Experimental Investigation of the Effects of Vegetation on the Physical Transport and Retention Pattern of Microplastics

Microplastics (MPs), plastic particles that range from 1 to 5 mm in size, are a growing concern in the oceans worldwide. The abundance of MPs particles in marine and riverine environments presents a risk to aquatic ecosystems, species, and food webs, and therefore a threat to human food safety. Rivers are critical carriers of almost 70%–80% of the plastic waste that reaches the oceans from land based sources. Recognizing the increasing environmental concern of MPs, it becomes vital to understand the dynamics of MPs in the riverine ecosystem systems. This particular study investigated the impact of vegetation on the transport and retention patterns of MPs in an open channel. Several experimental scenarios, with and without vegetation under high and low Reynolds numbers, were conducted in the eco-hydraulics flume to examine the flow hydrodynamics and the transport and retention pattern of MPs. For vegetation scenarios, plastic aquarium plants were attached to the flume bed with different vegetation densities and arrangements, for example, disperse vegetation and vegetation along sides in the observation area. An acoustic Doppler velocimeter (ADV) was utilized to measure the flow hydraulics in the observation area. The retention and transport of MPs was appeared to be more prominent for large vegetation density and low flow velocity. The relationship of hydraulic parameters like average turbulence kinetic energy, average shear velocity, and average flow velocity with retention coefficient was pretty good for disperse vegetation arrangement as compared to the vegetation along the sides.