Spatiotemporal distribution of microplastics in the Gansu section of the Yellow River and its influencing factors

The Yellow River, the second-longest river in China, is a major channel for the transport of microplastics. In this study, we investigated the occurrence, spatiotemporal distribution, and influencing factors of microplastics in the main stem and major tributaries of the Gansu section of the Yellow River. The average annual microplastic concentrations in the surface water and sediments of the main stem of the Yellow River were relatively low at 1502.99 p m − 3 and 206.86 p kg − 1 , respectively. The chemical composition of microplastics in surface water and sediments comprised polyethylene terephthalate, polyvinyl chloride, polypropylene, polyethylene, and polyamide, with particle sizes generally below 1,000 μm. Fibers were more abundant in surface water, while fragments predominated in sediments. The spatial variation of microplastics in surface water was dominated by population density, while in sediments, this was primarily affected by population density and average annual flow. The temporal variation of microplastics in surface water was positively affected by monthly averages of flow and sediment concentration, while the temporal variation of microplastics in sediments was negatively influenced by the two factors. Riverine microplastics exhibited distinct spatial vertical distribution characteristics related to their physicochemical properties. In months with higher average monthly flow, the vertical distribution of microplastics in rivers was more uniform, whereas months with lower average flow exhibited more pronounced vertical variation. Our findings provide a reference for the impact of population density and river flow on the environmental behavior of microplastics in freshwater ecosystems.