The behavior of the lutocline as a measure of fine sediment mixing in high-concentration estuaries is briefly examined with reference to the Jiaojiang estuary in China. A lutocline mixing index is introduced and shown to correlate empirically with the rate of turbulent kinetic energy production in such a way that with increasing energy production lutocline mixing increases. Suspended sediment concentration and energy production together govern the turbulent mixing length, hence lutocline mixing, which appears to be measurably modulated by sediment settling, interparticle interaction, and cohesion. Further understanding of lutocline response to tidal forcing will require direct and long-term measurements of turbulent fluxes, especially within the zone of lutocline occurrence and in the high-concentration suspension underneath.
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