The mixing of 210Pb and tagged particles is examined in a lattice-automaton model for bioturbation containing small deposit feeders. The values of the biodiffusion coefficient, DB, calculated using typical biological parameter values, i.e., size, abundance, feeding and locomotion rates, are similar to those expected from marine sediments of a given sedimentation rate. Most biological parameters appear to exert primarily linear effects on DB values, while most nonlinearities seem to be model artifacts or failures of the assumptions in the basic DB model. The model highlights the importance of ingestion-egestion, over simple particle displacement, as an agent of bioturbation. The tagged particles are used to calculate root-mean-squared displacement plots, which are linear over long time spans, indicating diffusive behavior. However, initial trends on such plots are not usually linear, indicating that the calculated DB is time dependent for surprisingly long periods after the beginning of such experiments. The latter constitutes a warning to the interpretation of short-term tracer experiments where tagged-particles are salted onto the sediment-water interface and mixing is dominated by small deposit feeders.