The Three Gorges Dam alters the spatial distribution and flux of microplastics in the Yangtze River

The construction of dams disrupts the natural connectivity of rivers, potentially altering the distribution and movement of pollutants. However, the impacts of dams on microplastic (MP) flux are scarcely considered. By integrating previous findings and conducting supplementary sampling, we mapped the distribution of MPs in the Three Gorges Reservoir (TGR), covering surface water, sediment, the hydro-fluctuation belt, and the riparian zone. The TGR serves as a significant accumulation zone for MPs, with a notably higher concentration of MPs in its water compared to the upstream river water. In the reservoir, MPs are concentrated in the upstream and downstream sections of the water column, the hydro-fluctuation belt and sediment, whereas in the riparian zone, concentrations are higher in the downstream section. The distribution of MPs in reservoir water is strongly correlated (R² > 0.9) with regional gross domestic product (GDP) and sewage discharge, whereas the factors influencing MPs in sediment, the hydro-fluctuation belt, and the riparian zone are more complex. Human activities, particularly wastewater discharge in populated areas, predominantly contributed 49.89 % to the MPs load in the reservoir. The TGR captures approximately 11,091 ± 6,998 tons of MPs annually, constituting 28.18 % of the MPs flux from the upper Yangtze River.