Repeated erosion of cohesive sediments with biofilms K. Valentine1,*, G. Mariotti1,**, and S. Fagherazzi1 1Department of Earth and Environment, Boston University, 22015 Boston, USA *now at: Boston College, 02467 Chestnut Hill, USA **now at: Massachusetts Institute of Technology, 02139 Cambridge, USA
Abstract. This study aims to explore the interplay between biofilms and erodability of
cohesive sediments. Erosion experiments were run in four laboratory annular
flumes with natural sediments. After each erosion the sediment was allowed
to settle, mimicking intermittent physical processes like tidal currents and
waves. The time between consecutive erosion events ranged from 1 to 12 days.
Turbidity of the water column caused by sediment resuspension was used to
determine the erodability of the sediments with respect to small and
moderate shear stresses. Erodability was also compared on the basis of the
presence of benthic biofilms, which were quantified using a Pulse-Amplitude
Modulation (PAM) Underwater Fluorometer. We found that frequent erosion lead
to the establishment of a weak biofilm, which reduced sediment erosion at
small shear stresses (around 0.1 Pa). If prolonged periods without erosion
were present, the biofilm fully established, resulting in lower erosion at
moderate shear stresses (around 0.4 Pa). We conclude that an unstructured
extracellular polymeric substances (EPS) matrix always affect sediment
erodability at low shear stresses, while only a fully developed biofilm mat
can reduce sediment erodability at moderate shear stresses.
Citation: Valentine, K., Mariotti, G., and Fagherazzi, S.: Repeated erosion of cohesive sediments with biofilms, Adv. Geosci., 39, 9-14, doi:10.5194/adgeo-39-9-2014, 2014.