Nitrification in Andisol containing ammonium sulfate was observed at 22, 24 and 26℃ (batch tests). The decrease in ammonium nitrogen (NH4-N) and increase in nitrate nitrogen (NO3-N) in the batch tests were simulated well by a first-order transformation. The first-order rate constant decreased dramatically with decreasing temperature. Simultaneously, column experiments, in which ammonium sulfate solution was dripped for 9 d and then pure water was dripped for 20 d, were performed at the same temperature for the batch tests. NH4-N remained in the upper soil layer due to adsorption, and NO3-N produced by nitrification leached downward. The NO3-N production decreased as temperature decreased. Then, using Richard's equation and an advection-dispersion model with Gapon convention for cation exchange and first-order transformation for nitrification, the column experiments were calculated with the rate constant obtained by the batch tests. When dissolved and absorbed NH4-N were assumed to have the same rate constant, the calculation overestimated the NO3-N profile in the column experiments. However, the calculation could reproduce the column experiment under the assumption that the absorbed NH4-N had a smaller rate constant than the dissolved NH4-N and started to nitrify when the concentration of the dissolved NH4-N fell below 4 mmol L-1.
Biostimulation of a petroleum-contaminated soil is a remediation technique that stimulates indigenous microorganisms capable of degrading pollutants with adding of phosphorus, nitrogen compounds, and oxygen. This study is conducted to evaluate the purification effect and influence factors of bioremediation with purification promotion materials including Ryukyu limestone for petroleum-contaminated Kunigami-maji soil, in the northern part of Okinawa Island. Soil remediation tests in our laboratory were conducted to purification characteristics and influential factors for bioremediation. As for the Total Petroleum Hydrocarbons (TPH) removal action, it was confirmed to evaluate purification speed using a primary equation quantitatively. It was confirmed that oil purification speed (removal rate constants of THP) could be improved in the range of 5-20% of water-contents in the soil by adding Ryukyu limestone in contaminated soil more than 5%. It was also clarified that Ryukyu limestone powder (125µm or less) showed the highest TPH purification effect among addition materials of shell pieces and building stones. It was considered that the breathability to be necessary for the metabolism activities of the solution microbe for petroleum-contaminated Kunigami-maji soil, the porous nature of the Ryukyu limestone and the surface was maintained as habitation area of oil solution bacteria. It was suggested that TPH removal performance improved as a result that purification speed was promoted by the activation of the solution microbe, increase in slight biomass, neutralization of the soil.
Slant shear tests and direct shear tests were conducted to determine shear bond strength between inorganic materials. Shear bond strength of bonded interface between mortar and polymer cement mortar (PCM) obtained by slant shear test increased with an increase in compressive strength of PCM, but friction angle didn't change. Since this trend is consistent with general properties of inorganic materials, slant shear test would be a valid method to determine shear bond strength. Shear strength of mortar obtained by direct shear test, which is simpler method than slant shear test, was similar with that calculated from the Mohr-Coulomb failure criterion using compressive and tensile strength. Also, bond property of bonded interface between mortars obtained by direct shear test was similar with that obtained by slant shear test. Therefore, it seems reasonable to conclude that, regarding determination of shear bond strength, direct shear test can be an alternative method to slant shear test.
The objective of this paper is to extend the conventional Darcy-Brinkman equations, which are applicable only to saturated porous region, to unsaturated region because the Darcy-Brinkman equations for the unsaturated region have not be proposed yet. The conventional equations are derived by spatially averaging the Navier-Stokes equations over the saturated domain. Similarly, the extension of the Darcy-Brinkman equations to the unsaturated domain is achieved by spatially averaging the Navier-Stokes equations over the partially saturated porous domain. The extended equations include the time-derivative of volumetric water content in the continuity equation and reveal that viscous and inertia terms and the term derived from the Darcy's law in the equation of motion reflect the characteristics of partial saturation of voids in porous media.
