The purpose of this investigation is to evaluate performance of an appropriate composite material for a purification system of waste irrigation water. This material is consisted of a natural zeolitic tuff and waste cement slurry; the main component of the former is mordenite; the latter is covered over to make the fragile tuff strengthen. In this study, cyclic batch tests were conducted to reveal the removal performance for nitrogen and phosphate. As a result, the following conclusions are obtained;(1) the thickness of coating cement slurry that had no disadvantage for performance of removal of nitrogen and phosphate;(2) removal performance for ammonium was mainly contributed by ion absorption;(3) removal performance for phosphate was mainly contributed to absorption to microorganisms.

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Rice production with confidence and safety is one of the main issues in Asian countries. For the past few decades, reduction technique of rice cadmium (Cd) has been clarified. Hence ministry of Agriculture, Forestry and Fisheries and National Institute for Agro-Environmental Sciences (2002) recommended the flooding water of paddy before and after the heading, and soil improvement using fertilizers. However lots of farmers express concern over rice degradation, rumor damage into price down and destruction of plow pan at harvest.
Therefore to generalize the reduction technique of Cd uptake by rice, we measured soil pH and soil Eh continuously, and analyze Cd concentration in both soil and rice in three different cultivated paddy fields. We concluded that 1) flood water management stabilized soil pH in neutral, and lowered soil Eh before and after the heading, 2) organic fertilizer was effective to reduce Cd in rice, 3) soil pH and Eh were not always the strict indicator of Cd uptake by rice, 4) climate condition did not affect the Cd concentration in rice.

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For the evaluation of flood mitigation function of irrigation ponds, this paper analyzes the relationship between the flood mitigation ratio and delay ratio of the time of flood concentration, based on the hydrological records in the irrigation pond in Osaka Prefecture. Further, A new idea and evaluation method of the concentration time is suggested, and defined as “maximum time contributing to peak discharge”. New method of the flood mitigation value of irrigation ponds using the properties of the pond construction and the rainfall pattern was developed based on hydrological observation at 19 ponds and numerical simulations under several conditions. Results showed that the new method could sufficiently represent the flood mitigation value to the actual flood events. Therefore, it was expected that it can evaluate the flood mitigation function in many irrigation ponds.

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Most of old small earth dams for irrigation were mostly accumulated with the muddy soil in reservoir that caused the water pollution and the loss of reserved water. In order to make efficient use of the muddy soil as the embankment soil for reinforcing the damaged embankment, we have developed a new type method to repair the old small earth dam embankment by means of the stabilized muddy soil with cement stabilizer.
In this paper, we propose the design method to reinforce the old small earth dam embankment by constructing the sloping core zone by cement-mixed muddy soil. The strength parameters (c', φ') obtained from the tri-axial compression test is adopted to evaluate the stability of the reinforced embankment slope that compose of the existing embankment and sloping zones constructed by cement-mixed muddy soil in proposed design method.

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The native species, Carex dispalata, Carex thunbergii and Phalaris arundinacea, whose height does not obstruct the View, were compared with Phragmites australis for their adaptability to polluted water and their water purification capability. The results show a stable growing condition of Carex dispalata even in water with a relatively high pollution load. Although the TN values indicate that the purification capability of Carex dispalata is about 70% of the capability of Phragmites australis, the results also suggest nitrification to the root system caused by oxygen supply. The values of TP, COD, BOD show that the removal speed of Carex dispalata and Phragmites australis is about the same. Also the seasonal fluctuation of the contents of nitrogen and phosphorus, which are fixed in the above-the-ground part of Carex dispalata, is small, suggesting that the plants tend to retain these nutrients in the part rather than transporting them to the rhizomes. Therefore, it became clear that we can expect the water purification capability of Carex dispalata in water with a relatively high pollution load, and that it is a useful species for landscape creation and maintenance.

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In order to stabilize the construct effects of a pipe drain, it is necessary to use the filter material of a pipe drain. In this paper, we confirmed that the wood chip is suitable as filter material for a pipe drain.
The wood chip showed excellent permeability with a saturated hydraulic conductivity in the order of 10^-3m s^-1. It had also a wide C/N ratio and showed high resistance to rotting. The draining efficiency of the pipe drain using the wood chip was the same as that using a rice husk. The pipe drain using the wood chip had the sufficient draining efficiency 4 years later. The wood chip is easy to maintain the section of a drainage filter. And, the aging decrease rate of section area on the wood chip filter is smaller than its a rice husk, and the durable period of the wood chip as filter material is long. This reasons is that the rotting of the wood chip belonged to soft-rotting type, in which rotting is slow. But, the drain water of the pipe drain using wood chip was low pH condition. We expected that a pipe of underdrain using the wood chip was clogged by a iron deposit in a peat soil and a strong aside soil. Therefor, we concluded that the wood chip refrained from using as a filter material of a pipe drain in these soils.

