Temperature dependence of soil CO₂ flux and CO₂ production and consumption were investigated in the vadose zone of Arakawa Lowland in the Tokyo Metropolitan area of Japan. Investigations were based on the combined techniques of a closed chamber method for measuring CO₂ emission, frequent monitoring of the soil CO₂ concentration profile through the upper meter of the soil, and laboratory measurements of soilgas diffusivity for sampled, intact soil cores. Emission of CO₂ from the vadose zone to the air was measured during a monitoring period of 2 years and 8 months. The soil surface CO₂ flux increased with increasing soil temperature at 10 cm depth in two monitoring points located at about 10-m distance to each other. Calculated 𝑄₁₀ values defined as the increase in soil surface CO₂ flux per 10°C increase in soil temperature were approximately 2, at the two monitoring points. Approximately 90% of the emitted CO₂ was produced at surface soil layer.

 We developed a method for estimating the amount of water and material transport in the Yodo River Basin, and estimated the future changes due to population decline. In addition, a quantitative analysis of water and material dynamics in the basin and its impact on the inflow load to Osaka Bay was conducted. The results showed that the discharge of nitrogen and phosphorus from sewage treatment plants will decrease by 25.1 % and 20.6 %, respectively, in 2050, while the discharge of silicon will decrease by only 8.9 %, reflecting the differences in their addition and removal characteristics in the artificial water cycle system. The total loadings of nitrogen, phosphorus and silicon into the sea will decrease by 14.7 %, 7.8 % and 1.5 %, respectively, due to population decline in 2050. This suggests that the inflow loadings of nitrogen and phosphorus will be substantially reduced in the future without the need to promote the reduction of inflow loadings from land. It is estimated that although primary production will decrease in the inner part of the bay due to a relative decrease in nitrogen and increase in silicon in the future, it is unlikely that the dominant species will change from diatoms.

 The objective of this study was to develop a better understanding of the effects of pH and the arsenic content in naturally occurring arsenic-contaminated soil on leaching behavior with regard to removing a fine-grained fraction from soil. The arsenic contents of feed soils ranged from 6.6 to 13.1 mg/kg and the leaching values were between 0.005 and 0.057 mg/L. Soil slurry was separated into a fine-grained fraction and a coarse fraction by decanter centrifugation. A leaching test was applied to investigate leaching behavior of both a coarse fraction and a fine-grained fraction in a wide pH region by alkali/acid adding. As a result of this study, following observations were made; 1) the load-curve test results showed that the smaller the grain size, the greater both the arsenic content and the leaching value, 2) the applied leaching test provided a magnified observation of leaching behavior which is difficult to determine in a neutral region, 3) removal of a fine-grained fraction from soil slurry showed a possibility to produce clean soil that satisfied the environmental standard, and 4) increasing cut sizes of centrifugal separation, that is, decreasing the arsenic content in a coarse fraction was very effective in reduction of the leaching value in a coarse fraction that became clean soil.