Kinetics of tidal resuspension of microbiota:testing the effects of sediment cohesiveness and bioturbation using flume experiments

Abstract

Resuspension of the top few sediment layers of tidal mud flats is known to enhance planktonic biomass of microbiota (benthic dlatoms and bacteria). This process is mainly controlled by tidal shear stress and cohesiveness of mud, and 1s also influcnced by bioturbation activities. Laboratory experiments in a race track flume were performed to test the interactive effects of these factors on both the critical entrainment and resuspension kinetlcs of microbiota from sllt-clay sediments from the hlarennes-01eron Bay, France. The marine snail Hydrobia ulvae was used to mimic surface bioturbation activities. As expected, the klnetics of microbial resuspension versus shear stress were largely controlled by the cohesiveness of s~lt-clay sediments. However, our results indicate that the rffect of surface tracking by H. ulvae on microbial resuspension was clearly dependent on the Interaction between sediment cohesiveness and shear velocity. Evidence was also found that microphytobenthos dnd bacteria are not simultaneously resuspended from slit-clay bioturbated sediments. Thls supports the theory that diatoms within the easily eroded mucus matrix behave actively and bacteria a d h e r ~n g to fine silt particles eroded a t higher critical shear velocities behave passively.