Groundwater flow system was investigated at a upland field in the central part of Ibaraki Prefecture. Underground temperature survey was conducted to locate the groundwater vein streams and to determine the place for test boring. The depth down to the top of the groundwater vein stream was estimated to be 2.5 m from the ground surface at the boring point. Groundwater flow rate was measured by means of the groundwater surveyor and tracer test. It was also calculated using the hydraulic conductivity determined by in situ permeability test or effective grain size. The flow rate was less than 10 4 cm/s down to the depth of 3 m, greater than 10 4 cm/s at the depth deeper than 3 m. The flow rate at the depth of 3.6 m outside the groundwater vein stream was one-third of that at the same depth inside it. These results show the location and the depth of the groundwater vein stream estimated by means of the underground temperature survey were correct, and groundwater flows at higher flow rate in the groundwater vein stream than another part of the ground.
High-moor peat land has some useful function in environmental conservation involved by factors of its formation. For its conservation, it is desired to clarify water factor which plays an important part in its formation, especially water flow in peat layer. In this study, it was tried to do its flow in case of Akaiyachi high- moor peat land. The principal results are as follows. The groundwater in shallow layer of high-moor peat land flows down through the shallow layer along the gentle slope from the top of dome. Most of the rainfall flows down through the top layer of high moor peat land along the gentle slope. Most of the rainfall loss is due to the evapotranspiration of sphagna. Most of the groundwater is supplied by the cool water which springs directly from mountainous regions under the peat land to flows horizontally through the peat layer. This cool groundwater brings on decomposition control of plant remains which is indispensable for formation of peat land. In the future, for the conservation of Akaiyachi highmoor peatland, it is desired to conserve these water conditions. Also for the conservations of other high-moor peat lands, it will be pointed out to conserve almost the same water conditions as this peat land.
Soil water retention considering matric and osmotic potentials is a prerequisite for understanding saline irrigation and water stress in arid and semi-arid regions. The experiment was conducted to study salinity effect on pF, evapotranspiration and plant water stress. It was assumed that soil water potential is the sum of the matric and osmotic potentials. The experiment of plant water stress using Komatsuna was carried out in a growth chamber (phytotron) at 25°C temperature and a relative humidity of 70%. The results exhibit that soil salinity increased after each irrigation causing an increase in osmotic potential component of the total soil water potential. The evapotranspiration decreased as salt concentration increased which is due to higher osmotic potential component. Higher salt concentration could increase pF so that availability of water to plants decreased. The results of the experiment showed that the osmotic potential was the dominant component of the adjusted pF (including osmotic potential component) in saline water treatments. The osmotic potential component value also contributed in the wilting of the plants. The results of the study suggest that the concept of pF value including matric and osmotic potential components can be used in applying soil water retention curves of salt affected soils for the development of lands in arid and semi-arid regions.
The effect of organic matter and charge characteristics on clay dispersibility of the soils from a newly reclaimed agricultural land, Hikigawa, Wakayama Prefecture, was investigated from the changes with the passage of six years. The adjacent forest soils were examined as a comparison. In 1987 the reduced plant growth in the reclaimed agricultural land was attributed to the unfavorable physical properties of the soil induced by high dispersibility of clay. However, continuous application of a great amount of organic matter to the surface layer of the reclaimed area since 1989, resulted in an increase in total carbon content by ten times in 1993 in comparison with that of 1987, and also favorable plant growth had been obtained. In addition, during those six years, for the surface layer, clay dispersion ratio had decreased from 25% to less than 10% ; other physical properties such as water-stable aggregate content, solid phase ratio and hydraulic conductivity had also been improved. Little clay dispersion after saturated by sodium ion indicated that the binding agent of clay particles was hardly-exchangeable organic matter rather than easily-exchangeable cations. In contrast, for the subsoil which remained in lower level of organic matter, such changes in physical properties as the surface soil were not observed. Charge characteristics of clay particles in the subsoil largely determined the dispersion behavior.
Fundamental properties, especially specific surface of rock, are useful in order to understand their secondary properties. In boring samples, their fine soil particles are usually lost, therelore another fundamental property instead of specific surface is needed for site investigation. In this study, water absorption of rock, grain size distribution and compaction on volcaniclastic sedimentary soft-rock as called “Mizoguchi Tuff Brecca” were tested. The results obtained are as follows :
1. Water absorption of rock collected by boring does not change significantly t han that of test pit sample.
2. Higher value of water absorption of rock is observed in compaction as grain size distribution changes to fine side due to grain crushing.
3. As water absorption value of rock becomes higher, maximum dry density in compaction becomes lower.
4. Water absorption of rock is not only related to optimum water content but also maximum dry density in compaction, that is similar to specific surface.
Ion adsorption is one of the most important characteristics of soil. There have been many studies on ion adsorption in soils which have been carried out to elucidate the adsorption mechanisms. However, few studies have been carried out to elucidate them by determining changes in electric conductivity. Determining changes in electric conductivity is a more precise method than pH determination in the adsorption mechanisms when the ionic compositions of the solution systems are known. On the other hand, the existence of charged particles disturbs the correct measurement of electric conduction in an aqueous solution. Thus accurate conductivity data for solutions containing suspended solid particles are difficult to obtain using a conventional conductivity cell and the probe of a conductivity meter. This study deals with the development of new conductivity cells for determining electric conductivity of electrolyte solutions containing charged particles.Three types of prototype cells were developed in this study. Each of them was devised to avoid the effect of charged particles. Practical use of the above conductivity cells was also examined by determination of phosphate adsorption on clay minerals at 298.15 K. Clay minerals are one of the inorganic components in soils. Their characteristics are responsible for the chemical properties of soils. Stable conductivity data can be obtained rapidly and precisely by the three prototype cells. This study reached the following conclusions. ( i ) The new procedures for determining micro changes in electric conductivity of electrolyte solutions containing suspended particles were indicated, (ii) Simultaneous determination of changes in electric conductivity and pH will become a good indicator to elucidate the mechanisms of adsorption phenomena.
In order to obtain accurate value of coefficient of permeability of soil in laboratory, it is necessary to measure precisely the hydraulic gradient and the flow rate. A new precision hydraulic head difference generator was developed for this purpose. The new generator is divided into two parts. One is a water supply part which is composed of an outer tank and an inner tank floating on the water of outer tank. The other is a drain tank. When the volume of supply water stored in the inner tank is decreased as a result of percolation, the inner tank becomes light and is elevated by a buoyant force. The dimensions of these tanks were determined in such a way that the hydraulic head difference between the supply and the drain water is kept constant during percolation. The hydraulic head difference and the flow rate are measured by a precision differential pressure transducer and a load cell, respectively. These data are recorded by a computer which also control electric valves so as to enable the automatic operation of percolation test. In order to evaluate the performance of this apparatus, the change in hydraulic head difference was observed during percolation test. A similar test with an ordinary Mariotto bottle was also carried out. The results showed that the hydraulic head difference of the new apparatus was kept in a range of 0.02 cm, whereas that of the Mariotto type fluctuated in a range of 0.5 cm. The principle of the new generator can be applied to other kinds of apparatus which require constant hydraulic head difference.