THE INFLUENCE OF THE CAPE FEAR RIVER PLUME ON THE COMPOSITION OF SHELF SEDIMENTS

The Cape Fear River in southeastern NC discharges both particulate and dissolved organic matter into the coastal ocean. Total suspended solid (TSS) concentrations have been monitored at 7 stations in the river since 1996. These data indicate that TSS concentrations in the river vary seasonally and in association with drought events. Beginning in 2003, the Coastal Ocean Research and Monitoring Program (CORMP) at UNCW began the collection of TSS data in Cape Fear plume waters to determine the impact of terrestrial discharge on the coastal ocean. Side scan surveys collected in Long Bay, NC in the vicinity of the plume documented the presence of mud drapes on the seafloor. No such deposits have been observed in Onslow Bay, an area to the north that is not impacted by the river. Although a relationship between TSS in the Cape Fear Plume and the relative concentration of mud has not been established, the plume is believed to be the most reasonable source for the material. This project seeks to identify the distribution and composition of TSS in the Cape Fear River plume and to relate the distribution of deposited muds to the spatial distribution of the suspended plume. Grab samples collected in July 2003 indicate that the mean grain size ranges from 250mm to 1 mm. The percent mud content of bottom samples ranges from 1 to 93. In general, sea floor sediments usually have organic contents of less than 30%. A fluid mud of up to almost 1m in thickness is patchily distributed. TSS concentrations vary vertically and spatially. TSS concentrations range from 3.6 mg/L to 247.3 mg/L. The percentage of mud in bottom samples appears to be positively correlated with TSS concentration in the overlying plume waters. TSS concentrations in the plume do not appear to be consistently related to TSS concentrations in the river itself. All results in this poster are preliminary and will be further enhanced by subsequent data collected over the following 6 months. A positive correlation between distribution of the mud drapes and variations in discharged river material is ultimately expected. Further we expect these distributions to vary seasonally with river discharge.