Evaluation of forest decontamination using radiometric measurements

An experiment has been conducted to evaluate the additional dose reduction by clear felling contaminated forestry in Fukushima Prefecture, Japan, and using the timber to cover the areas with wood chips. A portable gamma spectrometry system, comprising a backpack containing a 3x3” NaI(Tl) detector with digital spectrometer and GPS receiver, has been used to map dose rate and radionuclide activity concentrations before, after and at stages during this experiment. The data show the effect of the different stages of the experiment on dose rate at different locations around the site. The spectrometric data have allowed the assessment of the contributions of natural and anthropogenic radionuclides to the dose rate at different parts of the site before and after the experiment. This has clearly demonstrated the value of radiometric methods in evaluating remediation, and the effect of other environmental processes. The value of spectrometric methods which directly measure radionuclide concentrations has also been shown, especially through the identification of the contribution of natural and anthropogenic activity to the measured dose rate. The experiment has shown that clearing trees and applying wood chips can reduce dose rates by 10-15% beyond that achieved by just clearing the forest litter and natural redistribution of radiocaesium

THE CHANGES IN STREAM WATER TEMPERATURE AND WATER QUALITY PARAMETERS DURING RAINFALL EVENTS IN FORESTED WATERSHEDS: SCALING OF OBSERVATIONS

ABSTRACT We studied the changes in stream water temperature (Tw) and water quality (Wq) during rainfall events in forested watersheds. The parameters ofWq (88, DOC, N03--N, DTN, Na+, 8i and r) were observedinfour regionsof Japan from June 2004 to December 2005. The R values between Tw and those Wq parameters and between specific discharge (Qs) and Wq were positive, exceptfor the negativeones (Na+ and Si). Similarto the relationbetweenQs vs. Tw, hysteretic loops in the relations between Qs vs. those Wqparameters were clockwise, exceptfor Na+ and Si as counter-clockwiseloops. This indicatesthat the\u27surface and subsurface flows contain higher concentrations of SS, DOC, IC, N03--N and DTN. To the contrary,the deeperpathwayscontainhigherconcentrationsof Na+ and Si. These results suggest that the changes in Tw and Wq could be used to interpret theflow paths. KeyWords: stream water temperature, water quality, rainfall event,hysteretic loop

Rain-induced bioecological resuspension of radiocaesium in a polluted forest in Japan

放射性セシウムを含む真菌類の大型胞子の放出が森林環境での雨により増加することを発見 --降水によるバイオエアロゾル大気放出の新証拠--. 京都大学プレスリリース. 2020-10-01.It is the conventional understanding that rain removes aerosols from the atmosphere. However, the question of whether rain plays a role in releasing aerosols to the atmosphere has recently been posed by several researchers. In the present study, we show additional evidence for rain-induced aerosol emissions in a forest environment: the occurrence of radiocaesium-bearing aerosols in a Japanese forest due to rain. We carried out general radioactive aerosol observations in a typical mountainous village area within the exclusion zone in Fukushima Prefecture to determine the impacts and major drivers of the resuspension of radiocaesium originating from the nuclear accident in March 2011. We also conducted sampling according to the weather (with and without rain conditions) in a forest to clarify the sources of atmospheric radiocaesium in the polluted forest. We found that rain induces an increase in radiocaesium in the air in forests. With further investigations, we confirmed that the fungal spore sources of resuspended radiocaesium seemed to differ between rainy weather and nonrainy weather. Larger fungal particles (possibly macroconidia) are emitted during rainy conditions than during nonrainy weather, suggesting that splash generation by rain droplets is the major mechanism of the suspension of radiocaesium-bearing mould-like fungi. The present findings indicate that radiocaesium could be used as a tracer in such research fields as forest ecology, meteorology, climatology, public health and agriculture, in which fungal spores have significance

Impacts of direct release and river discharge on oceanic 137Cs derived from the Fukushima Dai-ichi Nuclear Power Plant accident

A series of accidents at the Fukushima Dai-ichi Nuclear Power Plant (1F NPP) following the Great East Japan Earthquake and tsunami of 11 March 2011 resulted in the release of radioactive materials to the ocean. We used the Regional Ocean Model System (ROMS) to simulate the 137Cs activity in the oceanic area off Fukushima, with the sources of radioactivity being direct release, atmospheric deposition, river discharge, and inflow across the domain boundary. The direct release rate of 137Cs after the accident until the end of 2016 was estimated by comparing simulated results with measured 137Cs activities adjacent to the 1F NPP. River discharge rates of 137Cs were estimated by multiplying simulated river flow rates by the dissolved 137Cs activities, which were estimated by an empirical function. Inflow of 137Cs across the domain boundary was set according to the results of a North Pacific Ocean model. Because the spatiotemporal variability of 137Cs activity was large, the simulated results were compared with the annual averaged observed 137Cs activity distribution. Normalized annual averaged 137Cs activity distributions in the regional ocean were similar for each year from 2013 to 2016. This result suggests that the annual averaged distribution is predictable. Simulated 137Cs activity attributable to direct release was in good agreement with measurement data from the coastal zone adjacent to the 1F NPP. Comparison of the simulated results with measured activity in the offshore area indicated that the simulation slightly underestimated the activity attributable to inflow across the domain boundary. This result suggests that recirculation of subducted 137Cs to the surface layer was underestimated by the North Pacific model. During the study period, the effect of river discharge on oceanic 137Cs activity was small compared to the effect of directly released 137Cs

