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The impact of the earthquake and tsunami in the east coast of Japan in 11 March 2011 caused a loss of power at the Fukushima Dai-ichi Nuclear Power Plant (NPP) that resulted in one of the most important releases of artificial radioactivity to the environment. Although several works were devoted to evaluate the atmospheric dispersion of radionuclides, the impact of the discharges to the ocean has been less investigated. Here we evaluate the distribution of Fukushima-derived 90Sr and 89Sr throughout waters 30-600 km offshore in June 2011. Concentrations of 90Sr and 89Sr in both surface waters and shallow profiles ranged from 0.8 ± 0.2 to 85 ± 3 Bq m-3 and from 19 ± 6 to 265 ± 74 Bq m-3, respectively. Because of its short half-life, all measured 89Sr was due to the accident, while the 90Sr concentrations can be compared to the background levels in the Pacific Ocean of about 1.2 Bq m-3. Fukushima-derived radiostrontium was mainly detected north of Kuroshio Current, as this was acting as a southern boundary for transport. The highest activities were associated with near-shore eddies, and larger inventories were found in the closest stations to Fukushima NPP. The data evidences a major influence of direct liquid discharges of radiostrontium compared to the atmospheric deposition. Existing 137Cs data reported from the same samples allowed us establishing a 90Sr/137Cs ratio of 0.0256 ± 0.0006 in seawater off Fukushima, being significantly different than that of the global atmospheric fallout (i.e. 0.63) and may be used in future studies to track waters coming from the east coast of Japan. Liquid discharges of 90Sr to the ocean were estimated, resulting in an inventory of 53 ± 1 TBq of 90Sr in the inshore study area in June 2011 and total releases of 90Sr ranging from 90 to 900 TBq, depending upon the reported estimates of 137Cs releases that are considered. [ABSTRACT FROM AUTHOR]

In order to identify the causes of overestimate of the surface-level O 3 mixing ratio simulated by three regional chemical-transport models, NAQPMS v.3 (abbreviated as NAQM in this paper), CMAQ v.5.0.2, and CMAQ v.4.7.1, compared to the EANET observational data at a marine remote site at Oki in July 2010, analyses of hourly O 3 mixing ratios and net ozone production were made in the context of MICS-Asia III. In addition to Oki, model-simulated and observational data for two other EANET marine sites, Hedo and Ogasawara, were also examined. Three factors, i.e., long-range transport from the continent, in situ photochemical formation, and dry deposition of O 3 on seawater, have been identified as contributing to the overestimate by these regional models at Oki. The calculated O 3 mixing ratios during long-range transport from the continent were much higher for all three models than those of the observation. In situ photochemical formation, demonstrated by a distinct diurnal variation which was not discerned in the observational data, was seen in the simulated data of all three models and ascribed to the virtual transport of NO x from the southern urban areas of the main island of Japan. The overestimate of the O 3 mixing ratio in the background oceanic air mass has been discussed referring to dry deposition velocity (Vd) of O 3 over oceanic water. Sensitivity analysis of the dry deposition velocity to the concentration of O 3 was made for Oki in July. An increase in Vd from 0.0005 to 0.001 cm s -1 used in the standard runs for CMAQ by a factor of 10 decreases the O 3 mixing ratio by more than 20 ppbv on an event basis in certain periods of time and by ca. 4.9 ppbv as a monthly mean in July. The dry deposition velocity of O 3 in Bohai Bay and the Yellow Sea has been assumed to be comparable to that of the open ocean in all three models, which could have resulted in the overestimate of O 3 mixing ratios in this area and also in the long-range transport of O 3 from the continent to Oki. A higher value of dry deposition velocity in this marine area is expected considering the higher content of organics in the surface sea layer brought by rivers and atmospheric wet deposition. Empirical measurements of the mixing ratios and dry deposition flux of O 3 in this area are highly recommended, since they would affect the simulated mixing ratios in the downwind region in the Pacific Rim region. [ABSTRACT FROM AUTHOR]

