Kosuke Noborio

Screening of plants for phytoremediation of oil-contaminated soil

Several species of ornamental flowering plants were evaluated regarding their phytoremediation ability for the cleanup of oil-contaminated soil in Japanese environmental conditions. Thirty-three species of plants were grown in oil-contaminated soil, and Mimosa, Zinnia, Gazania, and cypress vine were selected for further assessment on the basis of their favorable initial growth. No significant difference was observed in the above-ground and under-ground dry matter weight of Gazania 180 days after sowing between contaminated and non-contaminated plots. However, the other 3 species of plants died by the 180th day, indicating that Gazania has an especially strong tolerance for oil-contaminated soil. The total petroleum hydrocarbon concentration of the soils in which the 4 species of plants were grown decreased by 45-49% by the 180th day. Compared to an irrigated plot, the dehydrogenase activity of the contaminated soil also increased significantly, indicating a phytoremediation effect by the 4 tested plants. Mimosa, Zinnia, and cypress vine all died by the 180th day after seeding, but the roots themselves became a source of nutrients for the soil microorganisms, which led to a phytoremediation effect by increase in the oil degradation activity. It has been indicated that Gazania is most appropriate for phytoremediation of oil-contaminated soil.

Contribution of Ebullition to Methane and Carbon Dioxide Emission from Water between Plant Rows in a Tropical Rice Paddy Field

Although bubble ebullition through water in rice paddy fields dominates direct methane (CH4) emissions from paddy soil to the atmosphere in tropical regions, the temporal changes and regulating factors of this ebullition are poorly understood. Bubbles in a submerged paddy soil also contain high concentrations of carbon dioxide (CO2), implying that CO2 ebullition may occur in addition to CH4 ebullition. We investigated the dynamics of CH4 and CO2 ebullition in tropical rice paddy fields using an automated closed chamber installed between rice plants. Abrupt increases in CH4 concentrations occurred by bubble ebullition. The CO2 concentration in the chamber air suddenly increased at the same time, which indicated that CO2 ebullition was also occurring. The CH4 and CO2 emissions by bubble ebullition were correlated with falling atmospheric pressure and increasing soil surface temperature. The relative contribution of CH4 and CO2 ebullitions to the daily total emissions was 95–97% and 13–35%, respectively.

Evaluating a dual-frequency-phase-shift soil moisture and electrical conductivity sensor

For soil water and solute transport research, time domain reflectometry (TDR) has been commonly used since its introduction to soil research in 1980 by Topp and his colleagues. Although TDR seems to be very versatile for laboratory and field experiments, it requires modest user skills for accurate measurements and the instrument itself is still expensive. A new soil moisture and electrical conductivity (EC) sensor was recently developed at a reduced cost. The new sensor independently measures soil water content, and soil bulk electrical conductivity using frequency phase-shift techniques, and soil temperatures using a thermistor. We evaluated the new sensor for measurements of water content, and EC using three different sensors in variably saturated soils. There was little deviation among the units for water content measurement except at near saturation. Separate exponential curves provided good calibrations for all the soils used in the full range of water content between air-dry and saturation. In saline water up to 54 mS m−1, the mV output in the EC measurement mode was linearly related to solution EC. Although slopes were quite similar among the three sensors, the intercepts differed from the manufacturer’s calibration. The calibrations for volumetric water content and electrical conductivity provided by the manufacturer were not good enough for any use. The temperature effect on volumetric water content could be negligible or easily compensated with a simple formula. Little EC dependency of the sensor on volumetric water content was observed.

Estimating Soil Moisture Distributions across Small Farm Fields with ALOS/PALSAR

The ALOS (advanced land observing satellite) has an active microwave sensor, PALSAR (phased array L-band synthetic aperture radar), which has a fine resolution of 6.5 m. Because of the fine resolution, PALSAR provides the possibility of estimating soil moisture distributions in small farmlands. Making such small-scale estimates has not been available with traditional satellite remote sensing techniques. In this study, the relationship between microwave backscattering coefficient (σ) measured with PALSAR and ground-based soil moisture was determined to investigate the performance of PALSAR for estimating soil moisture distribution in a small-scale farmland. On the ground at a cabbage field in Japan in 2008, the soil moisture distribution of multiple soil layers was measured using time domain reflectometry when the ALOS flew over the field. Soil moisture in the 0–20 cm soil layer showed the largest correlation coefficient with σ (r = 0.403). The σ values also showed a strong correlation with the ground surface coverage ratio by cabbage plants. Our results suggested that PALSAR could estimate soil moisture distribution of the 0–20 cm soil layer across a bare field and a crop coverage ratio when crops were planted.

Erratum to: An Improved Heat Flux Theory and Mathematical Equation to Estimate Water Vapor Advection as an Alternative to Mechanistic Enhancement Factor

The current study extended the theory of heat flux which was normally used to estimate the mechanistic enhancement factor. The current improved heat flux theory included three additional phenomena that were excluded from the simplified heat flux equation. Those three phenomena were the sensible heat by liquid water movement, the sensible heat by water vapor movement, and the partial derivative of matric pressure head effects on relative humidity with respect to temperature. The first phenomenon was found to be an important factor in relatively wet porous media, whereas the third phenomenon was found important near-dry porous media condition. Moreover, mathematical descriptions derived to allow direct conversion of mechanistic enhancement factor to water vapor advection term. The study used basic mass balance equation, ideal gas law, and air advection to describe the water vapor advection mechanism. The water vapor advection equation was found to be able to describe the influence of soil moisture content and air pressure.