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Ishimaru, Tsuneari; Niwa, Masakazu; Kurosawa, Hideki; Shimada, Koji
no journal, ,
It has been observed that hydrogen gas emissions from the subsurface along active faults exceed atmospheric concentrations. Experimental studies have shown that hydrogen gas is generated in a radical reaction of water with fractured silicate minerals due to rock fracturing caused by fault movement. Based on such research, we are investigating the applicability of a technique using hydrogen gas emissions from fracture zones. To start, we devised portable equipment for rapid and simple in situ measurement of hydrogen gas emissions. Then, we measured the hydrogen gas concentrations in emissions from major active faults and other geological features in Japan. As a result of the investigations, a tendency for high concentrations of hydrogen gas in active faults was recognized, in contrast with low hydrogen gas concentrations in emissions from geological features. It is inferred that the hydrogen gas migrates to ground surface along fractures associated with groundwater flow. Therefore, it is expected that by measurement of the hydrogen gas it will be possible to estimate hydraulic properties such as the continuity of groundwater pathways in fracture zones around a fault. Based on this understanding, we obtained multipoint hydrogen gas measurements across an exposed fault zone in the Atera Fault System, and provide a continuous cross-section from fault core to damage zone. The distribution of hydrogen gas emissions showed that large volumes of hydrogen gas emission occur where open fractures are significant and no emissions were observed in the central part of faults with abundant clay minerals. Using these simple methods, we have obtained data on the relative degree of permeability of the geological structures.
Yamamoto, Yuhei; Aosai, Daisuke; Mizuno, Takashi; Watanabe, Katsuaki*; Kogure, Toshihiro*; Suzuki, Yohei*
no journal, ,
no abstracts in English
Konno, Yuta*; Fukuda, Akari; Kozuka, Mariko*; Komatsu, Daisuke*; Tsunogai, Urumu*; Aosai, Daisuke; Mizuno, Takashi; Suzuki, Yohei*
no journal, ,
Our knowledge of biogeochemical processes mediated in those associated with freshwater should be integrated. We collected the groundwater samples from 200 m to 1150 m depths below ground level at Mizunami Underground Research Laboratory located in central Japan. We measured the concentration and both hydrogen and carbon isotopic compositions of dissolved methane, total inorganic carbon (TIC) and molecular hydrogen. The origin of methane could be speculated to be not biogenic CO
reduction or acetate fermentation but thermogenic or abiogenic. In contrast, C1/C2+C3 ratios supported biogenic methane production. The 300 m deep samples were enriched in hydrogen and acetate and depleted in sulfate, which is characteristic of acetogenesis. From these results, it is suggested that the production of acetate rather than methane could be dominant biogeochemical processes in the reducing portions of freshwater aquifers in granitic rocks.
Koarashi, Jun; Atarashi-Andoh, Mariko; Ishizuka, Shigehiro*; Kadono, Atsunobu*; Moriya, Koichi*; Nakanishi, Takahiro
no journal, ,
Accelerated release of carbon (C) previously stored in soils is considered one of the most important positive feedbacks from terrestrial ecosystems to the atmosphere in a future warmer world. We used 14C analysis following chemical fractionation to quantify the sizes and turnover times of C pools of Japanese forest soils. The 
C-based approach revealed higher variations of the family of MRTs soil by soil. The size of C pools that cycle slowly on timescales of 100-1000 years strongly correlated with the content of pyrophosphate-extractable Al. In contrast, faster-cycling C pools that turn over within decades showed a negative correlation with mean annual temperature at the sites. Our results suggest that C dynamics in the isolated SOC pools may be regulated by different mechanisms: temperature control on decadal cycling C versus mineralogy control on slower-cycling C, and clearly demonstrate that the forest soils will respond very differently to climate change over the next century.
Takemi, Tetsuya*; Nakayama, Hiromasa
no journal, ,
Atmospheric flows in urban areas are highly turbulent owing not only to meteorological disturbances but also to complex and complicated distribution of roughness obstacles (i.e., buildings). Numerical modeling is an important research for this purpose. In order to numerically examine flows over such highly rough urban surfaces, a large-eddy simulation (LES) approach is promising. In order to ensure the turbulent nature of flows in urban areas, an LES approach with a proper turbulence-generation technique is necessary. The present study proposes an approach to quantitatively simulate turbulent flows in a densely-built environment with the mixture of high-rise and low-rise buildings by coupling the WRF model and an LES model.