Kim, S.; Park, K., and Yang, B.-M., 2017. Validating the applicability of MACCS2 on the assessment of radionuclide deposition over the ocean in Fukushima Daiichi nuclear power plant accident case. In: Lee, J.L.; Griffiths, T.; Lotan, A.; Suh, K.-S., and Lee, J. (eds.), The 2nd International Water Safety Symposium. Journal of Coastal Research, Special Issue No. 79, pp. 55-59. Coconut Creek (Florida), ISSN 0749-0208. On 11 March 2011, an enormous earthquake and tsunami occurred and caused a severe nuclear accident at the Fukushima Daiichi Nuclear Power Plant (FDNPP) in Japan. Following the FDNPP accident, a significant amount of radionuclides were released into the environment. The radionuclides were released into the ocean by direct emission in liquid form or by atmospheric deposition onto the sea surface. According to the 2013 UNSCEAR report, atmospheric deposition of radionuclides significantly contributed to the contamination of the ocean, as did direct emission. The MELCOR Accident Consequence Code System 2 (MACCS2) is a code for estimating the off-site accident consequences of atmospheric radiological releases; the code utilizes the straight-line Gaussian plume model. In this study, to judge the code's applicability for estimating the radionuclide deposition over the sea surface in the Fukushima accident case, we conducted a comparative analysis of the MACCS2 results against previously published data. The long-range dispersion patterns from the MACCS2 calculation have a tendency simply to broaden from those of the short distance from the FDNPP. From the analysis detailed in this paper, we concluded that MACCS2 is applicable only for short-range dispersion (a few tens of kilometers) from an accident site, not for long-range dispersion as in the case of the Fukushima accident. The atmospheric deposition of radionuclides is a major cause of oceanic contamination; a large percentage of released radionuclides are deposited at long range from the accident site. Therefore, we suggest that any simulation code for atmospheric dispersion and deposition over the ocean should be based on another model, such as a Lagrangian or puff model, instead of on the Gaussian plume model, especially for long-range dispersion assessment. [ABSTRACT FROM AUTHOR]

Owing to the elevated loading of nitrogen through atmospheric deposition, some forested ecosystems become nitrogen saturated, from which elevated levels of nitrate are exported. The average concentration of stream nitrate eluted from upstream and downstream of the Kasuya Research forested catchments (FK1 and FK2 catchments) in Japan were more than 90 µ M, implying that these forested catchments were under nitrogen saturation. To verify that these forested catchments were under the nitrogen saturation, we determined the export flux of unprocessed atmospheric nitrate relative to the entire deposition flux (Matm/Datm ratio) in these catchments; because the Matm/Datm ratio has recently been proposed as a reliable index to evaluate nitrogen saturation in forested catchments. Specifically, we determined the temporal variation in the concentrations and stable isotopic compositions, including Δ17 O, of stream nitrate in the FK catchments for more than 2 years. In addition, for comparison, the same parameters were also monitored in the Shiiba Research forested catchment (MY catchment) in Japan during the same period, where the average stream nitrate concentration was low, less than 10 µ M. While showing the average nitrate concentrations of 109.5, 90.9, and 7.3 µ M in FK1, FK2, and MY, respectively, the catchments showed average Δ17 O values of + 2.6 ‰, + 1.5 ‰, and + 0.6 ‰ in FK1, FK2, and MY, respectively. Thus, the average concentration of unprocessed atmospheric nitrate ([NO 3- atm ]) was estimated to be 10.8, 5.1, and 0.2 µ M in FK1, FK2, and MY, respectively, and the Matm/Datm ratio was estimated to be 14.1 %, 6.6 %, and 1.3 % in FK1, FK2, and MY, respectively. The estimated Matm/Datm ratio in FK1 (14.1 %) was the highest ever reported from temperate forested catchments monitored for more than 1 year. Thus, we concluded that nitrogen saturation was responsible for the enrichment of stream nitrate in the FK catchments, together with the elevated NO 3- atm leaching from the catchments. While the stream nitrate concentration ([NO 3- ]) can be affected by the amount of precipitation, the Matm/Datm ratio is independent of the amount of precipitation; thus, the Matm/Datm ratio can be used as a robust index for evaluating nitrogen saturation in forested catchments. [ABSTRACT FROM AUTHOR]

