Incipient Erosion of Biostabilized Sediments Examined Using Particle-Field Optical Holography

Abstract

Laser holography allows images of three-dimensional space at ultra-high resolution to be recorded onto photographic plates. Recorded scenes can be "replayed" with a second laser beam into free space and optically "interrogated" using either a microscope or a camera by sequentially focusing on increasing distances from the hologram in the field of view (optical sectioning). From these sections, information on the relative locations and orientation in space of suspended particles as well as the morphology of particles can be obtained. This paper examines the utility of "in-line" laser holography to discriminate the size and the morphology of sand particles eroded under turbulent shear flow during benthic sediment transport. The influence of a commercially available adhesive polymer (xanthan gum, derived from the bacterium Xanthomonas campestris) on sediment stability and resuspended particle morphology is described. The major implications for carbon and sediment cycling within estuaries are highlighted.

The importance of high-resolution monitoring in erosion and deposition dynamics studies: examples from estuarine and fluvial systems

“…Simon et al, 2000) or, over seasonal time scales, biofilm activity (e.g. Black, 1997;Black et al, 2001).…”

“…This can induce several different and complex responses to the same destabilizing force, especially for cohesive materials (e.g. Lawler, 1994;Black, 1997;Black et al, 2001), imposing uncertainty on explanation and prediction. The mode of sediment deposition can also modify its subsequent erosional response (Lau and Droppo, 2000).…”

Low-temperature SEM imaging of polymer structure in engineered and natural sediments and the implications regarding stability

“…Sand and clay particles and polymers are thought to form complex matrices in natural systems, with the polymer increasing the sediment stability (Paterson, 1994;Black et al, 2001). Within this matrix are structures, such as plates and strands, which have been associated with the binding of particles within both artificial and natural sediments (Paterson, 1990;Tolhurst, 1999).…”

“…Recently inline laser holography has also been used to study the nature of the eroded particles (Black et al, 2001;Sun et al, 2002). Low-temperature scanning electron microscopy (Paterson, 1995) has been employed to analyse the structure of the extracellular polymeric substances (EPS) in sediments, and relate this, in a qualitative manner, to stability (Jones et al, 1969;Chenu and Jaunet, 1992;Chenu, 1993;Paterson et al, 1998;Taylor et al, 1999;Black et al, 2001). EPS is a generic term for polymeric material released from cells.…”

“…The LTSEM imaging of artificial sediments reported herein describes the structure of both bacterial EPS, a Xanthum gum polymer used as an analogue for diatom EPS (Black et al, 2001) and diatom EPS, and highlights the effects of sample preparation. In particular changes in the appearance of the polymers in artificial sand and clay systems due to desiccation, cryofixation (CF) and partial freeze-drying (PFD) are reported.…”