Do Feed Plants Provide Sufficient Sodium, Calcium and Magnesium to Sika Deer in Japan? An Analysis Using Global Plant Trait Data.

Deficient minerals in overabundant populations could act as an attractant to cull sika deer (Cervus nippon). Because selective culling of female deer is reported to be effective in reducing sika deer populations, it is particularly important to clarify the differences in mineral requirements between males and females. Here, using global plant trait data and a published list of sika deer feed plants in Japan, we estimated whether feed plants provide sika deer sufficient sodium (Na), calcium (Ca) and magnesium (Mg), and compared the results between males and females. An analysis of 191 feed plant species suggested that feed plants can provide sufficient Mg, whereas sufficient Na and Ca is not always provided, especially when the intake is small or the deer large. Na deficiency was more intense for lactating females than males, suggesting that Na can be an effective attractant for selectively culling female deer. In summary, this study demonstrated that sika deer in Japan might require extra Na and Ca sources in addition to feed plants, and therefore these minerals could be useful for developing effective culling methods.

Three-dimensional numerical analysis of acoustic energy absorption and generation in an air-jet instrument based on Howe's energy corollary.

The sounding mechanism of a recorder-like air-jet instrument at low Strouhal number is numerically investigated by three-dimensional direct aeroacoustic simulation and acoustic simulation. Howe's energy corollary is applied to estimate the acoustic energy generation and absorption induced by an oscillating jet and vortex shedding. The quantitative results show that the main acoustic energy generation occurs in the jet downstream, and the absorption occurs in the jet upstream. It is found that the region defined by the Q-criterion identifies the main acoustic energy generation (absorption) region in the downstream (upstream) region of the jet. The results indicate that the vortex shedding mainly induced by the jet deflection gives additional contributions to the acoustic energy absorption. The shed vortices affect the temporal structure of the acoustic energy transfer, in particular, the timing of the double peaks with respect to the jet displacement. If we focus only on the air-jet, the dominant peak is observed when the jet crosses the edge from the inside to the outside of the pipe, as reported in previous experimental works. However, when we include the contributions of shed vortices, the dominant peak appears when the jet dives under the edge, which is consistent with the jet-drive model.

Radiocesium leaching from litter during rainstorms in the Fukushima broadleaf forest.

Forests are important sources of dissolved radiocesium (137Cs) discharge downstream. To improve understanding of dissolved 137Cs discharge processes during rainstorms, we investigated the relationship between rainfall-runoff hydrological processes and the discharge of 137Cs leached from litter. Leaching tests were conducted with broadleaf litter collected in the area where saturated overland flow was generated during rainstorms in a broadleaf-tree-dominated forest. According to the leaching test results, the 137Cs leaching rate was higher in the early stage of the test and decreased afterward. There was no significant difference in the overall results between the agitation and non-agitation cases. The 137Cs leaching rate from litter after the 24-h test was up to 33.7%. A large proportion of the original 137Cs activity was present even after the tests, as leaching from litter during rainstorms in the headwater area could be an additional source of dissolved 137Cs in the stream water. If mixing of 137Cs originating from groundwater, soil water, and rainfall with the hydrological processes is assumed, differences between the observed and estimated 137Cs in the surface runoff water became larger under high flow conditions. This analysis indicates additional 137Cs loading on surface runoff water during rainstorms, where saturated surface area can expand as the surface runoff rate increases. Contact area between surface runoff and litter accumulated on the forest floor should increase and accelerate 137Cs leaching from the litter. Therefore, 137Cs leaching in the saturated surface area that is temporarily formed during rainstorms can play a principal role in dissolved 137Cs discharge during rainfall-runoff events. Contaminated litter in the temporally saturated region of forested headwaters is an important factor contributing to elevated levels of dissolved 137Cs during rainstorms in the Fukushima area.

Six-year monitoring study of 137Cs discharge from headwater catchments after the Fukushima Dai-ichi Nuclear Power Plant accident.

