Abstract
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.
Highlights
Muddy coastlines are common in macrotidal environments and near large rivers and deltas, hosting highly productive ecosystems (Woodroffe, 2002)
The purpose of this study is to examine the effects of repeated erosion events on the same cohesive sediment surface under similar conditions, elucidating how biotic and abiotic time-dependent processes affect erodability on a time scale on the order of weeks
Our experiments further explore this dichotomy to see if the sediment itself tends to reach a steady state of erosion after repeated exposure to flow
Summary
Muddy coastlines are common in macrotidal environments and near large rivers and deltas, hosting highly productive ecosystems (Woodroffe, 2002). A full understanding of the mechanisms responsible for the erosion of cohesive sediments in mudflats is important for the preservation of these delicate environments. The primary difficulty in studying erosion of cohesive sediments is the vast number of variables that influence erosion, ranging from grain size to ionic charge and sediment composition (Mehta et al, 1989; Schieber et al, 2007). Due to these difficulties, there are many unanswered questions about the elementary processes involved in the erosion of cohesive sediments
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