Biologically-initiated rock crust on sandstone: Mechanical and hydraulic properties and resistance to erosion

Slavík, Martin; Bruthans, Jiří; Filippi, Michal; Schweigstillová, Jana; Falteisek, Lukáš; Řihošek, Jaroslav

doi:10.1016/j.geomorph.2016.09.040

Cited by 42 publications

(32 citation statements)

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“…Considering that salt transport due to hydraulic movement is a dominant weathering mechanism (Huinink et al, 2004), reduced evaporation due to BRC coverage will also inevitably lead to decrease 40 weathering rate. Moreover, the obtained results stand in contrast to similar measurements performed on temperate sandy stones that showed no significant effect of BRC on water transport rates (Slavík et al, 2017).…”

Section: Composition and Chemical Characteristics Of The Rock Crustscontrasting

confidence: 99%

The origin and role of biological rock crusts in rocky desert weathering

Wieler¹,

Gillor²,

Angel³

2018

Preprint

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<p><strong>Abstract.</strong> In drylands, microbes that colonise rock surfaces were linked to erosion because water scarcity excludes traditional weathering mechanisms. We studied the origin and role of rock biofilms in geomorphic processes of hard lime and dolomitic rocks that feature comparable weathering morphologies though originating from arid and hyperarid environments, respectively. We hypothesised that weathering patterns are fashioned by salt erosion and mediated by the rock biofilms that originate from the adjacent soil and dust. We used a combination of microbial and geological techniques to characterise rocks morphologies and the origin and diversity of their biofilm. Amplicon sequencing of the SSU rRNA gene suggested that bacterial diversity is low and dominated by Proteobacteria and Actinobacteria. These phyla formed laminar biofilms only on rock surfaces that were exposed to the atmosphere and burrowed up to 6&#8201;mm beneath the surface, protected by sedimentary deposits. Unexpectedly, the microbial composition of the biofilms differed between the two rock types and was also distinct from the communities identified in the adjacent soil and settled dust, showing a habitat-specific filtering effect. Moreover, the rock bacterial communities were shown to secrete extracellular polymeric substances that form an evaporation barrier, reducing water loss rates by 65&#8211;75&#8201;%. The reduced water transport rates through the rock also limit salt transport and its crystallisation in surface pores, which is thought to be the main force for weathering. Concomitantly, the biofilm layer stabilises the rock surface via coating and protects the weathered front. Our hypothesis contradicts common models, which typically consider biofilms as weathering-promoting agents. In contrast, we propose the microbial colonisation of mineral surfaces acts to mitigate geomorphic processes in hot, arid environments.</p>

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Section: Composition and Chemical Characteristics Of The Rock Crustscontrasting

confidence: 99%

The origin and role of biological rock crusts in rocky desert weathering

Wieler¹,

Gillor²,

Angel³

2018

Preprint

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“…Weathering is an in situ set of processes that includes physical, chemical, and mechanical forces that result in the breakdown and transport of shattered fragments of the parent rock. Weathering can appear in a range of sizes and morphologies (Smith et al, 2005), including gravel shattering (Amit et al, 1996), surface crazing (Smith, 1988), ventifacts (Smith, 1988), micro-rills (Smith, 1988;Sweeting and Lancaster, 1982), and cavernous patterns ,also known as tafoni, honeycomb, or pitting (Mustoe, 1983;Viles, 2005). Weathering is an essential, although often neglected, element in the overall denudation of hot deserts.…”

Section: Introductionmentioning

confidence: 99%

“…Recent studies suggest that microbial activity also promotes the processes of calcrete and dolocrete formation (Alonso-Zarza et al, 2016;Alonso-Zarza and Wright, 2010). The accepted conceptual model for the formation of cavernous rock weathering in hot deserts involves the presence of permeable rocks that are subjected to soluble salts and repeated episodes of drying-rewetting cycles (Goudie et al, 2002;Smith, 1988;Smith et al, 2005). The proposed mechanisms assume that cavernous weathering results from physico-chemical processes including salt crystallization (Cooke, 1979;Scherer, 2004), incipient fractures (Amit et al, 1996), exfoliation (Shtober-Zisu et al, 2017), or stress erosion (Bruthans et al, 2014;McArdle and Anderson, 2001).…”

