Periodic Reporting for period 4 - GEOSTICK (Morphodynamic Stickiness: the influence of physical and biological cohesion in sedimentary systems)
Reporting period: 2021-11-01 to 2023-01-31
Riverine and coastal environments are some of the most sensitive systems to sea-level rise & environmental change. In order to manage these systems, & adapt to future changes, we desperately need to be able to predict how they will alter under various future climate change scenarios. This has direct societal relevance as flood risk is set to double by 2050. GEOSTICK has addressed these needs, which has been important because our predictive models for these environments are not yet robust enough to predict, with confidence, very far into the future. Moreover, we also need to improve how we use our understanding of modern environments in reconstructing paleo-environments, where significant assumptions have been made in the way in which relationships derived from the modern have been applied to the interpretation of ancient rocks. GEOSTICK has begun to address these primary shortfalls, namely that our present predictions are based on assumptions that these systems are composed of only non-cohesive sands. However, mud is the most common sediment on Earth & many of these systems are actually dominated by biologically-active muds & complex sediment mixtures. GEOSTICK has therefore found ways to incorporate the effect of sticky mud & sticky biological components into our predictions. Abiotic-biotic interactions \re now known to impact these relationships and GEOSTICK has addressed these questions - of how much: inclusion of only relatively small (<0.1% by mass) quantities of biological material into sediment mixtures can reduce alluvial bedform size by an order of magnitude.
The overarching aim of this work has been delivered - to develop and apply new predictive tools for modelling large-scale bio-morphodynamics of coasts, estuaries and riverine systems and has directly addressed the set of three critical knowledge gaps outlined in the project proposal.
The overarching aim of this work has been delivered - to develop and apply new predictive tools for modelling large-scale bio-morphodynamics of coasts, estuaries and riverine systems and has directly addressed the set of three critical knowledge gaps outlined in the project proposal.
The results show that two-dimensional mature ripples characterised by a continuous and straight ripple crestline were developed in the control experiment with pure sand and in the beds with the initial clay content <12%. Relatively smaller ripples evolved from substrates with higher clay fraction. As shown in Figure 1B, there was an inverse relation between the initial clay fraction and ripple length (λ) and height (η). Moreover, bed roughness (Ks=27.7η2/ λ) decreased with the initial clay fraction increasing. Experiments to study the initiation motion of substrates with varying degrees of cohesion (different cohesive to non-cohesive particle ratios) are in progress. Currently, motion detection algorithms are being developed to determine: 1) incipient motion thresholds, 2) characteristics of the winnowing processes, and 3) threshold for bed collapse (plucking as opposed to single particle erosion).
In terms of the numerical modelling components, for the detailed, small scale processes two bio-functions have been considered: 1) the bio-stabilization model considering the effect of the surface biofilm in increasing the bed resistance and 2) the bio-mediated sediment model to compute transport of biofilm-coated sediments, which considers the enhanced bed resistance and changes of bio-flocs dimensions on the sediment transport mechanism. A one-dimensional morphodynamic model for tide-dominated channels transporting non-uniform sand and interacting with the ocean has been implemented with both the bio-models and this has been published. The model stores the information of the stratigraphy of the deposit and simulations were performed on a scaled real case (Rotterdam Estuary) to (i) validate the model, (ii) analyse the sensitivity of model parameters, (iii) investigate the effect of hydroclimate changes on bio-stabilized sediment for 5 different cases (clean sediment/ logarithmic growth of surface biofilm/ logarithmic growth regulated by seasonality/ logarithmic growth regulated by catastrophic removal of biofilm/ logarithmic growth regulated by seasonality and catastrophic removal due to hydrodynamic forces (tides)), and (iv) investigate the impact of anthropogenic and land use changes mediated by biofilm with respect to grain size distribution for fine and coarse sediment mixtures. The surface biofilm growth model is implemented in Delft3D-FM. This unlocks new understandings that enable test on a simplified channel geometry and estuary model, and field scale application to the Wadden Sea. These outputs are in review.
