Overview

Project Highlights:

  • Enagagment with a ‘hot topic’ of global environmental concern
  • Will povide the first process-based estimates of rates of macroplastic transfer in river systems
  • Working with project partners actively engaged with pollution management and mitigation

Overview: Environmental pollution by synthetic polymers (plastics) is a global problem that severely impacts ecosystem form and function, human health, natural resource management and environmental aesthetics1-3. Although most attention has focussed on marine environments, there is an increasing awareness that much of the pollution originates on land2 and is transferred to the oceans by rivers4. As a result, there is a growing body of research that seeks to understand sources, levels and impacts of plastic contamination in a wide range of terrestrial and fluvial settings5. For example, sewage sludge contaminated by synthetic fibres or sedimented microplastics has been identified as a significant terrestrial source of microplastic pollution6, levels of contamination in some rivers have been shown to be greater than those observed in the oceans7 and plastics ingested by aquatic organisms have consequences for the trophic transfer of plastics through the food web8. As yet, however, there has been little research on the fundamental processes of plastic debris transport in these environments even though they are central to understanding, and making predictions of, rates of pollution transfer and residence times in sites of potential storage9. The fundamental phenomenon associated with the transport of plastic debris is the displacement of individual items, fragments and particles which is likely to be temporarily and intermittently interrupted by deposition, beaching on river banks and on floodplains and trapping by riparian vegetation (Figure 1). The aim of this study is to characterise the streamwise dispersal of macroplastic litter (> 5 mm) in rivers by considering the travel distances and fate of tagged plastic debris. The specific objectives of the study are to 1) classify the macroplastic debris occurring in fluvial environments in terms of form (size and shape) and materials (physical and chemical properties); 2) quantify the rate of streamwise dispersion for a range of representative macroplastic debris types over sequences of floods in a variety of channel types; and 3) develop a model for characterising the frequency distribution of travel distances of macroplastic debris in rivers that can be used to develop better predictions of macroplastic transfer through fluvial systems10.

Figure 1.  a) Schematic representation of the processes governing macroplastic transfer in rivers (after ref. 10) and b) macroplastic litter trapped by riparian vegetation in Willow Brook, an urban stream in Leicester, UK.

Methodology

The dispersal of macroplastic debris will be quantified in field experiments using macroplastic tracers tagged with a combination of active and passive radio frequency identification (RFID) transponders11. At each study site, tagged macroplastics will be introduced to the river and their movements between sites of temporary storage will be tracked over a series of flow events by periodically surveying the reach. Macroplastics exiting the study reaches will be identified automatically by RFID antennae installed above the channels and within their beds at cross-sections located at the end of the reaches. A comprehensive survey and classification of macroplastic litter found in fluvial systems will ensure that the tracers used in the study are representative. The distributions of tracer travel distances will be related to flow magnitude, reach characteristics (channel geometry, LiDaR derived metrics of riparian vegetation structure) and compared with theoretical probability density functions to develop a probabilistic model of macroplastic dispersion.

Training and Skills

Students will be awarded CENTA2 Training Credits (CTCs) for participation in CENTA2-provided and ‘free choice’ external training. One CTC equates to 1⁄2 day session and students must accrue 100 CTCs across the three years of their PhD.   In addition, the student will receive training in active and passive particle tracking technologies, methods of stream gauging and geomorphological survey, LiDaR techniques for characterising vegetation structure and probabilistic modelling.

Timeline

Year 1: Development of research proposal; identification of field sites; training in RFID tracking and LiDaR techniques; survey and classification of macroplastic litter in fluvial environments.

Year 2: Data collection and analysis

Year 3: Data analysis; writing up.

Partners and collaboration (including CASE)

Contacts in the Environment Agency and Severn Trent Water are being followed up.

Further Details

Dr. Mark Powell, School of Geography, Geology and the Environment, University of Leicester, LE1 7RH. Tel. 0116 2523850; dmp6:le.ac.uk.