Katsutoshi Seki

Ph. D.
Associate Professor
· Department of Accounting and Finance

Publications

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    ABSTRACT: Field-scale estimation of soil hydraulic parameters is important for describing water movement in vadose zones. The importance of soil water measurements has been acknowledged with increasing soil water measurements becoming available; thus, the estimation of hydraulic parameters from observed soil water would be quite useful for hydrological modeling. This study estimated the hydraulic parameters of Brooks-Corey and Mualem model using the monitored soil water changes at two depths together with the rainfall intensity at two soil plots in a tropical rain forest in Indonesia. A one-dimensional multi-scale parameterization method was used for the analysis, beginning with homogeneous parameterization and identifying the depth of discontinuity using refinement indicators, thus increasing the number of zones. A method for sequential parameterization was developed in each step of zoning. The measured and simulated volumetric water contents with the optimized parameters showed good agreement for one plot (standard error is 0.0419) with 2-zone parameterization, and the effects of the initial parameters derived from different pedo-transfer functions on the optimized hydraulic functions were small, confirming the robustness of this method. However, at another field site, agreement between measured and simulated water contents was not very good (standard error is 0.0854), because the effect of the soil water repellency might have influenced the results, and the effects of the initial parameters were large. The algorithm proposed in this study systematically determines the hydraulic parameter set that describes field-scale water flow.
    Geoderma 01/2015; 247-248:117-128. DOI:10.1016/j.geoderma.2015.02.013 · 2.51 Impact Factor
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    Katsutoshi Seki
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    ABSTRACT: Increased microbial activity leads to biological clogging (or bioclogging), i.e., the pore space is clogged by microbes and saturated hydraulic conductivity of porous media decreases. A series of column experiments were carried out to study the bioclogging of sand columns. Hydraulic conductivity remained unchanged when a sterilizing agent was applied; however, it decreased when a glucose solution was applied. In most cases, bioclogging proceeded from the inlet of the solution; but, in some cases, it started from the bottom or outlet of the column. In this experiment, the reduction of hydraulic conductivity was better explained by microcolony models compared to biofilm models.
    Open Journal of Soil Science 01/2013; 3(3):148-152. DOI:10.4236/ojss.2013.33017
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    Masako Kajiura, Takeshi Tokida, Katsutoshi Seki
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    ABSTRACT: Potential water repellency (PWR) is a common index to indicate the degree to which soils repel water. Soil organic matter (SOM) is a requisite substance for the water repellency but many studies have shown that SOM content alone could not fully account for the observed variation in PWR. We investigated potential factors responsible for PWR of soils in a tropical forest in East Kalimantan, Indonesia. In addition to the wellinvestigated soil properties (e.g., total SOM content, pH, and the amount of iron or aluminum oxides), we also focused on soil moisture content at the time of sampling and water-extractable organic matter (WEOM) content based on the hypothesis that PWR may depend on amphiphilic fractions, including WEOM, in the outermost layer of SOM adsorbed on soil particles — soil water may change the amount and/or the conformation of the amphiphilic fractions. Results showed that the degree of PWR had the highest correlation with the amount of WEOM, not with SOM, among the factors investigated (R2=0.29). The WEOM content (R2=0.65) better explained the variation in water repellency than SOM content (R2=0.47) even after soils were soaked in n-hexane (a non-polar solvent) and expected to have uniform SOM conformation (hydrophobic components dominant on the surfaces). The combination of soil moisture and SOM contents better explained the PWR than SOM content alone. These results suggest that soil water content can have substantial effects on PWR by changing the availability and/or conformation of the amphiphilic SOM, including WEOM.
    Geoderma 07/2012; 181-182:30-35. DOI:10.1016/j.geoderma.2012.02.028 · 2.51 Impact Factor
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    ABSTRACT: Salt accumulation is one of the most serious threats for plant production in northeast China. Field survey and one-year continuous monitoring on soil physical conditions and water table had been conducted in an experimental station of Northeast Forestry University at Heilongjian, China. Annual rainfall was 356 mm while potential evaporation during summer period of 2006 estimated by Thornsweit method was 540 mm. Soil of the study site was mostly clayey. Salt accumulation on soil surface showed heterogenous feature. Salt accumulated areas and vegetated areas adjoin above the same shallow salty ground water table. During summer, when soil water content was nearly saturated, rise in ground water table in response to rainfall was 7 to 12 times larger than the rain depth. This phenomenon is known as reverse-Wieringermeer effect. A 60% of cation contained by shallow ground water was Na and Ca and Mg dominated rest of 40%. However, more than 90% of cation detected at soil surface in salt accumulated areas and at soil layers deeper than 40cm from the surface in vegetated areas was Na. Dynamic behavior of shallow ground water and changes in carbonates solubility due to rise in soil CO2 concentration following soil respiration might affect salt accumulation at the experimental site.
