Spatial Heterogeneity and Ecological Risks of Microplastics in Freshwater Aquaculture Ponds Across Poyang Lake Basin

Freshwater aquaculture ponds are increasingly recognized as potential reservoirs and sources of microplastic (MP) pollution, yet the spatial heterogeneity and potential environmental drivers of MPs in inland aquaculture systems remain poorly understood. Water and surface-sediment samples were collected from 12 representative ponds in four regions of the Poyang Lake Basin (Jiangxi Province, China) during October–November 2022. MPs were extracted by density flotation and digestion and characterized by stereomicroscopy and Raman spectroscopy; spatial patterns were evaluated using one-way analysis of variance, principal component analysis, correlation analysis, and linear regression, and the polymer-related ecological risk was assessed with the polymer hazard index (PHI). MP abundances averaged 893.10 ± 87.61 items m−3 in surface water and 608.87 ± 186.68 items kg−1 dry weight in sediment; fibers dominated (about 51%), and 86.58–91.33% of particles measured 0.02–1 mm. Polyethylene (67.86%) and polypropylene (21.43%) dominated the water column, whereas polyamide (PA: 21.43%) was markedly enriched in sediment, and the first two principal components explained 90.0% of the total variance. MP abundance was positively associated with stocking density and with NH4+-N (r = 0.623, p < 0.05). PHl values indicated low polymer-related risk in the water column (mean: 8.79) but moderate risk in sediment (mean: 17.90). Sediment therefore acts as a long-term accumulation sink for denser and more hazardous polymers and warrants priority in monitoring and source-control strategies.