Since headwater catchments are the source areas of 137Cs for downstream river systems, 137Cs discharge from headwater areas needs to be evaluated. Dissolved form (Dissolved), coarse organic matter (Org), and suspended sediments (SS) were sampled and 137Cs concentrations were measured from June 2011 to November 2016 in four headwater catchments in Yamakiya District, located 35 km northwest of the Fukushima Dai-ichi Nuclear Power Plant (FDNPP). The data up to September 2013 (2.5 y after the accident) have been already published (Iwagami et al., 2017a, b). The data up to November 2016 (5.7 y after the accident) are newly reported in the present paper together with data at a new sampling site. The whole data from June 2011 to November 2016 is discussed. The normalized 137Cs concentrations (137Cs concentrations normalized by the average deposition density of each catchment) in Dissolved, Org, and SS were in the order of 10-6 m2/L, 10-2 m2/kg, and 10-1 m2/kg, respectively, before 2013 and declined to around 10-8 m2/L, 10-4 m2/kg, and 10-2 m2/kg, respectively, in 2016. As a result of the decontamination program, the discharge of SS increased, whereas 137Cs concentrations in SS declined significantly and the total flux of 137Cs decreased. Although the clear effect of land use on decline trend in normalized 137Cs concentrations in Dissolved was not found, more data are necessary for elucidating the relation between them.

Groundwater age and mixing process for evaluation of radionuclide impact on water resources following the Fukushima Dai-ichi nuclear power plant accident.

Radionuclide contamination of groundwater causes critical impacts on water resources, human lives, and ecosystems. The intrusion of radionuclides into the groundwater flow system in Fukushima, Japan, could be illuminated by determining groundwater age and mixing processes. To do this, periodical field surveys were conducted in catchments contaminated by the Fukushima Dai-ichi Nuclear Power Plant accident. Sampling began in May 2011, which was 2 months after the disaster, and continued through June 2012. Chlorofluorocarbon (CFCs), tritium, and oxygen and hydrogen stable isotopes were used as environmental tracers. The observed tritium concentrations suggested that the water contained accident-derived radionuclides that exceeded the natural background baseline. Groundwater ages in the selected two headwater catchments were estimated to be between 10 and 26 years by combined use of multiple CFCs concentrations. In addition, the governing groundwater flow system was mostly approximated by a piston flow model; however, modern water fraction was also suggested based on the relationship between CFC-11 and CFC-12. The estimated water age and isotopic signals among stream water, spring water, and groundwater revealed that the intrusion of radionuclides into the groundwater was caused by the mixing between groundwater and modern water sources such as soil water and precipitation with relatively high radionuclide concentrations. This mixing was facilitated by a weathered and fractured granite bedrock and a thin unsaturated subsurface layer in the study area. Continued long-term monitoring of radionuclides in the groundwater will be necessary for water resources management in the future. CAPSULE: Radionuclide intrusion into the groundwater is related to the mixing between radionuclide-poor groundwater and modern water with relatively high radionuclide concentration.

Vertical distribution and temporal dynamics of dissolved 137Cs concentrations in soil water after the Fukushima Dai-ichi Nuclear Power Plant accident.

Radiocesium (137Cs) migration from headwater forested areas to downstream rivers has been investigated in many studies since the Fukushima Dai-ichi Nuclear Power Plant (FDNPP) accident, which was triggered by a catastrophic earthquake and tsunami on 11 March 2011. The accident resulted in the release of a huge amount of radioactivity and its subsequent deposition in the environment. A large part of the radiocesium released has been shown to remain in the forest. The dissolved 137Cs concentration and its temporal dynamics in river water, stream water, and groundwater have been reported, but reports of dissolved 137Cs concentration in soil water remain sparse. In this study, soil water was sampled, and the dissolved 137Cs concentrations were measured at five locations with different land-use types (mature/young cedar forest, broadleaf forest, meadow land, and pasture land) in Yamakiya District, located 35 km northwest of FDNPP from July 2011 to October 2012. Soil water samples were collected by suction lysimeters installed at three different depths at each site. Dissolved 137Cs concentrations were analyzed using a germanium gamma ray detector. The dissolved 137Cs concentrations in soil water were high, with a maximum value of 2.5 Bq/L in July 2011, and declined to less than 0.32 Bq/L by 2012. The declining trend of dissolved 137Cs concentrations in soil water was fitted to a two-component exponential model. The rate of decline in dissolved 137Cs concentrations in soil water (k1) showed a good correlation with the radiocesium interception potential (RIP) of topsoil (0-5 cm) at the same site. Accounting for the difference of 137Cs deposition density, we found that normalized dissolved 137Cs concentrations of soil water in forest (mature/young cedar forest and broadleaf forest) were higher than those in grassland (meadow land and pasture land).

