Present environment of Dam Lake Sambe,southwestern Japan: a geochemical study of bottom sediments     

Mst. Hawa Bibi  Faruque Ahmed  Hiroaki Ishiga  Takashi Asaeda  Takeshi Fujino 《Environmental Earth Sciences》2010,60(3):655-670

Geochemical analyses of lakebed and core sediments from Lake Sambe on the outskirts of Oda City in Shimane prefecture in southwestern Japan were carried out in order to assess the water quality and the concentration and distribution patterns of sixteen elements. The lake water showed a stratified condition with respect to dissolved O₂, and As, Fe, and Mn concentrations in the bottom layers which increased in the summer. The chemical composition of the sediments, as measured by X-ray fluorescence, included major and trace elements (P, Ca, Sc, Ti, V, Cr, Fe, Ni, Cu, Zn, As, Sr, Zr, Pb, and Th), and total sulfur (TS). Elevated values of As, Zn, V, Fe, P, and TS were present in several layers of the upper cores (from 0 to 5 cm) and other surface sediments. Increases in the abundances of these metals in lake sediments are probably related to the reducing condition of the sediments, fine-grained organic rich sediments, and post-depositional diagenetic remobilization. Moreover, correlations between the concentrations of trace metals and iron in the sediments suggest their adsorption onto Fe (oxy)hydroxides, whereas correlations with sulfur indicate that they were precipitated as Fe-sulfides. The average abundances of As, Pb, Zn, and Cu exceeded the lowest effect level and Interim Sediment Quality Guideline values that the New York State Department of Environmental Conservation and the Canadian Council of Ministers of the Environment determined to have moderate impact on aquatic organisms. In addition, concentrations of As and Zn exceeded the Coastal Ocean Sediment Database threshold value, indicating potentially toxic levels. Therefore, the presence of trace metals in the lake sediments may result in adverse effects on biota health.  相似文献   

Thermochronology for the Granitic Pluton Related to Lead-Zinc Mineralization in Tsushima, Japan     

Hiroaki IKEMI  Nobutaka SHIMADA  Hitoshi CHIBA 《Resource Geology》2001,51(3):229-238

Abstract: K–Ar datings and oxygen isotope analyses revealed a cooling history of the Uchiyama granitic pluton, which is genetically related to the Pb-Zn deposits (Taishu mine) in the Tsushima Islands, Japan. The pluton intrudes into the Paleogene Taishu Group to form the biotite-hornfels zone, while the Taishu vein-type Pb–Zn deposits occur in fissures developed in the non-hornfels zone about 1 to 3 km westward from the contact. Amphibole and biotite K-Ar ages of the pluton have a wide range from 19 to 13 Ma. Oxygen isotopes of the biotite and coexisting quartz grains indicate that isotopic exchange reactions have occurred under subsolidus conditions, and that the K-Ar ages are affected by various cooling rates in the pluton. The mineralization age of the Taishu ore deposits is obtained for the first time to be 15.40.8 Ma by a K-Ar age of 2 M ₁–muscovite in a calcite–quartz–muscovite–chlorite veinlet of the Shintomi orebody. Whole rock K-Ar ages of biotite-hornfels near the pluton represent similar ages to the ore deposits. Using blocking temperature calculated from reported diffusivity for argon, the pluton was cooled from 560 to 350C in the period of 17 to 14 Ma. The vein formation took place after the time when temperature in wall rocks of the pluton had dropped below the brittle-plastic transition (about 400C). These results imply that the cooling of the pluton has caused injection of magmatic fluids into meteoric hydrothermal systems, and the Pb-Zn mineralization has occurred due to this mixing at the age of about 15 Ma.  相似文献   

Distribution of arsenic and other trace elements in the Holocene sediments of the Meghna River Delta, Bangladesh     

M. Hawa Bibi  Faruque Ahmed  Hiroaki Ishiga 《Environmental Geology》2006,50(8):1243-1253

Geochemical study of the Holocene sediments of the Meghna River Delta, Chandpur, Bangladesh was conducted to investigate the distribution of arsenic and related trace and major elements. The work carried out includes analyses of core sediments and provenance study by rare earth element (REE) analysis. Results showed that the cores pass downward from silty clays and clays into fine to medium sands. The uppermost 3 m of the core sediments are oxidized [average oxidation reduction potential (ORP) + 230 mV], and the ORP values gradually become negative with depths (−45 to −170 mV), indicating anoxic conditions prevail in the Meghna sediments. The REE patterns of all lithotypes in the study areas are similar and are comparable to the average upper continental crust. Arsenic and other trace elements (Pb, Zn, Cu, Ni, and Cr) have greater concentrations in the silts and clays compared to those in the sands. Positive correlation between As and Fe was found in the sediments, indicating As may be adsorbed on Fe oxides in aquifer sediments.  相似文献   

