The Xiamen Symposium on Marine Environmental Sciences (XMAS 2025)

Unmanaged microplastics released from land into ocean have received widespread public attention widely. While much effort has been devoted to understanding the transport mechanism of marine microplastics, field sampling of microplastics is still in its infancy and many problems remain. microplastics sometimes show characteristic spatial distributions at various scales because of a wave-induced Stokes drift, Langmuir circulation, and wind-induced turbulence, which requires an appropriate assessment of those physical effects on sampling methods to improve the spatial representativeness of sampling. Therefore, particle tracking was conducted to mimic microplastics within a non-hydrostatic circulation model, and particle collection characteristics were evaluated for three representative sampling methods (neuston net, Niskin bottle, Large Volume Water Transfer System). For the neuston net, the effect of the relative angle between wind direction and the net tow direction on sampling was evaluated. The results showed that the standard deviation of the collected number of particles was higher and the spatial representativeness became lower when the net was towed in the same directions as the streak of the Langmuir circulation, which is formed by tilting to the right in the downwind direction. Collected particles by Niskin bottles are likely to reflect the dominant vertical profile of microplastics which occupies over 80% of the total. Besides, there is a risk of reflecting a vertical profile that is less spatially representativeness of the remaining 20%. This research was performed by the Environment Research and Technology Development Fund (JPMEERF20221001) of the Environmental Restoration and Conservation Agency of Japan.