Geophysical monitoring and reactive transport modeling of ureolytically-driven calcium carbonate precipitation     

Wu Y  Ajo-Franklin JB  Spycher N  Hubbard SS  Zhang G  Williams KH  Taylor J  Fujita Y  Smith R 《Geochemical transactions》2011,12(1):7-20

Ureolytically-driven calcium carbonate precipitation is the basis for a promising in-situ remediation method for sequestration of divalent radionuclide and trace metal ions. It has also been proposed for use in geotechnical engineering for soil strengthening applications. Monitoring the occurrence, spatial distribution, and temporal evolution of calcium carbonate precipitation in the subsurface is critical for evaluating the performance of this technology and for developing the predictive models needed for engineering application. In this study, we conducted laboratory column experiments using natural sediment and groundwater to evaluate the utility of geophysical (complex resistivity and seismic) sensing methods, dynamic synchrotron x-ray computed tomography (micro-CT), and reactive transport modeling for tracking ureolytically-driven calcium carbonate precipitation processes under site relevant conditions. Reactive transport modeling with TOUGHREACT successfully simulated the changes of the major chemical components during urea hydrolysis. Even at the relatively low level of urea hydrolysis observed in the experiments, the simulations predicted an enhanced calcium carbonate precipitation rate that was 3-4 times greater than the baseline level. Reactive transport modeling results, geophysical monitoring data and micro-CT imaging correlated well with reaction processes validated by geochemical data. In particular, increases in ionic strength of the pore fluid during urea hydrolysis predicted by geochemical modeling were successfully captured by electrical conductivity measurements and confirmed by geochemical data. The low level of urea hydrolysis and calcium carbonate precipitation suggested by the model and geochemical data was corroborated by minor changes in seismic P-wave velocity measurements and micro-CT imaging; the latter provided direct evidence of sparsely distributed calcium carbonate precipitation. Ion exchange processes promoted through NH4+ production during urea hydrolysis were incorporated in the model and captured critical changes in the major metal species. The electrical phase increases were potentially due to ion exchange processes that modified charge structure at mineral/water interfaces. Our study revealed the potential of geophysical monitoring for geochemical changes during urea hydrolysis and the advantages of combining multiple approaches to understand complex biogeochemical processes in the subsurface.  相似文献   

Aeolian dust experiment on climate impact: An overview of Japan–China joint project ADEC   总被引：1，自引：1，他引：0  

M. Mikami  G.Y. Shi  I. Uno  S. Yabuki  Y. Iwasaka  M. Yasui  T. Aoki  T.Y. Tanaka  Y. Kurosaki  K. Masuda  A. Uchiyama  A. Matsuki  T. Sakai  T. Takemi  M. Nakawo  N. Seino  M. Ishizuka  S. Satake  K. Fujita  Y. Hara  K. Kai  S. Kanayama  M. Hayashi  M. Du  Y. Kanai  Y. Yamada  X.Y. Zhang  Z. Shen  H. Zhou  O. Abe  T. Nagai  Y. Tsutsumi  M. Chiba  J. Suzuki 《Global and Planetary Change》2006,52(1-4):142

The Aeolian Dust Experiment on Climate Impact (ADEC) was initiated in April 2000 as a joint five-year Japan–China project. The goal was to understand the impact of aeolian dust on climate via radiative forcing (RF). Field experiments and numerical simulations were conducted from the source regions in northwestern China to the downwind region in Japan in order to understand wind erosion processes temporal and spatial distribution of dust during their long-range transportation chemical, physical, and optical properties of dust and the direct effect of radiative forcing due to dust. For this, three intensive observation periods (IOP) were conducted from April 2002 to April 2004.The in situ and network observation results are summarized as follows: (1) In situ observations of the wind erosion process revealed that the vertical profile of moving sand has a clear size dependency with height and saltation flux and that threshold wind velocity is dependent on soil moisture. Results also demonstrated that saltation flux is strongly dependent on the parent soil size distribution of the desert surface. (2) Both lidar observations and model simulations revealed a multiple dust layer in East Asia. A numerical simulation of a chemical transport model, CFORS, illustrated the elevated dust layer from the Taklimakan Desert and the lower dust layer from the Gobi Desert. The global-scale dust model, MASINGAR, also simulated the dust layer in the middle to upper free troposphere in East Asia, which originated from North Africa and the Middle East during a dust storm in March 2003. Raman lidar observations at Tsukuba, Japan, found the ice cloud associated with the dust layer at an altitude of 6 to 9 km. Analysis from lidar and the radio-sonde observation suggested that the Asian dust acted as ice nuclei at the ice-saturated region. These results suggest the importance of dust's climate impact via the indirect effect of radiative forcing due to the activation of dust into ice nuclei. (3) Studies on the aerosol concentration indicated that size distributions of aerosols in downwind regions have bimodal peaks. One peak was in the submicron range and the other in the supermicron range. The main soluble components of the supermicron peak were Na⁺, Ca²⁺, NO₃⁻, and Cl⁻. In the downwind region in Japan, the dust, sea salt, and a mixture of the two were found to be dominant in coarse particles in the mixed boundary layer. (4) Observation of the optical properties of dust by sky-radiometer, particle shoot absorption photometer (PSAP), and Nephelometer indicated that unpolluted dust at source region has a weaker absorption than originally believed.A sensitivity experiment of direct RF by dust indicated that single scattering albedo is the most important of the optical properties of dust and that the sensitivity of instantaneous RF in the shortwave region at the top of the atmosphere to the refractive index strongly depends on surface albedo. A global scale dust model, MASINGAR, was used for evaluation of direct RF due to dust. The results indicated the global mean RF at the top and the bottom of the atmosphere were − 0.46 and − 2.13 W m^− 2 with cloud and were almost half of the RF with cloud-free condition.  相似文献   