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    K Seki
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    ABSTRACT: Due to the Fukushima Daiichi nuclear plant accident in Japan, huge amount of radionuclides were emitted to the environment. Remediation of soil contaminated with radionuclides is urgent and important. Several remediation techniques are reviewed, e.x., removing the surface soil, removing clay particle,application of fertilizers, and phytoremediation by plant. (This article is written in Japanese) 福島第一原子力発電所で2011年3月11日に起きた事故によって、環境中に大量の放射性物質が放出され、大気圏、水圏、土壌圏に拡散した。土壌圏に蓄積した放射性物質は、空間線量の上昇、土壌から植物への放射性物質の移行による食品汚染を引き起こしている。本稿では、放射性物質によって汚染された生活圏と農地の土壌除染手法について、既往の知見をまとめる。土壌汚染の対策として有効な手法は、表土除去、天地返し、粘土除去のような物理的対策であり、農地への肥料・石灰の施用、転作を組み合わせることもできる。ファイトレメディエーションと化学洗浄は有効性が確認されていない。広大な地域が汚染されているため、時間と費用が膨大にかかること、生じる膨大な放射性廃棄物の処分場が確保されていないこと、といった課題が残されている。
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    ABSTRACT: In a 110-day constant temperature experiment (20°C), we determined the effect of fresh organic matters (FOM): 0 (control); 1.81 g leaf litter (LL) carbon kg-1; and 2.12 g chicken manure (CM) carbon kg-1 in the stable soil organic carbon [mineral-associated organic carbon (MAOC)], labile soil organic carbon [soil microbial biomass carbon (SMBC)], and carbon dioxide (CO2) evolution of a volcanic ash soil from Tsumagoi, Gunma Prefecture, Japan (138°30'E, 36°30'N). Overall, CO2 evolution and SMBC increased after the treatment of soil with FOM, whereas MAOC decreased below its original level three days after FOM application. These data support the view that fresh OM promotes increases in SMBC and CO2 in the rapidly cycling active carbon pool and further suggest that the MAOC fraction, though stable as conventionally believed, can be a source of CO2. Our findings challenge the convention that only labile SOC is the source of short-term CO2 evolution from soils.
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    ABSTRACT: The atmospherically-derived cosmogenic (7-Be), anthropogenic (137-Cs), and airborne radionuclides (210-Pb_xs) were used to investigate the origin and travel time of the mobile soil particles discharged from the tile drain in a heavy clay soil. These radionuclides were accumulated mainly in the surface layer of the soil profile; nevertheless, they were detected with high activities in all the mobile soil particle samples collected from the tile drainage water in a rainfall event. This indicates that the major origin of the mobile soil particles discharged from the tile drain is the mobile soil particles in the uppermost surface soil. The average travel time of the mobile soil particles moving from the uppermost surface soil to the tile drain is estimated as about 35 d based on the difference in the activity ratio (7-Be/210-Pb_xs) of the mobile soil particles between in the surface runoff and in the tile drainage waters.
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    ABSTRACT: The ecological recovery of Dipterocarpaceae forest in East Kalimantan, Indonesia, after the forest fire in 1997–1998 was studied. Soil physical and chemical properties of the plots—heavily damaged by forest fire (HD), lightly damaged by fire (LD) and control site not burned by fire (K)—were investigated eight to nine years after the fire. Soil water content was monitored for one year in the HD and K plots. The white sand layer found in the HD plot had low water retention and high permeability. Therefore, soil was not saturated in the surface sandy layer during rainfall and water infiltrated quickly into the subsurface layer. Such sandy soil, often found in kerangas forest, generally has low pH and low nutrient availability. However, the sandy soil in the HD plot had higher pH and lower electrical conductivity (EC) than other pits at the upper boundary of the sandy soil. Total carbon, total nitrogen and water repellency were high at the lower boundary of the sandy layer. This may be because ash and charcoal produced by the fire have leached downwards.
