Transport of Fine Sediment Through a Wetland Using Radionuclide Tracers: Old Woman Creek, OH

Abstract

The Old Woman Creek estuary (OWC), a coastal wetland in Ohio, traps 47% of incoming suspended sediment and has a sedimentation rate of ∼1 cm/yr. Persistence of the OWC wetland and other coastal wetlands with high sedimentation rates seems problematic unless some previously trapped sediment is exported from the wetland. Suspended sediment, 7Be, and 210Pb xs budgets for a single runoff event in the OWC wetland were developed to understand short-term sediment dynamics. The budgets were balanced by subtracting the sum of the imports from the sum of the exports and attributing the difference to either deposition on, or resuspension from, the wetland bed. The wetland exported 118 ± 2%, 93 ± 1%, 74 ± 2% of the delivered sediment, 210Pb xs, and 7Be, respectively, during the studied event. The 7Be/ 210Pb xs ratios of the total suspended solids and bed sediment were distinct from one anther and used to quantify the relative proportions of recently delivered and resuspended bed material in the sediment efflux from the wetland. The 7Be/ 210Pb xs ratios suggest that 26 ± 20% of the sediment efflux was resuspended from the bed. While the wetland trapped 13 ± 3% of the sediment it received during the runoff event, resuspension and removal of previously deposited sediment in the wetland was sufficiently large to result in a net loss of sediment from the wetland during the event. Thus, the Old Woman Creek wetland is a sediment sink over the long-term, but can be a net exporter of sediment during single events.