How hydrodynamic conditions dominate the microplastic footprint in the largest freshwater lake in China.

Understanding the migration and diffusion process of microplastics (MPs) in lakes is of great significance to the cumulative assessment of controlling land-based MP pollution. The MPs in the surface water of Poyang Lake were identified to be mainly composed of three representative particles (>91 %): polyethylene (PE) fiber, polypropylene (PP) fragment and PE film, and this study explored the migration process of different types of MPs in three flow regimes. The results show that MP particles migrate northward under the gravity flow and jacking flow. The average time required for MPs to reach the northern lakes in jacking flow was 21.29 % shorter than that in gravity flow. Instead, MPs undergo reverse movement driven by back flow. The difference in migration rates due to MPs physical properties can reach up to 36 % in the same flow regime. The average concentration of PE fiber in the lake area is 30.61 % and 68.68 % higher than both, PP fragment and PE film. In addition, the accumulation hotspots of MPs under three flow regimes were investigated, and MP monitoring in the corresponding areas based on the flow regime can effectively reduce the ecological risk. In terms of ecological risk, the PLI reached Level IV in hotspot areas, indicating severe ecological risk. If considering that the MP type of Poyang Lake is dominated by PE and PP, only the PSL of the Hukou area reaches level II. This study provides reference and warning for tracking the paths and risks of land-based MPs entering freshwater lakes.