Spatiotemporal distribution and diversity of microplastics in the sediment of beaches in Xiamen City, China

Coastal ecosystems are plagued by high levels of microplastic pollution. Conducting baseline surveys is crucial to comprehend the distribution and influencing factors of this pollution. The present study investigates the spatiotemporal variation and diversity of microplastic on the coastal beaches in Xiamen City, China, considering the combined effects of seasons, human activities, and physicochemical properties of sediments. It is detected that the abundance of microplastics in Xiamen beaches was 0.271±0.01 items/g. The abundance of microplastics in dry season was significantly higher than in rainy season. In terms of spatial variation, the beaches that attracted a larger number of tourists exhibited significantly higher microplastic abundance. The temporal pattern of microplastic distribution on different beaches varied greatly due to region-specific human activities (e.g., mangrove restoration project) and sedimentary properties (e.g., bulk density). When the assemblage of microplastics in the coastal area was viewed as a biological community, the Shannon-Wiener index and Pielou’s index were higher in rainy season and in the beaches with high intensity of tourist activities, which suggests that the human activities and the surface runoff may contribute to the diversity of microplastics on coastal beaches. Future investigations are encouraged to combine controlled experiments and long-term monitoring at multiple scales to elucidate the underlying mechanisms and factors associated with microplastic pollution in coastal zone.