title: Selective transport of microplastics and mesoplastics by drifting in coastal waters.
abstract: The quantity and size distributions of small plastic fragments in the Seto Inland Sea, Japan were investigated using field surveys and a numerical particle-tracking model. The model was used to interpret the distributions of small plastic fragments and the possible transport processes in coastal waters. Of note, the size and quantity of mesoplastics (approximately >5mm) gradually increased close to the coast irrespective of the existence of river mouths, which probably act as a major source of anthropogenic marine debris. Additionally, microplastics were more dominant as we moved further offshore. The numerical model reproduced the near-shore trapping of mesoplastics, suggesting that mesoplastics are selectively conveyed onshore by a combination of Stokes drift and terminal velocity, dependent on fragment sizes. It is suggested that mesoplastics washed ashore on beaches degrade into microplastics, and that the microplastics, which are free from near-shore trapping, are thereafter spread offshore in coastal waters.
authors.affiliation: Research Institute for Applied Mechanics, Kyushu University, 6-1 Kasuga-Koen, Kasuga 816-8580, Japan. Electronic address: aisobe@riam.kyushu-u.ac.jp.
authors.forename: Atsuhiko
authors.initials: A
authors.lastname: Isobe
authors.affiliation: Graduate School of Science and Engineering, Ehime University, 2-5 Bunkyo-cho, Matsuyama 790-8577, Japan.
authors.forename: Kenta
authors.initials: K
authors.lastname: Kubo
authors.affiliation: Faculty of Science, Ehime University, 2-5 Bunkyo-cho, Matsuyama 790-8577, Japan.
authors.forename: Yuka
authors.initials: Y
authors.lastname: Tamura
authors.affiliation: Graduate School of Science and Engineering, Kagoshima University, 1-21-40 Korimoto, Kagoshima 890-0065, Japan.
authors.forename: Shin'ichio
authors.initials: S
authors.lastname: Kako
authors.affiliation: Tosa Food Business Creator Project Team, Kochi University, B-200, Monobe, Nankoku 783-8502, Japan.
authors.forename: Etsuko
authors.initials: E
authors.lastname: Nakashima
authors.affiliation: Institute of Lowland and Marine Research, Saga University, Honjo 1, Saga 840-8502, Japan.
authors.forename: Naoki
authors.initials: N
authors.lastname: Fujii
mesh_terms: D004784:Environmental Monitoring; D007564:Japan; D010316:Particle Size; D010969:Plastics / Q000032:analysis*; D045483:Rivers; D014866:Waste Products / Q000032:analysis*; D014872:Water Movements; D014876:Water Pollution
chemical_list: D010969:Plastics; D014866:Waste Products
keywords: Mesoplastics; Microplastics; Selective onshore transport; Stokes drift; Terminal velocity