Section: Introductionmentioning

confidence: 99%

The origin and role of biological rock crusts in rocky desert weathering

et al. 2019

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Abstract. In drylands, microbes that colonize rock surfaces have been linked to erosion because water scarcity excludes traditional weathering mechanisms. We studied the origin and role of rock biofilms in geomorphic processes of hard lime and dolomitic rocks that feature comparable weathering morphologies, although these two rock types originate from arid and hyperarid environments, respectively. We hypothesized that weathering patterns are fashioned by salt erosion and mediated by the rock biofilms that originate from the adjacent soil and dust. We used a combination of microbial and geological techniques to characterize rock morphologies and the origin and diversity of their biofilms. Amplicon sequencing of the SSU rRNA gene suggested that bacterial diversity is low and dominated by Proteobacteria and Actinobacteria. These phyla only formed laminar biofilms on rock surfaces that were exposed to the atmosphere and burrowed up to 6 mm beneath the surface, protected by sedimentary deposits. Unexpectedly, the microbial composition of the biofilms differed between the two rock types and was also distinct from the communities identified in the adjacent soil and settled dust, showing a habitat-specific filtering effect. Moreover, the rock bacterial communities were shown to secrete extracellular polymeric substances (EPSs) that form an evaporation barrier, reducing water loss rates by 65 %–75 %. The reduced water transport rates through the rock also limit salt transport and its crystallization in surface pores, which is thought to be the main force for weathering. Concomitantly, the biofilm layer stabilizes the rock surface via coating and protects the weathered front. Our hypothesis contradicts common models, which typically consider biofilms to be agents that promote weathering. In contrast, we propose that the microbial colonization of mineral surfaces acts to mitigate geomorphic processes in hot, arid environments.

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“…In contrast, field samples displayed an increase in surface hardness, in part due to the less-widely distributed grain loss in isolated 'pockets', permitting case hardening to develop in areas not experiencing concentrated grain loss (Mol and Viles, 2012;Viles et al, 2011). Biogenic case hardening may also explain the increase in surface hardness for field samples, while the saline brine of the laboratory experiments prevented the development of such a crust (Slavík et al, 2017).…”

Section: Controls On Visual Appearance and Surface Hardnessmentioning

confidence: 92%

Controls on the geotechnical response of sedimentary rocks to weathering

Vilder

Brain

Rosser

2019

Earth Surf Processes Landf

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Weathering reduces the strength of rocks and so is a key control on the stability of rock slopes. Recent research suggests that the geotechnical response of rocks to weathering varies with ambient stress conditions resulting from overburden loading and/or stress concentrations driven by near‐surface topography. In addition, the stress history experienced by the rock can influence the degree to which current weathering processes cause rock breakdown. To address the combined effect of these potential controls, we conducted a set of weathering experiments on two sedimentary lithologies in laboratory and field conditions. We firstly defined the baseline geotechnical behaviour of each lithology, characterising surface hardness and stress–strain behaviour in unconfined compression. Weathering significantly reduced intact rock strength, but this was not evident in measurements of surface hardness. The ambient compressive stress applied to samples throughout the experiments did not cause any observable differences in the geotechnical behaviour of the samples. We created a stress history effect in sub‐sets of samples by generating a population of microcracks that could be exploited by weathering processes. We also geometrically modified groups of samples to cause near‐surface stress concentrations that may allow greater weathering efficacy. However, even these pronounced sample modifications resulted in insignificant changes in geotechnical behaviour when compared to unmodified samples. The observed reduction in rock strength changed the nature of failure of the samples, which developed post‐peak strength and underwent multiple stages of brittle failure. Although weakened, these samples could sustain greater stress and strain following exceedance of peak strength. On this basis, the multi‐stage failure style exhibited by weaker weathered rock may permit smaller‐magnitude, higher‐frequency events to trigger fracture through intact rock bridges as well as influencing the characteristics of pre‐failure deformation. These findings are consistent with patterns of behaviour observed in field monitoring results. © 2019 John Wiley & Sons, Ltd.

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Biologically-initiated rock crust on sandstone: Mechanical and hydraulic properties and resistance to erosion

Cited by 42 publications

References 50 publications

The origin and role of biological rock crusts in rocky desert weathering

The origin and role of biological rock crusts in rocky desert weathering

The origin and role of biological rock crusts in rocky desert weathering

Controls on the geotechnical response of sedimentary rocks to weathering

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