The history of sediment accumulation in an oxbow lake located on the Mississippi alluvial floodplain was reconstructed based on sedimentation rates determined using 14C activities from bulk sediment fractions and from 210Pb and 137Cs measurements. Higher rates of sediment accumulation consistent with frequent flooding when first abandoned 3,800 to 5,000 years before the present were followed by slower sedimentation rates consistent with migration of the Mississippi river away from the oxbow and less frequent flooding. This low sedimentation rate persisted for several thousand years until the surrounding land was cleared for agricultural use in the late 19th century. A 50-fold increase in the rate of sediment accumulation has persisted from the time of land clearing to the present, doubling the total mass of accumulated sediment in a single century.