Sho Shiozawa

Vertical Migration of Radiocesium Fallout in Soil in Fukushima

The vertical migration of radiocesium fallout in the soil was monitored for 1 year at several locations in Fukushima after the nuclear power plant explosion. We determined the vertical gamma ray intensity profiles in boreholes in the soil using a scintillation survey meter with a lead collimator to restrict the incoming radiation, only allowing horizontal detection. The average migration distances of radiocesium at two time points were accurately determined based on the difference in the depth of the centroids of two gamma ray intensity profiles. The results showed that although the convective velocity of radiocesium was unexpectedly as high as 1/10th of the velocity of the infiltrating rainfall water 2–3 months after the nuclear plant accident, the velocity decreased to 1/100th–1/200th of that of the water after 6–12 months. This indicated that strong fixation of radiocesium to clay particles occurred during the initial 2–3 months. Radiocesium uptake by plant roots may have decreased remarkably along with the mobility of radiocesium in the soil.

Effects of salt accumulation on the leaf water potential and transpiration rate of pot-grown wheat with a controlled saline groundwater table

Abstract We investigated the effects of continuous salt accumulation in the root zone of wheat. Leaf water potential and transpiration rate were measured in plants grown in an experimental pot system. Plants were grown in a controlled-environment glasshouse in sand-filled pots, in which the groundwater table was maintained at a desired depth. Saline water was recharged from the base, providing constant water content in the unsaturated root zone. At 52 days after sowing, the water table was set at a depth of 47 cm from the soil surface. Groundwater and initial soil water were replaced with saline water with electrical conductivities (EC) of 0.2 dS m−1 (Control [C]), 8 dS m−1 (EC8) and 16 dS m−1 (EC16). The daily transpiration rate, leaf water potential (ψL ) and EC of the soil water at a depth of 45 cm were measured during the experiment. Stomatal behavior was expressed using the transpiration ratio E t /E tc (the ratio of the transpiration rates of EC8 and EC16 to that in the control). Our results indicated that ψL and E t /E tc gradually decreased with increasing soil water EC as a result of transpiration and water uptake by the roots. The final ψL values of EC8 and EC16 were –4.0 MPa and –7.0 MPa, respectively, and the final E t /E tc values of EC8 and EC16 were 0.3 and 0.2, respectively. E t /E tc decreased with decreasing ψL , and induced stomatal closure. The E t /E tc of the wheat was 0.5 when ψL was –2.5 MPa and 0.3 when ψL was –3.0 MPa. Although a reduction in ψL from –1.5 MPa to –3.0 MPa caused a steep decline in E t /E tc , a subsequent reduction of ψL to –7.0 MPa caused only a minor reduction. This relationship between stomatal behavior and salt accumulation is similar to that reported in previous studies for plants grown in drought conditions. Changes in the transpiration ratio were expressed in an empirical equation as a function of ψL .

Evaluation of a Drainage Project through Hydro-salinity and Groundwater Quality Mapping using GIS and Satellite Data

Degradation due to hydro-salinity in the Indus basin semi-arid irrigated areas of Pakistan has deteriorated the vast productive agricultural land. The present approach was an effort through various GIS and RS techniques using IRS-1B LISS II data along with field data/maps and soil-water quality indicators to provide information about the cause, extent and magnitude of the problem in a drainage project area. Strong relationship has been found between hydro-salinity prone areas and drainage network. Shortage of irrigation water has been found the most limiting factor to solve the twine menace. About 61.7 % of hydro-saline area occurred in hazardous groundwater quality and high watertable depth. The hazardous groundwater quality getting dominant, deteriorating the area by inducing salinity-sodicity, required immediate special reclamation and management measures. Saline areas mostly following the trends of occurrence of brackish groundwater quality and high watertable. The satellite (IRS-1B) data with adopted methodology has been found promising in potential to map hydro-salinity with few remote sensing indicators and field data.