Estuarine biofilm patterns: Modern analogues for Precambrian self‐organization

Abstract

This field and laboratory study examines whether regularly patterned biofilms on present‐day intertidal flats are equivalent to microbially induced bedforms found in geological records dating back to the onset of life on Earth. Algal mats of filamentous Vaucheria species, functionally similar to microbial biofilms, cover the topographic highs of regularly spaced ridge–runnel bedforms. As regular patterning is typically associated with self‐organization processes, indicators of self‐organization are tested and found to support this hypothesis. The measurements suggest that biofilm‐induced sediment trapping and biostabilization enhance bedform relief, strength and multi‐year persistence. This demonstrates the importance of primitive organisms for sedimentary landscape development. Algal‐covered ridges consist of wavy‐crinkly laminated sedimentary deposits that resemble the layered structure of fossil stromatolites and microbially induced sedimentary structures. In addition to layering, both the morphological pattern and the suggested formation mechanism of the recent bedforms are strikingly similar to microbialite strata found in rock records from the Precambrian onwards. This implies that self‐organization was an important morphological process in times when biofilms were the predominant sessile ecosystem. These findings furthermore emphasize that self‐organization dynamics, such as critical transitions invoking ecosystem emergence or collapse, might have been captured in fossil microbialites, influencing their laminae. This notion may be important for paleoenvironmental reconstructions based on such strata. © 2019 The Authors. Earth Surface Processes and Landforms published by John Wiley & Sons Ltd

A Convolution Method to Assess Subgrid‐Scale Interactions Between Flow and Patchy Vegetation in Biogeomorphic Models

“…At a small scale, within the vegetation patches, flow velocities and erosion are reduced (e.g., Nepf, 2012) resulting in improved plant growth (positive feedback van Wesenbeeck et al, 2008). At a larger scale, the water is partly forced to flow around the vegetation patches, leading there to increased flow velocities (Zong & Nepf, 2010), potential erosion (Bouma et al, 2007), and to inhibition of plant growth just next to the vegetation patch (negative feedback van Wesenbeeck et al, 2008). Scale-dependent biogeomorphic feedbacks have been studied extensively over the past decade.…”

“…Their strength is reported to depend on many characteristics, such as patch size (Licci et al, 2019;Vandenbruwaene et al, 2011), stem density (Bouma et al, 2009), stem height (Gu et al, 2018), stem stiffness (Bouma et al, 2013;Marjoribanks et al, 2019;Ortiz et al, 2013;Schwarz et al, 2015), interpatch distance (de Lima et al, 2015;Meire et al, 2014;Vandenbruwaene et al, 2011), lateral expansion rate (Schwarz et al, 2018), and flow velocity (Bouma et al, 2013;Marjoribanks et al, 2019;Vandenbruwaene et al, 2011). Several studies have also shown that strong scale-dependent feedbacks are needed to result in the self-organization of regular spatial biogeomorphic patterns at the landscape scale (Rietkerk et al, 2004;Schwarz et al, 2018;Temmerman et al, 2007;van de Koppel et al, 2012). Given the above description of the scale dependency of biogeomorphic feedbacks, it becomes evident that their representation within numerical models is highly dependent on the grid size, which raises a balance problem between domain size and computational time.…”

River, Coastal and Estuarine Morphodynamics Selected papers from the 10th anniversary of the RCEM Symposium

“…The study of van de Vijsel et al . () reveals a striking similarity between present‐day sedimentary patterns in ridges and sedimentary patterns found in ancient stromatolites and Precambrian microbialite strata. Their laboratory study shows that biofilm sediment trapping and stabilization in ridges of present‐day intertidal flats is found to be characterized by indicators of self‐organization, suggesting an intriguing hypothesis whereby self‐organization dynamics might have been captured in fossil microbialites, a notion that may be important for paleoenvironmental reconstruction.…”

“…By analysing the effects of the impinging wind waves on the retreat of salt-marsh boundaries, and how the temporal evolution of wind-wave fields over the last centuries affects erosional dynamics, they highlight that relating salt-marsh lateral erosion rates to mean wave-power densities provides a valuable tool to address long-term tidal morphodynamics. The study of van de Vijsel et al (2020) reveals a striking similarity between present-day sedimentary patterns in ridges and sedimentary patterns found in ancient stromatolites and Precambrian microbialite strata. Their laboratory study shows that biofilm sediment trapping and stabilization in ridges of present-day intertidal flats is found to be characterized by indicators of self-organization, suggesting an intriguing hypothesis whereby self-organization dynamics might have been captured in fossil microbialites, a notion that may be important for paleoenvironmental reconstruction.…”

“…The 17 collected contributions include four state-of-science papers concerning the most recent advances in computational morphodynamic modelling of coupled flow-bed-sediment systems (Shimizu et al, 2019), a critical analysis of existing data on vegetation-flow-sediment interactions obtained through both laboratory experiments and field campaigns (Tinoco et al, 2020), a review of existing moving-boundary theories of shorelines with two extensions to allow inclusion of firstorder effects of waves and tides (Voller et al, 2020), and an overall assessment of the role played by wave forcing on the hydro-morphodynamics in shallow nearshore areas and at river mouths (Brocchini, 2019). The other 13 papers cover different topics about morphodynamics, spanning multiple environments, tackling concepts and processes with the aid of refined theoretical and numerical tools (Redolfi et al, 2019;Tambroni et al, 2019), grounding the results on laboratory data (Finotello et al, 2019;Geng et al, 2019;Matoušek et al, 2019, Porcile et al, 2020 and field observations (Fogarin et al, 2019;Tommasini et al, 2019), and making use of interdisciplinary approaches (Calvani et al, 2019;Chen et al, 2019;Pivato et al, 2019;van de Vijsel et al, 2020) also to develop new conceptualizations (Schlömer et al, 2020).…”