CHAPTER 6. COUPLING WITH OTHER SYSTEMS 



NATURAL COUPLINGS WITH HEADWATER TRIBU- 

 TARIES AND ESTUARIES 



Bottomland hardwoods are coupled to 

 other upstream and downstream systems 

 principally by river flows. Tributaries 

 and terrestrial inputs via valley walls 

 serve as linkages to upland ecosystems 

 that flank the floodplains laterally, but 

 upstream-downstream linkages are function- 

 ally more important. For example, Apala- 

 chicola River flows are coupled both to 

 the mountains of northern Georgia and to 

 coastal estuaries by significant metero- 

 logical and biological phenomena. The 

 Apalachicola River is a driving force and 

 regulating mechanism mediating the chem- 

 istry and biology of Apalachicola Bay. 

 The salinity regime of the bay is largely 

 a function of river flow fluctuations and 

 patterns of local rainfall. River flow in 

 turn is controlled by plant cover and 

 floodplain and upland watershed drainage 

 (Livingston et al. 1976). 



Livingston et al. (1975, 1976) showed 

 that the cyclic productivity of Apalachi- 

 cola Bay not only depends on annual pulses 

 of organic detritus and silt from bottom- 

 land hardwoods, but also on the large- 

 scale import of detritus during a major 5- 

 to 7-year pulse originating in the moun- 

 tains of north Georgia. These longer 

 pulses are linked with peaks in commercial 

 fish catches (Livingston et al. 1S76; 

 Meeter etal. 1979) through the trophic 

 dynamics of the detrital food web. Second- 

 ary production may be keyed to these link- 

 ages to the point that each kind of tree 

 leaf may have its own special estuarine 

 food web (Sheridan and Livingston 1979; 

 White et al. 1979). An important point is 

 that this 5- to 7-year pulse very strongly 

 involves the bottomland hardwood Zone V 

 from which accumulated organic matter is 

 exported. The importance of periodic 

 flooding thus extends well beyond the 1- 

 to 2-year flood cycle. 



Apalachicola Bay is not the only 

 example of an estuary dependent on water 

 pulses and intact forests. Day et al. 

 (1977) found that a Louisiana river swamp 

 (Bayou des Allemands) fed pulses of car- 

 bon, nitrogen, and phosphorus to Barataria 

 Bay (which produces 45% of the State's 

 commercial fish catch) precisely when 

 migrant species were entering the estuary 

 for feeding and spawning. Similar phenom- 

 ena have been noted in Chesapeake Bay 

 (Copeland 1966). In fact, estuaries in the 

 Southeast generally are more productive in 

 areas near the mouths of rivers (Copeland 

 1966). 



The importance of freshwater delivery 

 from the Piedmont and Coastal Plain via 

 floodplain rivers cannot be overestimated. 

 Deliveries to estuaries include large 

 amounts of organic matter and vitamins 

 such as Bi2 from blackwater rivers (Burk- 

 holder and Burkholder 1956). Both micro- 

 organisms and plankton are capable of 

 rapidly and efficiently absorbing leached 

 DOC in coastal environments (Crow and 

 MacDonald 1978) and may be able to use 

 riverine DOC. Thomas (1966) speculated 

 that the Altamaha flushed the rich phos- 

 phates of the estuaries seaward as far as 

 24 km (15 mi). Windom et al. (1975) 

 showed that the nutrient load in riverine 

 discharge in the South Atlantic Bight is 

 equivalent to 100% of the annual inorganic 

 phosphorus requirement and 20% of the 

 nitrogen requirement of salt marshes in 

 the region. Annual freshwater discharge 

 onto shelf areas is equal to 39% of the 

 total water volume out to the 20-m con- 

 tour, perhaps contributing significant 

 amounts of trace minerals, silicates, 

 organic nutrients, and humic acids (Haines 

 1975). Under the influence of wind and 

 high water, the Suwannee River (FL) peri- 

 odically turns the Continental Shelf 

 waters black and pushes water hyacinth 

 rafts as far as the Cedar Keys area, 11 

 nautical miles from its mouth. 



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