Diurnal variations in streamflow and water quality during the summer dry season     

Daiji Kobayashi  Yuji Kodama  Yoshiyuki Ishii  Yumiko Tanaka  Keisuke Suzuki 《水文研究》1995,9(7):833-841

In a headwater basin covered with boreal forest in northern Japan, the summer dry flow was monitored each summer from 1985 to 1993. Streamflow and specific electrical conductance fluctuated diurnally and these variations were attributed to daytime evapotranspiration. In 1989, the daytime reduction in streamflow and conductance were accompanied by a reduction in the HCO^?₃ concentration. The low flow hydrograph was separated into two components using HCO^?₃ and Cl^? concentrations in August 1989, assuming low flow to be a mixture of delayed subsurface flow and of quick shallow flow. The slight diurnal variation in the ratio of shallow flow to subsurface flow caused the diurnal variation in conductance by changing the HCO^?₃ concentration.  相似文献   

Comparison of stable isotopes,ratios of Cl/Cl and I/I in brine and deep groundwater from the Pacific coastal region and the eastern margin of the Japan Sea     

Yasunori Mahara  Tomoko Ohta  Tomochika Tokunaga  Hiroyuki Matsuzaki  Eiji Nakata  Yuki Miyamoto  Yukihiro Mizuochi  Toshiharu Tashiro  Masahiro Ono  Toshifumi Igarashi  Keisuke Nagao 《Applied Geochemistry》2012

Fifty-three samples, including brines associated with oil and natural gas reservoirs and groundwater samples from deep boreholes, were collected from the Pacific and Japan Sea coastal regions in Japan. The ¹²⁹I/¹²⁷I and ³⁶Cl/Cl ratios, and stable isotopes (δD and δ¹⁸O) are compared to investigate differences related to the geotectonic settings of the two regions. The δD and δ¹⁸O data indicate that brine and groundwater from the Pacific coastal region reflect mixing of meteoric water with connate seawater in the pores of sedimentary rocks. On the other hand, brine and groundwater from the Japan Sea coastal region have been hydrothermally altered. In particular, brines associated with petroleum accumulations at Niigata and Akita showed the same isotopic characteristics as fluids found in the Kuroko deposits of the Green Tuff region in northeastern Japan. There is little difference in the ³⁶Cl/Cl ratios in brine and groundwater from the Pacific and Japan Sea coasts. Most brine and some deep groundwater, except those from the Pleistocene Kazusa Group, have already reached the average secular equilibrium ratio of 9.9 ± 2.7 × 10⁻¹⁵ for their mudstone and sandstone reservoirs. There was no correlation between the ³⁶Cl/Cl ratios and differences in geotectonic setting between the Pacific and the Japan Sea coast. The molar I/Br ratio suggests that the I in all of water samples was of biogenic origin. The average ¹²⁹I/¹²⁷I ratio was 290 ± 130 × 10⁻¹⁵ to 294 ± 105 × 10⁻¹⁵ in both regions, showing no relationship to the different geotectonic settings. The uncontaminated brine and groundwater samples are likely to have retained the original ¹²⁹I/¹²⁷I ratios of marine I released from the old organic matter stored in sedimentary rock.  相似文献   

Assessment of rainfall-induced shallow landslides in Phetchabun and Krabi provinces,Thailand     

Keisuke Ono  So Kazama  Chaiwat Ekkawatpanit 《Natural Hazards》2014,74(3):2089-2107

Shallow landslides are a common type of rainfall-induced landslide, and various methods are currently used to predict their occurrence on a regional scale. Physically based models, such as the shallow landslide instability prediction (SLIP) model, have many advantages because these models can assess the hazards of shallow landslides dynamically, based on physical stability equations that consider rainfall as a triggering factor. The main objective of this research is to test the SLIP model’s potential to predict shallow landslide hazards in Thailand. To achieve this goal, the SLIP model was applied to two massive landslide events in Thailand. The results predicted by the SLIP model for the two study areas are outlined, and the model prediction capabilities were evaluated using the receiver operating characteristic plot. The Phetchabun results showed that the western part of the catchment had the lowest factor of safety (F _S) value, whereas the Krabi results showed that the slopes surrounding the peak of Khao Panom Mountain had the lowest F _S value, explaining the highest potentials for shallow landslides in each area. The SLIP model showed good performance: The global accuracies were 0.828 for the Phetchabun area and 0.824 for the Krabi area. The SLIP model predicted the daily time-varying percentage of unstable areas over the analyzed periods. The SLIP model simulated a negligible percentage of unstable areas over all considered periods, except for expected dates, suggesting that the prediction capability is reasonably accurate.  相似文献   