    Journal of Tropical Forest Science 01/2010; 22(4):414-424. · 0.67 Impact Factor
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    K Seki
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    ABSTRACT: Volcanic ash soils have excellent soil hydrological properties, as high water retentivity and high water permeability compared with other clayey soils. They contain abundant allophane and organic matter. Having well developed aggregated structures, vol- canic ash soils have large porosities as much as 8 0%, retain water inside soil aggregate, allow the water move easily through large pores between aggregate and macropores, and consequently have high permeabilities. In this study, various soil hydrological properties of a volcanic ash soil in Japan are shown and discussed;volumetric ratio of solid, liquid, and gas phases, particle density, hardness, pH, EC, soil organic matter (ignition loss) soil texture, specific surface area, soil water retention, curve and saturated and unsaturated hydraulic conductivity. The soil texture was clas- sified as light clay, pH was around 6, and ignition loss was 17 to 27%. Although soil hydrological properties of Andosols change with changing pH because of the pH-dependent charges of allophane, water retention curves and unsaturated hydraulic conductivities were not affected by the electrolyte(NaCl)concentrations used in the measurement. These soil hydrological peculiarities of Andosols were attributed to the stability of soil structures at neutral pH range, where critical coagulation concentration (CCC) was very low.
  • Li Wang, Katsutoshi Seki, T. Miyazaki, Y. Ishihama
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    ABSTRACT: The causes of soil alkalinization in the Songnen Plain of Northeast China were mainly analyzed from two aspects, natural and anthropogenic. Natural factors of alkalinization are parent materials, topographic positions, freeze-thaw action, wind conveyance, water properties and semi-arid/sub-humid climate. Some of them were always being neglected, such as freeze-thaw action and wind conveyance. Anthropogenic causes are mainly population pressure, overgrazing and improper agricultural and economic policies. In recent decades, overgrazing played a main role in secondary soil alkalinization, which led to the decline of Leymus chinensis grasslands. Now, the alkalinization is very severe, and more than 3.2 × 106 ha area has been affected by salt, which becomes one of the three largest sodic–saline areas in the world.
    Paddy and Water Environment 09/2009; 7(3). DOI:10.1007/s10333-009-0166-x · 1.25 Impact Factor
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    Saito H, Seki K, Šimůnek J
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    ABSTRACT: There are two approaches available for mapping water retention parameters over the study area using a spatial interpolation method. (1) Retention models can be first fitted to retention curves available at sampling locations prior to interpolating model parameters over the study area (the FI approach). (2) Retention data points can first be interpolated over the study area before retention model parameters are fitted (the IF approach). The current study compares the performance of these two approaches in representing the spatial distribution of water retention curves. Standard geostatistical interpolation methods, i.e., ordinary kriging and indicator kriging, were used. The data used in this study were obtained from the Las Cruces trench site database, which contains water retention data for 448 soil samples. Three standard water retention models, i.e., Brooks and Corey (BC), van Genuchten (VG), and Kosugi (KSG), were considered. For each model, standard validation procedures, i.e., leave-one-out cross-validation and split-sample methods were used to estimate the uncertainty of the parameters at each sampling location, allowing for the computation of prediction errors (mean absolute error and mean error). The results show that the IF approach significantly lowered mean absolute errors for the VG model, while also reducing them moderately for the KSG and BC models. In addition, the IF approach resulted in less bias than the FI approach, except when the BC model was used in the split-sample approach. Overall, IF outperforms FI for all three retention models in describing the spatial distribution of retention parameters.
