Microplastics Rapidly Sink and Beach in a Whole-Lake Experiment

Although advances in oceanographic and limnological modeling have increased our understanding of microplastic transport and persistence, we require more knowledge to effectively protect biodiversity. We initiated a whole-lake experiment (the pELAstic project) to measure the real-world fate and transport of microplastics. We added microplastics to a boreal lake, simulating stormwater input, at loading concentrations predicted to achieve environmentally relevant concentrations. Here, we introduce our experiment and describe the particle budget from the first microplastic addition. We observed rapid transport of microplastics to different ecosystem compartments. Transport patterns could not be fully explained by initial particle size and density, highlighting how natural processes modify plastic fate in real-world systems. Microplastic fragments rapidly redistributed─exiting the water column and settling on the bottom and shorelines. A particle budget across the water column, bottom sediments, and beaches accounted for 77% of the polyethylene, 48% polystyrene, and >100% polyethylene terephthalate. “Missing” plastic was likely in the nearshore littoral. Our observations suggest that if we prevent further inputs to aquatic ecosystems, microplastics will quickly disappear from the water column─washing up on shorelines and settling on the bottom. Thus, understanding rates of microplastic deposition and burial is critical to forecast the legacy of microplastic pollution.