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

Perkins, Rupert; Davidson, I.; Paterson, David M.; Sun, Hongyue; Watson, John; Player, M.A.

doi:10.1016/j.geoderma.2005.08.017

Cited by 10 publications

(12 citation statements)

References 25 publications

Supporting

Mentioning

Contrasting

Order By: Relevance

“…In the bottom two layers, localized coating was observed but infilling and bridging was rare with connections only between smaller grains. Care must be taken in interpreting SEM images of polymeric material since the preparation of sediments for sampling can distort the natural matrix and so while the presence of EPS and its effects can be supported the exact confirmation of the material must be viewed with caution [ Perkins et al ., ].…”

Section: Resultsmentioning

confidence: 99%

Hindered erosion: The biological mediation of noncohesive sediment behavior

Chen

Zhang

Paterson

et al. 2017

Water Resources Research

View full text Add to dashboard Cite

Extracellular polymeric substances (EPS) are ubiquitous on tidal flats but their impact on sediment erosion has not been fully understood. Laboratory-controlled sediment beds were incubated with Bacillus subtilis for 5, 10, 16, and 22 days before the erosion experiments, to study the temporal and spatial variations in sediment stability caused by the bacterial secreted EPS. We found the biosedimentary systems showed different erosional behavior related to biofilm maturity and EPS distribution. In the first stage (5 days), the biosedimentary bed was more easily eroded than the clean sediment. With increasing growth period, bound EPS became more widely distributed over the vertical profile resulting in bed stabilization. After 22 days, the bound EPS was highly concentrated within a surface biofilm, but a relatively high content also extended to a depth of 5 mm and then decayed sharply with depth. The biofilm increased the critical shear stress of the bed and furthermore, it enabled the bed to withstand threshold conditions for an increased period of time as the biofilm degraded before eroding. After the loss of biofilm protection, the high EPS content in the sublayers continued to stabilize the sediment (hindered erosion) by binding individual grains, as visualized by electron microscopy. Consequently, the bed strength did not immediately revert to the abiotic condition but progressively adjusted, reflecting the depth profile of the EPS. Our experiments highlight the need to treat the EPS-sediment conditioning as a bed-age associated and depth-dependent variable that should be included in the next generation of sediment transport models. Plain Language Summary Sedimentology and geomorphology have traditionally been seen as fields in which physical and chemical processes dominate. However, microbial communities should never be bystanders, because they suffuse all sedimentary environments on earth. Under hydrodynamic forces, they take part in an impressive range of sediment processes and thus exercising a formative influence on coastal evolutions. Bio-sediments exhibit more complex characteristics than abiotic systems, and lead to different modelling methods compared to those in traditional settings. For instance, the thresholds for sediment initiation and subsequent erosion rates are no longer solely related to particle properties (e.g., particle size, the most widely used), but mediated by glue-like extracellular polymeric substances (EPS) secreted by microbes. From this point of view, it is easy to understand why sediments in field observations behave differently from predictions, usually appearing considerably strengthened. Our results indicate that the EPS mediation in sediment stability may vary with the rhythms of microbial growth, and re-profile the sediment stability during different stages of cementing processes. A conceptual framework for sediment erosion is hence put forward to transform traditional sediment system to EPS-sediment system.

show abstract

Section: Resultsmentioning

confidence: 99%

Hindered erosion: The biological mediation of noncohesive sediment behavior

Chen

Zhang

Paterson

et al. 2017

Water Resources Research

View full text Add to dashboard Cite

show abstract

“…Convoluted pores increase tortuosity and decrease permeability, whilst reduced advection and diffusion is experienced as a result of increases in fluid viscosity due to the gelling properties of EPS (Krembs et al 2011). EPS is an unstructured, amorphous gel-solution matrix (Perkins et al 2006) and the 2 fractions (colloidal and bound) cannot be distinguished with the LTSEM imagery, especially as LTSEM has to be interpreted with care since artefacts are frequent (Perkins et al 2006). Despite not being able to distinguish the EPS fractions with the LTSEM, clear differences can be seen in the amount of material present within the sediment matrix among various times of the year (Fig.…”

Section: Influence Of Eps On Permeabilitymentioning

confidence: 99%

Temporal variation in the sediment permeability of an intertidal sandflat

Zetsche¹,

Paterson²,

Lumsdon³

et al. 2011

Mar. Ecol. Prog. Ser.

