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.
