H11A-0287 INVITED 0800h
Soil Respiration Controls Ionic Nutrient Concentration In Percolating Water In Rice Fields
Soil water in the plow layer in rice fields contains various kinds of cations and anions, and they are lost from the plow layer by water percolation. Some portions of CO$_{2}$ produced by respirations of rice roots and soil microorganisms are also leached by water percolation to the subsoil layer as HCO$_{3}$$^{-}$. As the electrical neutrality of inorganic substances in percolating water is maintained when they are assumed to be in the form of simple cations and anions, soil respiration accelerates the leaching of ionic nutrients from the plow layer by water percolation. The proportion of inorganic carbon ($\Sigma$CO$_{2}$) originated from photosynthates in the total $\Sigma$CO$_{2}$ in soil solution in the plow layer was from 28 to 36 % in the rice straw amended soil and from 16 to 31 % in the soil without rice straw amendment in a soil pot experiment with rice plant after the maximum tillering stage. Most of $\Sigma$CO$_{2}$ in percolating water from the plow layer accumulates in the subsoil layer. Periodical measurement of $\Sigma$CO$_{2}$ in percolating water at 13 and 40 cm soil depths indicated that 10 % of total soil organic C in the plow layer was leached down from the plow layer (13 cm), and that about 90 % of it was retained in the subsoil layer to the depth of 40 cm. Water soluble organic materials are also leached from the plow layer by water percolation, and the leaching is accelerated by soil reduction. Soil reduction decreased the content of organic materials that were bound with ferric iron in soil (extractable by 0.1M Na$_{4}$P$_{2}$O$_{7}$ + NaBH$_{4}$) and increased the content of organic materials that were extractable by the neutral chelating solution (0.1M Na$_{4}$P$_{2}$O$_{7}$). In addition, water percolation transformed the latter organic materials to those that were extractable by water and a neutral salt. Considerable portions of organic materials in percolating water are adsorbed in the subsoil layer, and then partially decomposed and polymerized to specific soil organic materials in the subsoil. Organic materials that were leached from the plow layer by percolating water amounted to 170 kgC ha$^{-1}$ in a Japanese rice field, among which 120 kgC of organic materials were adsorbed in the subsoil layer between 13 and 40 cm depth.
H11A-0288 0800h
Influence of Soil Moisture on Microbial Activity in a Primary Acidification of Pyritic Soils
Soil moisture had a grate influence on soil acidification in pyritic soils. The acidification was occurred by chemical and bacterial processes of pyrite oxidation. It was reported that the bacterial oxidation was accelerated by soil moisture at near the condition of plastic limited. We investigated the accelerated soil moisture condition by matric potential and changes of bacterial activity using a soil taken from polder land of the Lake Nakaumi. Six levels of soil moisture conditions were prepared by drying. The samples were incubated at 30oC with keeping these moistures, and populations of Gram-positive and -negative bacteria (GPB and GNB) and Thiobacillus ferrooxidans (total, adsorbed and free forms) were determined. Soil acidification was accelerated at the moisture range from -6.0kPa to -35kPa while drying at 5.4g/h of evaporation rate. Samples drying at 12.0g/h ceased acidifying over -35kPa. On the other hand, a drop of pH value was accelerated at -35kPa when the samples was kept under their moisture conditions. The moisture condition seemed to be suitable for bacterial oxidation. The major bacteria under most of the moisture conditions were GPB, but T. ferrooxidans, one of GNB, was predominated at -35kPa. Under this moisture condition, the growth rate of T. ferrooxidans was highest and the population of GPB decreased during the exponential growth stage of T. ferrooxidans. Acidification of the soil seemed to be depending on proliferation of T. ferrooxidans not on the cell number of T. ferrooxidans. The growth rate of both absorbed and free forms of T. ferrooxidans was highest at -35kPa of all soil moisture conditions. The survival rate of T. ferrooxidans was highest at -3.5kPa and that of the free forms decreased at -35kPa. At -3,000kPa the absorbed forms of T. ferrooxidans had very small population and then decreased. The free forms were not detected. These data indicated that growth habitat of T. ferrooxidans were influenced by soil moisture. The accelerated moisture condition of -35kPa had a uniqueness on the bacterial populations and was suitable for proliferation of T. ferrooxidans. These results showed that high growth rate of T. ferrooxidans had a great influence on high rate of acidification in pyritic soils. The mechanism supposed to be that motility of the bacteria was influenced by shrinkage level of soil matrix and also that the environment was suitable for getting their energy to keep them alive.
H11A-0289 INVITED 0800h
Modeling of Bioclogging in Porous Media - Approaches and Uncertainties
The ability of microorganisms to reduce the hydraulic conductivity of porous media is known as biological clogging or bioclogging. Bioclogging has been observed in many environmental and engineered systems and has been the subject of numerous laboratory experiments. Results of these experiments show that the buildup of biomass due to microbial growth within the pores can reduce the hydraulic conductivity of a porous medium by several orders of magnitude. Thus, models simulating the movement of water and chemical species in a medium affected by bioclogging have to address this issue appropriately. For this reason, a number of modeling approaches have been developed, which couple the reduction of hydraulic conductivity with a reduction of porosity caused by microbial biomass growth. These approaches differ in terms of assumptions made on biomass composition, configuration, and distribution within the porous media. As a result, the predictions of these models regarding the clogging efficiency of biomass differ, too. Here, an evaluation of several of bioclogging models is presented. Model predictions are compared with experimental data and the sensitivity of model output towards internal parameters is tested. Results show that the clogging models can be described by a limited number physical parameters, of which values might be derived from experimental observations (e.g., residual hydraulic conductivities of clogged media). In contrast, the in-situ measurement of several properties of the clogging biomass is still a challenge, limiting accurate predictions of bioclogging. Biomass properties (e.g., the biomass density, the flow resistance of the biomass and the biomass distribution at the pore scale) hardly determined in clogging experiments, so far, have a major impact on model simulations.