Atmospheric deposition is one of the main sources of dissolved iron (Fe) in the ocean surfaces. Atmospheric processes are recognized as controlling fractional Fe solubility (Fe sol %) in marine aerosol particles. However, the impact of these processes on Fe sol % remains unclear. One of the reasons for this is the lack of field observations focusing on the relationship between Fe sol % and Fe species in marine aerosol particles. In particular, the effects of organic ligands on Fe sol % have not been thoroughly investigated in observational studies. In this study, Fe species in size-fractionated aerosol particles in the Pacific Ocean were determined using X-ray absorption fine structure (XAFS) spectroscopy. The internal mixing states of Fe and organic carbon were investigated using scanning transmission X-ray microscopy (STXM). The effects of atmospheric processes on Fe sol % in marine aerosol particles were investigated based on the speciation results. Iron in size-fractionated aerosol particles was mainly derived from mineral dust, regardless of aerosol diameter, because the enrichment factor of Fe was almost 1 in both coarse (PM >1.3) and fine aerosol particles (PM 1.3). Approximately 80 % of the total Fe (insoluble + labile Fe) was present in PM >1.3 , whereas labile Fe was mainly present in PM 1.3. The Fe sol % in PM >1.3 was not significantly increased (2.56±2.53 %, 0.00 %–8.50 %, n=20) by the atmospheric processes because mineral dust was not acidified beyond the buffer capacity of calcite. In contrast, mineral dust in PM 1.3 was acidified beyond the buffer capacity of calcite. As a result, Fe sol % in PM 1.3 (0.202 %–64.7 %, n=10) was an order of magnitude higher than that in PM >1.3. The PM 1.3 contained ferric organic complexes with humic-like substances (Fe(III)-HULIS, but not Fe-oxalate complexes), and the abundance correlated with Fe sol %. Iron(III)-HULIS was formed during transport in the Pacific Ocean because Fe(III)-HULIS was not found in aerosol particles in Beijing and Japan. The pH estimations of mineral dust in PM 1.3 established that Fe was solubilized by proton-promoted dissolution under highly acidic conditions (pH < 3.0), whereas Fe(III)-HULIS was stabilized under moderately acidic conditions (pH 3.0–6.0). Since the observed labile Fe concentration could not be reproduced by proton-promoted dissolution under moderately acidic conditions, the pH of mineral dust increased after proton-promoted dissolution. The cloud process in the marine atmosphere increases the mineral dust pH because the dust particles are covered with organic carbon and Na. The precipitation of ferrihydrite was suppressed by Fe(III)-HULIS owing to its high water solubility. Thus, the organic complexation of Fe with HULIS plays a significant role in the stabilization of Fe that was initially solubilized by proton-promoted dissolution. [ABSTRACT FROM AUTHOR]