Development of regional simulation of seismic ground‐motion and induced liquefaction enhanced by GPU computing     

Ryota Kusakabe  Kohei Fujita  Tsuyoshi Ichimura  Takuma Yamaguchi  Muneo Hori  Lalith Wijerathne 《地震工程与结构动力学》2021,50(1):197-213

Much research has been conducted for physics‐based ground‐motion simulation to reproduce seismic response of soil and structures precisely and to mitigate damages caused by earthquakes. We aimed at enabling physics‐based ground‐motion simulations of complex three‐dimensional (3D) models with multiple materials, such as a digital twin (high‐fidelity 3D model of the physical world that is constructed in cyberspace). To perform one case of such simulation requires high computational cost and it is necessary to perform a number of simulations for the estimation of parameters or consideration of the uncertainty of underground soil structure data. To overcome this problem, we proposed a fast simulation method using graphics processing unit computing that enables a simulation with small computational resources. We developed a finite‐element‐based method for large‐scale 3D seismic response analysis with small programming effort and high maintainability by using OpenACC, a directive‐based parallel programming model. A lower precision variable format was introduced to achieve further speeding up of the simulation. For an example usage of the developed method, we applied the developed method to soil liquefaction analysis and conducted two sets of simulations that compared the effect of countermeasures against soil liquefaction: grid‐form ground improvement to strengthen the earthquake resistance of existing houses and replacement of liquefiable backfill soil of river wharves for seismic reinforcement of the wharf structure. The developed method accelerates the simulation and enables us to quantitatively estimate the effect of countermeasures using the high‐fidelity 3D soil‐structure models on a small cluster of computers.  相似文献   

Effects of hypoxia on benthic organisms in Tokyo Bay, Japan: a review     

Kodama K  Horiguchi T 《Marine pollution bulletin》2011,63(5-12):215-220

Bottom hypoxia (dissolved oxygen concentration ≤2 ml l(-1)) from anthropogenic eutrophication is a growing global concern. Here, we summarized characteristics of hypoxia and its effects on benthic organisms in Tokyo Bay. Despite recent decreases in nutrient inputs, hypoxia has been increasing in duration and spatial extent, suggesting that the substantial loss of tidal flats from reclamation is contributing to a decrease in the ability of Tokyo Bay to recycle nutrients. Hypoxia develops in the central to northern part of the bay and persists from spring to autumn, causing defaunation of benthic organisms. After the abatement of hypoxia in autumn, the defaunated area is recolonized, either through migration or larval settlement. Some megabenthic species with a spawning peak in spring and summer experience failure of larval settlement, which is probably due to hypoxia. The adverse effects of hypoxia are an impediment to recovery of benthic organisms in Tokyo Bay.  相似文献   

Resource Development and the Perpetuation of Poverty in Rural Laos     

Yayoi Fujita Lagerqvist  Laura Woollacott  Avakat Phasouysaingam  Southida Souliyavong 《The Australian geographer》2014,45(3):407-417

ABSTRACT

Government efforts to industrialise and modernise the Lao economy through intensive resource development are having adverse effects on rural livelihoods as resources are degraded and access to limited land and natural resources has intensified. In one of the country's key river basins, Nam Ngum, a series of resource developments including hydropower, mining and agricultural plantations have modified the landscape over the last four decades. Uncoordinated resource developments are putting intense pressure on increasingly scarce natural resources and affecting the lives of people who are dependent on them. Economic diversification of rural households in Feuang District in the Nam Ngum River Basin has created significant discrepancies between the rich and the poor, yet all households remain primarily dependent on agriculture. Land is of enduring importance to rural livelihoods. National development intervention has failed to secure basic livelihoods for rural households.  相似文献   

