May the Shields theory be extended to cohesive and adhesive benthic sediments?

Abstract

A threshold criterion for incipient motion of cohesive‐adhesive sediments, based on moment balance and dimensional considerations, is here developed. The criterion discriminates between single particles and flocs critical conditions and induces a modification to the traditional Shields curve, commonly adopted for noncohesive particles. This modification is particularly effective for the smaller size particles but tending to vanish for the larger ones. The proposed approach is validated on the basis of experiments performed on sediment cores, sampled at different depths, from seven lakes with different trophic conditions and organic matter content. The incipient motion conditions are evaluated by means of an original procedure based on image analysis techniques, which enables the entrainment between single particles and flocs to be distinguished. The adhesion force, which is mainly due to the biological activity at the sediment water interface, is estimated following the proposed criterion and it is found to depend on the organic matter content. In particular the cores sampled in the littoral photic zone are characterized by a bell shaped dependence between adhesion coefficient and organic matter content, which is typical for indicators of biological activity of the littoral ecosystems.

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

“…The implementation of biological processes into sediment transport equations that have traditionally been modelled as abiotic systems is expected to result in better predictions of sediment dynamics (Black et al, 2002;Righetti and Lucarelli, 2007;Gerbersdorf et al, 2011;Parsons et al, 2016). Our study confirms that extracted EPSs xanthan gum and carrageenan are not perfect analogues of natural biofilms (Perkins et al, 2004), but they are capable of introducing realistic biological cohesion into flume facilities in a fast and controlled manner for a range of commonly used conditions.…”

“…Many studies have attempted to quantify biostabilisation in a variety of environments (Paterson, 1989;Dade et al, 1990;Amos et al, 1998;Tolhurst et al, 1999Tolhurst et al, , 2003Friend et al, 2003a;Droppo et al, 2007;Righetti and Lucarelli, 2007;Vignaga et al, 2012;Graba et al, 2013;Thom et al, 2015). These studies generally show a positive correlation between EPS content and sediment stability measured as the threshold for erosion, although variations in space and time (Friend et al, 2003b;Thom et al, 2015) and between cohesive and noncohesive sandy environments are large.…”

“…Biofilm formation affects sediment erosion, transport, deposition and consolidation (Righetti and Lucarelli, 2007;Gerbersdorf and Wieprecht, 2015). There is, for example, evidence that diatom blooms alter sediment dynamics at the scale of entire estuaries (Kornman and De Deckere, 1998), illustrating the potential effects micro-organisms can have on system-wide sediment fluxes.…”

Combining Field and Laboratory Measurements to Determine the Erosion Risk of Cohesive Sediments Best

“…Measurements of erosion thresholds of cohesive sediments have been conducted in different environments including sea beds [41,42], wetlands and tidal flats [43,44], lakes [45], mountain reservoirs [46] and in different river sections where fine sediment can deposit such as groyne fields, side structures or harbors [26,34,47]. Debnath and Chaudhuri [48] published an overview with a wide range of erosion thresholds including mostly marine, estuarine, and tidal environments.…”

Form, function and physics: the ecology of biogenic stabilisation

“…However, whether it is about mimicking cohesion (Lick et al 2004) or adding a combination of cohesion and adhesion coefficients (Righetti and Lucarelli 2007), there is still a significant lack of suitable data and appropriate measuring devices to strengthen the empirical dataset and validate the models (Grabowski et al 2011). …”