Temporal changes in dissolved 137Cs concentrations in groundwater and stream water in Fukushima after the Fukushima Dai-ichi Nuclear Power Plant accident.

The concentration of dissolved 137Cs in groundwater and stream water in the headwater catchments in Yamakiya district, located ∼35 km north west of Fukushima Dai-ichi Nuclear Power Plant (FDNPP), was monitored from June 2011 to July 2013, after the earthquake and tsunami disaster. Groundwater and stream water were sampled at intervals of approximately 2 months at each site. Intensive sampling was also conducted during rainstorm events. Compared with previous data from the Chernobyl NPP accident, the concentration of dissolved 137Cs in stream water was low. In the Iboishi-yama catchment, a trend was observed for the concentration of dissolved 137Cs in stream water to decline, which could be divided into two phases by October 2011 (a fast flush of activity as a result of rapid washoff and a slow decline as a result of soil fixation and redistribution processes). The highest 137Cs concentration recorded at Iboishi-yama was 1.2 Bq/L on August 6, 2011, which then declined to 0.021-0.049 Bq/L during 2013 (in stream water under normal water-flow conditions). During the rainfall events, the concentration of dissolved 137Cs in stream water increased temporarily. The concentration of dissolved 137Cs in groundwater at a depth of 30 m at Iboishi-yama displayed a decreasing trend from 2011 to 2013, with a range from 0.039 Bq/L to 0.0025 Bq/L. The effective half-lives of stream water in the initial fast flush and secondary phases were 0.10-0.21 and 0.69-1.5 y, respectively in the three catchments. The effective half-life of groundwater was 0.46-0.58 y at Koutaishi-yama and 0.50-3.3 y at Iboishi-yama. The trend for the concentration of dissolved 137Cs to decline in groundwater and stream water was similar throughout 2012-2013, and the concentrations recorded in deeper groundwater were closer to those in stream water. The declining trend of dissolved 137Cs concentrations in stream water was similar to that of the loss of canopy 137Cs by throughfall, as shown in other reports of forest sites in the Yamakiya district.

Contribution of radioactive 137Cs discharge by suspended sediment, coarse organic matter, and dissolved fraction from a headwater catchment in Fukushima after the Fukushima Dai-ichi Nuclear Power Plant accident.

Radiocesium (137Cs) migration from headwaters in forested areas provides important information, as the output from forest streams subsequently enters various land-use areas and downstream rivers. Thus, it is important to determine the composition of 137Cs fluxes (dissolved fraction, suspended sediment, or coarse organic matter) that migrate through a headwater stream. In this study, the 137Cs discharge by suspended sediment and coarse organic matter from a forest headwater catchment was monitored. The 137Cs concentrations in suspended sediment and coarse organic matter, such as leaves and branches, and the amounts of suspended sediment and coarse organic matter were measured at stream sites in three headwater catchments in Yamakiya District, located ∼35 km northwest of Fukushima Dai-ichi Nuclear Power Plant (FDNPP) from August 2012 to September 2013, following the earthquake and tsunami disaster. Suspended sediment and coarse organic matter were sampled at intervals of approximately 1-2 months. The 137Cs concentrations of suspended sediment and coarse organic matter were 2.4-49 kBq/kg and 0.85-14 kBq/kg, respectively. The 137Cs concentrations of the suspended sediment were closely correlated with the average deposition density of the catchment. The annual proportions of contribution of 137Cs discharge by suspended sediment, coarse organic matter, and dissolved fraction were 96-99%, 0.0092-0.069%, and 0.73-3.7%, respectively. The total annual 137Cs discharge from the catchment was 0.02-0.3% of the deposition.