H11A-0290 0800h
Flow Characteristics in Permeable Reactive Barrier Affected by Biological Clogging
Permeable reactive barriers (PRB) are becoming popular for the in situ remediation of contaminated groundwater. The efficiency of the PRB is affected by permeability of the reactive zone, because when permeability decreases contaminants can bypass the reactive zone without degraded. One of the factors affecting permeability of the permeable reactive zone is biological clogging of soil pore, i.e., biomass buildup and resultant decrease in hydraulic conductivity. So far biological clogging in laboratory was mostly observed in one-dimensional flow field, but the actual flow field in PRB is better simulated in two-dimensional flow field. The objective of this study is to observe the flow characteristics in PRB by using simulated flow cells in laboratory, by comparing one-dimensional and two-dimensional flow field. One-dimensional flow field was simulated by 20 cm length and 1 cm width flow cell, and two-dimensional flow field was simulated by 20 cm length and 10 cm width flow cell. Each flow cell was operated under water-saturated conditions, in horizontal position, and at a constant temperature of 20 degree centigrade. Glass beads of 0.1 mm mean diameter was packed uniformly in the flow cells and inoculum was injected into the nutrient injection ports at the middle of the flow cells. After 24 h incubation time continuous flow was started. Background flow of de-ionized water was supplied to the inlet ports, and the mineral medium was supplied from the nutrient injection ports. The flux was measured every day and local hydraulic head distribution was measured by water manometer, and hydraulic conductivity was calculated. The flow cell experiments were continued for 9 days. In one-dimensional flow cell, hydraulic conductivity of the nutrient supplied part decreased to about half of the initial value in 9 days flow period, where the hydraulic conductivity of the part where nutrient was not supplied remained constant. Bacterial and fungal number in the moderately clogged zone, where nutrient was supplied, increased in two orders of magnitude and the decrease in the hydraulic conductivity was associated with biomass buildup. In two-dimensional flow cell, biomass buildup of the nutrient supplied zone was also observed and moderately clogged biobarrier was formed. Unlike one-dimensional flow cell, where flux was kept uniform throughout the flow cell, the flux decreased at the biobarrier and the preferential flow between biobarriers was invoked. Flux at the preferential flow path was higher than average flux in the whole cell. This result suggests that biological clogging of PRB wells can cause changes in flow field pattern of contaminant plume, even if the extent of clogging is moderate.
H11A-0291 0800h
Phytoremediation of soils contaminated by cadmium
Phytoremediation is a technique to clean up soils contaminated with heavy metals. Advantages of this method are that (1) This technique is suitable to cleanup soils slightly contaminated with heavy metals in relatively wide area. (2) The expense for clean up is lower than civil engineering techniques. (3) This method can remove heavy metals fundamentally from contaminated. (4) The heavy metals are able to recycle by ashing of plants. Many researches have been done on the phytoremediation up to now, but almost all these researches were devoted to clarify the phytoremediation from the view point of plants themselves. However, few efforts have been devoted to analyze the migrations of heavy metals in soils during the phytoremediation process. The objective of this study is to clarify the features of Cd migration when plant roots are absorbing Cd from the ambient soils. Especially, we focused on finding the Cd migration pattern by changing the soil condition such as plant growing periods, planting densities, and the initial Cd concentration in soils. We planted sunflowers in columns filled with Cd contaminated soils because sunflower is a well-known hyperaccumulator of Cd from soils. By cutting the shoots of plants at the soil surface, and by keeping the plant roots in the soils without disturbance, the Cd concentrations, moisture contents, pH distributions, EC distributions, and dry weight of residual roots in the soils were carefully analyzed. The experimental results showed that (1)The growth of the planted sunflowers were suffered by applying of Cd. (2)The decrease of suction was affected by water uptake by roots at the depth from 0 to 5 cm. Water contents with plants in soils decrease more than without plants. (3)Cd adsorption by roots was predominant within 5cm from soil surface. In addition, it was also shown that there was an optimal Cd concentration where Cd is most effectively adsorbed by the plant. In this experiment we found that 40 to 60 mg kg-1 was the optimal concentration. By a trial calculation, it was revealed that more than 30 times of planting-cultivating processes were needed to decrease the Cd concentration from 9.75 to 0.4 mg Cd kg-1. When the sunflower was not planted, Cd did not move in the soils even when the soil water the sunflower was planted, Cd in the soil moved toward the plant roots associating with the water uptake by the roots. This Cd movement may have enhanced by the secretion of organic acid from plant roots.
H11A-0292 0800h
The Finite Size Lyapunov Exponent Applied to Modeled Bacterial Movement
The dispersion of microbes or other particles of interest can be characterized by the Finite Size Lyapunov Exponent. The microbial motion can be considered as a Levy motion. A combination of theoretical and numerical results on the Finite Size Lyapunov Exponent for Levy motions from a probabilistic definition of the FSLE will be presented. Microscale and macroscale results will be discussed.