To clarify the source of nitrate increased during storm events in a temperate forested stream, we monitored temporal variation in the concentrations and stable isotopic compositions including Δ17 O of stream nitrate in a forested catchment (KJ catchment, Japan) during three storm events: I, II, and III (summer). The stream showed a significant increase in nitrate concentration, from 24.7 to 122.6 µ M, from 28.7 to 134.1 µ M, and from 46.6 to 114.5 µ M, during the storm events I, II, and III, respectively. On the other hand, the isotopic compositions (δ15 N, δ18 O, and Δ17 O) of stream nitrate showed a decrease in accordance with the increase in the stream nitrate concentration, from + 2.5 ‰ to - 0.1 ‰, from + 3.0 ‰ to - 0.5 ‰, and from + 3.5 ‰ to - 0.1 ‰, for δ15 N; from + 3.1 ‰ to - 3.4 ‰, from + 2.9 ‰ to - 2.5 ‰, and from + 2.1 ‰ to - 2.3 ‰ for δ18 O; and from + 1.6 ‰ to + 0.3 ‰, from + 1.4 ‰ to + 0.3 ‰, and from + 1.2 ‰ to + 0.5 ‰, for Δ17 O during the storm events I, II, and III, respectively. Besides, we found strong linear relationships between the isotopic compositions of stream nitrate and the reciprocal of stream nitrate concentrations during each storm event, implying that the temporal variation in the stream nitrate can be explained by simple mixing between two distinctive endmembers of nitrate having different isotopic compositions. Furthermore, we found that both concentrations and the isotopic compositions of soil nitrate obtained in the riparian zone of the stream were plotted on the nitrate-enriched extension of the linear relationship. We concluded that the soil nitrate in the riparian zone was primarily responsible for the increase in stream nitrate during the storm events. In addition, we found that the concentration of unprocessed atmospheric nitrate in the stream was stable at 1.6 ± 0.4, 1.8 ± 0.4, and 2.1 ± 0.4 µ M during the storm events I, II, and III, respectively, irrespective of the significant variations in the total nitrate concentration. We concluded that the storm events have fews impacts on the concentration of unprocessed atmospheric nitrate in the stream, and thus the annual export flux of unprocessed atmospheric nitrate relative to the annual deposition flux can be a robust index to evaluate nitrogen saturation in forested catchments, irrespective to the variation in the number of storm events and/or the variation in the elapsed time from storm events to sampling. [ABSTRACT FROM AUTHOR]

Abstract: This paper presents measurements of the effect of the atmospheric radioactive release from the Fukushima Dai-ichi nuclear power station at three sites belonging to the Spanish environmental monitoring system. Measured values varied depending on the locations of the sites in Spain and their respective climatic characteristics. 134Cs, 136Cs, 137Cs, 131I, and 132Te activity concentrations in filter samples were studied and associated levels of 131I fallout were estimated from wet and dry deposition. Particulate aerosol activity concentrations ranges, in μBq/m3, were 1.63–3080 (131I), 2.8–690 (137Cs), 1.3–620 (134Cs) and 3.6–330 (132Te), while the associated 131I fallout was roughly estimated to be less than 20 Bq/m2, Gaseous 131I was also detected and the 131I-gaseous/131I-total ratio increased at the three stations from approximately 0.75 at the end of March to 0.85–0.9 during the first few days of April. Finally, the presence of 131I in some crucial parts of the food chain was also studied. 131I was detected in samples from goat''s and cow''s milk (maximum levels of 1.11 Bq/L) and in broadleaf plants (maximum level 1.42 Bq/kg). [Copyright &y& Elsevier]

We have measured artificial radionuclides, such as 90Sr and 137Cs, in atmospheric depositions since 1957 in Japan. We observed the variations in 90Sr and 137Cs, which were emitted from atmospheric nuclear tests and nuclear power plant accidents, due to their diffusion, deposition, and resuspension. In March 2011, the Fukushima Daiichi Nuclear Power Plant accident occurred in Japan, and significant increases in 90Sr and 137Cs were detected at our main site in Tsukuba, Ibaraki. Our continual observations revealed that the 137Cs monthly deposition rate in 2018 declined to ~ 1/8100 of the peak level, but it remained more than ~ 400 times higher than that before the accident. Chemical analysis suggested that dust particles were the major carriers of 90Sr and 137Cs during the resuspension period at our main site. Presently, the effective half-life for 137Cs deposition due to radioactive decay and other environmental factors is 4.7 years. The estimation suggests that approximately 42 years from 2011 are required to reduce the atmospheric 137Cs deposition to a state similar to that before the accident. The current 90Sr deposition, on the other hand, shows the preaccident seasonal variation, and it has returned to the same radioactive level as that before the accident. [ABSTRACT FROM AUTHOR]