    Hydrology and Earth System Sciences 01/2009; DOI:10.5194/hess-13-453-2009 · 3.64 Impact Factor
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    ABSTRACT: The organic carbon of particle size
    Geophysical Research Letters 01/2009; 36(1). DOI:10.1029/2008GL036436 · 4.46 Impact Factor
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    ABSTRACT: The understanding of the gaseous adsorption process and the parameters of volatile organic compounds such as organic solvents or fuels onto soils is very important in the analysis of the transport or fate of these chemicals in soils. Batch adsorption experiments with six different treatments were conducted to determine the adsorption of isohexane, a gaseous aliphatic, onto volcanic ash soil (Tachikawa loam). The measured gas adsorption coefficient for samples of Tachikawa loam used in the first three treatments, Control, AD (aggregate destroyed), and AD-OMR (aggregate destroyed and organic matter removed), implied that the aggregate structure of volcanic ash soil as well as organic matter strongly enhanced gas adsorption under the dry condition, whereas under the wet condition, the aggregate structure played an important role in gas adsorption regardless of the insolubility of isohexane. In the gas adsorption experiments for the last three treatments, soils were sieved in different sizes of mesh and were separated into three different aggregate or particle size fractions (2.0-1.0mm, 1.0-0.5mm, and less than 0.5mm). Tachikawa loam with a larger size fraction showed higher gas adsorption coefficient, suggesting the higher contributions of macroaggregates to isohexane gas adsorption under dry and wet conditions.
    Journal of hazardous materials 12/2008; 166(1):207-12. DOI:10.1016/j.jhazmat.2008.11.008 · 4.33 Impact Factor
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    Saito H, Seki K, Šimůnek J
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    ABSTRACT: This study compares the performance of two geostatistical approaches, parametric and non-parametric, to evaluate the spatial distribution of water retention curves. Data used in this study were obtained from the Las Cruces trench site database that contains water retention data for 448 soil samples. In a commonly used parametric approach, three standard water retention models, i.e. Brooks and Corey (BC), van Genuchten (VG), and log-normal (LN), were first fitted to each data set. For each model, a cross validation procedure was used to estimate parameters at each sampling location, allowing computation of prediction errors. In a rarely used non-parametric approach, a cross validation procedure was first used to directly estimate water content values for eleven pressure heads at each sampling location and then the three water retention models were fitted using the same automated procedure to compute prediction errors. The results show that the non-parametric approach significantly lowered prediction errors for the VG model, while moderately reducing them also for the LN and BC models.
    Hydrology and Earth System Sciences Discussions 01/2008; DOI:10.5194/hessd-5-2491-2008 · 3.59 Impact Factor
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    K Seki
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    ABSTRACT: The soil hydraulic parameters for analyzing soil water movement can be determined by fitting a soil water retention curve to a certain function, i.e., a soil hydraulic model. For this purpose, a program which performs nonlinear fitting of soil water retention curves to 4 models, Brooks and Corey model, van Genuchten model, Kosugi's lognormal pore-size distribution model, and Durner's bimodal pore-size distribution model, by Levenberg-Marquardt method was developed. The program was written in GNU Octave, a high-level language primarily intended for numeric calculation. It was shown that the developed program actually works fine with many soil water retention curves in UNSODA database. It was also shown that by comparing coefficients of determination and fitting curves of each model, the most appropriate hydraulic model for a certain soil can be selected. Therefore this program not only calculates the necessary parameters, but also helps determining which model is to be used for a particular purpose.
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    ABSTRACT: In this study, we evaluated the mobility of 90Sr in ploughed upland soil, which affects the residual amount in the soil and plant uptake on the basis of long-term monitoring data. Paired samples of soil and wheat grain were taken annually from 1961 to 1995 from 8 agricultural fields in Japan, and the concentrations of exchangeable 90Sr in soil and total 90Sr in wheat grain were determined. The concentration of exchangeable 90Sr in ploughed soil decreased exponentially with time. The environmental factor responsible for the decrease of exchangeable 90Sr in the ploughed layer, lambda(e), was determined from the monitoring data of exchangeable 90Sr in the ploughed soil and the amount of fallout-derived deposition. The lambda(e) was larger from 1970 to 1980 than it was from 1980 to 1995, suggesting that an easily removable fraction of 90Sr in soil was preferentially lost from ploughed soil. Among various soil properties that we investigated, the main factor controlling the long-term mobility of 90Sr from ploughed upland soil and 90Sr uptake by wheat grain was the cation-exchange capacity (CEC) of soil. Our experimental results indicate that the entrapment of 90Sr on a cation-exchange site retards the downward migration and wheat uptake of 90Sr from ploughed soil. The empirical parameters that we obtained based on the long-term observation of a wheat-cultivated upland field in Japan could be used as reference data in order to roughly estimate the mobility of 90Sr in ploughed soil and soil-borne 90Sr transfer to wheat grain in the humid Japanese climate.
