Abstract
Rivers form major conduits for land-derived plastic waste and their sediments have been found to retain high levels of microplastics (MPs; plasticsThis study investigated the spatio-temporal variations in MP presence within coarse-granular, mixed sediments of the River Thames (UK) catchment. Samples were taken on a seasonal basis over 30 months (July 2019 – Dec 2021) from 12 sampling sites, classified as rural, urban and industrial locations. MPs were extracted from sediment using density flotation, then visually counted and investigated using ATR-FTIR.
MPs were pervasive in the sediment of the R. Thames catchment, with concentrations reaching 4,241 items kg-1 d.w. (dry weight). The surrounding land use affected the detected MP concentrations and was reflected in the morphology and composition of MPs retained in sediments. On a smaller scale, MP concentrations in sediment did not substantially vary across the channel.
MP presence in sediment exhibited a pronounced temporal variability, generally increasing in low-flow conditions and decreasing following high-flow events. Despite their ability to form robust contaminant sinks, this study suggests that gravel-dominated riverbeds might have the capacity to act as either MP sinks or sources depending on flow regime.
MP concentrations did not correlate with the abundance of fine sediment (63 – 250 µm) on a spatial scale and under low-flow conditions, but the two were found to co-occur during high flow events, providing insights into the potential of tracking MPs using fine sediment grains as a proxy.
This study describes the extent and potential origins of MP pollution in a historically and ecologically important river. Through investigating MP presence in sediment in different flow conditions, it likely provides a more accurate assessment of MP levels and sources compared to most MP studies conducted under baseflow conditions. Finally, it represents one of the first attempts to understand MP mobility in-situ and under a wide range of flows. Understanding the potential of MPs to be remobilised is particularly important given the current changes to the climate, which are predicted to increase the frequency and magnitude of flooding, degrade the stability of riverbeds and facilitate pollutant dispersal in aquatic settings.
| Date of Award | Apr 2023 |
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| Original language | English |
| Awarding Institution |
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| Supervisor | Anne Ockelford (Supervisor), James Ebdon (Supervisor) & Cundy Andrew (Supervisor) |