Tatemasa Hirata

Temporal moments analysis of preferential solute transport in soils

Temporal moments analysis of solute breakthrough curves is used to investigate the preferential leaching of chloride, nitrate and phosphate through an Australian soil. Recent studies have shown that current models and methods do not adequately describe the leaching of nutrients through soil, often underestimating the risk of groundwater contamination by surface-applied chemicals, and overestimating the concentration of resident solutes. This inaccuracy results primarily from ignoring soil structure and non-equilibrium between soil constituents, water and solutes. Therefore simple models are required to accurately characterise solute transport in natural and agricultural soils under non-equilibrium conditions. A multiple sample percolation system, consisting of 25 individual collection wells was constructed to study the effects of localised soil heterogeneities on the transport of nutrients (NO3−, Cl−, PO43−) in the vadose zone of an agricultural soil predominantly dominated by clay. Using data collected from the multiple sample percolation experiments, this paper compares and contrasts the performance of temporal moments analysis with two mathematical models for predicting solute transport, the advective-dispersion model with a reaction term (ADR) and a two-region preferential flow model (TRM) suitable for modelling preferential transport. The values for solute transport parameters predicted by temporal moments analysis were in excellent agreement with experimental data and results from ADR and TRM. It is concluded that temporal moments analysis when applied with other physical models such as the ADR and TRM, provide an excellent means of obtaining values for important solute transport parameters and gaining insight of preferential flow. These results have significant ramifications for modelling solute transport and predicting nutrient loadings.

Determination of the abundance of δ15N in nitrate ion in contaminated groundwater samples using an elemental analyzer coupled to a mass spectrometer

A rapid method for measuring the delta15N of nitrate ion in water samples using an isotope ratio mass spectrometer coupled to an elemental analyzer system (EA-MS) was investigated. The water should be removed from the analytical sample before measurement with this system. We investigated the application of a super-absorbent polymer resin powder to various water samples. Each 1 mg of polymer resin powder can absorb about 50-100 mg of solution depending on the concentrations of major ions. Only samples which contain more than 100 mg l(-1) of nitrate-nitrogen are suitable to be absorbed by the polymer resin for the determination of delta15N of nitrate. Preconcentration by rotary evaporation was necessary for dilute samples but the temperature should be kept below 60 degrees C. The polymer resin (about 8 mg) containing the nitrate was directly analyzed using an EA-MS after being oven-dried at 80 degrees C. Good accuracy (precision +/- 0.3%) for delta15N measurements of nitrate-nitrogen in a sample without any isotope fractionation effects during pre-treatment was observed. Results for delta15N of nitrate in contaminated groundwater samples collected in the spring at a tea plantation area in Shizuoka, Japan, were from 9.8 to 10.6%, which were close to the delta15N abundance in organic fertilizers.

Analysis of organic nitrogen compound in domestic sewage in Yamato River using a social experimental test

A social experimental test to reduce the amount of organic pollutant from households was performed along the Yamato River in Japan. The river is polluted with organic compounds in sewage and has the highest biological oxygen demand (BOD) of all rivers managed by Japanese government. Because of this, the government carried out a cleaning campaign to improve the water quality in the Yamato River between 1985 and 2005 by constructing river purification facilities and sewerage systems. We evaluated these efforts of the sewage systems and the river water cleaning campaign by measuring the change in the amount o f nitrogen compounds and by pollutant load analysis.

Physical and Dynamic Properties of Soil Cement Diaphragm Walls and Seismic Performance Evaluation Using Seismic Response Analysis

本研究では, 廃棄物処分場等の鉛直遮水工として適用されることが多いソイルセメント系連続地中壁の物理・力学特性に関する種々の室内試験を実施するとともに, 地震応答解析によりソイルセメント系連続地中壁の耐震性能評価を行った。その結果, 1) ソイルセメント連続地中壁は, 兵庫県南部地震クラスの巨大地震 (レベル2地震動) に遭遇すると, 引張強度不足に起因してクラック等が発生し遮水機能が大幅に低下する可能性があること, 2) ベントナイトの混合比率を大幅に増加させることによって, 固化後でも塑性状態を維持し得るソイルセメント・ベントナイト連続地中壁の造成が可能となること, 3) ソイルセメント系連続地中壁の耐震性能評価を行う場合, ソイルセメント連続地中壁では引張応力に対する安全率に, またソイルセメント・ベントナイト連続地中壁ではせん断応力に対する安全率に着目すればよいことを明らかにした。

NUMERICAL SIMULATION ON NATURAL ATTENUATION OF CHLORINATED ETHENES IN AN AQUIFER

In order to evaluate the natural attenuationof chlorinatedethenes, especially trichloroethylene (TCE) anddichloroethylenes (DCEs) in an aquifer, the effects ofdispersion-and-dilution and biodegradation on the concentrations of TCE and DCEs were investigated using numerical simulation. The resultsobtained in this study can be summarized as follows: (1) In an aquifer with high biodegradation rate of DCEs (first order rateconstantof DCEs is over 2.0×10-3/d), the concentrationratioof DCEs to TCE is less than 1.0. (2) In an aquifer with highdispersion-and-dilution rate (groundwater velocity is over 0.6m/d-1.0m/d), the concentration ratio of DCEs to TCE is less than 1.0. (3) When the first order rate constantof DCEs is less than 1.0×10-3/d and the groundwater velocity is less than 0.4m/d-0.7m/d, DCEs tend to accumulate in an aquifer.

