Sediment-Associated Radiocesium Originated from Fukushima Daiichi Nuclear Power Plant Flowing from Ohori River to Lake Teganuma

Abstract

Radiocesium has been deposited after the Fukushima Daiichi Nuclear Power Plant (FDNPP) accident and affix to the soils inland. The soils flowed into Lake Teganuma through Ohori River. Field observation was carried out to quantify radiocesium, associated with sediments, transported around Lake Teganuma and Ohori River from October 2011 to March 2014. We quantified the sediment transported to Ohori River and found that the total radiocesium stock in Ohori River was 2,190 MBq which was mostly attached to the fine-grained sediment of silt in 2012. The radiocesium, transported as a suspended sediment in the Ohori River watershed, was approximately 10 percent of the total fallout of 2 TBq. The total flux of radiocesium in Ohori River were 3,800 MBq in 2012 and reduced to 6.65 MBq in 2013. These results denote that most of the radiocesium-polluted sediments were transported downstream in 2011 and sharply decreased after 2012. When a similar study was conducted in Abukuma River, only 1% of the total fallout was calculated indicating transport was 10 times that of the Abukuma River. This is attributed to be urbanization of Teganuma basin in comparison to the Abukuma basin, thus more cesium were transported in a shorter time period.

Air dose rates and cesium-137 in urban areas—deposition, migration, and time dependencies after nuclear power plant accidents

“…These annual loss rates are larger than those reported for other land uses on hillslopes (0.0029% −12%) [19,27] and for catchments (0.4%−1.4%) [22], even without human activities in the evacuation zone. This rapid removal of 137 Cs from urban areas is also consistent with larger wash-off from urbanized catchments compared with other land uses reported by studies of Cs in river systems [22,54,55]. These studies indicate that the recovery in urban areas from radiocesium contamination is faster than in other terrestrial environments.…”

The ecological half-life of radiocesium in surficial bottom sediments of five ponds in Fukushima based on in situ measurements with plastic scintillation fibers

“…The likely main contributors to the declining trend include (a) hydraulic ushing out of sediments and (b) downward migration of radiocesium through sedimentation and diffusion-advection. Hydraulic ushing may strongly affect shallow ponds (for example P1, P3 and P4) because they can be easily agitated by strong winds, 17,43 heavy rains and typhoons; 15 and ponds of large catchment-to-surface-area ratios which yield low radiocesium trap efficiency 21 so that radiocesium-rich ne sediments are ushed out. Yoshimura et al 44 observed such hydraulic ushing in some Fukushima ponds of low trap efficiency.…”

Long-term prediction of $$^{137}$$Cs in Lake Onuma on Mt. Akagi after the Fukushima accident using fractional diffusion model

“…The results suggest that the FDM prediction will lead to a longer period of contamination with low-level 137 Cs than the TDM prediction.During the Fukushima Daiichi Nuclear Power Plant (FDNPP) accident, aquatic ecosystems are contaminated with radioactive 137 Cs 1-6 . At present, the activity concentration of 137 Cs in river water is quite low [7][8][9] . However, in closed lakes, there is a problem of long-tailed temporal change in low-level radioactive contamination because the activity concentration declines steeply immediately after the accident, but then turns to a gradual decrease 6,10 .…”