Wet deposition fluxes of ions at a coastal site in southwestern Japan in the period 1996-2003 were investigated to quantify the respective contributions of cyclone-, stationary front- and typhoon-associated rains. On average, the deposition fluxes of terrigenous- origin ions, nss-SO42-, NO3-, NH4+ and nss-Ca2+ were 37.6±7.3, 16.3±4.2, 19.0±3.4 and 9.6±4.8 meq m-2 yr-1, and those of Na+ and Cl-, the major ions in sea water, were 97.0±38.2 and 115.2±48.2 meq m-2 yr-1, respectively. Cyclone-associated rain constituted more than 50% of the fluxes of the terrigenous ions in almost all years. Stationary front-associated rain also contributed significantly, although the contribution was lower than the contribution by Cyclone-associated rain in almost all years. In particular, the wet deposition flux of nitrogen compounds of NO3- and NH4+, which are important nutrients for micro-bioactivities in sea surface water, was dominated by cyclone-associated rain. Due to the extreme abundance of Na+ and Cl- in the rainwater of typhoons, the fluxes of Na+ and Cl- were contributed substantially by typhoons in years with typhoons' passage although cyclones were still the largest contributor to the fluxes. These results indicate the dominance of cyclones in the wet deposition to the East China Sea areas and the necessity to take rain types into account for a more accurate elucidation of the temporal and spatial variation of the wet deposition. [ABSTRACT FROM AUTHOR]

A series of accidents at the Fukushima Dai-ichi Nuclear Power Plant following the Great East Japan Earthquake and tsunami of 11 March 2011 resulted in the release of radioactive materials to the ocean by two major pathways: direct release from the accident site and atmospheric deposition. A 1yr, regional-scale simulation of 137Cs activity in the ocean offshore of Fukushima was carried out, the sources of radioactivity being direct release, atmospheric deposition, and the inflow of 137Cs deposited into the ocean by atmospheric deposition outside the domain of the model. Direct releases of 137Cs were estimated for 1 yr after the accident by comparing simulated results and measured activities adjacent to the accident site. The contributions of each source were estimated by analysis of 131I/137Cs and 134Cs/137Cs activity ratios and comparisons between simulated results and measured activities of 137Cs. The estimated total amounts of directly released 131I, 134Cs, and 137Cs were 11.1 ± 2.2PBq, 3.5±0.7PBq, and 3.6 ±0.7 PBq, respectively. Simulated 137Cs activities attributable to direct release were in good agreement with measured 137Cs activities not only adjacent to the accident site, but also in a wide area in the model domain, therefore this implies that the estimated direct release rate was reasonable. Employment of improved nudging data by JCOPE2 improved both the offshore transport result and the reproducibility of 137Cs activities 30 km offshore. On the other hand, simulated 137Cs activities attributable to atmospheric deposition were low compared to measured activities. The rate of atmospheric deposition into the ocean was underestimated because of a lack of measurements of deposition into the ocean when atmospheric deposition rates were being estimated. Simulated 137Cs activities attributable to the inflow of 137Cs deposited into the ocean outside the domain of the model were in good agreement with measured activities in the open ocean within the model domain after June 2012. The consideration of inflow is important to simulate the 137Cs activity in this model region in the later period of the simulation. The contribution of inflow increased with time and was dominant (more than 99 %) by the end of February 2012. The activity of directly released 137Cs, however, decreased exponentially with time and was detectable only in the coastal zone by the end of February 2012. [ABSTRACT FROM AUTHOR]