Speciation of Chromium in Artificially Contaminated Soil Reference Material GSJ JSO-2 Using XANES and Chemical Extraction Methods     

Hiroshi Tsuno  Atsuyuki Ohta  Hiroyuki Kagi  Noboru Imai  Hiroaki Tao  Masaharu Nomura 《Geostandards and Geoanalytical Research》2006,30(1):55-62

The oxidation states of chromium in GSJ JSO-2 (artificially contaminated soil) and three other geochemical reference materials (GSJ JSO-1, JLS-1 and JMS-1) were observed using X-ray near edge structure (XANES). For comparison, other artificially contaminated soil materials (mimic-JSO-2) were prepared by adding Cr(VI) into JSO-1. Their oxidation states of chromium were determined using XANES. The chromium contents were 1118 μg g^-1 for JSO-2, 1352 μg g^-1 for mimic-JSO-2 and 69-113 μg g^-1 for the other reference materials. Most chromium was present as hexavalent in mimic-JSO-2. No hexavalent species were detected in other samples. These results for chromium oxidation state in JSO-2 and mimic-JSO-2 obtained with XANES resembled those obtained from a chemical extraction method. The present JSO-2 has no trace of Cr(VI), although Cr(VI) was added as a major species during preparation. On the other hand, the content of Cr(VI) obtained in mimic-JSO-2 agreed with the original Cr(VI) content. A time-elapse study showed that Cr(VI) contents in mimic-JSO-2 decreased gradually to 70% of the original abundance during 240-day preservation in dry conditions. Moreover, the abundance of Cr(VI) decreased markedly to 15% after 240 days in the wet mimic-JSO-2 containing 20% m/m of water. These experiments suggested that soil humidity enhanced the reduction of Cr(VI) and that Cr(VI) was reduced even in dry conditions. Consequently, it is reasonable to infer that Cr(VI) doped into JSO-2 was completely reduced to Cr(III) during the preservation period of 5 years. The certification of the long-term stability of the chemical form in reference materials will be much more important in future.  相似文献   

Ore value-tonnage diagrams for resource assessment   总被引：4，自引：0，他引：4  

Tetsuya Shoji  Hiroaki Kaneda 《Natural Resources Research》1998,7(1):25-36

An ore value-tonnage diagram has been proposed for assessing mineral resources. Diagrams of W+Mo, and Pb+Zn deposits show a good linearity between ore value and logarithms of cumulative ore tonnage. Diagrams of the massive sulfide, orthomagmatic, placer, porphyry, replacement, and stratabound types are also linear. It is assumed, therefore, that deposits of each of these commodities and these types belong to a single population. In contrast, the ore value-tonnage relations of all the deposits analyzed here is approximated by the combination of two exponential functions. The same feature is seen for deposits of the Cu+W+Mo, Cu+Pb+Zn, and Au+Ag commodities, and of the vein and unconformity-related types. This suggests that deposits belonging to each of such categories are divided into the high and low value groups. We can expect, accordingly, to find high value deposits of such categories.  相似文献   

Rapid change in nitrate and sulfate concentrations observed in early stage of precipitation and their deposition processes     

Hiroaki Minoura  Yasunobu Iwasaka 《Journal of Atmospheric Chemistry》1996,24(1):39-55

The concentrations of H⁺, nitrate (NO₃ ^-), and sulfate (SO₄ ^2-) in rainwater and their temporal changes were analyzed on the basis of continuous observation from 1 July 1991 to 30 June 1992 at a suburb of Nagoya, Japan. The yearly average for pH was 4.4. In general, an increasing pH with increase in precipitation amount was observed for rain events. Relatively high pH rainwater was sometimes observed at the beginning of rainfall, even though high concentrations of NO₃ ^- and SO₄ ^2- were involved. The high pH values were considered to be caused by the neutralization process with particulate matter containing cations. The yearly averaged ratio of equivalent concentration of nitrate to sulfate (N/S) in rainwater was 0.58. In the early stage of rain, the N/S value was usually more than 1.0 due to the difference of scavenging process between NO₃ ^- and SO₄ ^2-. High values of N/S ranging from 5 to 10 were found under the atmospheric conditions of calm winds and low humidity, during which it is possible that atmospheric particles float for a long time in the air before a rain event. The adsorption of NO₃ ^- in the early stage of rainfall by particulate matter was suggested from the difference in scavenging processes of NO₃ ^- and SO₄ ^2-. A possible scavenging process, called limb cloud scavenging, is presented to explain the interaction of particles and nitrate ions at the early stage of rain. In limb cloud scavenging, the repeated migration of cloud particles or raindrops between the inside and outside of clouds increases the absorption of ions to a highly condensed level, thus increasing the N/S value of rainwater. The influence of global scale seasonal phenomena with large amounts of particulates, such as typhoons or Asian dust storms, was also studied.  相似文献   

