CHAPTER 3 

 PRIMARY PRODUCTIVITY AND NUTRIENT CYCLING 



Most aquatic systems such as rivers 

 and estuaries depend on sources of organic 

 matter outside the system (i.e., 

 allochthonous: dissolved and particulate 

 orqanic matter from associated wetlands) 

 and within the system (i.e., autoch- 

 thonous: phytoplankton, benthic plants). 

 Tnorqanic nutrients (phosphorus, nitrogen) 

 and orqanic matter (dissolved, particu- 

 late) are swept into aquatic systems by 

 rainfall, overland runoff, and river 

 flooding. The extremely complex chemical 

 processes involved in the transformation 

 of nutrients into plant and animal biomass 

 are not well understood and are intri- 

 cately related to microbioloqical 

 activity. One important qeneral ization 

 based on the long-term field studies is 

 that the Apalachicola estuary is 

 inextricably linked to the river in terms 

 of freshwater input and the movement of 

 dissolved and particulate orqanic material 

 into the estuary. River input is sea- 

 sonally and annually pulsed, and such 

 influx of materials has an important 

 influence on allochthonous and 

 autochthonous sources of orqanic matter 

 throuqhout the Apalachicola estuary. 



et al. 1P77; Elder and Cairns 1982; Elder 

 and Mattraw 1^82; Mattraw and Elder 1980, 

 1982). Over time, the Apalachicola River 

 has meandered in broad curves through the 

 flood plain, Erosional and depositional 

 processes have led to the development of 

 shoals, backswamps, channels, sloughs, 

 levees, and oxbow lakes. The dynamics of 

 the Apalachicola River affect the 

 transport of dissolved and particulate 

 substances into receiving aquatic areas. 

 However, such transport of allochthonous 

 substances depends on complex interactions 

 of river flooding with factors such as 

 wetland productivity, decomposition 

 processes, the timing and relative heights 

 of the flood staqe, the heiqhts of 

 surroundinq lands, soil types, and 

 drainaqe characteristics of the flood 

 plain. The unifyinq characteristics of 

 the wetland inputs are the distribution 

 and environmental functions of the 

 bottomland hardwood forests of the 

 Apalachicola floodplain (Figure 21). 



Nutrient fluxes and primary 

 productivity of the river-estuary system 

 have been studied for over a decade; the 

 followinq is a review of the available 

 information concerning the Apalachicola 

 system. 



3.1. PRIMARY PRODUCERS 



3.1.1. Allochthor-ous Sources 



a. Freshwater wetlands . The 

 production and decomposition of orqanic 

 matter in the floodplain wetlands 

 represents one facet of estuarine 

 productivity (Livinqston l<581a; Livinqston 



EVAPO-TRANSPIRATION 



RflIN - 



DISCHARGE 



STAGE^___^ 



ELEVATION ^ 



SOILS- 



FLOODPLAIN 

 f INUNDATION 



> TREE 



DISTRIBUTION 



POSITION 



O^ V LEAF 



PRODUCTION 



ATMOSPHERE 



^NUTRIENTS 

 DETRITUS 



RIVER- 

 BAY 



TRANSPORT 



fJ 



Fiqure 21. Nutrient/detritus transport 

 mechanisms and lonq-term fluctuations in 

 detrital yield to the Apalachicola River 

 flow (modified from Mattraw and Elder 1980 

 and Livingston unpubl.). 



28 



