This exciting project is a joint project between the Universities of Brighton and Southampton with input from project partners at the University of Illinois.
Global plastic production has increased exponentially since the 1960s, with 299 million tonnes produced annually. Plastics, and particularly microplastics (plastic particles typically less than 5mm in size), are now globally ubiquitous and are found in freshwater to deep marine environments, posing a potentially significant risk to environmental and human health. While many researchers have documented microplastic contamination in environments and organisms around the world, processes of environmental cycling and transfer remain relatively poorly defined, particularly in freshwater systems. Within river channels, it is the sediment bed that plays a vital role in mediating transfers since microplastics are buried and stored within sediments on the river bed.
During flood events, erosion of the bed surface means deeply buried microplastics are exchanged with the surface across the active layer and are potentially re-mobilised, producing hot spots of contamination. Active layer dynamics are driven by the interaction between the flow regime and the properties of the sediment surface. We have very little grasp on the magnitudes of floods required to mobilise sediment beds or the depths to which sediment beds are disturbed during a flood. Further, given that the climate change forecast is for a greater number of higher magnitude, more frequent floods, we need to know how rivers will respond so as to mitigate against the potential for contaminant remobilisation in the future.
The successful candidate will work with the project team to generate a new quantitative understanding of the effect of flood magnitude on microplastic remobilisation from sediment beds, achieved. To do this, an integrated approach that combines laboratory, field and modelling experiments will be used. Laboratory experiments will use the flume facilities at Brighton to test the impact of flood magnitude on bed erosion characteristics. The sediment bed will be seeded with microplastics and exposed to different magnitude flood waves. High resolution laser scanning of the sediment bed will be directly coupled with turbulent flow data collected using an Acoustic Doppler Velocimeter. Sediment cores taken during the experiments will be analysed using the 3D CT scanner at the μ-VIS X-Ray Imaging Centre (University of Southampton) to establish the changes to the contaminant profile during the flood wave. Laboratory experiments will be validated by fieldwork undertaken as necessary in the southern UK and Midlands to quantify relationships between bed turnover rate and the flow regime under natural hydrodynamic settings.
Experimental and field data will provide a unique set of boundary conditions and validation data for numerical model application. A 1D morphodynamic model of active layer development will be used to quantify and model the evolution of the bed surface in response to changing flood dynamics, such as to predict the likely remobilization potential of microplastics.
This will enable the candidate to:
- determine the link between the sediment bed disturbance depths, near bed flow dyanmics and sediment fluxes, and the flow regime;
- improve the process representation within an existing 1D morphodynamic model of active layer development in non-cohesive, mixed grain-sized rivers
- to predict the timing and magnitude of microplastic release based on bed disturbance depths across a range of discharges.