Temporal dynamics of dissolved organic carbon (DOC) produced in a microcosm with red tide forming algae <Emphasis Type="Italic">Chattonella marina</Emphasis> and its associated bacteria     

Minoru Wada  Yukiko Takano  Saki Nagae  Yuka Ohtake  Yu Umezawa  Shinichi Nakamura  Makoto Yoshida  Yukihiko Matsuyama  Mitsunori Iwataki  Satoshi Takeshita  Tatsuya Oda 《Journal of Oceanography》2018,74(6):587-593

Acute and severe hypoxia associated with harmful algal bloom has become one of the major causes for the environmental deterioration of coastal areas. Although it is generally thought that a large part of the dissolved oxygen consumption at a bloom site is initiated by heterotrophic bacteria that attack organic matter derived from dead or dying algal cells, precise microbial processes leading to the hypoxia are yet to be examined. Here we show temporal dynamics of extracellular dissolved organic carbon (DOC) of the red tide forming raphidophyte Chattonella marina and bacterial populations associating with the algae under laboratory conditions. During the growth of non-axenic strains of C. marina, we monitored abundance of algae, associated bacteria, and DOC in the culture media. Bacterial cell abundance increased in response to the increase in DOC both at the beginning and the late log phase of the algal growth. Flow cytometric analysis revealed that transient increase in the percentage of respiratory-active bacterial cells also coincided with the timing of the increase in bacterial abundance and DOC. These results strongly suggest that DOC released from growing C. marina fuels respiration and growth of planktonic bacteria surrounding the algae. This has implications for the role of DOC released from C. marina bloom before the collapse in mediating interactions between neighboring algae and bacterial assemblage which may eventually lead to algal bloom-associated hypoxia.  相似文献   

Estimation of sub-annual inter-catchment groundwater flow using short-term water balance method     

Tomohiro Egusa  Tomoki Oda  Takanori Sato  Tomo'omi Kumagai 《水文研究》2021,35(9):e14368

Predicting inter-catchment groundwater flow (IGF) is essential because IGF greatly affects stream water discharge and water chemistry. However, methods for estimating sub-annual IGF and clarifying its mechanisms using minimal data are limited. Thus, we quantified the sub-annual IGF and elucidated its driving factors using the short-term water balance method (STWB) for three forest headwater catchments in Japan (named here catchment A, B and As). Our previous study using the chloride mass balance indicated that annual IGF of catchment A (49.0 ha) can be negligible. Therefore, we calculated the daily evapotranspiration (ET) rate using the Priestley–Taylor expression and the 5-year water balance in catchment A (2010–2014). The sub-annual IGF of the three catchments was then calculated by subtracting the ET rate from the difference between rainfall and stream discharge during the sub-annual water balance periods selected using the STWB. The IGF rates of catchment B (7.0 ha), which is adjacent to catchment A, were positive in most cases, indicating that more groundwater flowed out of the catchment than into it, and exhibited positive linear relationships with rainfall and stream discharge. This suggested that as the catchments became wetter, more groundwater flowed out of catchment B. Conversely, the IGF rates of catchment As (5.3 ha), included in catchment A, were negative in most cases, indicating that more groundwater flowed into the catchment than out from it, and exhibited negative linear relationships with rainfall and stream discharge. Given the topography of the catchments studied, infiltration into the bedrock was the probable reason for the IGF outflow from catchment B. We hypothesized that in catchment As, the discrepancy between the actual hydrological boundary and the surface topographic boundary could have caused an IGF inflow. This study provides a useful tool for determining an IGF model structure to be incorporated into rainfall-runoff models.  相似文献   

Topography of the Moho and Conrad discontinuities in the Kyushu district,Southwest Japan     

