Impacts of underwater topography on the distribution of microplastics in lakes: A case from Dianchi Lake, China

The spatial distribution of microplastics and the factors influencing their distribution in lakes are important aspects of plastics pollution studies. This study investigated the impacts of lake underwater topography on the spatial distribution of microplastics in Dianchi Lake in China. Data on spatial distribution of microplastics were obtained by pump sampling, microscopic examination, and polymer identification. Parameters of underwater topography were extracted from an isobaths map of Dianchi Lake. The relationships between underwater topography and the abundance of microplastics were analyzed. The results showed that for the northern part of the lake, water depth, slope gradient, relief, roughness and surface curvature have significant relationships with the spatial distribution of microplastics. In the southern part, only roughness showed a significant relationship. The roughness is the only important factor which impacts the microplastics distribution in both parts of the lake and the whole lake. These differences between the northern part and the southern part of the lake are related to the stronger circular currents in the southern part of the lake. These results showed that the impacts of underwater topography manifest themselves well when lake currents are weak, and these impacts are reduced or muted when lake currents are strong. Our research results provide a good reference for understanding distribution and migration principle of microplastics in lakes.