Horizontal and vertical distribution of microplastics in dam reservoir after impoundment

In freshwater ecosystems, microplastics (MPs) are commonly found in reservoirs. However, limited information is available on the distribution of MPs in the reservoirs. In this study, we investigated the horizontal and vertical distribution characteristics of MPs in the Guanyingyan reservoir (the upper reaches of the Yangtze River, China) after impoundment and the influence of free-floating plant residues on the distribution of MPs. Results indicated that the MPs abundance in the horizontal distribution of the reservoir decreased significantly while the distance from the dam increased. The abundance of MPs in shoreline waters (average: 8.45 items L-1) was significantly higher than that in central waters (average: 4.80 items L-1). As for the vertical distribution, the percentages of fibers in the three water layers (surface, intermediate, and deep) have less variation when compared to other types of MPs. Besides, MPs who are less than 0.5 mm in size are the majority. With deeper underwater, there would be more MPs with particles smaller than 200 mu m in size. At the same time, there would be fewer MPs with particles ranging from 200 to 500 mu m in size. PS, PP, and PE are the main polymer types of surface water, while PVC, PE, and PET are the common type in deep water. In shoreline water, the dry weight of floating plant residues showed a positive correlation with microplastic abundance in different layers. As above said, this study confirmed that MPs in reservoirs after impoundment would tend to accumulate in the front section of the reservoir and the shoreline water. Besides, free-floating plant residues would accumulate in reservoirs, resulting in the sinking of MPs.

Automated summary

This study investigated the horizontal and vertical distribution characteristics of microplastics (MPs) in the Guanyingyan reservoir in China. The results showed that the abundance of MPs decreased with the distance from the dam, and shoreline waters had a higher abundance of MPs compared to central waters. The majority of MPs were smaller than 0.5 mm in size, with higher percentages of smaller particles at deeper depths. The polymer types varied between surface water and deep water, with different correlations between MPs and floating plant residues in different layers.