Contamination level of mercury in red meat products from cetaceans available from South Korea markets     

Endo T  Yong-Un M  Baker CS  Funahashi N  Lavery S  Dalebout ML  Lukoschek V  Haraguchi K 《Marine pollution bulletin》2007,54(6):669-677

Levels of total mercury (T-Hg) were surveyed in red meat (n=73) and liver (n=3) from toothed whales, dolphins and porpoises (odontocetes) sold for human consumption in the coastal cities of South Korea. High concentrations of T-Hg were found in the liver products of finless porpoises (18.7 and 156 microg/wet g) and common dolphins (13.2 microg/wet g). The T-Hg concentrations in red meat products were highest in the false killer whale (9.66+/-12.3 microg/wet g, n=9), bottlenose dolphin (10.6+/-12.6 microg/wet g, n=3) and killer whale (13.3 microg/wet g, n=1), and lowest in Cuvier's beaked whale and the harbour porpoise (0.4-0.5 microg/wet g). Thus, most of the products that originated from odontocetes exceeded the safety limit of 0.5 microg/wet g for T-Hg set by the South Korean health authorities for the fishery industry. Pregnant women and other vulnerable sectors of the population living in South Korea should therefore limit their consumption of odontocete products.  相似文献   

Decrease in anthropogenic nutrients and its effect on the C/N/P molar ratio of suspended particulate matter in hypertrophic Dokai Bay (Japan) in summer     

Kenichiro Hamada  Naoko Ueda  Machiko Yamada  Kuninao Tada  Shigeru Montani 《Journal of Oceanography》2012,68(1):173-182

Biologically important nutrient concentrations in Dokai Bay have declined as a result of reductions in anthropogenic inputs of total nitrogen and total phosphorus. A decrease in nutrient concentrations affects phytoplankton growth, thereby changing the biochemical characteristics of autochthonous particulate matter. We therefore investigated changes in the C/N/P molar ratio of suspended particulate matter (SPM) in the summer, when phytoplankton growth is vigorous, before environmental quality standards (EQSs) were attained (1995–1998) and afterward (2006–2009). We found that the ratio of particulate organic nitrogen (PON) to particulate phosphorus (PP) changed in conjunction with changes in the ratio of dissolved inorganic nitrogen to dissolved inorganic phosphorus (DIP) that resulted from reductions in nutrient loading. Furthermore, we suggest that because the DIP concentration in seawater was high before EQSs were attained, inorganic phosphorus was possibly adsorbed onto SPM. After the attainment of EQSs, however, the DIP concentration fell, and PON/PP was high. Phosphorus limitation of phytoplankton growth in the mouth of the bay may explain the high PON/PP ratios after EQS attainment.  相似文献   

Sources of uncertainty in estimating stream solute export from headwater catchments at three sites          下载免费PDF全文

Ruth D. Yanai  Naoko Tokuchi  John L. Campbell  Mark B. Green  Eiji Matsuzaki  Stephanie N. Laseter  Cindi L. Brown  Amey S. Bailey  Pilar Lyons  Carrie R. Levine  Donald C. Buso  Gene E. Likens  Jennifer D. Knoepp  Keitaro Fukushima 《水文研究》2015,29(7):1793-1805

Uncertainty in the estimation of hydrologic export of solutes has never been fully evaluated at the scale of a small‐watershed ecosystem. We used data from the Gomadansan Experimental Forest, Japan, Hubbard Brook Experimental Forest, USA, and Coweeta Hydrologic Laboratory, USA, to evaluate many sources of uncertainty, including the precision and accuracy of measurements, selection of models, and spatial and temporal variation. Uncertainty in the analysis of stream chemistry samples was generally small but could be large in relative terms for solutes near detection limits, as is common for ammonium and phosphate in forested catchments. Instantaneous flow deviated from the theoretical curve relating height to discharge by up to 10% at Hubbard Brook, but the resulting corrections to the theoretical curve generally amounted to <0.5% of annual flows. Calibrations were limited to low flows; uncertainties at high flows were not evaluated because of the difficulties in performing calibrations during events. However, high flows likely contribute more uncertainty to annual flows because of the greater volume of water that is exported during these events. Uncertainty in catchment area was as much as 5%, based on a comparison of digital elevation maps with ground surveys. Three different interpolation methods are used at the three sites to combine periodic chemistry samples with streamflow to calculate fluxes. The three methods differed by <5% in annual export calculations for calcium, but up to 12% for nitrate exports, when applied to a stream at Hubbard Brook for 1997–2008; nitrate has higher weekly variation at this site. Natural variation was larger than most other sources of uncertainty. Specifically, coefficients of variation across streams or across years, within site, for runoff and weighted annual concentrations of calcium, magnesium, potassium, sodium, sulphate, chloride, and silicate ranged from 5 to 50% and were even higher for nitrate. Uncertainty analysis can be used to guide efforts to improve confidence in estimated stream fluxes and also to optimize design of monitoring programmes. © 2014 The Authors. Hydrological Processes published John Wiley & Sons, Ltd.  相似文献   

