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

Abstract

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.

Identification and extraction of cementation patterns in sand modified by MICP: New insights at the pore scale

“…Biofilms are generally considered to be heterogeneous matrices composed of microbial communities and extracellular polymers (EPS, microbial cell metabolites), which are formed by microbial attachment and growth in natural environments and engineered systems. They stabilize spatial organization mainly by providing intercellular scaffolds formed by EPS [ 83 ], and are therefore essential for stabilizing sediments [ 29 ]. Due to their structural irregularities, biofilms may also have a significant impact on the hydrodynamics of porous media [ 22 ].…”

“…The role of the biofilm as a collector continuously attracts bacteria, further enhancing their deposition [ 23 ]. According to Stoke’s law [ 24 , 27 , 31 ], the settling velocity is proportional to the diameter squared and density of the microbial floc, which shows the importance of biofilm thickness and density in preventing washout [ 24 , 29 , 30 ]. Unfortunately, biofilms degrade over time without a nutrient supply [ 32 ].…”

“…Microbial biofilms have been demonstrated effectiveness in controlling water seepage from hydraulic barriers in soils by reducing fluid flow rate [21][22][23][24][25], pore throat size [25,26], free pore volumes [23,27,28], and flow channels [23,28]. Moreover, microbial biofilms have been shown to enhance the shear strength [25,29,30] and viscosity [23,27,28], thereby positively affecting seepage resistance. The role of the biofilm as a collector continuously attracts bacteria, further enhancing their deposition [23].…”

Biophysical contexture of coastal biofilm-sediments varies heterogeneously and seasonally at the centimeter scale across the bed-water interface

“…Some of these produce extracellular polymeric substances (EPS) to attach to sand grain surfaces (Gobet et al, 2012;Chen et al, 2017b). The natural rhythmicity of EPS production by diatom has been extensively investigated, which were reported to be well associated with its migration across the sediment-water interface in response to both internal (i.e., the endogenous rhythms) and external factors (i.e, environmental stresses such as hydrodynamic forces and radiation) (de Brouwer and Stal, 2001;Orvain et al, 2003;Perkins et al, 2004;Chen et al, 2022). Direct microscopic observations and technologies have revealed that more than 99.9% of the bacteria live in the form of biofilms on a variety of interfaces (Donlan and Costerton, 2002).…”