Catchment-wide flooding significantly altered microplastics organization in the hydro-fluctuation belt of the reservoir

Hydro-fluctuation belt (HFB) is the most sensitive area of a large reservoir. This research aimed to identify the impact of catastrophic flooding on the local microplastics organization in the HFB soil of the Three Gorges Reservoir, the largest reservoir in China. We found that the catchment-wide flooding efficiently alleviated the local microplastics abundance from 7,633 to 4,875 items/kg (from 44 to 18 mg/kg) but added to the pollution risk in the reservoir body. After flooding, the overall size distribution of local microplastics was minimally altered. Interestingly, the preferential retention of the small-sized polyethylene was found in HFB after flooding. Approximately 5.0×10(14) items (∼2,360 tons) of microplastics were evacuated into the reservoir, equivalent to 15.8 wt% of the plastic flux of the Yangtze River into the ocean. We observed that HFB is a significant source of local microplastics in reservoir, and the long-term source–sink transformation mechanism in the HFB should be further investigated.