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The erosion threshold of biotic sediments: a comparison of methods

Abstract Laboratory and field studies were carried out to determine the effect of biofilms on sediment erodibility. In the laboratory setting, a diatom culture of Nitzschia curvilineata was incubated on sediment and eroded in a recirculating flume at successive stages of growth. Several methods for determining erosion thresholds were employed: (1) the visual determination of particle and bed threshold, (2) an extrapolation method and (3) a digitiza tion method. A comparison of the derived erosion thresholds by these three methods is discussed. In the field setting, an in situ flume (Sea Carousel) was deployed at stations along a transect in a microtidal temperate estuary (Upper South Cove, Nova Scotia, Canada). The extrapolation method was used to determine the erosion thresholds of seabed constituents, such as chlorophyll, phaeopigment and sediment. The differences observed between the erosion threshold of chlorophyll, phaeopigment, and sediment lead to ambiguities in the definition of the erosion threshold of a seabed.