Microalgal mediation of ripple mobility

Friend, Patrick L.; Lucas, Cathy H.; Holligan, P. M.; Collins, Michael B.

doi:10.1111/j.1472-4669.2007.00108.x

Cited by 37 publications

(35 citation statements)

References 61 publications

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“…This is in contrast with findings from sites where a smoother surface is found in winter due to reduction of biological (macrofaunal) activity (e.g., Anderson 1983), but supports observations on microphytobenthos inhibiting surface ripple migration (Friend et al 2008). In most mud transport models, including ours, bed roughness resulting from microtopography (such as sand ripples) is held constant over time, and spatial differences in bed roughness as revealed by the remote sensing data are also not incorporated.…”

Section: Discussioncontrasting

confidence: 54%

Spatial heterogeneity in estuarine mud dynamics

et al. 2010

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The fate of mud in an estuary over an entire year was unravelled using complementary, independent, spatially explicit techniques. Sequential ERS-2 SAR and Envisat MERIS-FR data were used to derive synoptic changes in intertidal bottom mud and suspended particulate matter (SPM) in the top of the water column, respectively. These satellite data were combined with in situ measurements and with a high resolution three-dimensional cohesive sediment model, simulating mud transport, resuspension, settling and deposition under the influence of tides, wind, waves and freshwater discharge. The spatial distribution of both bottom mud and SPM as observed by in situ and satellite techniques was largely explained by modelled estuarine circulation, tidal and wind-induced variations in vertical mixing and horizontal advection. The three data sources also showed similar spring-neap and seasonal variations in SPM (all factor 1.5 to 2), but semi-diurnal tidal variations were underestimated by the model. Satellite data revealed that changes in intertidal bottom mud were spatially heterogeneous, but on average mud content doubled during summer, which was confirmed by in situ data. The model did not show such seasonal variation in bed sediment, suggesting that seasonal dynamics are not well explained by the physical factors presently implemented in the model, but may be largely attributed to other (internal) factors, including increased floc size in summer, temporal stabilisation of the sediment by microphytobenthos and a substantially lower roughness of the intertidal bed in summer as observed by the satellite. The effects of such factors on estuarine mud dynamics were evaluated.

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Section: Discussioncontrasting

confidence: 54%

Spatial heterogeneity in estuarine mud dynamics

et al. 2010

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“…(10), may support the alternate states model of van de Koppel et al (2001), see also Friend et al (2008), which advocates that a sediment bed tends to switch between two stable states: low concentrations of diatoms (main EPS producers) and high bed shear stress, as for Sites 1 and 2, versus high concentrations of diatoms and low bed shear stress, as for Site 3. The bed would have been in an unstable state between these limits, if the model of van de Koppel et al (2001) .…”

Section: Comparing the Laboratory And Field Datasupporting

confidence: 56%

“…This is below the 3-5% clay content found for the transition to a cohesion-dominated eroding bed (van Ledden et al, 2004), but above the EPS fraction (0.026%) found to stabilize wave ripples by Friend et al (2008). These results have important implications for sediment transport modelling.…”

Section: Implications For Sediment Transport Modelling Geomorphologymentioning

confidence: 74%

“…Low stress promotes biological production and mud deposition, which has been proposed as an explanation for ripple stabilization in the field (Friend et al, 2008), whereas high stress winnows cohesive material and provides poor conditions for microbial growth (van de Koppel et al, 2001). Friend et al (2008) found that a microalgal bloom coinciding with neap tides was sufficient to stabilize ripples on tidal flats for a period of four weeks. The influence of bed shear stress may lead to switching between alternate stable seabed states of cohesive erosion-resistant beds with well-developed biofilms and non-cohesive mobile beds, in environments with varying bed shear stress (van de Koppel et al, 2001).…”