A database of water and heat observations over grassland in the north-east of Japan

A highly valuable database of long-term hydrometeorological measurements is presented, containing in situ observations for a period of 37 years from a well-maintained grassland in the north-east of Japan. The observations include shortwave radiation, net radiation, air and dew point temperatures at three elevations, soil temperature at four depths, sensible heat flux, soil heat flux, wind speed, relative humidity, air pressure and precipitation. The heights of measurements are 1.6, 12.5 and 29.5 m above ground, with the soil-layer observations at depths of 0.02, 0.1, 0.5 and 1 m. This high-quality database includes four temporal resolutions of 10 s, 0.5 h, 1 h and 24 h, with the hourly data presented here. Monthly and annual statistics are presented at the database web page of the Center for Research in Isotopes and Environmental Dynamics and Prediction of the University of Tsukuba, http://doi.org/10.24575/0001.198108. We validated the data by comparing them with published data from the local meteorological agency in Tateno operated by the Japan Metrological Agency, including the average, maximum and minimum values of air temperature, shortwave radiation, wind speed, relative humidity and precipitation. We have generated a daily downward longwave radiation time series with a method developed by Kondo and Xu (1997) based on the observations from the database. This constructed time series agrees well with observations collected between 2002 and 2006, as evaluated based on the values of the Nash–Sutcliffe efficiency (=0.947) and percent bias (=1.486). For the whole database, annually averaged values show a positive trend in precipitation, air temperature, shortwave radiation, net radiation and sensible heat flux over the past 37 years, with a negative trend detected for wind speed, soil heat flux and soil temperature

Effects of Thinning on Flow Peaks in a Forested Headwater Catchment in Western Japan

This study examined the changes in rainfall-runoff characteristics in the year prior to and after intensive thinning of 50% in number in a steep headwater catchment, covered with 46-year-old Japanese cedar and cypress in western Japan. The magnitude of event peak flow, event quick flow, event water yield, and event response time did not change after thinning. Because 70% of rainfall events had multiple flow peaks, relationships between each flow peak and the rainfall just prior to that peak were also analyzed. The increases in accumulated quick flow, flow rise and flow drop were significant after thinning. The flow drop following each flow peak increased, and led to a lower initial flow in subsequent peaks, resulting in no increase in peak size. The flow peaks in events with over 30 mm rainfall amount and over 2 mm/h average rainfall intensity showed significant increases in flow peak, flow rise, flow drop, and accumulated quick flow, which suggests that the catchment exhibited more shallow flow paths during large rainfall amounts after thinning. No changes were identified using event-based analysis, but changes in flow peaks were detected, which indicates the importance of examining all flow peaks when investigating rainfall-runoff characteristics of headwater catchments

The seasonal variations of atmospheric 134,137Cs activity and possible host particles for their resuspension in the contaminated areas of Tsushima and Yamakiya, Fukushima, Japan

A large quantity of radionuclides was released by the Fukushima Daiichi Nuclear Power Plant accident in March 2011, and those deposited on ground and vegetation could return to the atmosphere through resuspension processes. Although the resuspension has been proposed to occur with wind blow, biomass burning, ecosystem activities, etc., the dominant process in contaminated areas of Fukushima is not fully understood. We have examined the resuspension process of radiocesium (134,137Cs) based on long-term measurements of the atmospheric concentration of radiocesium activity (the radiocesium concentration) at four sites in the contaminated areas of Fukushima as well as the aerosol characteristic observations by scanning electron microscopy (SEM) and the measurement of the biomass burning tracer, levoglucosan.The radiocesium concentrations at all sites showed a similar seasonal variation: low from winter to early spring and high from late spring to early autumn. In late spring, they showed positive peaks that coincided with the wind speed peaks. However, in summer and autumn, they were correlated positively with atmospheric temperature but negatively with wind speed. These results differed from previous studies based on data at urban sites. The difference of radiocesium concentrations at two sites, which are located within a 1 km range but have different degrees of surface contamination, was large from winter to late spring and small in summer and autumn, indicating that resuspension occurs locally and/or that atmospheric radiocesium was not well mixed in winter/spring, and it was opposite in summer/autumn. These results suggest that the resuspension processes and the host particles of the radiocesium resuspension changed seasonally. The SEM analyses showed that the dominant coarse particles in summer and autumn were organic ones, such as pollen, spores, and microorganisms. Biological activities in forest ecosystems can contribute considerably to the radiocesium resuspension in these seasons. During winter and spring, soil, mineral, and vegetation debris were predominant coarse particles in the atmosphere, and the radiocesium resuspension in these seasons can be attributed to the wind blow of these particles. Any proofs that biomass burning had a significant impact on atmospheric radiocesium were not found in the present study