Anthropogenic activities and hydrologic environment of Danjiangkou Reservoir regulate soil microplastics in the water level fluctuation zone

Abstract

Information about microplastics (MPs) in the water-level fluctuation zone (WLFZ), a transitional zone between aquatic and terrestrial ecosystems, remains relatively limited. To address this knowledge gap, this study selected the WLFZ (150–170 m) of Danjiangkou Reservoir and conducted large-scale sampling of soil and shoreline water samples before the rainy season. The aim was to investigate the distribution and characteristics of MPs in the WLFZ and to identify the key influencing factors. The results showed that the abundance of soil MPs in the WLFZ ranged from 144 to 1050 items/kg. The MPs abundance in the Dan Reservoir was higher than that in the Han Reservoir. Specifically, the mainstream exhibited higher MPs abundance than the tributaries in the Dan Reservoir, whereas the tributaries in the Han Reservoir were larger than the mainstream. The abundance of soil MPs in bare land and farmland was significantly higher than in grassland and woodland. The MPs are predominantly the size of 0.1–1 mm, the shape of fibers and pellets, the color of transparent and blue, and the polymer types are mainly polypropylene (PP) and polyethylene (PE). Among all influencing factors, human activities (distance from village and population density) and land use was identified as determinants of MPs abundance. The hydrological environment of the reservoir, including water level fluctuations, reservoir bays and banks, and mainstreams and tributaries, influenced the redistribution of MPs. This study systematically reveals the distribution of MPs pollution in the WLFZ and provides a key scientific basis for the prevention and control of MPs pollution.