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Transport and retention of micro-polystyrene in coarse riverbed sediments: effects of flow velocity, particle and sediment sizes
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Researchers conducted column experiments to investigate how polystyrene microplastic fragments are transported and retained in coarse riverbed sediments under different flow conditions. They found that most particles were captured in the upper 15-20 centimeters of sediment, but smaller fragments between 100-500 micrometers could penetrate to depths of at least 50 centimeters. The study suggests that riverbeds can act as both temporary sinks and long-term retention sites for microplastics, slowing their transport from streams to oceans.
Abstract Riverbed sediments have recently been found to be an important reservoir for microplastics. But the hydrogeological factors that control the abundance of microplastics are complex and conceptual frameworks priorising the parameters affecting their transport and retention during deep riverbed filtration are still missing. In this study a series of saturated column experiments was conducted to investigate the vertical distribution patterns of secondary polystyrene fragments (100–2000 μm) in dependence on their particle size, grain size of the sediment, seepage velocity and duration of infiltration flow. The columns with a length of 50 cm were operated with flow velocities between 1.8 m d −1 and 27 m d −1 . Invasive samples obtained after the experiments were density separated and then depth profiles of microplastic concentrations were retrieved using fluorescence imaging analysis. Most polystyrene particles were retained in the upper 20 cm and 15 cm of the medium gravel and coarse sand sediments, respectively. Through the high particle retention riverbed sediments can act as a temporary sink or long term retention site for the transport of microplastic particles (MPPs) from streams to oceans. A small fraction of particles ranging from 100 to 500 μm in size was observed down to infiltration depths of 50 cm suggesting that MPPs at the pore scale have the potential to be advectively transferred via hyporheic exchange or induced bank filtration into coarse riverbed sediments and alluvial aquifers. MPP abundance over column depth follows an exponential relationship with a filter coefficient that was found to depend significantly on the flow rate, MPP and sediment grain size, as indicated by multiple linear regression (R 2 = 0.92). The experimentally derived empirical relation allows to estimate particle abundances of initially negatively buoyant MPP in riverbed sediments by surface water infiltration.
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Dataset accompanying the publication "Transport and retention of micro-Polystyrene in coarse riverbed sediments: Effects of flow velocity, particle and sediment sizes"
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This is an additional data repository accompanying the same study on microplastic transport in riverbed sediments. The data is provided to support reproducibility and further analysis of microplastic fate in freshwater environments.
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