The delivery of upland sediments by 

 the rivers is especially important to 

 estuarine systems. Rivers directly or 

 indirectly provide sands for the construc- 

 tion of coastal features. The Piedmont is 

 one of the major sources of sediments that 

 are deposited in estuaries or picked up by 

 longshore currents and carried southward. 

 The Santee River (SC) is (or was) the 

 possible source of hornblende-rich sands 

 of Georgia's continental shelf (Carver 

 1971). During extreme floods, silts from 

 upstream may be deposited on downstream 

 salt marshes. Lunz (1938) described the 

 effects of a Santee River flood which 

 deposited a layer of silt 25 mm (1 inch) 

 thick in marshes in the Cape Romain area. 



COUPLING WITH RIVER DELTAS 



How alluvial rivers are coupled to 

 their deltas was exemplified by the down- 

 stream effect of the diversion of 88% of 

 the Santee River's flow into the tidally 

 dominated Cooper River to gain 1.5% of 

 South Carolina's electric generating power 

 (Kjerfve 1976). The Cooper River subse- 

 quently eroded so severely that the U.S. 

 Army Corps of Engineers annually dredged 

 7600 X 10-^ m-^ of sediments from the 

 Charleston estuary. Saltwater intrusion 

 drastically changed the vegetation in the 

 delta of the Santee from fresh to brack- 

 ish. Santee rice plantation managers had 

 to convert wetlands (former rice fields) 

 which were being managed as freshwater 

 impoundments for waterfowl habitat to 

 brackish water management units. A hard 

 clam ( Mercenaria mercenaria ) industry 

 evolved within the expanded estuarine 

 zones of the mouth of the river. Upstream 

 the growth rate of water tupelo was appar- 

 ently reduced following diversion (R.A. 

 Klawitter, retired forester, Northern 

 Forest Fire Laboratory, Missoula, MT; per- 

 sonal communication). 



As a result of the nature of the 

 integral coupling, any n,dnipulation in the 

 upstream reaches of a river can have pro- 

 nounced effects at all levels on the sys- 

 tem below. Dredging and especially short- 

 ening the river by cutting across meander 

 loops have increased bank erosion by 

 increasing water velocity. Conversely, 

 downstream alterations may affect systems 



upstream. Dredging the Savannah's channel 

 in the estuarine sector has allowed salt 

 water intrusion much farther upstream 

 (Joseph Birch, University of Georgia, 

 Institute of Ecology, Athens; personal 

 communication). Dredging in the Savannah 

 severely reduced larval niayflies, stone- 

 flies, true flies, and beetles, important 

 aquatic foods for fish (Patrick et al. 

 1967). 



In addition to couplings with head- 

 waters and lower estuaries, floodplains 

 are coupled laterally with the uplands on 

 either side via tributaries as well as 

 sheet flow and colluvial soil deposition 

 directly from the adjoining bluffs. Intact 

 tributaries are extremely important to 

 periodic movements of fish and other fauna 

 (Hall 1971; Gasaway 1973). In North Caro- 

 lina, tributaries functioned as corridors 

 for mass movements of large fish moving 

 upstream and large movements of smaller 

 fish moving downstream, as well as for 

 significant movements of frogs, crayfish, 

 and turtles in both directions (Hall 

 1971). These movements are seasonal, a 

 fact making it imperative not to judge the 

 importance of tributaries from limited 

 temporal sampling of the fauna. 



CHEMICAL COUPLING WITH THE UPLANDS 



Although tributaries and non-point 

 source runoff add pesticides, nutrients, 

 toxic metals, coliform bacteria, and other 

 substances to river systems, water quality 

 may improve significantly as water flows 

 through the floodplain. The floodplain 

 with its vast backswamp functions as an 

 important filter and sink for agricultural 

 excesses of nutrients and biocides. One 

 of the first studies of filtering capacity 

 (Kitchens et al. 1975) indicated that the 

 Santee River floodplain significantly 

 reduced bacterial counts and nutrient con- 

 centrations from the polluted Wateree 

 tributary. Nutrient reduction, particu- 

 larly phosphorus, was attributed to assim- 

 ilation by aquatic vegetation, mat algae, 

 and trees as water passed through the 

 swamp. Yarbro (1979) found agricultural 

 inputs dominated the phosphorus budget of 

 a small North Carolina Dlackwater creek 

 swamp, totalling 300 mg P/m2/yr as com- 

 pared to 70 mg P/m^/yr from rainfall and 



104 



