CLAY AND SILT FLOCCULATION AT THE PETITCODIAC RIVER ESTUARY, NEW BRUNSWICK, CANADA

Within the reaches of the Petitcodiac estuary abundant fluid mud containing 24-67% clay is observed. The considerable amounts of clay contribute to the formation of creeping fluid-mud sheets and viscous streams on the tidal flats. Larger proportions of silt and sand in the deposits with lesser amount of clay fraction (6-23%) are associated with the development and preservation of current ripples and erosional ripple ridges on the channel bed and tidal flats.

We further observe that clay flocs entangle silt- and even sand-sized grains while in suspension. In the process of settling, silt and plankton particles are efficiently swept from the water column. As a result, the flocculated sediments contain up to 75 % silt and 10-15% of diatoms. Flocculation aquarium experiments, using Petitcodiac sediments, confirm our field observations.

SEM and microscopic imaging of fluid mud show that a substantial amount of bioclastic material (articulated and detached diatom frustules) is present within the flocs. Moreover, extracellular polymeric substance (i.e. mucous) appears to play a role in floc growth and aggregation.