    Science of The Total Environment 02/2007; 372(2-3):595-604. DOI:10.1016/j.scitotenv.2006.10.011 · 3.16 Impact Factor
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    K. Seki
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    ABSTRACT: The soil hydraulic parameters for analyzing soil water movement can be determined by fitting a soil water retention curve to a certain function, i.e., a soil hydraulic model. For this purpose, the program "SWRC Fit," which performs nonlinear fitting of soil water retention curves to 5 models by Levenberg-Marquardt method, was developed. The five models are the Brooks and Corey model, the van Genuchten model, Kosugi's log-normal pore-size distribution model, Durner's bimodal pore-size distribution model, and a bimodal log-normal pore-size distribution model propose in this study. This program automatically determines all the necessary conditions for the nonlinear fitting, such as the initial estimate of the parameters, and, therefore, users can simply input the soil water retention data to obtain the necessary parameters. The program can be executed directly from a web page at http://purl.org/net/swrc/ ; a client version of the software written in numeric calculation language GNU Octave is included in the electronic supplement of this paper. The program was used for determining the soil hydraulic parameters of 420 soils in UNSODA database. After comparing the root mean square error of the unimodal models, the van Genuchten and Kosugi's models were better than the Brooks and Corey model. The bimodal log-normal pore-size distribution model had similar fitting performance to Durner's bimodal pore-size distribution model.
    Hydrology and Earth System Sciences Discussions 01/2007; DOI:10.5194/hessd-4-407-2007 · 3.59 Impact Factor
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    ABSTRACT: Permeable reactive barriers (PRBs) are an alternative technique for the biological in situ remediation of ground water contaminants. Nutrient supply via injection well galleries is supposed to support a high microbial activity in these barriers but can ultimately lead to changes in the hydraulic conductivity of the biobarrier due to the accumulation of biomass in the aquifer. This effect, called bioclogging, would limit the remediation efficiency of the biobarrier. To evaluate the effects bioclogging can have on the flow field of a PRB, flow cell experiments were carried out in the laboratory using glass beads as a porous medium. Two types of flow cells were used: a 20- × 1- × 1-cm cell simulating a single injection well in a one-dimensional flow field and a 20- × 10- × 1-cm cell simulating an injection well gallery in a two-dimensional flow field. A mineral medium was injected to promote microbial growth. Results of 9 d of continuous operation showed that conditions, which led to a moderate (50%) reduction of the hydraulic conductivity of the one-dimensional cell, led to a preferential flow pattern within the simulated barrier in the two-dimensional flow field (visualized by a tracer dye). The bioclogging leading to this preferential flow pattern did not change the hydraulic conductivity of the biobarrier as a whole but resulted in a reduced residence time of water within barrier. The biomass distribution measured after 9 d was consistent with the observed clogging effects showing step spatial gradients between clogged and unclogged regions.
    Ground Water Monitoring and Remediation 05/2006; 26(3):68 - 76. DOI:10.1111/j.1745-6592.2006.00086.x · 1.05 Impact Factor
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    ABSTRACT: Zero Flux plane (ZFP) is defined as a plane, which separates two zones of upward and downward movement of water in soil with upward and downward flow occurring simultaneously. In this study, the analysis of the ZFP movements was carried out by two sets of laboratory experiments and numerical simulations, especially paying attention to the effect of the periodical water supply. In the first set of experiment and simulation, surface Andisol soil was used and water was supplied only one time. Evaporation rate was set to 0.15 cm/day, and water was drained from the bottom of the column. The total potential profile and the ZFP movement of experiment and simulation agreed reasonably well. In the second set of experiment and simulation, subsurface Andisol was used and water was supplied periodically. In both experiment and simulation, ZFP appeared at soil surface every time water was supplied, and it gradually moved downward until it reached to the depth of 30 cm, when the ZFP disappeared. We discussed that such disappearance of the ZFP is observed when the initial soil water content at the deep zone is relatively high. In contrast, when the initial soil water content at the deep zone is relatively low, as reported in previous studies, ZFP continues to move downward for a relatively long period. Simulation of ZFP movement was also conducted for different types of soils. Based on the results of this study, a strategy for the periodical water supply in arid and semiarid regions using this ZFP concept was proposed.

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