EVALUATION OF SEDIMENTATION RATES AND HISTORY WITHIN TWO TRIBUTARIES OF THE NEUSE RIVER ESTUARY, NORTH CAROLINA

Estuaries along the Atlantic and other coasts are lined with small tributaries which act as sediment traps and filters for increasing amounts of runoff from the surrounding landscape. Several cores were collected in two tributaries (Slocum and Hancock Creeks) of the Neuse River Estuary (NRE) to evaluate the sedimentation in these areas. The NRE is a shallow, microtidal system that has been impacted by development and plagued with symptoms of eutrophication over the past 20 years. Extensive research has been conducted to understand the complex nutrient dynamics, but little information is available on the sediment dynamics of the NRE system, and especially the tributaries. The objectives of this research are: to determine if tributaries are functioning as sediment sinks, to evaluate element concentration changes with time, and to identify stratigraphic and environmental changes over the past century. The sediments were analyzed for a number of geochemical and radionuclide (210Pb and 137Cs) quantities to measure rates of sediment accumulation and evaluate the nature of the material being stored. Cores were selected from each creek to be processed for elemental concentrations of Al, Cd, Ca, Cr, Cu, Fe, Pb, Mg, Mn, Ni, K and Na using an inductively coupled plasma optical emission spectrometer (ICP-OES) after sediment was subjected to a nitric acid digestion (EPA method 3051). Grain size distributions are also being measured to identify stratigraphic changes and potential effects on the accumulation rates. Collectively, these data and previous work provides a detailed history of sedimentation in these tributaries. Sediment accumulation rates range from 0.28 to 0.39 cm/yr and 0.19 to 0.34 cm/yr for Slocum Creek and Hancock Creek, respectively. Preliminary elemental concentration data show surface intervals with higher values that decrease with depth in the core. These tributaries have effectively trapped sediment that might have been supplied to the main estuary over the course of landscape development.