Beryllium-7 Elucidate Sediment Dynamics of the Branford River Estuary, Connecticut, USA

Abstract

Berrylium-7 elucidates sediment dynamics (i.e., sources, sinks, deposition, and resuspension) in a Connecticut estuary. Average annual atmospheric deposition of 7 Be is 290 mBq cm −2 year −1. Sediment samples from 43 locations within the estuary show that 7 Be deposition is spatially complex, but were statistically indistinguishable a year apart. Weekly time series of sediments indicate that levels are nearly constant on this shorter time scale once radioactive decay is taken into account. 7 Be levels in sediments are a balance between steady losses through radioactive decay and periodic pulse inputs following rainstorms. The water column was measured intensively during three rain events, showing that 7 Be is removed rapidly from the water column, with a rate constant averaging 1.00 ± 0.12 day −1. A mass balance shows that 7 Be is supplied about equally by direct precipitation onto the estuary's surface and inflow from the watershed. Losses from the water column are split between net sedimentation (43%) and tidal flushing (57%). Variations in sedimentary 7 Be levels at very short (meters) and longer (km) distances, and changes at time scales from hours to years, indicate that a large number of samples are required to capture all the variability in these highly dynamic systems. The current study differs from previous research in that a large number of measurements were conducted on a smaller system, and a full mass balance was developed.