KINETICS OF TIDAL RESUSPENSION OF MICROBIOTA - TESTING THE EFFECTS OFSEDIMENT COHESIVENESS AND BIOTURBATION USING FLUME EXPERIMENTS

Resuspension of the top few sediment layers of tidal mud flats is know n to enhance planktonic biomass of microbiota (benthic diatoms and bac teria). This process is mainly controlled by tidal shear stress and co hesiveness of mud, and is also influenced by bioturbation activities. Laboratory experiments in a race track flume were performed to test th e interactive effects of these factors on both the critical entrainmen t and resuspension kinetics of microbiota from silt-clay sediments fro m the Marennes-Oleron Bay, France. The marine snail Hydrobia ulvae was used to mimic surface bioturbation activities. As expected, the kinet ics of microbial resuspension versus shear stress were largely control led by the cohesiveness of silt-clay sediments. However, our results i ndicate that the effect of surface tracking by H. ulvae on microbial r esuspension was clearly dependent on the interaction between sediment cohesiveness and shear velocity. Evidence was also found that microphy tobenthos and bacteria are not simultaneously resuspended from silt-cl ay bioturbated sediments. This supports the theory that diatoms within the easily eroded mucus matrix behave actively and bacteria adhering to fine silt particles eroded at higher critical shear velocities beha ve passively.