Effects of temporal dynamics and vertical structure of the seagrass Zostera caulescens on distribution and recruitment of the epifaunal encrusting bryozoa Microporella trigonellata     

Naoko Kouchi  Masahiro Nakaoka  & Hiroshi Mukai 《Marine Ecology》2006,27(2):145-153

Seagrass is an ephemeral habitat for epifaunal sessile invertebrates attaching on seagrass leaves, and spatial and temporal dynamics of seagrasses strongly affect the distribution of epifauna. Zostera caulescens Miki, a seagrass species endemic to Japan, provides a complex habitat for epifauna with two types of shoots: vegetative, less than 1 m tall, and flowering, 5–7 m tall. We conducted monthly field observations and a manipulative field experiment to investigate the effects of the seagrass vertical structure and its temporal variation on the distribution and recruitment of the encrusting bryozoan Microporella trigonellata. The density of M. trigonellata on the leaves of flowering shoots, located at the seagrass canopy, varied temporally, reaching maximum in summer and minimum in winter. In contrast, M. trigonellata density on the leaves of vegetative shoots near the sea floor was consistently low throughout the study period. Early recruit bryozoans also showed this temporal and vertical variation in density; thus spatial and temporal variation in recruitment determined the distribution of the whole colonies. The field experiment revealed that the recruitment rate of M. trigonellata was significantly higher at the higher position of the water column (3 m above the sea floor) than at the lower position (0.5 m) in June. However, the recruitment rate was higher at the lower position in October when most of the flowering shoots started falling down. The temporal change in bryozoan habitat selection is considered to be adaptive to maintain their population on the seagrass leaves that show complex temporal dynamics.  相似文献   

Dynamics of microphytobenthic biomass in a coastal area of western Seto Inland Sea, Japan   总被引：2，自引：0，他引：2  

Hitomi Yamaguchi  Shigeru Montani  Hiroaki Tsutsumi  Ken-ichiro Hamada  Naoko Ueda  Kuninao Tada 《Estuarine, Coastal and Shelf Science》2007,75(4):423-432

This study focused on the causes of the variation in microphytobenthic biomass and the effects of this variation on macrobenthic animals in the western Seto Inland Sea, Japan, where the importance of microphytobenthos as the primary food source for benthic animals has been recently reported. We investigated the microphytobenthic biomass together with light attenuation of seawater, phytoplanktonic biomass, macrobenthic density and biomass at eight stations (water depth = 5–15 m) during four cruises in 1999–2000. The increased light attenuation coefficient of the water column associated with increased concentration of the phytoplanktonic Chl-a caused a decrease in light flux that reached the seafloor. The biomass of the microphytobenthos within the upper 1 cm of the sediment, 1.9–46.5 mg Chl-a m⁻², was inversely correlated with the phytoplanktonic biomass in the overlying water column, 10.9–65.0 mg Chl-a m⁻². Thus, interception of light by phytoplankton is considered to be a main cause of the variation in the microphytobenthic biomass. The microphytobenthos biomass showed a significant positive correlation with the macrobenthic density (78–9369 ind. m⁻²) and biomass (0.4–78.8 gWW m⁻²). It appears that the increase in oxygen production by the microphytobenthos allowed macrobenthic animals to become more abundant, as a consequence of oxygenation of the organically enriched muddy sediments (14.5 ± 2.69 mg TOC g⁻¹). This study suggests that the variation in the microphytobenthic biomass is influenced by the phytoplanktonic biomass due to shading effect, and the balance between these two functional groups might affect the variability in the macrobenthic density and biomass.  相似文献   

A review of fossil rhinoceroses from the Neogene of Myanmar with description of new specimens from the Irrawaddy Sediments   总被引：1，自引：0，他引：1  

Zin-Maung-Maung-Thein  Masanaru Takai  Takehisa Tsubamoto  Naoko Egi  Thaung-Htike  Takeshi Nishimura  Maung-Maung  Zaw-Win 《Journal of Asian Earth Sciences》2010,37(2):11

Four genera and one indeterminate genus (total eight species) of fossil rhinoceroses (Mammalia; Perissodactyla; Rhinocerotidae) are recognized from the Neogene of central Myanmar. In the early Miocene, most area of central Myanmar were under the shallow marine condition, and no rhinocerotid remain has been documented yet. During the middle to late Miocene, the rhinocerotid remains are commonly found and are represented by “Diceratherium” naricum, Brachypotherium perimense, Brachypotherium fatehjangense and an indeterminate rhinocerotid. In the latest Miocene, these archaic rhinoceroses became extinct. In the late Neogene, the extant genera, Rhinoceros (late Miocene to Pleistocene) and Dicerorhinus (Plio-Pleistocene) first appeared in Myanmar. They appear to have dispersed to the Island Southeast Asia from the continental Asia during the early Pleistocene to middle Pleistocene when the eustatic sea level became low remarkably.  相似文献   

Factors controlling the acid‐neutralizing capacity of Japanese cedar forest watersheds in stands of various ages and topographic characteristics     