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The failure of embankment such as a levee and an earth dam may be caused by overflow, seepage (water leakage), scour or crack. The common cause of failure is piping (seepage path) through embankments. This paper shows a simple method of a numerical simulation for piping failure in order to investigate the process, that is, the piping phenomenon is assumed as the optimal permeability field under a certain condition and the seepage property of the field changes to adjust to neighboring environmental changes using cell automaton. The simple rule that a permeability coefficient changes depending on seepage velocity generated in the seepage field is applied to the cell automaton and the piping phenomenon is simulated in a cross section of the embankment with the finite element saturated seepage analysis.

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Agricultural field of arid regions would be exposed to the risks of water scarcity and soil degradation, including salt accumulation. Suitable methods and schedules of irrigation are required to avoid these problems. This study examines the ability of an arranged irrigation method (“2 Depths”: Subsurface irrigation at two depths) in sandy soil. As a first experiment, numerical simulation was conducted to compare the soil water movement with “2 Depths” and with the traditional subsurface irrigation method (“1 Depth”). As a second, field experiment was implemented to measure the dry mattars, water use efficiencies and evapotranspirations of sorghum and the distributions of water and salts in the soil with “2 Depths” and with “Sprinkler” irrigation using saline water. Results of numerical simulation showed that “2 Depths” could increase soil moisture and make soil water distribution uniform. The growth and water use efficiencies of sorghum with “2 Depths” are greater than that of “Sprinkler ”. It was concluded that “2 Depths” is advantageous to save irrigation water and to grow plants.

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The accurate evaluation of lake level is essential in managing a lake as a fresh water resource. In this study, a model to estimate lake level was developed and tested for Lake Ikeda by hydrologic budget analysis during 31 years from 1967 to 1997. Discharge from the lake catchment area and leakage from the lake bottom were estimated based on the Tank Model and Darcy's law, respectively. The model parameters for hydrogeologic properties around the lake catchment area and the lake bottom were calibrated by the SCE-UA (Shuffled Complex Evolution) method. From 1967 to 1980, the estimated lake level roughly agreed with the measured one. By re-calibrating the parameters for changes in the conditions of the hydrologic setting, the estimated lake level agreed well with the measured one from 1983 to 1997. The model developed in this study can be useful in the water management of Lake Ikeda.

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Construct effects and soil conditions suitable of the low-cost digging underdrain by trencher type excavator without envelope are studied.
1. The digging underdrainage requires the construction of drain hole that is 7 cm wide, 40 cm height in the soil depth 60 to 120 cm and a hole with a diameter of 20 cm, and the upper side of drain hole is closed by soil lid and filled up the digging soil. This drain hole without envelope is constructed by farm tractor with the trencher.
2. The digging underdrain that has a big hole is able to drain excess water as a pipe drainage.
3. As for durability of the digging underdrain, drain hole became a little small 7 years later in peat soil. Although 40% of drain hole decrease 10 years later. The transformation of the drain hole become remarkably 5 years later in alluvial soil. The digging underdrain was difficult to construct in diluvial soils, because the drain hole collapsed easily. Therefore the digging underdrain should be applied in a peat soil and alluvial soils, on converted upland filed from paddy, primarily upland filed and grassland.
4. A cost of construction the digging underdrain is a little higher than a conventional mole drainage.

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The aim of the present study is to obtain quantitative information on egg hatching with respect to temperature and light to clarify the effect of cultivation methods on Sympetrum frequens. Eggs of the species were collected on October in 2004 at Akita prefecture located at north of Japan, and the eggs had been laid on soil surface of paddy field till April in 2005. The eggs (3 trays with 30 eggs each) were held under four constant temperature (5°C, 10°C, 15°C and 20°C) with a photoperiod (L: D, 14: 10; relative light intensity, 3000 Lux) and 20°C in the dark. Cumulative hatching percentage under 20°C with and without light was 98.9% and 95.6% respectively. The percentage under 15°C, 10°C and 5°C were 95.6%, 88.9% and 84.4%, respectively. These results suggest that the dragonfly do not require light for hatching and hatching is suppressed by low temperature such as 5°C. Mean hatching days with light under 20°C, 15°C, 10°C and 5°C were 3.5, 4.8, 11.6 and 41.0 respectively. Reciprocal of variance of hatching day under these conditions were 0.15, 0.09, 0.03 and 0.02 respectively. These results indicate that the eggs under 20°C and 15°C hatched faster and more uniformly than those under 10°C and 5°C. Based on these results, theoretical lower thermal threshold and thermal constants for hatching were estimated at 4.9°C and 54.6 degree-days. According to these results, the effects of cultivation methods on hatching of this species were discussed.

