2024-05-09 カーディフ大学
◆研究チームは、3000個のプラスチック破片を実際の川の条件を模倣した人工水路に投入し、複数のカメラでミリメートル単位で追跡しました。この分析から、異なる形状とサイズのプラスチックが川で多様な方法で輸送されることが明らかになりました。さらに、沈むプラスチックの動きを解明し、沈殿物の方程式を適用してプラスチックの量を予測する新しい方法を提案しました。
＜関連情報＞
- https://www.cardiff.ac.uk/news/view/2813840-scientists-develop-new-method-for-quantifying-invisible-plastics-in-rivers
- https://www.sciencedirect.com/science/article/pii/S0043135424002082
乱流輸送における非浮力プラスチックの垂直構造について On the vertical structure of non-buoyant plastics in turbulent transport
James Lofty, Daniel Valero, Antonio Moreno-Rodenas, Biruk S. Belay, Catherine Wilson, Pablo Ouro, Mário J. Franca
Water Research Available online:13 February 2024
DOI:https://doi.org/10.1016/j.watres.2024.121306
Highlights
- 400 settling tests and 3000 plastic samples in river-like transport were tracked.
- A multimodal distribution of plastic settling velocity was observed.
- Three plastic transport layers are observed; surfaced, suspended and bed load.
- Particle-bed dynamics caused concentration profiles to depart from a Rouse profile.
- New transport theories are derived from the stochastic nature of settling plastic.
Abstract
Plastic pollution is overflowing in rivers. A limited understanding of the physics of plastic transport in rivers hinders monitoring, the prediction of plastic fate and restricts the implementation of effective mitigation strategies. This study investigates two unexplored aspects of plastic transport dynamics across the near-surface, suspended and bed load layers: (i) the complex settling behaviour of plastics and (ii) their influence on plastic transport in river-like flows. Through hundreds of settling tests and thousands of 3D reconstructed plastic transport experiments, our findings show that plastics exhibit unique settling patterns and orientations, due to their geometric anisotropy, revealing a multimodal distribution of settling velocities. In the transport experiments, particle-bed interactions enhanced mixing beyond what established turbulent transport theories (Rouse profile) could predict in low-turbulence conditions, which extends the bed load layer beyond the classic definition of the bed load layer thickness for natural sediments. We propose a new vertical structure of turbulent transport equation that considers the stochastic nature of heterogeneous negatively buoyant plastics and their singularities.
Graphical abstract
