Catchments in crisis: Quantifying soil erosion and pollutant flux from drainage basins to coasts

River catchments are suffering from increased soil erosion, and are carrying more and more pollutants (e.g. microplastics, pharmaceuticals). The result is poor water quality in most UK rivers, and pollutants being stored on floodplains or transported to coasts with risks to marine life. Our ability to map and forecast the sources, transport, and deposition of particulates is essential to support catchment management, improve water quality, and assess anthropogenic impacts on marine ecosystems. However, management strategies to improve water quality are undermined by a lack of baseline data, the difficulty of identifying erosion hotspots and high pollutant input locations. Additional complications arise from an unaccounted bedload component to sediment, soil, and pollutant transport.

By taking a source-to-sink approach, linking the flux of particles from drainage basins to sedimentary basins over human timescales, the dispersal of particulates from catchments to coasts can be better quantified and forecast. Any attempts to forecast particulate flux to marine environments will need to account for climate change projections, the likely increased high intensity precipitation events, and therefore increased erosion of river banks and sedimentation on floodplains. A further complication is that there is not only a horizontal flux of pollutants, but a vertical flux: once deposited in fluvial, floodplainestuarine, and coastal environments, sediment and associated particulates can be subject to infiltration, bioturbation, and resuspension. 

A critical step is systematic sampling of river waters and river bed and floodplain deposits in order to provide a baseline dataset. Data from repeat sampling campaigns, augmented with satellite data, will help to identify spatial and temporal trends in erosion risk, which are not identified using existing methods that often rely on static landuse maps. Richardson et al. (2019) showed that traditional land-use maps do not capture seasonal variation in erosion risk due to variation in land management and the presence of bare landTherefore, adaptable management plans can be developed that integrate temporal variations in rainfall with climate change projections.

Field data from the River Ouse catchment will be augmented with earth observation data after large precipitation events to identify the location of erosion hotspots (‘Critical Source Areas’)new drainage pathways, and estimates of suspended load concentrations. Understanding variation in baseline fluxes of sediment, soils, and pollutants in river catchments is vital as the UK moves towards a payment for public goods approachTherefore, this studentship has the chance to inform policy. 

Aim and Objectives  

The principal aim of the proposed PhD project is to improve forecasting of horizontal and vertical particle flux through drainage basins to coasts in order to inform catchment managers and policy makers. To advance our understanding, the following objectives will be addressed: 

  • Examine the detailed grain characteristics (size, shape, mineralogy) of sediment transported and deposited in the River Ouse catchment.
  • Identify and assessing seasonal erosion hotspots, and the impacts of large magnitude events, using earth observation data and climate projection models. 
  • Investigate the role of artificial drainage networks, including underfield drainage, on soil erosion 
  • Develop experimental and theoretical models to quantify the role of flooding in pollutant dispersal and storage within fluvial systems. 
  • Collect and analyse sediment cores from estuarine and coastal settings to investigate the vertical flux of pollutants.
  • Combine these approaches to develop new baseline datasets, and predictive models, that capture the erosion, transport, (transient) storage, and deposition of pollutants from catchments to coasts.

 

PhD Schedule, Outputs and Training 

This PhD will commence before the end of 2021 and run for 3.5 years. During this period, the student will be eligible for all the postgraduate training typically provided to students attending the University as part of the Panorama DTP. The student will receive training in relevant software packages, field-based description, experimental techniques and data analysis, technical/scientific writing, and presentation of research to both scientific and public audiences. The student will be based and mentored, by experts in process sedimentology and geomorphology, in the School of Earth and Environment (SEE) at the University of Leeds, and in collaboration with the Energy and Environment Institute (EEI), University of Hull. The student will benefit from being part of vibrant multi-institution research groups covering Earth surface processes, water engineering and pollutants between SEE and the EEI. 

Richardson, J.C., Hodgson, D.M., Kay, P., Aston, B.J. and Walker, A.C., 2019. Muddying the picture? Forecasting particulate sources and dispersal patterns in managed catchments. Frontiers in Earth Science, 7, p.277.