Hitoshi Oda  Takashi Ushio 《Journal of Seismology》2007,11(2):221-233

The first P-arrival time data from local earthquakes are inverted for two-dimensional variation of the depths to the Conrad and Moho discontinuities in the Kyushu district, southwest Japan. At the same time, earthquake hypocenters and station corrections are determined from the data. The depths to the discontinuities are estimated by minimizing the travel time residuals of first P-arrival phases for 608 earthquakes observed at 57 seismic stations. In the land area of Kyushu, the Conrad and Moho discontinuities are located within the depth ranges of 16–18 and 34–40 km, respectively. The Conrad discontinuity is not as largely undulated as the Moho discontinuity. The depth to the Moho is deep along the east coast of Kyushu, and the deepest Moho is closely related to markedly low velocity of P wave. We regard the deepest Moho as reflecting the Kyushu–Palau ridge subducting beneath the Kyushu district, together with the Philippine Sea slab. In western Kyushu, the shallow Moho is spreading in the north–northeast–south–southwest direction in the Okinawa trough region. Based on the presence of low-velocity anomaly in three-dimensional velocity structure and seismogenic stress field of shallow crustal earthquakes, the shallow Moho is interpreted as being due to lower crustal erosion associated with a small-scale mantle upwelling in the Okinawa trough region. The velocity discontinuity undulation basically has insignificant effect on hypocenter determination of the local earthquakes, but the Moho topography makes changes in focal depths of some upper mantle earthquakes. The depth variation of the Moho discontinuity has a good correlation with the Bouguer gravity anomaly map; i.e., the shallow Moho of western Kyushu and the deep Moho of eastern Kyushu closely correlate with the positive and negative Bouguer gravity anomalies, respectively.  相似文献   

Mathematical modeling of biologically mediated redox processes of iron and arsenic release in groundwater     

Abdur Razzak  Kenji Jinno  Yoshinari Hiroshiro  Md. Abdul Halim  Keita Oda 《Environmental Geology》2009,58(3):459-469

A one dimensional reactive transport model was developed in order to illustrate the biogeochemical behavior of arsenic and iron reduction and release to groundwater that accounts for the reaction coupling the major redox elements under reducing environment. Mass transport equation and the method of characteristics were used considering fundamental geochemical processes to simulate transport processes of different pollutants in mobile phase. The kinetic sub-model describes the heterotrophic metabolisms of several microorganisms. To model a complete redox sequence (aerobic or denitrifiers, Fe(III)-reduction, respiration bacteria of iron and arsenic compounds, and As(V) reduction) four functional bacterial groups (X ₁, X ₂, X ₃, and X ₄) were defined. Microbial growth was assumed to follow Monod type kinetics. The exchange between the different phases (mobile, bio, and matrix) was also considered in this approach. Results from a soil column experiment were used to verify the simulation results of the model. The model depicts the utilization of oxygen, nitrate, iron oxide and arsenic as electron acceptors for oxidation of organic carbon (OC) in a column. The OC as electron donor is one of the most important factors that affect the iron and arsenic reduction bacterial activity.  相似文献   

On statistical description of stress and fabric in granular materials     

M. M. Mehrabadi  S. Nemat-Nasser  M. Oda 《国际地质力学数值与分析法杂志》1982,6(1):95-108

The notion of overall macroscopic stress in granular masses is examined from a fundamental point of view by a statistical consideration of the contact forces that are transmitted by the contacting granules at the microscale. This examination leads in a natural way to relations between the macroscopic stress and the resulting granular fabric. The overall stresses are expressed in terms of the contact forces in two different but complementary ways: (1) by a statistical averaging over the sample volume of contact forces and “branches” which are vectors connecting the centroids of two contacting granules; and (2) by defining the overall tractions transmitted across an interior imagined plane as the sum of the contact forces which represent the mechanical effect of granules on one side of a unit area of this plane, upon those on the other side. Conditions under which the two representations of overall stresses are equivalent, are examined in detail. In addition, explicit results are given, which, define stresses in terms of the fabric and other microstructural characteristics of the granular mass.  相似文献   

Sea-level change and remagnetization of continental shelf sediments off New Jersey (ODP Leg 174A): magnetite and greigite diagenesis   总被引：1，自引：0，他引：1  

Hirokuni Oda  Masayuki Torii 《Geophysical Journal International》2004,156(3):443-458

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Correlation of cylindrical tank wall buckling with an earthquake motion recorded at a small distance from the tank     