View full text Add to dashboard Cite

Rapid organic matter turnover is driven by advective transport processes in sandy permeable sediments, allowing them to act as biocatalytic filters. This filtering capacity is largely defined by the permeability of the sediment, which describes the flow of water through a porous medium. However, little is known about the temporal variability of sandflat permeability under natural conditions. Therefore, the changes in sediment permeability in an intertidal sandflat were measured over a year. The results demonstrated temporal variation in permeability related to the sediment water content and concentration of extracellular polymeric substances (EPS) in the pore space. The refractory bound fraction of EPS was one of the main contributors to this variation. Proteins associated with the bound EPS fraction appeared to covary with the effect of EPS on permeability. Levels of EPS proteins were as high (415 to 2170 µg g −1 bovine serum albumin equivalents) as carbohydrate levels (560 to 1400 µg g −1 D-glucose equivalents) in this sediment. Elevated levels of EPS were observed in the summer corresponding to low permeability, which also corresponded with microphytobenthic blooms and resulting production of exudates. A powerful storm event during the experiment with associated wind-generated waves resulted in a reworking of the sediment. This cleared pore spaces, resuspended material and reduced sediment compaction, effecting an overall change in permeability from 3.6 × 10 −11 to 4.8 × 10 −11 m 2 . The hypotheses that sandy sediment permeability varies with time and is influenced by EPS production were supported, and the effect of an episodic storm event was recorded.

show abstract

“…In addition, the functional role played by different EPS compositions may be important as well. Recent research has revealed that while the polysaccharides dominate the cohesion of the biofilm, protein contributes more to the structural integrity of the biofilm matrix (Flemming & Wingender, 2010; Gerbersdorf et al., 2008; Gerbersdorf & Wieprecht, 2015; Pennisi, 2002). In this study, the raised amount of the total EPS in Cycle 2 was mainly attributed to the rapid accumulation of the total polysaccharides, while the protein concentration was still low as compared to that in Cycle 3 (Figure 4a).…”

Section: Resultsmentioning

confidence: 99%

The Resilience of Biofilm‐Bound Sandy Systems to Cyclic Changes in Shear Stress

Chen

Zhang

Townend

et al. 2022

Water Resources Research

View full text Add to dashboard Cite

Sand‐attached benthic biofilms drive many important biogeological processes and serve as cooperative “ecosystem engineers”. In aquatic environments, biofilms undergo periodic detachment and re‐colonization due to the regular changes in hydrodynamic forcing. However, legacy impacts of past microbial actions on current biofilm formation and the biostabilization of the substratum sands are yet to be fully understood. In this study, a systematic set of flume experiments were conducted to investigate the effects of different depositional histories. Changes in the erosion threshold and rate of erosion were determined from the time sequences of suspended sediment concentrations. The contents of extracellular polymeric substances (EPS) and particle morphology of the biofilm‐bound sandy matrix were analyzed. Surprisingly, biostabilization is disturbance‐stimulated, rather than disturbance‐limited, as previously thought. Bio‐sandy beds cultivated under intensive disturbance presented an EPS accumulation in each cycle, and showed a more rapid increase in bed strength and stability than when rarely disturbed. All colonies from previous cycles exhibited traces of EPS as “footprints”. These stimulated and possibly accelerated the process of recolonization, thereby enhancing the erosion resistance of the bed. In contrast, a stabilized bed was better suited to mature microbial communities. A modified “Windows of Opportunity” framework was therefore put forward. Although biostabilization was not established within short quiescent periods, the system created the “opportunity” to become established in subsequent “windows” by seeding the colonization process. The stabilization, destabilization and re‐stabilization of biofilm may imply a much more important role as ecosystem engineers and is relevant for a range of engineered bio‐systems.

show abstract

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

Cited by 10 publications

References 25 publications

Hindered erosion: The biological mediation of noncohesive sediment behavior

Hindered erosion: The biological mediation of noncohesive sediment behavior

Temporal variation in the sediment permeability of an intertidal sandflat

The Resilience of Biofilm‐Bound Sandy Systems to Cyclic Changes in Shear Stress

Contact Info

Product

Resources

About