资源环境科技发展态势分析平台

1. Key points

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Little is known about how much plastic debris ends up in the ocean during heavy storms, such as tropical cyclones.

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Floating plastic surveys in Sagami Bay, Japan were undertaken before and after the passage of a Category 4 typhoon. As a result, the abundance of floating plastics increased ca. 250 times in numerical density and ca. 1300 times in mass immediately after the storm.

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Although a significant amount of plastic debris was found immediately after the storm, much of this was rapidly swept away from coastal to open waters over a short period of time. To better estimate the annual load of plastics from land to sea it is important to consider the increase in leakages of plastic debris into the ocean associated with extreme storm events such as typhoons.

2. Overview

A research team led by Ryota Nakajima, a researcher at the Research Institute for Global Change (RIGC), Marine Biodiversity and Environmental Assessment Research Center (BioEnv), Marine Plastics Research Group (M-Plastics), Japan Agency for Marine-Earth Science and Technology (JAMSTEC) confirms the view that a tremendous amount of plastic debris can be transported from the land to sea by a typhoon, and that the majority of the debris is swept away from the coastal water to the open ocean over a short period of time.

Each year, approximately 10 million metric tons of land-based plastic debris makes its way into the ocean. However, the annual load of plastic debris being transported from land to sea has rarely considered the debris leakage associated with extreme storms. Thus it is important to investigate to what extent plastic debris is transported from land to sea by an extreme storm.

The research team investigated the changes in the abundance and composition of floating microplastics (*1) and mesoplastics (*2) in Sagami Bay before and after Typhoon Faxai, a Category 4 typhoon, which passed over the bay. As a result, The concentrations (number of particles/km²) of micro- and mesoplastics were two orders of magnitude higher 1-day after the typhoon than the values recorded pre-typhoon, and the mass (g/km²) of plastic particles (sum of micro- and mesoplastics) increased 1300 times immediately after the storm. However, the remarkably high abundance of micro- and mesoplastics found at 1-day after the typhoon returned to pre-typhoon levels in just two days. Model simulations also suggested that during an extreme storm a significant amount of micro- and mesoplastics can be rapidly swept away from coastal to open waters over a short period of time. The annual load of plastic debris being transported from land to sea will be underestimated if episodic storm events are not fully considered. In order to halt the leakage of plastic debris from land to sea, it is important to take measures that consider unexpected natural disasters such as typhoons.

This finding will be published in Frontiers in Marine Science on January 13th (Japan time).

Title: Plastic after an extreme storm: The typhoon-induced response of micro- and mesoplastics in coastal waters
URL: 10.3389/fmars.2021.806952

Authors: Ryota Nakajima¹, Toru Miyama¹, Tomo Kitahashi¹, Noriyuki Isobe¹, Yuriko Nagano¹, Tetsuro Ikuta¹, Kazumasa Oguri^1,2, Masashi Tsuchiya¹, Takao Yoshida¹, Kunihiro Aoki¹, Yosaku Maeda¹, Kiichiro Kawamura³, Maki Suzukawa³, Takuya Yamauchi⁴, Heather Ritchie⁵, Katsunori Fujikura¹, Akinori Yabuki¹

Affiliations:
1　Japan Agency for Marine-Earth Science and Technology (JAMSTEC), Japan
2　University of Southern Denmark, Denmark
3　Yamaguchi University, Japan
4　Kumamoto University, Japan
5　Royal Zoological Society of Scotland, United Kingdom