The work addressing WP6 and the geological record has been particularly fruitful. Anoxic conditions were characteristic of marine sediments throughout the Precambrian, with infauna evolving during the mid to late Cambrian. How early infauna colonised such hostile sediments is controversial. Thin section analysis and CT scans of samples taken from Bell Island, Newfoundland, were examined to study the distribution of and changes in the preserved species of trace fossils (fossil burrows) in response to the presence of Precambrian-like conditions and matgrounds preserved in the lithology. Bell Island’s trace fossils imply that opportunistic animals with simple, near surface but densely packed burrows were much more successful in Precambrian conditions (Fig. 6). Experimental work (see WP2) indicates that opportunistic, deposit feeding animals, are less impacted by anoxia, producing extensive burrows under both oxygenated and anoxic conditions. Unlike the Bell Island trace makers, these animals produce relatively deep burrows.
In terms of the numerical modelling components, for the detailed, small scale processes two bio-functions have been considered: 1) the bio-stabilization model considering the effect of the surface biofilm in increasing the bed resistance and 2) the bio-mediated sediment model to compute transport of biofilm-coated sediments, which considers the enhanced bed resistance and changes of bio-flocs dimensions on the sediment transport mechanism. A one-dimensional morphodynamic model for tide-dominated channels transporting non-uniform sand and interacting with the ocean has been implemented with both the bio-models and this has been published. The model stores the information of the stratigraphy of the deposit and simulations were performed on a scaled real case (Rotterdam Estuary) to (i) validate the model, (ii) analyse the sensitivity of model parameters, (iii) investigate the effect of hydroclimate changes on bio-stabilized sediment for 5 different cases (clean sediment/ logarithmic growth of surface biofilm/ logarithmic growth regulated by seasonality/ logarithmic growth regulated by catastrophic removal of biofilm/ logarithmic growth regulated by seasonality and catastrophic removal due to hydrodynamic forces (tides)), and (iv) investigate the impact of anthropogenic and land use changes mediated by biofilm with respect to grain size distribution for fine and coarse sediment mixtures. The surface biofilm growth model is implemented in Delft3D-FM. This unlocks new understandings that enable test on a simplified channel geometry and estuary model, and field scale application to the Wadden Sea. These outputs are in review.
The work addressing WP6 and the geological record has been particularly fruitful. Anoxic conditions were characteristic of marine sediments throughout the Precambrian, with infauna evolving during the mid to late Cambrian. How early infauna colonised such hostile sediments is controversial. Thin section analysis and CT scans of samples taken from Bell Island, Newfoundland, were examined to study the distribution of and changes in the preserved species of trace fossils (fossil burrows) in response to the presence of Precambrian-like conditions and matgrounds preserved in the lithology. Bell Island’s trace fossils imply that opportunistic animals with simple, near surface but densely packed burrows were much more successful in Precambrian conditions (Fig. 6). Experimental work (see WP2) indicates that opportunistic, deposit feeding animals, are less impacted by anoxia, producing extensive burrows under both oxygenated and anoxic conditions. Unlike the Bell Island trace makers, these animals produce relatively deep burrows.
Progress across the 6 work packages has been to plan with little variation or delays, the extension enabled the outcomes delayed by COVID19. Research has been conducted that addresses the knowledge gap on relative timescales and efficiencies of biotic and abiotic processes within system functioning and system linkage tipping-points with a specific focus on climate change (past and future). It adds a chemical dimension, which goes beyond the initial proposal. It covers (1) the link between sediment biochemical profiles (EPS chemistry) and sediment stickiness, and (2) how changes to the chemically-mediated interactions within biofilms and between biofilms & grazers affect sediment stability today and under climate change scenarios. For (1), initial test samples of Humber sediment revealed a promising diversity of fatty acids and enabled the development of an extraction & analytical protocol (similar protocol for amino acids in progress) for samples collected during future field campaigns, where sediment cohesion will also be determined in situ. For the most common biomolecules an investigation of the physical-chemical basis of biomolecules sticking to sediment particles by means of computational models and experiments on chemical binding will be the focus of future work. For aspect (2), available literature on autoinducers, chemicals that mediate environmental biofilm bacteria-bacteria/ bacteria-microalgae interactions, was reviewed and synthesised with related physico-chemical data, which revealed that these chemicals are highly pH dependent and likely affected by temperature changes, hence potentially affected by climate change. N-Acetyl homoserine lactones, known to be required for growth, EPS production and reproduction in sediment-associated biofilms, are more stable in lower pH conditions.