From water to sediment: A meta-analysis of microplastic distribution and the impact of dams in reservoir ecosystems.

Microplastics (MPs) have become major contaminants in freshwater ecosystems. While numerous studies have characterized MPs in reservoirs, a comprehensive synthesis focusing on in-reservoir variations and dam-related influences is still lacking. This study investigates the spatial distribution of MPs in reservoir water and sediment based on data synthesized from 34 peer-reviewed studies covering 36 reservoirs across diverse climatic and hydrological regions worldwide, with a focus on the trapping effects of dams. Using a combination of generalized linear mixed models (GLMM) and generalized additive mixed models (GAMM), the study analyzed MP abundance patterns in relation to distance to the dam and identified key environmental and anthropogenic factors influencing their distribution. The results show that MPs tend to accumulate near dams, suggesting a trapping effect, while upstream MP concentrations decline with increasing distance. Vertical stratification patterns were observed in both water and sediment, indicating different transport mechanisms. Additionally, exposure to MPs significantly affected benthic organisms, particularly in terms of growth and reproduction, with effects intensifying over longer exposure durations. These findings highlight the need for improved monitoring and management strategies in reservoirs to mitigate MP pollution and its ecological consequences.