CHARACTERISTICS OF SEDIMENTS TRANSPORTED AND DEPOSITED IN THE CAPE FEAR RIVER ESTUARY, SOUTHEASTERN NORTH CAROLINA

The objectives of this study are to characterize the mineralogy and textural attributes of alluvial sediments throughout the Cape Fear River Basin and to determine if sediments recently deposited in the lower watershed were derived from the upper watershed. Sediment is delivered to the estuary from the Piedmont-draining main stem Cape Fear River (brownwater stream) and the Coastal Plain draining Black and Northeast Cape Fear Rivers (blackwater streams). Total suspended solid (TSS) concentrations in the Cape Fear River are 2 to 4 times greater than in the blackwater streams suggesting that little particulate matter enters the estuary from the blackwater systems. Mineralogical analyses, including point counts of sand-sized overbank alluvium and x-ray diffraction of clay-sized overbank alluvium, show a diverse mineral suite (e.g. illite, feldspar) in the brownwater system and a mineral suite consisting primarily of highly weathered minerals (e.g. vermiculite, kaolinite) in the blackwater system. In the downstream direction of the brownwater system, there is a reduction in weatherable minerals and an increase in the proportion of quartz. Grain size distributions of overbank alluvium do not vary in a predicable fashion. The results of this project are relevant to the management of coastal waters fed by Piedmont and Coastal Plain draining rivers of the Atlantic drainage.