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To clarify the factors affecting 137Cs transfer from soil to brown rice in comparison with 133Cs transfer and also to determine the key parameters of the solid-liquid partition coefficient (K d), c...

Land use shows the interaction between human and nature, and its impacts especially on runoff have received global attention and required more research studies. However, watershed database is generally available only for very large scales and not yet adapted to small scales. This paper presents a methodology for watershed delineation and potential influence assessment of runoff on the small watersheds in Japan based on the locations of the official observatory point data. Flow direction, flow accumulation, snap pour point and watershed recognition were analyzed by using the D8 algorithm and 10 m × 10 m DEM data of Japan. Totally 3831 watersheds were delineated by defining snapping pour point distance of 50 m as the input value, and the nation-wide watershed database was established. According to the suggestion of Notification No. 521 from the Ministry of Land, Infrastructure and Transport of Japan and land use/land cover data from JAXA satellite Alos-2, comprehensive runoff coefficient (CRC) was calculated by the weighted average method and divided into 10 levels by the equal interval method using ArcGIS. The obtained watershed boundary lines were almost identical to the ridge lines in the mountain area which accounts for more than half of Japan. The CRC values in the biggest cities such as Tokyo and Osaka were the highest, indicating these cities would receive the highest impacts of runoff. These results can provide the technical support for the decision-making on watershed management. The creation of small-scale watershed database would provide basic materials for the subsequent research such as flood prevention, water shortage and biogeochemical cycle of the sustainable regional development.

To examine the effects of phenolic acids, which are generated by the decomposition of cell walls in plant residues, and other constituents on the stability of soil aggregates, phenolic acids and carbohydrates were mixed into three different types of soil. After a 1-month incubation, the plot containing soil mixed with phenolic acids showed the greatest mean weight diameter of all the soils. In the treated soils, before incubation, the decline of saturated water permeability during continuous water percolation was mitigated in the plot containing soil mixed with phenolic acids compared with that in the other plots. Soil aggregates were synthesized with the addition of phenolic acids and carbohydrates using two methods (mixing and surface brushing) and were incubated for 153 days. The aggregate stability was greatest in the plots surface-brushed with phenolic acids for Andosol and gray lowland soil, whereas the aggregate stability was most stable in the plots mixed with phenolic acids for yellow soi...

Rice absorbs radiocesium dissolved in soil solution. However, quantitative determination of dissolved radiocesium is difficult because large volume of water should be collected from paddy soil. We investigated whether a sheet capable of effectively trapping cesium (zinc-substituted Prussian blue (ZnPB) sheet) can be used to evaluate the level of dissolved 137Cs to be absorbed by rice. A new device equipped with ZnPB sheet was invented to trap only radiocesium dissolved in soil solution, which is passed through a membrane filter covering the ZnPB sheet. A rice pot-culture experiment using three paddy soils with different 137Cs concentrations and physico-chemical properties collected from Fukushima Prefecture was conducted under different fertilization or rice-planting treatments. The results showed that 137Cs concentration in brown rice was positively correlated with the 137Cs concentration in soil solution with a contribution ratio of regression R2 of 0.91 and a p value less than 0.01, and also with the 137Cs-trapping rate by ZnPB sheet (amount of 137Cs trapped by ZnPB sheet per unit area of sheet and unit time) buried in soil with a R2 value of 0.89 and a p value less than 0.01. Moreover, field-cropping experiments conducted at the three paddy fields under conventional agricultural practices showed positive correlation between the 137Cs concentration in brown rice and 137Cs-trapping rate by ZnPB sheet. Both the pot and field experiments showed that the 2 weeks of the early stage of rice growth is appropriate as the ZnPB buried period because K additive fertilization is still in time to restrict 137Cs uptake by rice plant, and because the highest 137Cs-trapping rates of the ZnPB plate as compared with the following periods and high R2 values of those regression curves. . The proposed method might be used to roughly evaluate the vulnerability of soil to 137Cs transfer to rice and to identify the area in which effective countermeasure should be applied intensively.