Keitaro Fukushima  Naoko Tokuchi 《水文研究》2009,23(2):259-271

Acid‐neutralizing capacity (ANC) is an important index for streamwater acidification caused by external factors (i.e. chronic acid deposition) and internal factors such as soil acidification due to nitrification. In this study, the influence of forest clear‐cutting and subsequent regrowth on internal acidification was investigated in central Japan, where stream pH (near 7·0) and ANC (above 0·1 meq L^?1) are high. pH, the concentrations of major cations (Na⁺, K⁺, Mg²⁺ and Ca²⁺), major anions (NO₃^?, Cl^? and SO₄^2?) and dissolved silica (Si), and ANC were measured in 33 watersheds of various stand ages, during 2002 to 2004. Only NO₃^? concentration decreased with stand age, whereas pH, ANC, and concentrations of the sum of base cations (BC) and Si were negatively correlated with the minimum elevation of the watershed. The correlation between the BC/Si ratio and minimum elevation suggested that factors contributing to acid neutralization changed at 1100 m above sea level. In watersheds at lower elevations (?1100 m), the relatively high contribution of soil water with longer soil contact times should result in higher ANC, and cation exchange reactions should be the dominant process for acid neutralization due to deposition of colluvial soils on the lower slope. In contrast, in higher‐elevation watersheds (≥1100 m), weathered residual soils are thin and the small contribution of deeper groundwater results in lower ANC. These results suggest that the local acid sensitivity is determined by the hydrological and geomorphologic factors generated by steep topography. Copyright © 2008 John Wiley & Sons, Ltd.  相似文献   

Long-term variability of the low-luminosity active galactic nucleus of M81     

Naoko Iyomoto  Kazuo Makishima 《Monthly notices of the Royal Astronomical Society》2001,321(4):767-775

Long-term X-ray variability of the low-luminosity active galactic nucleus of M81 was studied, using 16 ASCA observations spanning 5.5 yr. The object exhibits a factor of 3 variation over the 5.5 yr. The source intensity was relatively constant within each observation which lasted typically for one day, but intra-day variability by 30 per cent was detected on the 15th observation. The power-spectral density (PSD) was estimated in a 'forward' manner, over a frequency range of 10^−8.2–10^−4.3 Hz (period range of 0.25 d–5.5 yr), by utilizing the structure function and extensive Monte Carlo simulations in order to overcome the very sparse and uneven data samplings. When the PSD is assumed to be white below a 'break frequency' f _b and falls off as ∝  f ^{− α} above f _b, where f is frequency and α is a positive parameter, the M81 light curve is well described with 1/ f _b≥800 d and α =1.4±0.2.  相似文献   

An experimental study on the burrowing activity of river crabs on subsurface water movement and piping erosion     

Yuichi Onda  Naoko Itakura 《Geomorphology》1997,20(3-4)

The effects of the burrowing activity of river crabs on subsurface water movement and piping erosion were studied through a flume experiment. Cohesive field soil was used and constant fluvial head was applied. During the experiments with river crabs, burrows were excavated downwards under the groundwater level. At the outlet of each burrow, the crabs excavated pellets of soil and stacked them in piles, in the form of cone mounds. These mounds acted as effective dams for subsurface outflow, but they sometimes collapsed. The roofs of the burrows also caved in occasionally, whereby the crabs would excavate new burrows. The burrowing activity of the crabs led to marked erosion. In contrast, no marked erosion was observed in experiments without crabs, indicating that piping erosion occurs through the assistance of burrowing activity. It was observed that burrowing activity and piping erosion was pronounced when the hydraulic head was not significantly high (0.21–0.25). Analysis of the potential distribution of the soil mass indicated that the head loss close to the burrow was small in the case of experiments with crabs. This suggests that the burrow enhances rapid discharge of subsurface water. Consequently, burrowing activity was found to play an important role in piping erosion and rapid discharge of subsurface water.  相似文献   

Has the plate boundary shifted from central Hokkaido to the eastern part of the Sea of Japan?     

Naoko Kato  Hiroshi Sato  Masayuki Orito  Kazuomi Hirakawa  Yasutaka Ikeda  Tanio Ito   《Tectonophysics》2004,388(1-4):75

A NS trending Cenozoic fold-and-thrust belt has developed in the western part of the Hidaka Collision Zone (HCZ), central Hokkaido, Japan. A quantitative estimation of the late Cenozoic convergence rate at the front of the Hidaka thrust system is important in revealing the plate tectonic framework around northern Japan. High-resolution seismic reflection profiling across the active fault-related folds was carried out to ascertain the temporal change in the crustal shortening rate. Overlapping ramp anticlines and growth folds within thrust sheets were examined using balanced cross-sections combined with industry seismic and drilling data. The rate of shortening was examined using a 3.5 Ma horizon and late Quaternary horizons at 115 and 41 ka. These horizons show that the convergence rate of the Hidaka thrust system has not decreased during the last 3.5 Ma. This suggests that the plate boundary between the Eurasian (Amurian) and North American (Okhotsk) plates has not jumped from the central part of Hokkaido to the eastern part of the Sea of Japan since 3.5 Ma and that a significant amount of plate convergence is still being absorbed in the Hidaka Collision Zone.  相似文献