The Effects of Large Roughness Elements on the In-stream Transport and Retention of Polystyrene Microplastics

Abstract

Abstract The dominant mechanisms controlling the concentration and transport of microplastics (MPs) in riverine systems are not fully understood yet. Polystyrene (PS) is a highly abundant MP in streams and rivers. This study investigated the impact of large roughness elements (LREs) on in-stream transport and retention patterns of polystyrene-microplastics (PS-MPs). Experiments were conducted with and without LREs under a range of shear Reynolds numbers (𝑅𝑒∗) in an eco-hydraulics flume. We found a clear dependence of MPs’ velocity on 𝑅𝑒∗ in LREs-dominated channel. The results also revealed that the LREs-generated turbulence kinetic energy (TKE) can be a good predictor of PS-MPs transport and retention rate. This indicates the effectiveness of TKE in retaining PS-MPs as they travel through streams and rivers. The presence of LREs increases the PS-MPs capture and decreases their velocity of transport. This suggests that PS-MPs retention can be increased by increasing the LRE density in reverine systems.