On 11 March 2011, an earthquake occurred about 130 km off the Pacific coast of Japan's main island Honshu, followed by a large tsunami. The resulting loss of electric power at the Fukushima Dai-ichi nuclear power plant developed into a disaster causing massive release of radioactivity into the atmosphere. In this study, we determine the emissions into the atmosphere of two isotopes, the noble gas xenon-133 (133Xe) and the aerosol-bound caesium-137 (137Cs), which have very different release characteristics as well as behavior in the atmosphere. To determine radionuclide emissions as a function of height and time until 20 April, we made a first guess of release rates based on fuel inventories and documented accident events at the site. This first guess was subsequently improved by inverse modeling, which combined it with the results of an atmospheric transport model, FLEXPART, and measurement data from several dozen stations in Japan, North America and other regions. We used both atmospheric activity concentration measurements as well as, for 137Cs, measurements of bulk deposition. Regarding 133Xe, we find a total release of 15.3 (uncertainty range 12.2-18.3) EBq, which is more than twice as high as the total release from Chernobyl and likely the largest radioactive noble gas release in history. The entire noble gas inventory of reactor units 1-3 was set free into the atmosphere between 11 and 15 March 2011. In fact, our release estimate is higher than the entire estimated 133Xe inventory of the Fukushima Dai-ichi nuclear power plant, which we explain with the decay of iodine-133 (half-life of 20.8 h) into 133Xe. There is strong evidence that the 133Xe release started before the first active venting was made, possibly indicating structural damage to reactor components and/or leaks due to overpressure which would have allowed early release of noble gases. For 137Cs, the inversion results give a total emission of 36.6 (20.1-53.1) PBq, or about 43% of the estimated Chernobyl emission. Our results indicate that 137Cs emissions peaked on 14-15 March but were generally high from 12 until 19 March, when they suddenly dropped by orders of magnitude at the time when spraying of water on the spentfuel pool of unit 4 started. This indicates that emissions may not have originated only from the damaged reactor cores, but also from the spent-fuel pool of unit 4. This would also con- firm that the spraying was an effective countermeasure. We explore the main dispersion and deposition patterns of the radioactive cloud, both regionally for Japan as well as for the entire Northern Hemisphere. While at first sight it seemed fortunate that westerly winds prevailed most of the time during the accident, a different picture emerges from our detailed analysis. Exactly during and following the period of the strongest 137Cs emissions on 14 and 15 March as well as after another period with strong emissions on 19 March, the radioactive plume was advected over Eastern Honshu Island, where precipitation deposited a large fraction of 137Cs on land surfaces. Radioactive clouds reached North America on 15 March and Europe on 22 March. By middle of April, 133Xe was fairly uniformly distributed in the middle latitudes of the entire Northern Hemisphere and was for the first time also measured in the Southern Hemisphere (Darwin station, Australia). In general, simulated and observed concentrations of 133Xe and 137Cs both at Japanese as well as at remote sites were in good quantitative agreement. Altogether, we estimate that 6.4 PBq of 137Cs, or 18% of the total fallout until 20 April, were deposited over Japanese land areas, while most of the rest fell over the North Pacific Ocean. Only 0.7 PBq, or 1.9% of the total fallout were deposited on land areas other than Japan. [ABSTRACT FROM AUTHOR]

Recent climate change, especially during the 2000s, may be the primary reason for the expansion of the Asian dust source region. The change in the dust source region was investigated by examining anthropogenic radionuclides contained in surface soil samples from Mongolia. Surface soil was globally labeled by radioactive fallout from nuclear testing during the late 1950s and early 1960s, but there are no current direct sources for anthropogenic radionuclides in the air (before the Fukushima nuclear power plant accident in 2011). Radionuclides in the atmosphere are therefore carried mainly by wind-blown dust from surface soil, that is, aeolian dust. Asian dust carries traces of 90Sr, 137Cs, and other anthropogenic radionuclides; the heaviest deposition occurs in spring and has been recorded in Japan since the early 1990s. The composition of anthropogenic radionuclides in atmospheric depositions would be affected by a change in the dust source. Previous studies of atmospheric deposition at long-term monitoring sites (e.g. in Tsukuba, Japan) have detected changes in the 137Cs/90Sr ratio and in the specific activity of the radionuclides. These changes in the composition of observed atmospheric depositions are supposed to reflect changes in the climatic conditions of the dust source region. To investigate this dust source change, we conducted a field survey of radionuclides (90Sr and 137Cs) in surface soil samples in September 2007 in the eastern and southern regions of Mongolia, where dust storms have occurred more frequently since 2000. The specific activities of both radionuclides as well as the 137Cs/90 Sr ratio in the surface soil were well correlated with annual average precipitation in the Mongolian desert-steppe zone. Higher specific activities and a higher 137Cs/90Sr ratio were found in grassland regions that experienced greater precipitation. These findings suggest that the increased specific activities and the activity ratio detected in atmospheric depositions in Japan during years with frequent Asian dust transport events in the 2000s are a sign of grassland degradation. [ABSTRACT FROM AUTHOR]