The Distribution and Migration of 137Cs in Oak (Quercus serrata) and Cedar (Cryptomeria japonica) Forest Organic Fractions

To analyse the 137Cs distribution and migration under various fractions of organic matter layers, this study investigated easily recognizable, originally shaped organic L-fractions, and not easily recognizable, early fermented and fragmented organic F-fractions, of both oak (Quercus serrata) and cedar (Cryptomeria japonica) sampled from Osawa watershed sites at Nihonmatsu City, Fukushima Prefecture, Japan. The organic materials were put on top of soil columns from Field Museum (FM) Tamakyuryo in Hachioji City, Tokyo. The 137Cs vertical distribution in forest soil profiles was analyzed using the relaxation mass depth, ho (kg m−2). Soil columns with both L and F- organic layer fractions of both oak and cedar, labelled as Oak-L, Oak-F, Cedar-L and Cedar-F with four replications (n = 16), were set up by the laboratory column-based method and kept under five months’ incubation period. Soil columns after incubation were sampled at depths of 0–1 cm, 1–2 cm, 2–5 cm and 5–10 cm. Results of 137Cs inventory in the organic fractions showed that 86% (oak and cedar) of the total organic layer fractions 137Cs inventory accumulated within the F-layer, indicating that the transformation of litter is a huge source for potentially mobile 137Cs, especially the oak F-layer (67% 137Cs inventory) and further continuous transfer into the forest soil mineral layers. A higher ho in L treated soils (Oak-L and Cedar-L) compared to the F treatments implied that the low 137Cs amounts penetrated faster and deeper due to their water-soluble nature. Furthermore, Cedar-F showed a higher ho of 24.3 kg m−2 than Oak-F of ho, 14.0 kg m−2, and a significant positive relationship between 137Cs retention and total carbon (TC) (p < 0.05) suggested the influence of soil organic matter on 137Cs penetration and retention. The C/N (carbon nitrogen ratio) results revealed that organic matter fractions of high C/N including 137Cs, as observed in Cedar-F, in which decomposition does not advance, penetrates soil depths while the organic matter fraction of low C/N, observed in Oak-F, showed that decomposition advanced to release 137Cs which was held by adsorption unto the RIP (radiocesium interception potential) of soil surface. In addition, infiltration by water as a transportation process was suggested to largely influence the downward migration and retention of 137Cs at lower depths of Cedar-F.

Concentration and vertical flux of Fukushima-derived radiocesium in sinking particles from two sites in the Northwestern Pacific Ocean

At two stations in the western North Pacific, K2 in the subarctic gyre and S1 in the subtropical gyre, time-series sediment traps were collecting sinking particles when the Fukushima Daiichi Nuclear Power Plant (FNPP1) accident occurred on 11 March 2011. Radiocesium (134Cs and 137Cs) derived from the FNPP1 accident was detected in sinking particles collected at 500 m in late March 2011 and at 4810 m in early April 2011 at both stations. The sinking velocity of 134Cs and 137Cs was estimated to be 22 to 71 m day−1 between the surface and 500 m and >180 m day−1 between 500 m and 4810 m. 137Cs concentrations varied from 0.14 to 0.25 Bq g−1 dry weight. These values are higher than those of surface seawater, suspended particles, and zooplankton collected in April 2011. Although the radiocesium may have been adsorbed onto or incorporated into clay minerals, correlations between 134Cs and lithogenic material were not always significant; therefore, the form of the cesium associated with the sinking particles is still an open question. The total 137Cs inventory by late June at K2 and by late July at S1 was 0.5 to 1.7 Bq m−2 at both depths. Compared with 137Cs input from both stations by April 2011, estimated from the surface 137Cs concentration and mixed-layer depth and by assuming that the observed 137Cs flux was constant throughout the year, the estimated removal rate of 137Cs from the upper layer (residence time in the upper layer) was 0.3 to 1.5% yr−1 (68 to 312 yr). The estimated removal rates and residence times are comparable to previously reported values after the Chernobyl accident (removal rate: 0.2–1%, residence time: 130–390 yr).

Cesium, iodine and tritium in NW Pacific waters – a comparison of the Fukushima impact with global fallout

Radionuclide impact of the Fukushima Dai-ichi nuclear power plant accident on the distribution of radionuclides in seawater of the NW Pacific Ocean is compared with global fallout from atmospheric tests of nuclear weapons. Surface and water column seawater samples collected during the international expedition in June 2011 were analyzed for 134Cs, 137Cs, 129I and 3H. The 137Cs, 129I and 3H levels in surface seawater offshore Fukushima varied between 0.002–3.5 Bq L−1, 0.01–0.8 μ Bq L−1, and 0.05–0.15 Bq L−1, respectively. At the sampling site about 40 km from the coast, where all three radionuclides were analyzed, the Fukushima impact on the levels of these three radionuclides represent an increase above the global fallout background by factors of about 1000, 30 and 3, respectively. The water column data indicate that the transport of Fukushima-derived radionuclides downward to the depth of 300 m has already occurred. The observed 137Cs levels in surface waters and in the water column are in reasonable agreement with predictions obtained from the Ocean General Circulation Model, which indicates that the radionuclides have been transported from the Fukushima coast eastward. The 137Cs inventory in the water column (the area from 34 to 37° N, and from 142 to 147° E) due to the Fukushima accident is estimated to be about 2.2 PBq. The amount of 129I and 3H released and deposited on the NW Pacific Ocean after the Fukushima accident was estimated to be about 7 GBq and 0.1 PBq, respectively. Due to a suitable residence time in the ocean, Fukushima-derived radionuclides will provide useful tracers for isotope oceanography studies on the transport of water masses in the NW Pacific Ocean.

Assesment of soil erosion by 137Cs technique in native forests in Londrina City, Parana, Brazil

The aim of this work was to assess the soil erosion process in native forest by the 137Cs methodology. The mass balance model was applied to assess the rates of soil loss in three native forests around of Londrina city, Paraná, Brazil. 137Cs distribution depth was of exponential type for the three forests and 137Cs inventory was 241 Bq m-2 for Mata 1, 338 Bq m-2 for Mata 2 and 325 Bq m-2 for Mata UEL. The soil loss value calculated for three native forests was: 6,684 kg ha-1 yr-1 for Mata 1, 1,788 kg ha-1 yr-1 for Mata 2 and 4,524 kg ha-1 yr-1 for Mata UEL.