The use of 7Be and 210Pbxs to differentiate fine suspended sediment sources in South Slough, Oregon

Suspended sediment was collected in the South Slough, National Estuarine Research Reserve, Oregon, over 8 tidal cycles during and following a single runoff event. The sediment was analyzed for its radionuclide signature to determine the relative contributions of different sources of sediment to the efflux from the estuary. Suspended sediment in the estuary is a mixture of sediment from three potential sources: the river system, Coos Bay, and the estuarine bed. Each source material has a distinctive Be-7:Pb-210(XS) ratio. The ratios of the source sediments decreased in magnitude in the following order: iiverine > bay > bed. The ratios of the suspended sediment collected within a subsection of the South Slough estuary reflected the relative mixture of the source areas. The Be-7:Pb-210(XS) ratios provided a means of not only differentiating between resuspended bed sediment and freshly delivered sediment from both the river system and Coos Bay, but also calculating the relative amount of resuspended bed sediment in the suspended sediment collected. in the estuary. The sampled subsection of the South Slough estuary was a net sink of sediment during a 100-h sampling period associated with the runoff event, but the radionuclide analysis suggests that approximately 39% of the sediment efflux was resuspended bed sediment.