Data for The hyporheic exchange of microplastics

The transport of microplastics in the hyporheic zone remains poorly understood with few studies attempting to quantify microplastic hyporheic exchange processes. A laboratory scale erosimeter was utilized in combination with fluorometric techniques to quantify the dispersion of 3D-pore scale stained microplastics across the hyporheic zone. Rhodamine WT dye, Polypropylene (PP), polyethylene (PE), and polymethyl methacrylate (PMMA) were well-mixed within the riverbed and individually tested using solute transport theory for three sediment diameters and five bed shear velocities (u_*) found in the natural environment. Effective dispersion coefficients for solutes significantly differed from that of PE and PMMA in most cases, where a limit as to how slow they could disperse was observed and a method for predicting polymer dispersion was proposed. When u_* ≥ 0.0304 m/s, PMMA followed the same pathways as solutes and solute transport models were successfully implemented to predict its fate. PP near the riverbed interface ascended to the surface but flocculation and aggregation deeper in the riverbed prevented dispersion calculations. When polymer buoyancy becomes the dominant process, high concentrations of lighter than water microplastics ascend into the water column and high concentrations of denser than water microplastics descend through pore water into groundwater systems. Unless density modification processes occur, pelagic organisms will be more exposed to polymers with densities 1 g/cm³ and benthic organisms to polymers with densities 1 g/cm³ in fluvial systems. These findings highlight polymer density and aggregation ability as major factors for determining microplastic fate at lower velocities.