Section: Introductionmentioning

confidence: 99%

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Bedform migration in a mixed sand and cohesive clay intertidal environment and implications for bed material transport predictions

et al. 2018

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a b s t r a c t a r t i c l e i n f oMany coastal and estuarine environments are dominated by mixtures of non-cohesive sand and cohesive mud. The migration rate of bedforms, such as ripples and dunes, in these environments is important in determining bed material transport rates to inform and assess numerical models of sediment transport and geomorphology. However, these models tend to ignore parameters describing the physical and biological cohesion (resulting from clay and extracellular polymeric substances, EPS) in natural mixed sediment, largely because of a scarcity of relevant laboratory and field data. To address this gap in knowledge, data were collected on intertidal flats over a spring-neap cycle to determine the bed material transport rates of bedforms in biologically-active mixed sand-mud. Bed cohesive composition changed from below 2 vol% up to 5.4 vol% cohesive clay, as the tide progressed from spring towards neap. The amount of EPS in the bed sediment was found to vary linearly with the clay content. Using multiple linear regression, the transport rate was found to depend on the Shields stress parameter and the bed cohesive clay content. The transport rates decreased with increasing cohesive clay and EPS content, when these contents were below 2.8 vol% and 0.05 wt%, respectively. Above these limits, bedform migration and bed material transport was not detectable by the instruments in the study area. These limits are consistent with recently conducted sand-clay and sand-EPS laboratory experiments on bedform development. This work has important implications for the circumstances under which existing sand-only bedform migration transport formulae may be applied in a mixed sand-clay environment, particularly as 2.8 vol% cohesive clay is well within the commonly adopted definition of "clean sand".

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“…Schmidt et al 2015Schmidt et al , 2016Thom et al 2015). Beyond the microbial impact on surface stability, the lateral movement of sediment can be severely influenced during bedform development and migration (Friend et al 2008;Hagadorn and McDowell 2012;Malarkey et al 2015;Parsons et al 2016) but this phenomenon is also highly significant for the erosion thresholds of deeper sediment layers (Gerbersdorf et al 2007;Chen et al 2017). Last but not least, EPS has been shown to promote the aggregation and deposition of suspended material (Eisma 1986;Mietta et al 2009;Manning et al 2010).…”

Section: Is Sediment Biostabilisation Important?mentioning

confidence: 99%

Form, function and physics: the ecology of biogenic stabilisation

et al. 2018

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Purpose The objective of this work is to better understand the role that biological mediation plays in the behaviour of fine sediments. This research is supported by developments in ecological theory recognising organisms as Becosystem engineers^and associated discussion of Bniche construction^, suggesting an evolutionary role for habitat modification by biological action. In addition, there is acknowledgement from engineering disciplines that something is missing from fine sediment transport predictions. Materials and methods Advances in technology continue to improve our ability to examine the small-scale 2D processes with large-scale effects in natural environments. Advanced molecular tools can be combined with state-of-the-art field and laboratory techniques to allow the discrimination of microbial biodiversity and the examination of their metabolic contribution to ecosystem function. This in turn can be related to highly resolved measurements and visualisation of flow dynamics. Results and discussion Recent laboratory and field work have led to a paradigm shift whereby hydraulic research has to embrace biology and biogeochemistry to unravel the highly complex issues around on fine sediment dynamics. Examples are provided illustrating traditional and more recent approaches including using multiple stressors in fully factorial designs in both the laboratory and the field to highlight the complexity of the interaction between biology and sediment dynamics in time and space. The next phase is likely to rely on advances in molecular analysis, metagenomics and metabolomics, to assess the functional role of microbial assemblages in sediment behaviour, including the nature and rate of polymer production by bacteria, the mechanism of their influence on sediment behaviour. Conclusions To fully understand how aquatic habitats will adjust to environmental change and to support the provision of various ecosystem services, we require a holistic approach. We must consider all aspects that control the distribution of sediment and the erosion-transport-deposition-consolidation cycle including biological and chemical processes, not just the physical. In particular, the role of microbial assemblages is now recognised as a significant factor deserving greater attention across disciplines.

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Microalgal mediation of ripple mobility

Cited by 37 publications

References 61 publications

Spatial heterogeneity in estuarine mud dynamics

Spatial heterogeneity in estuarine mud dynamics

Bedform migration in a mixed sand and cohesive clay intertidal environment and implications for bed material transport predictions

Form, function and physics: the ecology of biogenic stabilisation

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