Numerical simulation of groundwater flow for a coastal plain in Japan: data collection and model calibration   总被引：1，自引：0，他引：1  

Bin He  Keiji Takase  Yi Wang 《Environmental Geology》2008,55(8):1745-1753

Using a three-dimensional finite element model, this study characterizes groundwater flow in a costal plain of the Seto Inland Sea, Japan. The model characterization involved taking field data describing the aquifer system and translating this information into input variables that the model code uses to solve governing equations of flow. Geological geometry and the number of aquifers have been analyzed based on a large amount of geological, hydrogeological and topographical data. Results of study demonstrate a high correlation between the ground surface elevation and the groundwater level in the shallow coastal aquifer. For calibrating the numerical groundwater model, the groundwater flow was simulated in steady state. In addition, the groundwater level and trend in the transient state has also been elucidated. The numerical result provides excellent visual representations of groundwater flow, presenting resource managers and decision makers with a clear understanding of the nature of the types of groundwater flow pathways. Results build a base for further analysis under different future scenarios.  相似文献   

Quaternary changes in delivery and accumulation of organic matter in sediments of Lake Biwa, Japan     

Philip A. Meyers  Keiji Takemura 《Journal of Paleolimnology》1997,18(3):211-218

A 911-m-long sediment core from Lake Biwa, Japan, provides a record of organic matter delivery and accumulation in this large lake during a succession of tectonic and climatic changes dating back to the latest Pliocene. Sediments deposited since 430 ky are profundal; older sediments vary in setting between shallow-water and fluviodeltaic conditions, with occasional deep-water intervals. C/N ratios identify algal production as the dominant source of organic matter throughout the core, although the proportion of land-derived contributions episodically increases in the fluviodeltaic and shallow-water sediments. Rates of organic matter delivery and burial in lake sediments change in response to glacial-interglacial climate changes over the past 430 ky. Sediments deposited during interglacial intervals have organic carbon mass accumulation rates up to 9 times greater than those from glacial intervals, reflecting interglacial climates that were wetter than glacial climates. Algal production of organic matter increased during interglacial times because of greater wash-in of soil nutrients, and organic matter preservation was enhanced because of faster sedimentation rates.  相似文献   

Numerical study for specifying the major origin of low salinity water associated with <Emphasis Type="Italic">Chattonella</Emphasis> (Raphidophyceae) blooms in Tachibana Bay,Japan     

Kazuhiro?AokiEmail author  Manabu?Shimizu  Hiroshi?Kuroda  Toshifumi?Yamatogi  Naoya?Ishida  Shigeru?Kitahara  Keiji?Hirano 《Journal of Oceanography》2016,72(5):811-816

In both 2009 and 2010, massive Chattonella blooms occurred in Tachibana Bay. Observation results show that high cell densities of Chattonella were distributed in the central area of Tachibana Bay with low salinity water. Model results indicate that the low salinity water originated from the Ariake Sea and intruded into Tachibana Bay during the northerly or weak winds. It is suggested that low salinity water was mainly discharged from the northern area of the Ariake Sea. Northerly wind enhanced the horizontal advection of the low salinity water intruding into Tachibana Bay originating from the northern area of the Ariake Sea.  相似文献   

Distribution of nano-phytoplankton including fragile flagellates in the subtropical northwestern Philippine Sea     

Takashi Tsuji  Rokuro Adachi 《Journal of Oceanography》1979,35(3-4):173-178

Distribution of nano-phytoplankton was studied during May–June 1971 in the subtropical northwestern Philippine Sea. Plankton samples were collected at various depths between 0 and 200 m. A gentle gravity filtration technique was employed to concentrate the samples. They were then examined without fixation under a microscope. The average cell number of total nano-phytoplankton was 1×10⁴2×10⁴/l, and nano-flagellate cell number often accounted for more than 90% of the total cell number of nano-phytoplankton, consisting mainly ofGymnodinium lacustre, Amphidinium sp., and unidentified small nano-flagellates. The distribution of nano-phytoplankton did not correlate with vertical profiles of chlorophylla.  相似文献   

N2 fixation variability in the oligotrophic Sulu Sea, western equatorial Pacific region over the past 83 kyr     

Keiji Horikawa  Masao Minagawa  Yoshihisa Kato  Masafumi Murayama  Seiya Nagao 《Journal of Oceanography》2006,62(4):427-439

N₂ fixation is an important biological process that adds new nitrogen to oceans and plays a key role in modulating the oceanic nitrate inventory. However, it is not known how, when, and where N₂ fixation rates have varied in response to past climate changes. This study presents a new record of nitrogen isotopic composition (δ¹⁵N) over the last 83 kyr from a sediment core (KH02-4 SUP8) taken in the Sulu Sea in the western equatorial Pacific region; data allow the N₂ fixation variability in the sea to be reconstructed. Sediments, sinking, and suspended particulate organic matter (POM) all have lighter isotopic values compared to the δ¹⁵N values of substrate nitrate (av. 5.8‰) in North Pacific Intermediate Water. These lighter δ¹⁵N values are regarded as reflecting N₂ fixation in the Sulu Sea surface water. A δ¹⁵N mass balance model shows that N₂ fixation rates were significantly enhanced during 54–34 kyr in MIS-3 and MIS-2. It has been speculated that higher interglacial denitrification rates in the Arabian Sea and the eastern tropical Pacific would have markedly decreased the global oceanic N inventory and contributed to the increase in N₂ fixation in oligotrophic regions, but such a model was not revealed by our study. It is possible that changes in N₂ fixation rates in the Sulu Sea were regional response, and accumulation of phosphate in the surface waters due to enhanced monsoon-driven mixing is thought to have stimulated enhancements of N₂ fixation during MIS-3 and MIS-2.  相似文献   

