Catalogus

This study evaluated short-term sediment dynamics of natural resuspension events and deposition rates in these two estuaries with the use of short-lived radioisotopes, ⁷Be, ¹³⁷Cs, and ²³⁴Th. Sediment cores at nine sites in the estuaries have been collected at least bimonthly since May 2001. In general, tracers indicate a depositional environment with minimal episodes of removal. The largest sediment removal occurred in August 2001 in the Neuse River where an estimated 2.2 cm of sediment were removed over the previous 6-week period. This removal mechanism essentially advects porewater nutrients into the water column. Calculated advective fluxes of ammonium and phosphate based on this resuspension event were approximately six times greater than the average diffusive flux measured in the same general area of the river. Longer-term deposition rates, using ¹³⁷Cs, ranged from 1.4 to greater than 5 mm year⁻¹, comparable to earlier studies in the area and agree well with the interpretation of the short-lived tracers. In addition, meteorological (wind speed and direction), turbidity, and bottom current data were collected and indicated that these resuspension events occur when passing fronts developed wind speeds in excess of 4 m s⁻¹ with rapid shifts in direction. Currents exhibited estuarine flow reversals associated with wind events and apparently have some control over the sediment removal processes.