Modulation of constituent release across the mud-water interface by water waves

Mechanisms that contribute to the modulation of the release flux of conservative constituents from bottom mud by water waves have been investigated. Laboratory flume tests were carried out by initially inoculating fluid-like clayey muds with dyes used as generic constituent surrogates. For each combination of dye and mud, dissolved and particle-bound release fluxes were determined as functions of wave and mud properties by numerically modeling constituent and sediment transport. Ln the absence of sediment entrainment the dissolved constituent flux in the interfacial diffusive sublayer is mainly governed by the rate of diffusion in mud heaving under wave action and by the rate of mass transfer across the sublayer. The diffusion coefficient in mud appears to be related to the rate of wave energy dissipation by internal friction, and the sublayer diffusion coefficient is found to follow a Chilton-Colburn type relationship for boundary layer mass transfer. When entrainment of sediment and associated pore water occurred, particle-bound constituent release became important. However, partial return of the entrained sediment and water due to redeposition of mud flocs caused the net rate of constituent release to the ambient water column to be a comparatively small fraction of the total rate of release. This observation implies that transport models for nutrients and contaminants must accurately account for the two-way interfacial exchange of sediment and water to avoid a possible overprediction of constituent release at the mud boundary.