Estuarine sedimentation rates have traditionally been determined by indirect means or by estimation. A recently developed and potentially useful, absolute dating method for modern sediments--lead-210--previously has been applied with success to lacustrine and continental-shelf sediments. The results of the present study indicate that lead-210 may be useful in the estuarine environment as well.

The Rhode River estuary is a shallow, western arm of Chesapeake Bay. Piston cores 2 m long were collected in areas of suspected high deposition rates throughout the estuary. Subsamples taken at regular intervals down

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the cores were leached for lead. Activity levels of the lead isotope were counted for 24 hours on an alpha spectrometer. A constant exponential decrease of lead-210 with depth was found, implying a relatively constant flux of the isotope from the atmosphere to the estuary, with little bioturbation and negligible vertical diffusion of lead within the sediment. The resulting sedimentation rates show that parts of the estuary have been filling rapidly with sediment over the past 100 years.

The lead-210 technique appears to be readily extendable to estuaries and to any other environment of relatively undisturbed deposition.

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