A model of sediment transport under the influence of surface bioturbation: generalisation to the facultative suspension-feeder Scrobicularia plana

Flume experiments were designed to study how sediment erodibility was modified by the facultative suspension-feeder Scrobicularia plana living at different densities in sediment beds of various degrees of compaction. Two separate erosion phases were identified from the resuspension kinetics: (1) erosion of an unconsolidated surficial layer (i.e. fluff layer) and (2) the subsequent bed erosion. S. plana were found to influence both erosion phases: (1) erosion rates of the fluff layer were controlled by bioturbation activities, the extents of which were influenced by bivalve density and the degree of compaction of the sediments, and (2) critical thresholds of the subsequent bed erosion decreased as clam density increased, likely due to depressions in the sediment bed that were created by siphon activity. A 1-dimensional vertical model was modified to incorporate the effects of S. plana on fluff layer formation through pseudofaeces production. The modifications to the model and results are compared to a similar approach for Hydrobia ulvae published earlier, and are discussed with respect to the definition of functional groups of bioturbators in sediment transport models. By discussing effects of spatial grouping and analogies to other organisms, this study shows how the influence of one species on sediment resuspension may be generalised and used for model descriptions of other species of the same behavioural type. Model developments on pseudofaeces production show that there are asymmetric effects generated over time and by bivalve density for S. plana, which do not occur for H. ulvae.