Flexible Livelihoods in a Complex World: Asian lives and economies in transition     

Yayoi Fujita Lagerqvist 《The Australian geographer》2014,45(3):261-268

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Magma discharge variations during the 2011 eruptions of Shinmoe-dake volcano, Japan, revealed by geodetic and satellite observations     

Tomofumi Kozono  Hideki Ueda  Taku Ozawa  Takehiro Koyaguchi  Eisuke Fujita  Akihiko Tomiya  Yujiro J Suzuki 《Bulletin of Volcanology》2013,75(3):1-13

We present precise geodetic and satellite observation-based estimations of the erupted volume and discharge rate of magma during the 2011 eruptions of Kirishima-Shinmoe-dake volcano, Japan. During these events, the type and intensity of eruption drastically changed within a week, with three major sub-Plinian eruptions on January 26 and 27, and a continuous lava extrusion from January 29 to 31. In response to each eruptive event, borehole-type tiltmeters detected deflation of a magma chamber caused by migration of magma to the surface. These measurements enabled us to estimate the geodetic volume change in the magma chamber caused by each eruptive event. Erupted volumes and discharge rates were constrained during lava extrusion using synthetic aperture radar satellite imaging of lava accumulation inside the summit crater. Combining the geodetic volume change and the volume of lava extrusion enabled the determination of the erupted volume and discharge rate during each sub-Plinian event. These precise estimates provide important information about magma storage conditions in magma chambers and eruption column dynamics, and indicate that the Shinmoe-dake eruptions occurred in a critical state between explosive and effusive eruption.  相似文献   

Revisiting ocean thermal energy conversion   总被引：1，自引：0，他引：1  

Rod Fujita  Alexander C. Markham 《Marine Policy》2012,36(2):463-465

Increasing concerns regarding oil spills, air pollution, and climate change associated with fossil fuel use have increased the urgency of the search for renewable, clean sources of energy. This assessment describes the potential of Ocean Thermal Energy Conversion (OTEC) to produce not only clean energy but also potable water, refrigeration, and aquaculture products. Higher oil prices and recent technical advances have improved the economic and technical viability of OTEC, perhaps making this technology more attractive and feasible than in the past. Relatively high capital costs associated with OTEC may require the integration of energy, food, and water production security in small island developing states (SIDSs) to improve cost-effectiveness. Successful implementation of OTEC at scale will require the application of insights and analytical methods from economics, technology, materials engineering, marine ecology, and other disciplines as well as a subsidized demonstration plant to provide operational data at near-commercial scales.  相似文献   

Mathematical modeling of biologically mediated redox processes of iron and arsenic release in groundwater     

Abdur Razzak  Kenji Jinno  Yoshinari Hiroshiro  Md. Abdul Halim  Keita Oda 《Environmental Geology》2009,58(3):459-469

A one dimensional reactive transport model was developed in order to illustrate the biogeochemical behavior of arsenic and iron reduction and release to groundwater that accounts for the reaction coupling the major redox elements under reducing environment. Mass transport equation and the method of characteristics were used considering fundamental geochemical processes to simulate transport processes of different pollutants in mobile phase. The kinetic sub-model describes the heterotrophic metabolisms of several microorganisms. To model a complete redox sequence (aerobic or denitrifiers, Fe(III)-reduction, respiration bacteria of iron and arsenic compounds, and As(V) reduction) four functional bacterial groups (X ₁, X ₂, X ₃, and X ₄) were defined. Microbial growth was assumed to follow Monod type kinetics. The exchange between the different phases (mobile, bio, and matrix) was also considered in this approach. Results from a soil column experiment were used to verify the simulation results of the model. The model depicts the utilization of oxygen, nitrate, iron oxide and arsenic as electron acceptors for oxidation of organic carbon (OC) in a column. The OC as electron donor is one of the most important factors that affect the iron and arsenic reduction bacterial activity.  相似文献   

Horizontal displacements in Japan     

Naomi Fujita 《Tectonophysics》1974,23(4):419-422

Recent horizontal displacements in Japan are discussed by using the results of the first-order triangulation surveys. Large horizontal displacements are found in East Hokkaido, Tohoku, South Kanto, Tokai and Nankai districts (Fig.1). Crustal activity in these districts is also briefly discussed. The original triangulation survey in Japan neglected Laplace (azimuth) observations and consequently rotation and divergence around the assumed fixed point often appear as horizontal displacements. This is especially true in the central Japan where horizontal displacements result from cancelling the apparent rotation and divergence around the assumed fixed point (Fig.2).On the other hand, strain measurements avoid such shortcoming. Considering with the results of the first triangulation, the horizontal earth-strain can be calculated for every subsequent triangulation net. It is interesting that the velocity of the maximum shear strain is almost 2–3 · 10^/t7/year throughout Japan (Fig.3), even though the seismic activities show large regional discrepancies.  相似文献