George C. Manos  Heki Shibata  Tatsuya Shigeta 《地震工程与结构动力学》1989,18(2):169-184

The bulging observed on the wall of a ground supported cylindrical storage tank, located at the Chiba Experimental Station of the University of Tokyo, is investigated. This damage is correlated with a ground motion recording obtained very near the tank base during a moderately strong earthquake that occurred on September 25, 1980 not far from the Chiba Experimental Station. From this correlation the importance of the horizontal excitation in amplitude and direction is clearly established. In addition, good agreement can be seen between the predicted tank wall earthquake performance, derived by an empirical approach proposed by the first author, and the shell deformation observed at the Chiba Experimental Station.  相似文献   

Effect of occurrence rate of acoustic emissions on their statistical behavior     

Hitoshi Oda  Haruo Koami  Kiyoshi Seya 《Pure and Applied Geophysics》1989,130(1):5-29

The parameterm in Ishimoto-Iida's relation was investigated for acoustic emissions (AEs) occurring in rock samples under uniaxial compression. In the experiment, we found: 1) The large AEs are counted without serious error but the number of small AEs is systematically underestimated at high AE rates, 2) the frequency distribution of maximum AE amplitudes becomes nonlinear in logarithmic scale with increasing AE rate, and 3) there exists a strong negative correlation betweenm-value and AE rate. The miscount of small AEs was interpreted as due to overlap of the large and small AEs. We call the miscount masking effect. A statistical analysis based on the masking effect showed that them-value decreases more effectively as the AE rate increases, and thus the masking effect is a possible origin both for the nonlinear frequency distribution of maximum AE amplitudes and for the negative correlation ofm-value with AE rate. We emphasize that one should be careful of the masking effect to examine correctly the change, ofm-value. In order to eliminate the masking effect, AEs should be measured by a measurement system with low sensitivity. Even if the masking effect is eliminated, them-value decreases before the main fracture of a rock sample. Them-value is a key parameter to predict the main fracture.  相似文献   

Alteration of the equal settling ratio of fine particles by vertically-oscillating water     

Tatsuya Oki  Mikio Kobayashi  Shuji Owada  Daiki Matsuura 《International Journal of Mineral Processing》2007

An equal settling ratio is an important factor in estimating particle separation accuracy. However, this factor is often calculated using the settling velocity in stationary water, there are no examples of calculation of the equal settling ratio in an actual separator. This is difficult because particle movement in a separator is very complicated, and even simple periodic motions, such as the oscillation field used with many separators, are ignored in many cases. The authors have previously reported on the relation between the equal settling ratio and the oscillation frequency by analysis of particle movement in vertically oscillating water, using spherical particles of glass (average size 435 μm) and zirconia (202 μm) which have the same settling velocity in stationary water. In this study, the influence of particle diameter on the change in the settling velocity in oscillating water was experimentally investigated for three pairs of glass and zirconia particles having different sizes under 0.5 mm, which have the same settling velocity in stationary water. The settling velocities of different-sized particles decreased at different rates in oscillating water, indicating that the equal settling ratio is reduced by water oscillation. We conclude that water oscillation improves the accuracy of size separation for glass particles over 300 μm and zirconia particles over 150 μm when glass and zirconia particles are separated from each other with the difference of these settling velocities.  相似文献   

Steady flow approximations to the heliumR-process     

A. G. W. Cameron  J. J. Cowan  H. V. Klapdor  J. Metzinger  T. Oda  J. W. Truran 《Astrophysics and Space Science》1983,91(2):221-234

R-process yields for a helium layer have been calculated within a network of 6033 heavy nuclei using a steady flow approximation. The calculation of the neutron capture cross sections has been improved. The beta decay rates computed by Klapdor and his colleagues have been used in the calculation. We find that ther-process yield peaks near mass numbers 80 and 130 require a neutron number density of approximately 10²⁰ cm^?3 and a freezing time comparable to or less than 0.1 s. The peak near mass number 195 requires a neutron number density of about 10²¹ cm^?3 and a freezing time comparable to or less than about 0.01 s. The individual yield features of the steady flowr-process depend entirely upon the neutron capture cross sections of the nuclei along the flow path and the beta decay rates, which can shift the flow path and thereby introduce inappropriate capture cross sections into the determination of the yields.  相似文献