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The authors had proposed a new method of nitrate nitrogen (NO₃-N) removal for drainage from agricultural fields with a layer of waste sludge that was disposed of from rural sewage plants. The present study subsequently investigated nitrate removal ability of the sludge layer. The results indicated that waste sludge (around four months after the removal from a wastewater treatment process) possessed higher nitrate removal potential than upland soil as follows.(1) The sludge contained 10⁶-10⁸ MPN·g^-1MLSS of denitrifying bacteria (MPN; most probable number, MLSS; mixed liquor suspended solids).(2) The sludge showed NO₃-N removal rate of 0.76 mgN·g^-1MLVSS·gd^-1 at 20°C and 10 mgN·gl^-1 of NO₃-N and oxygen consumption rates of 5.9-16.8 mgO·gg^-1MLVSS·gd^-1 at 20°C (MLVSS; mixed liquor volatile suspended solids). In addition, sludge layers that were formed at around 96 % of the moisture content, showed low hydraulic conductivity of 10^-6 cm·s^-1, which was comparable to clay. Such low permeability will ensure sufficient retention time for denitrification when water infiltrates through a sludge layer.

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We have studied on the harmonization of development and environmental conservation in Cidanau watershed of West Java, Indonesia, where the natural environment has been getting worse recently, and we have reported some results of three topics. One is a report on the socio-economic change and the recent environmental change by studying literatures and field surveys. Second is a report on green vegetation change and land use change in Cidanau watershed by using remote sensing images observed in 1994 and 2000. The last is a report on hazard mapping of soil loss in Cidanau watershed by using GIS, based on USLE.
Based on these research, we conclude following findings. 1) Large area of forest near Rawa Danau, which is tropical pure water swamp forest and registered as a green belt, had been deforested accompanied with the increment of population from 1994 to 2000. 2) Some small scaled developments were occurred in other places such as sloped lands, but they had low risks of soil loss from the view point of soil conservation in the whole watershed.
Finally, we conclude these results and summarized the characteristics of the land use change and environmental change in this area. After that, we refer the significance of environmental policies such as environmental education or improvement of land registration system.

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In this study, the shape of the “pore system formed by roots”(hereafter P. S. R.) that is found in the middle & lower Pleistocene series of volcanic ash soil formation in the northern Iwate region was investigated. As a result, the following new facts and a proposition are presented.(1) The decaying state in the shape of the P. S. R. was recognized in all horizons that were investigated. And the range of the decay extended over all degrees from light damage to the disappearance of the P. S. R.(2) A new index, “decaying level” was proposed, and the progress of decay in the P. S. R. was classified into 4 steps, expressed as the level of decay. The 4 steps are shown by an index number from 1 to 4 and are called, for example, “decaying level 2.” Decaying level 4 indicates the strongest decay, and it means the disappearance stage of the P. S. R.(3) The vertical distribution of the decaying level that was found in the soil layers investigated shows that the decaying level did not simply increase in parallel with the aging time of the layers.

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This study was carried out to clarify the consumptive use of soil moisture in the orchard reclaimed 3 years ago.
At the time of investigation, the orchard was anticipated that the soil physical property has not always been ensured good tree growth. Furthermore, it was the situation that could not carry out the irrigation for peach plant during 1992-1993 and pear plant during 1993-1994. Under this condition, the mechanism of soil moisture consumption and the capillary water supply from deep soil layer were investigated.
As the result, it was clarified that the capillary water supply was affected by the physical condition, water retention and weather condition. And it was clarified that was also affected by the difference of root zone by tree species. Besides, the capillary water supply obtained from the deep soil layer over 100cm was 0.1 to 5.3mm/d.

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To characterize carbon and nitrogen stable isotope ratio of terrestrial materials is essential for the food web analysis in the paddy ecosystem. We have analyzed carbon and nitrogen stable isotope ratios of deciduous leaves, forest soil and canal sediment in a paddy field at hill-bottom (Yatsuda) area. Correlation was not observed between carbon stable isotope ratios (δ¹³C) of leaves and soil. However, negative correlation was observed between δ¹³C of soil and soil water content. It is likely that decomposition rate which will be considerably controlled by soil water content was involved with the δ¹³C values. Negative nitrogen stable isotope ratios (δ¹⁵N) of leaves indicated that forest in the Satoyama absorbed the nitrogen derived from rain water. There was correlation between δ¹⁵N of soil and soil water content at the right bank.δ¹⁵N values of sediment in the right canal where the water velocity is low were significantly higher than the left. Denitrification, which is affected by water velocity, will be promoted at the right bank. Ascents of δ¹³C and δ¹⁵N accompanied by decay of terrestrial organic matter mainly occur in terrestrial area in comparison with aqua area.

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