11:25 〜 11:40
[MIS19-08] Spatiotemporal distribution of microplastics in sediments of Otsuchi Bay, Japan
キーワード：マイクロプラスチック、沿岸域、堆積物
The number of MPs drifting in the Japanese coastal waters was estimated at 1720000 pcs km-2, which was 27 times higher than the global average (Isobe et al., 2015). Previous studies have indicated that 73% of missing MPs accumulated on the seabed as sediments (Matsuguma et al., 2017). However, our knowledge about MPs contamination in sediments is still insufficient in coastal areas of Japan. The influence of river water on the behavior of MPs is also unclear. In order to solve the above problems, we observe the spatiotemporal distribution of MPs concentrations and composition in sediments on the sea floor in Otsuchi Bay, one of the small ria bays in Sanriku on the Pacific coast of Tohoku, Japan.
The survey was conducted in March and September 2021 at the three stations in Otsuchi Bay. The seabed sediments were sampled by a G.S.-type core sampler (ASYURA) at each station. The sediment cores were sliced onsite into 5-cm intervals and stored in a dark, cold chamber. The MPs concentration was measured with reference to Masura et al. (2015). The sample was analyzed by FTIR-microscope (Thermo Fisher Scientific Nicolet iN10). The spectrum of the MPs particles was measured by analytical software, OMNIC (version 9.12).
The concentrations of seabed sediments at Sta.1, 2, and 3 in Mar 2021 were 13.6±9.8, 1.7±0.6, 2.6±0.3 pcs g-1 DW and in Sep were 2.8±0.3, 2.6±1.4, 5.1±1.2 respectively. The MPs concentration at Sta.1 was significantly higher than that of Sta.2 in Mar 2021 (Kruskal-Wallis test, p < 0.05). At Sta.1, the concentration in Mar was significantly higher than that in Sep (t-test, p < 0.05). In Mar, the polymer type was domain by the low-density MPs (PE, PP, and co-polymer). In Sep, the composition of high-density MPs (PA, PS) was increased in Sta.2 and Sta.3.
The MPs concentration in sediment in Otsuchi Bay in Mar is indicated to be higher toward the inner part of the bay which is located on the estuary of the Otsuchi River. The results might be explained by that the deposition of particles containing MPs is likely strongly affected by the enhanced outflow of the Otsuchi River in the estuary, especially during the period of heavy rains. Furthermore, the seasonal change in Sta.1 also shows the possibility that the MPs were likely influenced by the outflow of the Otsuchi River system.
The survey was conducted in March and September 2021 at the three stations in Otsuchi Bay. The seabed sediments were sampled by a G.S.-type core sampler (ASYURA) at each station. The sediment cores were sliced onsite into 5-cm intervals and stored in a dark, cold chamber. The MPs concentration was measured with reference to Masura et al. (2015). The sample was analyzed by FTIR-microscope (Thermo Fisher Scientific Nicolet iN10). The spectrum of the MPs particles was measured by analytical software, OMNIC (version 9.12).
The concentrations of seabed sediments at Sta.1, 2, and 3 in Mar 2021 were 13.6±9.8, 1.7±0.6, 2.6±0.3 pcs g-1 DW and in Sep were 2.8±0.3, 2.6±1.4, 5.1±1.2 respectively. The MPs concentration at Sta.1 was significantly higher than that of Sta.2 in Mar 2021 (Kruskal-Wallis test, p < 0.05). At Sta.1, the concentration in Mar was significantly higher than that in Sep (t-test, p < 0.05). In Mar, the polymer type was domain by the low-density MPs (PE, PP, and co-polymer). In Sep, the composition of high-density MPs (PA, PS) was increased in Sta.2 and Sta.3.
The MPs concentration in sediment in Otsuchi Bay in Mar is indicated to be higher toward the inner part of the bay which is located on the estuary of the Otsuchi River. The results might be explained by that the deposition of particles containing MPs is likely strongly affected by the enhanced outflow of the Otsuchi River in the estuary, especially during the period of heavy rains. Furthermore, the seasonal change in Sta.1 also shows the possibility that the MPs were likely influenced by the outflow of the Otsuchi River system.