Hiso River watershed (HRW) is within a radiocesium contaminated area caused by the disaster in Fukushima Daiichi nuclear power plant (FDNPP). The FDNPP accident resulted in enormous changes in land use in HRW. It's urgently needed to evaluate impacts of climate and land-use changes on hydrological process, which further control pollutants transport in HRW. A combination method of Statistical DownScaling Model (SDSM) and Soil and Water Assessment Tool (SWAT) was applied to generate future climatic and hydrologic variables. Future climate data was obtained from three Representative Concentration Pathway (RCP2.6, 4.5 and 8.5) scenarios of a single General Circulation Models in three future periods of 2030s, 2060s and 2090s (2010–2039, 2040–2069, 2070–2099), with a baseline period (1980–2009). According to land-use change in HRW during 2013–2017, three land-use change scenarios under the three future climate scenarios were established. Results suggested that SDSM showed good capabilities in capturing daily maximum/minimum temperature and precipitation. The SWAT model presented good performances in simulating monthly and yearly streamflow. Results also suggested projected higher temperatures and lower rainfall led to decreased annual water yield and evapotranspiration (ET). The annual water yield and ET decreased in most seasons while had a slight increase in spring. RCP8.5 scenario always generated larger magnitudes for climatic variables and water balance components compared with other climate scenarios. Land-use changes had strong impact on surface runoff and groundwater flow. These results emphasize the necessity of considering impacts of climate and land-use changes on hydrological processes when making decontamination policy in radiocesium contaminated areas.

The aim of this study was to evaluate the impact of land use on nitrate nitrogen (NO3-N) in shallow groundwater (G-N) and total nitrogen (N) in river water (R-N). The study area consisted of 26 watersheds (1342 km2) covering 72% of Kagawa Prefecture in Japan. We estimated G-N specific concentrations, which showed the magnitude of the upland fields, paddy fields, forests and urban land-use contributions to watershed-mean G-N. G-N specific concentrations were gained as partial regression coefficients using a multiple regression analysis of the watershed-mean G-N concentrations and the land-use ratios in each of the 26 watersheds. The results showed that the G-N specific concentration, which was gained as the partial regression coefficient for the multiple regression analysis, was 15.2 mg L−1, 10.3 mg L−1, 2.3 mg L−1 and 2.5 mg L−1 for the upland fields, paddy fields, forests and urban land-use types, respectively. R-N pollution load runoff to the river mouth was calculated by multiplying R-N specifi...

To contribute to the prediction of rainfall-related disasters, specific concentration factors that indicate the suspended solid (SS), total nitrogen (TN), and total phosphorus (TP) load intensities to river water for each land-use type were calculated using a simple watershed land-use model across Japan by applying the following multiple regression equation, according to the land-use ratios and published SS, TN and TP data. C=i=14aixi C: SS, TN and TP concentrations (mg L-1); ai: SS, TN and TP specific concentration factor for land use i; xi: ratio of land use i; land use: 1 paddy fields, 2 upland fields, 3 forests, 4 urban areas. The land-use ratios for watersheds, whose lower ends were observation points of river water quality, were determined by the GIS technique using a published database of DEM and LULC mesh data. The SS specific concentration factor was 15.4 (from a 95% lower limit value of 12.0 to a 95% upper limit value of 18.8), 11.5 (7.4 to 15.6), 3.9 (2.6 to 5.1), and 11.2 (9.2 to 13.2) for paddy fields, upland fields, forests and urban areas, respectively (n=5103). The TN specific concentration factor was 1.67 (from a 95% lower limit value of 1.34 to a 95% upper limit value of 2.01), 4.08 (3.64 to 4.51), 0.76 (0.67 to 0.90), and 3.57 (3.38 to 3.76) for paddy fields, upland fields, forests and urban areas, respectively (n=3256). The TP specific concentration factor was 0.146 (from a 95% lower limit value of 0.119 to a 95% upper limit value of 0.172), 0.172 (0.138 to 0.206), 0.044 (0.033 to 0.055), and 0.267 (0.253 to 0.282) for paddy fields, upland fields, forests and urban areas, respectively (n=3256). These specific concentration factors had regional tendencies, such as suburban or rural, intensive or extensive agriculture, and so on.

The dual isotope approach using the stable isotope ratios of nitrate nitrogen (δ15NNO3) and oxygen (δ18ONO3) is a strong tool for identifying the history of nitrate in various environments. Basically, a rapid procedure for determining δ15NNO3 and δ18ONO3 values is required to analyze many more samples quickly and thus save on the operational costs of isotope-ratio mass spectrometry (IRMS). We developed a new rapid procedure to save time by pre-treating consecutive samples of nitrous oxide microbially converted from nitrate before IRMS determination. By controlling two six-port valves of the pre-treatment system separately, IRMS determination of the current sample and backflush during the next sample pre-treatment period could be conducted simultaneously. A set of 89 samples was analyzed precisely during a 25-h continuous run (17 min per sample), giving the fastest reported processing time, and simultaneously reducing liquid nitrogen and carrier helium gas consumption by 35%. Application of the procedure to an irrigated rice paddy watershed suggested that nitrate concentrations in river waters decreased in a downstream direction, mainly because of the mixing of nitrate from different sources, without distinct evidence of denitrification. Our procedure should help with more detailed studies of nitrate formation processes in watersheds.