首页|The role of turbulence in the deposition of intrinsically buoyant MPs
The role of turbulence in the deposition of intrinsically buoyant MPs
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Elsevier
Intrinsically floating microplastics (MP) such as polyethene (PE) or polypropylene (PP) are among the mostcommon MPs found in aquatic sediments. There must hence be mechanisms that cause lighter-than-water MPs todeposit despite them being buoyant. How these MPs end up in the sediment bed is only partly understood. Thisstudy explores how turbulence in the water can affect the vertical movement of buoyant MP and bring them incontact with the bed. The deposition of PE (995 kg m~(-3)) in slow-flowing water (average flow velocities of 1.85and 4.17 cm s~(-1)) was measured by tracking them and analyzing their motion in an open, rectangular, glass-sidedflume. Flow characteristics in terms of turbulent kinetic energy and shear velocity were measured by particleimage velocimetry. Experiments were conducted at a water depth of 27 cm and at various hydraulic conditionscreated by adjusting inflow speeds and using different bed materials: medium gravel, fine gravel, medium sand,cohesive sediment, and glass. The results showed that the vertical velocity of the MPs in the turbulent flowregimes varied over 4 orders of magnitude from their predicted rising velocity in quiescent water (laminar flow).Turbulence mixing resulted in distribution throughout the water column with a substantial quantity consistentlysubject to downward vertical transport, which in turn increased the chance of the PE particles encountering thebed and potentially getting immobilized. This work provides a plausible explanation and further experimental validation for the concept of mixing induced transfer of MPs from the water surface to the sediments of shallowwaters.
Aalborg University, Section of Civil and Environmental Engineering, Department of the Built Environment, Thomas Manns Vej 23, 9220 Aalborg Ost, Denmark
LEESU, Ecole des Ponts, Univ Paris Est Creteil, Marne-la-Vallee, France
Institute for Environmental Sciences, RPTU Kaiserslautern-Landau, Landau, Germany
NETL
NSTL
Elsevier
