Transport and Fate of Microplastics in Freshwater Sediments
Final Report Abstract
Within the DFG-funded project ‘Transport and Fate of Microplastics in Freshwater Sediments’ research was conducted to further uncover how microplastic particles (here >20 µm) move through rivers, river networks and catchments. This research combined flume experiments conducted in the Ecolab outdoor laboratory environment of the University of Birmingham, UK with data from modelling studies as well as field sampling campaigns. Flume (mesocosm) experiments were conducted to study the settling behaviour of Polyamide microplastic fragments and fibres with respect to gravitational settling and hyporheic exchange processes. This settling behaviour was studied with respect to the impact of flow velocity, particle shape and sediment grain size distribution. It was found that turbulent flow and other hyporheic exchange processes as they occur also near the riverbed have a profound influence on MP settling behaviour. On the one hand, particles denser than water can not only settle by gravity but also become resuspended into the water column, which leads to terminal settling times greater than anticipated when using classical particle theory. On the other hand, hyporheic exchange processes can force MPs into the sediment bed where they can remain for prolonged amounts of time, which leads to a much slower downstream transport of MP than predicted by global plastic export models. These experimental findings support findings of modelling experiments that looked into MP residence times in different stream classes (headwaters to mainstems). Additional water and sediment samples from various stream environments around the world that were analysed during the project helped to further improve our understanding of MP fate and transport processes. For example, it was found that endorheic basins (those not terminating into an ocean) such as the Okavango Delta, Botswana, can act as a major plastic sink and future research has to account for this type of sink in global models as well as in studies on local ecosystem health. It was also found that on a catchment scale microplastic particles are not just transported downstream once they enter the river channel but are often rerouted and redistributed within the catchment or even neighbouring catchments during water management (e.g., water abstraction for agriculture). This further complicates MP loading estimates for larger rivers and river networks. My contribution to studying the impact of sampling techniques on microplastic recovery rates in streambed sediments (Wazne et al., in preparation) showed that while sediment scooping is an efficient technique that can be applied quickly on a larger scale, other techniques such as freeze coring can recover a higher percentage of the anticipated microplastic particles. Techniques such as sampling resuspended sediment or pumping porewater from the streambed on the other hand might have strong influence on microplastic particle size recovered during sampling, with smaller particles recovered more abundantly. Overall, the project contributed to improving our understanding of MP transport processes in riverine environments and provided insight into some of the drivers responsible for MP pollution in different river systems and networks. The information gained in this project will be helpful in future studies and can serve as a baseline when aiming to establish long-term monitoring concepts and networks, choosing adequate field sampling techniques or for further improving global and local plastic transport models.
Publications
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Easy and accessible way to calibrate a fluorescence microscope and to create a microplastic identification key. MethodsX, 10(2023), 102053.
Kukkola, Anna; Krause, Stefan; Yonan, Yasmin; Kelleher, Liam; Schneidewind, Uwe; Smith, Gregory H. Sambrook; Nel, Holly & Lynch, Iseult
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Microplastics and nanoplastics in agriculture—A potential source of soil and groundwater contamination?. Grundwasser (2022, 12, 29).
Moeck, Christian; Davies, Grace; Krause, Stefan & Schneidewind, Uwe
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Microplastic accumulation in endorheic river basins – The example of the Okavango Panhandle (Botswana). Science of The Total Environment, 874(2023, 5), 162452.
Kelleher, Liam; Schneidewind, Uwe; Krause, Stefan; Haverson, Lee; Allen, Steve; Allen, Deonie; Kukkola, Anna; Murray-Hudson, Mike; Maselli, Vittorio & Franchi, Fulvio
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Microplastic accumulation in riverbed sediment via hyporheic exchange from headwaters to mainstems. Science Advances, 8(2).
Drummond, Jennifer D.; Schneidewind, Uwe; Li, Angang; Hoellein, Timothy J.; Krause, Stefan & Packman, Aaron I.
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Microplastic distribution and characteristics across a large river basin: Insights from the Neuse River in North Carolina, USA. Science of The Total Environment, 878(2023, 6), 162940.
Kurki-Fox, J. Jack; Doll, Barbara A.; Monteleone, Bonnie; West, Kayla; Putnam, Gloria; Kelleher, Liam; Krause, Stefan & Schneidewind, Uwe