Removal techniques of heavy metals in contaminated soil are sometimes unfeasible because of high cost and/or low efficiency on a large scale, and thus the immobilization process of metals in soils using soil amendments has been gaining prominence as an alternative solution, which aims at suppressing uptake of toxic metals to crops. We focused on the potential of organic matter as an aid in heavy metal-immobilization, and assessed the availability of cow manure and methane fermentation digestive liquid (hereafter, CM and LM respectively) for establishment of safe farming by carrying out batch tests covering Cu, Cd and Pb. The results from the experiments showed that CM had high immobilization effect, especially for Cu, available forms decreased by approximately 90%. However, it was found that the immobilization effect on Cd was less than that on the others and that the mobility of Cd was enhanced under coexistence of other metals, which suggested that the immobilization manner in a dune sand was significantly different among metals as well as environmental conditions. Besides, although the availability of LM was lower than CM, the analysis of speciation indicated that LM also had the potential to reduce phytoavailability of metals.
Through examination of measures taken in the Great East Japan Earthquake and the Niigata Prefecture Chuetsu Earthquake, we discussed the necessity of planned systematic disaster recovery according to the disaster level, and proposed characteristics and composition that the plan should provide. In the agricultural rural development field, planning for disaster recovery is not currently made, but planning for large-scale disasters leads to speeding up and improving efficiency of restoration and reduction of work burden. The disaster recovery plan has the effect of (1) clarifying the recovery policy, (2) reducing the task right after the disaster, and (3) ensuring uniformity of restoration correspondence. Depending on the form of the damage, the afflicted area can be divided into individual damage zone, multi-unit damaged zone, areal damaged zone, and disaster levels are different depending on the combination. In this paper, we categorized disaster levels into three categories, and showed a systematic disaster recovery method for each level.
Members of land improvement districts (LIDs) that operate and maintain irrigation/drainage facilities polarize into large-scale agriculture management entities and small-scale farm households. In a general meeting for decision making of a LID, the present method for setting the number of voting rights, “one person one vote”, is advantageous for small-scale farm households because they occupy most of the seats in the LID. For that reason, large-scale agriculture management entities that cultivate most of the farmland in a LID, may be discouraged from fulfilling their duties because they have an inequity in decision making. Therefore, this study proposed and analyzed a new method “adding voting rights according to the area of farmland” with confirmation of the validity of the method using statistical data from a model LID. The following results were observed: (1) the number of voting rights for a member should be the sum of “one per member” and “a number obtained by sharing the subtotal of voting rights, which is equivalent to the number of total members, according to the area of his/her farmland”, and (2) when the new method is introduced, attention must be paid to the promotion of consensus building using workshop techniques within large-scale agriculture management entities before voting.
Fresh groundwater lenses develop on relatively large atoll islands and play a key role in providing stable freshwater supply. The Republic of the Marshall Islands in the Pacific Ocean sometimes suffer from drought caused by El Niño. About half of its population lives in the capital, Majuro, and securing freshwater resources for these people is a crucial issue. There is a fresh groundwater lens (Laura Lens) on Laura Island in Majuro Atoll. In this research, the current status of Laura Lens was investigated as up-coning that mixes seawater into fresh groundwater could render the fresh groundwater lens unusable. Electrical conductivities (ECs) of the groundwater at different depths in the monitoring wells were observed to determine the Laura Lens interface depths. ECs of groundwater surface at resident shallow wells were also observed to determine the planar Laura Lens interface. Locations of these interfaces, which have ECs equivalent to 200 mS/m, were calculated by interpolation. The Laura Lens storage volume from 2010 to 2013 was estimated by inputting the data into Surfer software. The results of groundwater observations showed that up-coning, similar to the one that occurred in 1998 which had resulted in serious drought, could still be observed. It was also found that the Laura Lens storage volume had decreased and that most of the fresh groundwater that seeped into Laura Lens had flowed out into the sea. Therefore, it is necessary to conserve and use the fresh groundwater lens.