Particle-tracking simulation for the drift/diffusion of spilled oils in the Sea of Okhotsk with a three-dimensional, high-resolution model     

Jun Ono  Kay I. Ohshima  Keisuke Uchimoto  Naoto Ebuchi  Humio Mitsudera  Hajime Yamaguchi 《Journal of Oceanography》2013,69(4):413-428

To conduct the simulation of oil spills in the Sea of Okhotsk, we developed a three-dimensional, high-resolution ocean circulation model. The model particularly improved the reproducibility of velocity field during the strong stratification period. Particle-tracking experiments with the effects of evaporation and biodegradation were performed using the combined data of daily ocean currents from the present model and the hourly diurnal tidal currents from the tidal model. The results are shown by the relative concentration of the particles averaged over the 8 years of 1998–2005 based on the ensemble forecast idea. For the case of particles released from the Sakhalin II oil field, the particles deployed in September–January are carried southward by the East Sakhalin Current, finally arriving at the Hokkaido coast, after 60–90 days. The particles deployed in March–August are diffused offshore by the synoptic wind drift, and hardly transported to regions south of Sakhalin. For the case of particles released from the region off Prigorodnoye, the oil export terminal, after the diffusion by the synoptic wind drift, a part of them are carried offshore of Hokkaido by the Soya Warm Current. The particles released in November–April flow out to the Japan Sea through the Soya Strait, mainly by the synoptic wind drift and secondly by the diffusion due to strong tidal currents around the Soya Strait. By considering the effects of evaporation and biodegradation, the relative concentration of the particles is considerably decreased before arriving at the Hokkaido coast, particularly in the case of drift from the Sakhalin II oil field.  相似文献   

81Kr‐Kr age and multiple cosmic‐ray exposure history of the Vaca Muerta mesosiderite     

Ken‐ichi BAJO  Keisuke NAGAO 《Meteoritics & planetary science》2011,46(4):556-573

Abstract– Noble gas isotopic compositions were measured for a eucritic pebble and bulk material of a silicate–metal mixture from the Vaca Muerta mesosiderite as well as pyroxene and plagioclase separated from the eucritic pebble by total melting and stepwise heating methods. Trapped noble gases were degassed completely by a high‐temperature thermal event, probably at the formation of the Vaca Muerta parent body (VMPB). The presence of fissiogenic Xe isotopes from extinct ²⁴⁴Pu in the bulk samples might be a result of rapid cooling from an early high‐temperature metamorphism. High concentrations of cosmogenic noble gases enabled us to determine precise isotopic ratios of cosmogenic Kr and Xe. Spallogenic Ne from Na and unique Ar isotopic compositions were observed. The ⁸¹Kr‐Kr exposure age of 168 ± 8 Myr for the silicate pebble is distinctly longer than the age of 139 ± 8 Myr for the bulk samples. The precursor of the pebble had been irradiated on the surface of the VMPB for more than 60 Myr (first stage irradiation), with subsequent incorporation into bulk materials approximately 4 Gyr ago. The Vaca Muerta meteorite was excavated from the VMPB 140 Myr ago (second stage irradiation). Relative diffusion rates among the cosmogenic Ar, Kr, and Xe based on data obtained by stepwise heating indicate that Kr and Xe can be partially retained in pyroxene and plagioclase under the condition that resets the K‐Ar system. This result supports the presence of fission Xe and of excess concentration of cosmogenic Kr, which could have survived the thermal event approximately 3.8 Gyr ago.  相似文献