Historically, soil physics research in Japan and worldwide has focused on soil-water physics with a majority of studies on cultivated surface soils, and with the objective of optimizing water supply to plants and minimize leaching of pesticides and nutrients below the root zone. Recently, transport, fate and emissions of greenhouse gases such as carbon dioxide and methane is an area where rapidly growing environmental concerns about global warming and climate effects has provided new challenges for soil physicists. Another important challenge originates from the increasing problems in most urban areas with contaminated sites, where soil and groundwater have been polluted with EICs (Environmental Impact Chemicals) including gasoline and chlorinated compounds. To respond to these challenges, a broader focus in soil physics research and more emphasis on soil physical properties and processes in an environmental engineering perspective is needed. Improved understanding and better predictive models together with reliable in-situ measurement methods for a larger variety of soil physical parameters can give soil physicists a major role within the rapidly emerging research field that combines environmental engineering and polluted soil science ; soil environmental engineering. Detailed knowledge of soil physical processes in all three soil compartments (the soil-air, water and particle phases) is the platform for soil environmental engineering, including :
-Realistic calculations of transport and fate of EICs at contaminated soil sites
-Risk assessments concerning indoor and outdoor air and groundwater pollution
-Development and optimization of remediation methods for soil and groundwater
In this perspective, future soil physics research should focus on chemical diffusion, sorption, release, and convective transport in both the soil-water and soil-air phases and, also, evaluate the significance of particle-facilitated chemical transport through soil. As examples of less investigated soil physical parameters that are key parameters in soil environmental engineering, we advocate the importance of gas and solute diffusivity, air permeability, and vapor sorption coefficients in relation to both risk assessment and to remediation by soil vapor extraction and pump and treat methods. For soil environmental engineering purposes, not only the surface soil but the entire vadose zone between the soil surface and the groundwater table should be considered during studies of soil physical parameters. The dominating role of soil-physical processes in controlling and optimizing biodegradation of pollutants during soil remediation should be investigated and highlighted. With this emerging role of soil physics in environmental engineering combined with the rapid developments in process understanding and non-destructive measurement equipments, we are on the brink of an exciting new era in soil physics.
Rainwater dynamics at forested hillslopes are one of the most important themes in forest hydrology, because they have large effects on storm and base flow hydrographs, occurrences of slope failures, material transports in forest ecosystem, and stream water chemistry. Rainwater infiltration and discharge processes at forested hillslopes can be effectively studied by using methodologies developed in soil physical studies, which includes methods for determining saturated-unsaturated soil hydraulic properties, equipments for measuring matric potential and water content in field soils, and numerical simulation techniques for saturated-unsaturated soil water flow. This paper introduces several previous and new studies which applied the methodologies of soil physics to the analyses of rainwater dynamics at forested hillslopes. Topics includes characteristics of forest soil hydraulic properties in comparison with disturbed sandy and loamy soils, effects of pore structure of forest soil on rainwater infiltration, indices of water holding capacity of forest soils, effects of soil water-repellency on heterogeneous infiltration and occurrence of surface runoff, experiments and modeling of soil-pipe flow, as well as rainwater infiltration in weathered bedrock.
In the Asian countries, there are many important wall paintings on earthen walls of temples and other historical buildings. Because earth can be considered as a porous material, there is water redistribution in the walls due to the change of the surrounding environmental conditions. Water evaporates under dry conditions from the wall surface and salts accumulate near the surface zone and can cause salt efflorescence damages in the wall paintings. In order to develop suitable protective measures, it is necessary to know the water content profiles and water movement in the earthen walls. For this purpose, a model earthen wall has been built up in the historical folklore museum in Sapporo. The water redistribution in the earthen wall was measured by using a TDR (Time Domain Reflectometry) apparatus. The numerical simulation of water movement in the model wall was performed with the Delphin4 program developed by the TU Dresden. The material data, such as moisture retention curve, liquid water conductivity and water vapor diffusivity of the model earthen wall and climate data of the location Sapporo were taken into account for simulation. For development of suitable protective measures, it is quite important to have non destructive methods to understand the water regime in porous materials. The good agreement between simulation results and measured moisture profiles in position and time show the validity of using the Delphin4 program for development and evaluation of conservation measures of historical buildings and stone monuments.
This study focused on the effect of raindrop impact on the crust formation processes using two clay loam soils, Hokudai and Biei from Hokkaido, Japan. Four different treatments AD (air dried), PS (large aggregate), BD (bulk density) and WET (wet) have been prepared from disturbed samples in a laboratory. A miniature type rainfall simulator with rainfall intensity of 63 mm/hr was used for duration of one hour from a height of 170 cm to measure the impact of raindrop on bare soils. The final infiltration rates were PS > AD > WET > BD by raindrop impact. Therefore, the impact of raindrop in impeding infiltration was high in smaller aggregates of AD and WET treatments compared with PS. Furthermore, the impact was higher for Biei soil than for Hokudai soil. The hydraulic conductivity of the crust layer for Hokudai and Biei had different trends. The order of reduction for Hokudai soil was WET > PS > AD > BD. The reason for this trend could be the aggregate stability or resistance to breakage. While the magnitude of reduction in Biei was AD > PS > WET > BD. The initial moisture content appears to be more important factor for Biei soil.