Laboratory experimentation and field sampling programs were used to examine the contribution of the conveyor-belt feeding/biodeposition activity of orbiniid polychaetes, Scoloplos spp., to bioturbation in intertidal sediments of Lowes Cove, Maine. Laboratory measurements of particle reworking rates were incorporated into steady-state and transient-state diagenetic models to predict subduction velocities of marker layers in incubated cores from Lowes Cove and to predict the in situ activity-depth profile of the radionuclide Be-7 (half-life = 53.3 d), a useful, naturally-occurring tracer of rapid mixing processes.Incubated cores containing a complete macrofauna from the Cove were mixed bioadvectively with little random mixing (peak-broadening of the marker) detectable. The conveyor-belt activity of Scoloplos spp. accounted fully for particle subduction in these cores.The Be-7 activity-depth profile of a sediment core taken from Lowes Cove was consistent with a conveyor-belt diagenetic model based upon (1) seasonal variations in the surface biodeposition rate of Scoloplos spp. and (2) a constant Be-7 activity at the sediment surface. Although the surface Be-7 activity in principal may be affected by seasonal changes in the rates of atmospheric deposition and dilution with radioactively dead sediment emplaced by conveyor-belt activity, such effects apparently did not dominate features of this Be-7 profile.The control by these polychaetes of sediment turnover and incorporation of reactive chemical species across the sediment surface may explain in part why local patches with characteristic worm abundance and standing crop are maintained year to year in Lowes Cove.