As emerging contaminants, microplastic (MP) pollution in freshwater environments has received increasing attention due to their potential hazardous effects on human and environmental health. However, there is still limited understanding on variability of MP diversity and distribution patterns in riverine ecosystem compartments and field data are also lacking. This has hindered understanding and science-based information regarding mechanisms of fate and transport in freshwater environments. Hence, our study focused on reporting variability of MP diversity and distribution patterns in riverine ecosystem compartments. By undertaking MP community analyses, we found that distribution and variation in MP characteristics and communities among ecosystem compartments differed significantly. Moreover, structural characteristics of MP communities across compartments were distinct but not fully isolated, reflecting a balance between dispersion and niche differentiation (environmental filtering). Specifically, surface water and sediments mainly accumulated a greater abundance of smaller-sized, low-density, and fibrous MPs. MP distribution patterns were similar and mainly affected by population density, flow velocity, and precipitation. The distance-decay relationship of MP communities in surface water was stronger (p < 0.001) compared to sediments and soils. The longitudinal connectivity of the river, input of pollution sources and tributaries also facilitated transport of MP particles. Meanwhile, the retention of MPs in sediment was significantly influenced by MP characteristics and sediment grain size; and higher observed diversity (1.82) and abundance of MPs (130.32 items/kg) deposited in sediment also suggested continuous accumulation. The transport of MPs in riparian soils revealed a preference via vertical pathways and to adjacent sites. Considering limited transport capacity and significant correlations between topsoil and water/sediment, riparian soil may act as a potential long-term sink for river MPs. Our case-specific results are analyzed within a wider framework to further understand fate and transport dynamics of MPs within global riverine ecosystems.
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