit the levees. 

 River banks are occupied by willows and 

 birches. Terraces or basin depressions 

 are inhabited by hardwood swamp species. 

 Cypress-tupelo associations are often 

 located in sloughs. Backswamps are 

 characterized by blackgum and sweetbay 

 associations. 



The bottomland hardwood community of 

 the Apalachicola floodplain produces larae 

 amounts of potentially exportable material 

 (Elder and Cairns 1982). The weighted 

 mean of litterfall was 800 grams m'^ with 

 overall annual deposition within the 454 

 km-^ bottomland hardwood flood plain of 

 360,000 metric tons (mt) (396, 7?0 tons) of 

 organic matter. These production levels 

 are similar to those observed in egua- 

 torial forests but are higher than those 

 noted in cool temoerate forests and most 

 warm-temperate forests. Levee vegetation 

 produced more litterfall per ground 

 surface area than did the swamp 

 vegetation. The seasonal distribution of 

 litterfall was characterized by a sharp 

 late autumn peak. The three most abundant 

 flood plain tree species (tupelo, cypress 

 and ash) accounted for over 50% of the 

 total leaf-fall, even though these species 

 were the least productive of those 

 analyzed on the basis of mass-per-stem 

 biomass. 



Annual flooding is a major factor for 

 mobilization of substances out of the 

 flood plain. Flooding leads to immersion 

 of litter material, enhanced decomoosi tion 

 rates, and transfer of the breakdown: 

 products (nutrients and detritus) to 



associated aquatic systems (Cairns I'^Bl, 

 Elder -and Cairns 1^82). The river is thus 

 closely associated with the rich 

 productivity of the Apalachicola wetlands 

 and is the primary agent for movement of 

 organic matter out of the floodplain. In 

 this way, the forested Apalachicola River 

 flood plain is an important source of 

 organic carbon for the estuary. Spring 

 floods during March and April of 1980 

 deposited 35,000 mt (38,570 tons) of 

 detritus derived from litterfall into the 

 Apalachicola estuary (Mattraw and Elder 

 1982). During one year of observation, 

 total organic carbon deposits in the bay 

 amounted ' to 214,000 mt (235,830 tons). 

 Total nitrogen and total phosphorus inputs 

 to the river during the same period were 

 21,400 (23,593) and l,fi50 mt (1,818 tons), 

 respectively (Mattraw and Elder 1<582). 

 The annual detrital organic carbon input 

 was 30,000 metric tons (Mattraw and Elder 

 1982). Mattraw and Elder (1^82) estimated 

 that an 86-day period of winter and spring 

 flooding accounted for 53, 60, 48, and 56 

 percent of the annual total organic 

 carbon, particulate organic carbon, total 

 nitrogen, and total phosphorus transport, 

 respectively. Flood characteristics are 

 important determinants of the amounts and 

 forms of transported materials. While 

 there was an annual net export of 

 nutrients to the estuary, it is likely 

 that the wetland system acted as a 

 nutrient sink during certain periods of 

 the year. Although nutrients are released 

 to the river by flood-plain vegetation, 

 such compounds are subiect to active 

 recycling within the receiving aquatic 

 systems. 



The considerable exoort of 

 particulate matter from the flood plain is 

 consistent with previous findings. 

 Livingston (1981a) and Livingston et al . 

 (1976a) found a direct relationship 

 between river flooding and the appearance 

 of micro- and macroparticulate matter in 

 the estuary. Results of long-term studies 

 of the significance of river-derived 

 particulate organic matter to the estuary 

 (Livingston 1981a, b) indicate that the 

 exact timing of the peak river flows and 

 the seasonal changes in the oroductivity 

 of wetlands vegetation are key 

 determinants of short-term fluctuations 

 and long-term trends of the input of 

 allochthonous organic matter into the 



29 