LIVING LIMIT OF LARVA OF DRAGONFLY IN RIVERS WITH DOMESTIC SEWAGE INFLOW IN THE SOUTHERN PART OF OSAKA

Living limits about Na and Cl concentrations of larva of dragonfly were studied. As Na and Cl concentrations in river water increased, the number of larva decreased and species composition of larva changed from Stylogomphus suzukii to Calopterx atrata. Na and Cl concentrations were thought to be mixing ratio of domestic sewage and domestic sewage was thought to contain toxic substance. Davidius nanus was distributed widely in the river water from low to high mixing ratio of domestic sewage. Living limits of maximum Na and Cl concentrations for Calopterx atrata and Davidius nanus were 50 and 80 mg/l. The values were living limit of all larva of dragonfly observed in the southern part of Osaka. In the long term, the living limits of maximum Na and Cl concentrations for larva of dragonfly were 38 and 59 mg/l. When anionic surface active agent is 3.8 to 6.2mg/l, larva of dragonfly disappeared.

Behavior of soil nitrogen and leaching of metal elements from arable land

In Japan, large amounts of fertilizer nitrogen are applied to tea plantations. We collected samples of tea plantation soil each season for a year. Samples were analyzed for their contents of various inorganic chemicals and total N. Nitrogen was present mainly in the top 0 to 30 cm of soil. However, at times the concentration of nitrate N in the soil water was more than 35 mg L−1, even in the deepest layers. The contents of various metal elements in the soil were examined. Ba, Fe, Sr and Zn contents were high in the top 0 to 30 cm of soil. But Al and Mn contents were not always high in the top 0 to 30 cm of soil. From the correlation analysis among contents of various inorganic chemicals, it was suggested that increased leaching of Al, Mn, and Zn from tea plantation soil occurred with increased nitrate N concentration.

ESTIMATION OF BOD LOADS CONSIDERING WATER TEMPERATURE IN THE YAMATO RIVER CATCHMENTS

Calculated Pollutant load per unit production and actual pollutant load of Yamato River were estimated. The actual pollutant load was determined from measured flow rates and concentrations. As a result, actual BOD load showed seasonal changes with low values of summer and high values of winter. The change depended on temperature because a rate of decomposition of organic compound depends on temperature. The actual BOD loads between two pints along the Yamato River with no branch river and no drainage were measured and a rate of decomposition between them was calculated. The calculated seasonal BOD load from pollutant load unit production method including rate of decomposition showed the same pattern of the actual BOD load. The total BOD load value by unit production including decomposition calculated method was 4 times of the actual load. As BOD was not measured at flood condition, the actual BOD did not include floating material at the condition of high flow rate and then was smaller than the calculated load per unit production.

CHARACTER OF COD VALUES WITH FLOW RATE CLAFIED BY ONE HOUR AUTOMATIC MEASUREMENT IN THE YAMATOGAWA RIVER

COD was previously measured from sampled water. Then 1 month measurement does not include flood condition because of safety for sampling. 1 hour measurement is automatically sampled and measured in situ at station and then includes flood condition. To clarify difference between 1 month measurement and 1 hour measurement , using both measuring results of flow rate, COD, TB and EC values of the Yamatogawa river, effect of flow rate on COD , TB and EC values was clarified. COD and TB values increased with flow rate. EC value decreased as flow rate increased . The relationships between COD and flow rate, TB and flow rate were very similar. Therefore , COD was more strongly influenced by floating material than soluble substances because TB was concentration of floating material . Using the relationships between COD and flow rate, COD loads were calculated. As a result , the COD load calculated by the 1 hour measurement was more about 2 times than the COD load calculated by the 1 month measurement.

CHANGES OF SUBSTANCES DERIVED FROM DOMESTIC SEWAGE IN YAMATOGAWA RIVER BASIN

Seasonal Concentrations of BOD, NH4+-N and interfacial active agent derived from domestic sewage were high in winter and low in summer. The concentrations decreased with an increase in water temperature. Generally, river water contains organic compounds and Cl- derived from domestic sewage and Cl- was quite stable in rivers. As the ratios of BOD/Cl- and NH4+-N/Cl- decreased down the stream and changed seasonally, organic compounds were thought to be decomposed during flow. NO3--N/Cl- which organic compounds were finally decomposed into, also decreased down the stream and were high in winter and low in summer. NO3--N was thought to be used for photosynthesis because pH, DO values and chlorophyll concentration of the Yamato river increased with temperature and decrease of NO3--N concentration.