The identification, counting, and measurement of phytoplankton by an image-processing system     

Ishii  T.; Adachi  R.; Omori  M.; Shimizu  U.; Irie  H. 《ICES Journal of Marine Science》1987,43(3):253-260

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Tributyltin and triphenyltin induce spermatogenesis in ovary of female abalone,Haliotis gigantea   总被引：1，自引：0，他引：1  

Horiguchi T  Kojima M  Kaya M  Matsuo T  Shiraishi H  Morita M  Adachi Y 《Marine environmental research》2002,54(3-5):679-684

Two-month flow-through exposure experiments of tributyltin (TBT) and triphenyltin (TPhT) were conducted with abalone, Haliotis gigantea. Nominal concentrations of 100 ng TBT/l and 100 ng TPhT/l caused significant spermatogenesis in ovaries of exposed females. There were also significantly more contracted primary oocytes observed in females exposed to either TBT or TPhT than controls. The incidence of two types of unknown cells was also significant in females exposed to TPhT. No significant histological changes were observed in testis of exposed males. This ovarian spermatogenesis caused by TBT and/or TPhT resembles gastropod imposex. Remarkably high concentrations of TBT and TPhT were observed in the head (including central nervous system ganglia), compared to muscles concentrations. Accumulation of TBT and TPhT in the head may disturb reproductive hormonal regulators through neuropeptides released from ganglia. This, as well as possible aromatase inhibition, may be one of the inducers for spermatogenesis in the abalone ovaries.  相似文献   

Recovery of surface albedo and plant cover after wildfire in a Picea mariana forest in interior Alaska   总被引：1，自引：0，他引：1  

Shiro Tsuyuzaki  Keiji Kushida  Yuji Kodama 《Climatic change》2009,93(3-4):517-525

Albedo influences vegetation structure, permafrost thawing, etc., in particular, after wildfires in Picea mariana forests in Alaska, USA, while albedo changes with plant succession. To understand interactions between albedo and ecosystem recovery after wildfire, surface albedo was measured in the spring and summer of 2005 at Poker Flat, interior Alaska, where P. mariana forest was dominant. The ground surface was mostly covered with Sphagnum moss before the 2004 wildfire, and was variously burned by the fire. The measured wavelengths ranged from 0.3 to 3.0 μm. We measured four independent variables, incidence, plant cover on the forest floor, cover of burned ground surface, canopy openness and incidence, to examine the determinants on surface albedo. Multiple regression analysis showed that total plant cover positively and mostly determines albedo, indicating that plant recovery is prerequisite to return high albedo. When the ground surface was damaged by fire, changes in albedo were mostly derived from decrease in reflectance wavelengths between 0.7 and 1.4 μm. The fluctuations of reflectance wavelengths did not differ greatly between damaged-moss and burned surfaces. We must mention the dynamics of Sphagnum to understand various environmental changes including surface albedo.  相似文献   

The degree of Cl-loss for the particulate matter (PM) and fog water sampled at the same air mass at the Hachimantai mountain range in northern Japan     

Ryoei Kikuchi  Makoto Takada  Keita Hifumi  Keiji Yoshimura  Toru Ozeki  Takashi Kimoto  Masahiro Kajikawa  Nobuaki Ogawa   《Atmospheric Research》2009,94(3):501-509

It is well known that sea-salt aerosols in particulate matter (PM) react with acids such as H₂SO₄ and HNO₃ during transportation and thereby lose chloride ions (Cl-loss). The PM and fog were sampled concurrently at different altitudes in the Hachimantai mountain range, northern Japan. The PM and fog sampled at different altitudes had nearly identical properties for the ion components. However, the PM was in a Cl-depleted state (more than 80% of all samples), but the fog water was not in so Cl-depleted state (less than 29%). As a result, it could be explained that this phenomenon caused because the fog droplets took up the gaseous state HCl other than sea-salt PM. After all Cl^- in the fog water recovered and was rather rich compared with the sea-salt or the PM by the uptake of the gaseous state HCl. Moreover, it was found that for PM_coarse(2.5 < D < 10), 86% of the acid (H₂SO₄ and HNO₃) was consumed for Cl-loss reactions and/or for dissolution of Ca and Mg in soil particles.  相似文献   

The operation and performance of Earthquake Early Warnings by the Japan Meteorological Agency     

Keiji Doi 《Soil Dynamics and Earthquake Engineering》2011

The Japan Meteorological Agency commenced an Earthquake Early Warning (EEW) provision service in August 2006 to advanced users and in October 2007 to the Japanese public. By the end of 2009, EEWs had been issued to advanced users for more than 2100 earthquakes and to the public for 11 earthquakes. Nearly 80% of seismic intensity predictions were accurate within ±1 intensity unit on JMA’s Seismic Intensity Scale. The Iwate-Miyagi Nairiku Earthquake in 2008 demonstrated the efficiency of EEWs in many places. However, there were other cases where the warnings were not issued in time for strong tremors. Further technical development is needed for both earthquake source parameter estimation and seismic intensity prediction. Public education in regard to the technical limitations and accuracy of EEWs as well as actions to take in response to such warnings are also indispensable.  相似文献