Impact of fish net pen culture on the benthic environment of a cove in South Japan     

Hiroaki Tsutsumi 《Estuaries and Coasts》1995,18(1):108-115

Over the past three decades, fish net pen culture has been developed in the coastal waters of Japan. However, serious organic pollution of the surrounding water and sediment followed the development of this new style of fishery. This paper reports a typical example of the environmental disturbance that has occurred due to the organic pollution resulting from fish net pen culture. Since fish cultivation was initiated in 1973, oxygen depletion of the bottom water and extremely reducing conditions within the sediment have occurred during the summer. These environmental disturbances resulted in unusual dynamics of the benthic communities including defaunation in the summer and recolonization of the azoic areas from autumn to the next spring. Significant changes in the benthic fauna were observed between benthic communities before and after organic pollution of the sediment. Molluscs were originally the most dominant benthic fauna. As organic pollution of the bottom sediment progressed, the molluscs were replaced by polychaetes. Likewise, total biomass of the benthic fauna decreased markedly over the past two decades. Prior to contamination, the organic matter deposited on the sediment was decomposed by the action of bacteria, ciliates, meiofauna, and macrofauna. The addition of organic material resulting from fish culture has overwhelmed these decomposition mechanisms, and conditions have worsened as organic matter is continuously added to the sediment. Contamination of marine sediment by the net pen cultivation of fish sets up a vicious cycle: the addition of exogenous sources of organic material increases the need for a more vigorous decomposition process while actually creating conditions that limit the rate of the necessary decomposition activity. The sustainable development of fish net pen culture will require the creation of a new technology that efficiently promotes the decomposition of organic matter deposited below the pen nets.  相似文献   

Inland penetration of the sea breeze over the suburban area of Tokyo     

Hiroshi Yoshikado  Hiroaki Kondo 《Boundary-Layer Meteorology》1989,48(4):389-407

Observational results of the structure of the sea breeze over the urban and suburban areas of Tokyo for four summer days are presented.On two of these days, the inland penetration of the sea breeze front could be clearly traced. In one case, the sea breeze was first observed along the shores of Tokyo Bay around 0900 JST, and propagated in three hours through the Tokyo City area, the width of which is about 20 km. It then advanced inland at a rate of 16 km h^–1. Prior to the arrival of the sea breeze at the suburban site, the mixing height had remained at about 600 m for four hours. With the arrival of the sea breeze front, accompanied by an abrupt change in wind speed and direction, the mixing height increased sharply to 1700 m. It is suggested that this behavior and the structure of the front are intensified due to the urban effect, or the difference in the thermal characteristics between the urban and rural areas.On the days without a sea breeze front, the land breeze system during the early morning was less intense, allowing the sea breeze to develop simultaneously with the inland valley wind and easily form a large-scale local wind system during the morning hours. In both cases, the vertical motion accompanying the local wind system works as a feedback mechanism to control the local winds by modifying the thermal and pressure fields.  相似文献   

新疆北部富蕴县沙尔布拉克玻安岩的地球化学特征及构造意义   总被引：19，自引：1，他引：19  

张海祥  牛贺才  于学元  Hiroaki Sato  Junichi Ito  单强 《地球化学》2003,32(2):155-160

详细的地球化学研究表明，新疆北部富蕴县沙尔布拉克中泥盆统北塔山组的辉石安山岩具有中等的SiO2含量（52.13%-60.45%)；高MgO(3.91%-9.31%)和相容元素（包括Ni、Cr、Co等）含量，以及高Mg^#和Al2O3／TiO2比值；低TiO2含量（0.21%-0.35%)；同时具有U型稀土元素分布模式；并强烈亏损高场强元素。这些特征均与玻安岩的地球化学特征一致，应属于玻安岩，形成于前弧环境。沙尔布拉克玻安岩的存在表明，古亚洲洋在早－中泥盆世向南发生了洋壳俯冲作用。  相似文献   

Correlation study between suspended particulate matter and DOAS data   总被引：2，自引：2，他引：0  

司福祺  刘建国  谢晶华  张玉钧  刘文清 《大气科学进展》2006,23(3):461-467

Continuous data of aerosol optical thickness monitored using differential optical absorption spectroscopy (DOAS) are correlated with the concentration of ground-measured suspended particulate matter (SPM). A high correlation is found between the DOAS and the ground SPM data, making it possible to calculate the mass extinction efficiency of the aerosols in the atmosphere. It is found that the value of mean mass extinction efficiency (MEE) varies over a range of 2.6–13.7m2 g?1, with smaller and larger values occurring for size distributions dominated by coarse and fine particles, respectively.  相似文献