Changes in the radioactive cesium concentrations of grasslands during the first year after the F ukushima D aiichi N uclear P ower P lant accident in east J apan

• Published in: Grassland science 2014-06, Vol.60 (2), p.69-75
• Main Authors: Yamamoto, Yoshito, Shibuya, Takeshi, Hirano, Kiyoshi, Shindo, Kazumasa, Mashiyama, Hideto, Fujisawa, Tamotsu, Nakamura, Michinaga, Tozawa, Yoshiro, Miyaji, Hirotake, Nakao, Seiji, Togamura, Yasuko
• Format: Article
• Language: English
• ISSN: 1744-6961; 1744-697X
• DOI: 10.1111/grs.12044

Radioactive cesium ( C s) concentration of vegetation and soil was monitored in grasslands in seven farms located at a distance ranging from 90 to 180 km from the F ukushima nuclear power plant during seven months following the reactor meltdown in M arch 2011. The monitored sites included six sown meadows used to produce hay or silage, three sown pastures and one native pasture used for cattle grazing. The radioactive C s concentrations of the soil ranged from 264–1593 Bq kg −1 dry matter ( DM ). The radioactive C s concentrations in vegetation (aboveground parts of dominant grasses) were high with values ranging from 639–19 823 Bq kg −1   DM for the meadows, 949–7161 Bq kg −1   DM for the sown pastures and 5088–358 549 Bq kg −1  DM for the native pasture. Although the radioactive C s concentrations tended to decrease over time in most grasslands, there was no clear decreasing trend for grassland soils low in exchangeable potassium concentration and clay content. The transfer of radioactive C s from soil to herbage tended to be lower in soils with higher exchangeable potassium concentration and clay content. Detailed measurements in one meadow showed highest radioactive C s concentration in surface litter, followed by standing dead and live plant material. Approximately, 71, 21 and 7% of radioactive C s in the meadows were present in the soil, litter and standing dead material, respectively. Further regular monitoring of radioactive C s concentration in grasslands in the affected areas surrounding the nuclear power plant is required to amend the existing guidelines regarding livestock feeding.