Horizontal transport of macro- and microplastics on soil surface by rainfall induced surface runoff as affected by vegetations

the aquatic environment but the process is still poorly understood. In this work, runoff plot experiment was carried out to study the horizontal transport of macro- and microplastics between 50 mm and 0.25 mm in size on the soil surface by rain induced runoff. The influences of vegetation cover, characteristics of plastics, and rainfall scenarios were investigated. Results showed that the presence of vegetation significantly enhance the retention of plastics by about 20% under the experimental conditions. Lower density and smaller (<1 mm) plastics were found to have higher mobility. The herb plant (Photiniaxfraseri Dress) showed a better interception efficiency on plastics than the shrub plant (Ophiopogonjaponicus (Linn. f.) Ker-Gawl.) at the same planting density, while increasing plant density contributed litter to the interception of microplastics. Increase rainfall amount from 20 mm to 60 mm enhanced the transport of plastics while repeating 20 mm rainfall every 3 days did not affect the transport of plastics significantly. The same processes may involve in the transport of plastics and soil particles by rainfall induced surface runoff. Strategies controlling soil erosion could also be used to prevent plastics in soil from entering the aquatic environment. However, effects and risks of plastics retained in the soil are still unclear, which need to be investigated in future.

Automated summary

This study investigates the horizontal transport of macro- and microplastics on the soil surface through runoff induced by rainfall. The presence of vegetation was found to significantly enhance the retention of plastics, and smaller and lower density plastics exhibited higher mobility. Herb plants showed better interception efficiency compared to shrub plants, and increasing plant density contributed to the interception of microplastics. Increasing rainfall amount enhanced the transport of plastics.