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
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.
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.