Quantifying biostabilisation effects of biofilm-secreted and extracted extracellular polymeric substances (EPSs) on sandy substrate

Abstract

Abstract. Microbial assemblages ("biofilms") preferentially develop at water-sediment interfaces and are known to have a considerable influence on sediment stability and erodibility. There is potential for significant impacts on sediment transport and morphodynamics, and hence on the longer-term evolution of coastal and fluvial environments. However, the biostabilisation effects remain poorly understood and quantified due to the inherent complexity of biofilms and the large spatial and temporal (i.e. seasonality) variations involved. Here, we use controlled laboratory tests to systematically quantify the effects of natural biofilm colonisation as well as extracted extracellular polymeric substances (EPSs) on sediment stability. Extracted EPSs may be useful to simulate biofilm-mediated biostabilisation and potentially provide a method of speeding up timescales of physical modelling experiments investigating biostabilisation effects. We find a mean biostabilisation effect due to natural biofilm colonisation and development of almost 4 times that of the uncolonised sand. The presented cumulative probability distribution of measured critical threshold for erosion of colonised sand reflects the large spatial and temporal variations generally seen in natural biostabilised environments. For identical sand, engineered sediment stability from the addition of extracted EPSs compares well across the measured range of the critical threshold for erosion and behaves in a linear and predictable fashion. Yet, the effectiveness of extracted EPSs to stabilise sediment is sensitive to the preparation procedure, time after application and environmental conditions such as salinity, pH and temperature. These findings are expected to improve biophysical experimental models in fluvial and coastal environments and provide much-needed quantification of biostabilisation to improve predictions of sediment dynamics in aquatic ecosystems.

Low-gradient, single-threaded rivers prior to greening of the continents

“…Microbial mats and biofilms can also provide cohesion to unconsolidated sand, and microbial sedimentary structures are prevalent in the Torridonian Supergroup (42). Experimental studies demonstrated that microbially bound medium-to-coarse sand can withstand a shear stress between 0.3 and 4 Pa without significant grain movement (43). The estimated range of τ b for the Torridonian rivers was 0.2-10 Pa (Fig.…”

Impacts of Severe Tropical Cyclone Olwyn and the biogeomorphic response, Hamelin Pool, Shark Bay, Western Australia

“…Biostabilisation within the upper intertidal zone varied considerably across the three study sites mapped in more detail and clearly affected the storm responses. The spatial distribution of erosional pockets and de‐levelling suggests that focussed high‐energy areas developed across the intertidal zone, since erosion of microbial mats requires significantly more force than erosion of non‐biostabilised sediment (Gerbersdorf & Wieprecht, 2015; Le Hir et al, 2007; Noffke et al, 2001; Noffke & Krumbein, 1999; Noffke & Paterson, 2008; Parsons et al, 2016; Paterson, 1994; Tolhurst et al, 2000; Van De Lageweg et al, 2018; Yallop et al, 1994). Erosion thresholds for biostabilised non‐cohesive sediments are many times higher than of non‐biostabilised controls (Chen et al, 2017; Le Hir et al, 2007; Lubarsky et al, 2010; Van De Lageweg et al, 2018).…”

“…The spatial distribution of erosional pockets and de‐levelling suggests that focussed high‐energy areas developed across the intertidal zone, since erosion of microbial mats requires significantly more force than erosion of non‐biostabilised sediment (Gerbersdorf & Wieprecht, 2015; Le Hir et al, 2007; Noffke et al, 2001; Noffke & Krumbein, 1999; Noffke & Paterson, 2008; Parsons et al, 2016; Paterson, 1994; Tolhurst et al, 2000; Van De Lageweg et al, 2018; Yallop et al, 1994). Erosion thresholds for biostabilised non‐cohesive sediments are many times higher than of non‐biostabilised controls (Chen et al, 2017; Le Hir et al, 2007; Lubarsky et al, 2010; Van De Lageweg et al, 2018). Furthermore, the degree of biostabilisation varies according to boundary layer roughness generated by the mat or biofilm, particle cohesion, Extracellular Polymeric Substance (EPS) character, the time of day, the season, the age of the biofilm, its desiccation history and the local hydrodynamic flow conditions under which it developed, as well as the microbial community and its structure (Flemming & Wingender, 2010; Gerbersdorf & Wieprecht, 2015; Paterson, 1994; Schmidt et al, 2018).…”

“…The contribution of pore pressure effects, to erosive affects, may be reduced across lithified structures, due to their reduced compressibility. However, the impact of hydrostatic and pore pressure effects on the erodibility of microbial mats is not wellunderstood, even though shear and surface down forces in biofilm destabilisation have been widely examined (Chen et al, 2017(Chen et al, , 2018(Chen et al, , 2019Hagadorn & McDowell, 2012;Malarkey et al, 2015;Parsons et al, 2016;Van De Lageweg et al, 2018).…”

Rusty river: Effects of tufa precipitation on sediment entrainment in the Estero Morales in the central Chilean Andes

“…A C C E P T E D M A N U S C R I P T 30 2014). The effectiveness of extracted extracellular polymeric substances (EPSs) on sediment stability was also demonstrated to be sensitive to environmental conditions such as salinity, pH and temperature (Van de Lageweg et al, 2018). Thus, one could expect that the combined effect of tufa precipitation and biofilms may lead to greater geomorphological stability (Batalla and Vericat, 2009).…”