1. Records of the riverine discharge of 129I in riverbank sediment after the Fukushima accident.
- Author
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Nakanishi, Takahiro, Sakuma, Kazuyuki, Ohyama, Takuya, Hagiwara, Hiroki, and Suzuki, Takashi
- Subjects
RIPARIAN areas ,FUKUSHIMA Nuclear Accident, Fukushima, Japan, 2011 ,SEDIMENTS ,WATERSHEDS ,NUCLEAR power plants ,OCEAN energy resources ,CESIUM - Abstract
Although
129 I discharge from watersheds is fundamental for assessing long-term radiation effects on aquatic ecosystems,129 I originating from the Fukushima nuclear accident is yet be evaluated. This study investigated the transport behavior of129 I by riverbank surveys conducted from 2013 to 2015 in a watershed where the129 I/137 Cs activity ratio is low in the mountainous area and high in the plain as of 2011. Until 2015, the129 I/137 Cs activity ratio of the levee crown in the studied watershed was similar to that of the surrounding area in 2011. However, the129 I/137 Cs ratios of the surface riverbank sediments were all low, indicating that radionuclides transported from the mountainous area were deposited on the riverbank in the plain. The vertical distribution of the129 I/137 Cs ratio in the riverbank sediments indicated that some129 I and137 Cs deposited during the accident remained in the lower layers, but most were eroded immediately after the accident. Based on the129 I/137 Cs ratios of sediments deposited on the riverbank, which remained constant until 2015 after the accident, the amount of129 I discharged to the ocean was determined from the previously evaluated137 Cs discharge. It was calculated that 1.8 × 105 Bq and 1.2 × 107 Bq of129 I were discharged with sediment from the studied watershed and the contaminated river watersheds (Abukuma River and Fukushima coastal rivers, including the study river), respectively. This amount of129 I was 0.3% of the129 I released from the Fukushima Dai-ichi Nuclear Power Plant into the ocean immediately after the accident. Furthermore, a comparison of the129 I/137 Cs ratio showed that the continuous129 I and137 Cs discharge from the river contribute little to their amount in the seafloor sediments along the Fukushima coast. [Display omitted] •129 I and137 Cs in riverbank affected by the Fukushima accident were investigated. •129 I/137 Cs ratio is a good indicator of the sediment source in a watershed. • Most of the sediment deposited on the riverbank was transported from upstream. • River discharge contributes little to the amount of129 I in the coastal area. [ABSTRACT FROM AUTHOR]- Published
- 2024
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