Downstream dispersal and transfer of macroplastics in river systems: a travel distance approach

Environmental pollution by synthetic polymers (plastics) is a global problem that severely impacts ecosystem form and function, human health, natural resource management and environmental aesthetics.

Although most attention has focused on marine environments, there is an increasing awareness that much of the pollution originates on land and is transferred to the oceans by rivers. 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 settings. For example, sewage sludge contaminated by synthetic fibres or sedimented microplastics has been identified as a significant terrestrial source of microplastic pollution, levels of contamination in some rivers have been shown to be greater than those observed in the oceans and plastics ingested by aquatic organisms have consequences for the trophic transfer of plastics through the food web.

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 storage. 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 systems.

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) transponders. 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.

Entry requirements
Applicants are required to hold/or expect to obtain a UK Bachelor Degree 2:1 or better in a relevant subject. The University of Leicester English language requirements apply where applicable.

How to apply
Please refer to the CENTA Studentship application information on our website for details of how to apply.

As part of the application process you will need to:
• Complete a CENTA Funding form – to be uploaded to your PhD application
• Complete and submit your PhD application online. Indicate project CENTA2-GGE11-POWE in the funding section.
• Complete an online project selection form Apply for CENTA2-GGE11-POWE