Influences of channelization on discharge of suspended sediment and wetland vegetation in Kushiro Marsh, northern Japan

The effects of wetlands on hydrology, water quality, and wildlife habitat are internationally recognized. Protecting the remaining wetlands is one of the most important environmental issues in many countries. However wetlands in Japan have been gradually shrinking due to agricultural development and urbanization, which generally lowers the groundwater level and introduces suspended sediment and sediment-associated nutrients into wetlands. We examined the influences of channelization on discharge of suspended sediment and wetland vegetation in Hokkaido, northern Japan. The impact of river channelization was confirmed not only by the sediment budgets but also by river aggradation or degradation after the channelization and by the resultant vegetational changes. The budgets of suspended sediment demonstrated that wash load was the predominant component accounting for 95% of the total suspended load delivered into the wetland. This suspended sediment was primarily transported into the wetland by flooding associated with heavy rainfall. Twenty-three percent of the wash load and 63% of the suspended bed material load were deposited in the channelized reach, which produced aggradation of about 2 m at the end of the reach. A shorting of the length of the channel, due to channelization of a meandering river, steepened the slope and enhanced the stream power to transport sediment. This steepening shifted the depositional zones of fine sediment 5 km downstream and aggraded the riverbed. Development of the watershed may increase not only the water discharge but also the amount of suspended sediments. The aggradation reduced the carrying capacity of the channel and caused sediment ladened water to flood over the wetlands. The fine sediment accumulated on the wetlands gradually altered the edaphic conditions and wetland vegetation. A low percentage (10 to 15%) of organic contents of wetlands' soil is more evidence indicating that the present condition is far different from normal. Original vegetation such as sedges and Alnus japonica were disappearing from the adjacent areas of the river channel and were being replaced by willow trees (Salix spp.).     

High thallium content in Kuroko-type ore

Tl, Ga and Ge contents of Kuroko and other types of ore deposits were analysed semiquantitatively and quantitatively. The results show that Tl content is extremely high in Kuroko-type deposits compared to other types of mineralization. The T1 content is especially high in yellow ore and pyrite crystals; thus this element is considered to be incorporated in pyrite.     

Case study of debris flow disaster scenario caused by torrential rain on Kiyomizu-dera,Kyoto, Japan - using Hyper KANAKO system

This paper presents debris-flow numerical simulations using the Hyper KANAKO system, developed by the authors. The system uses the debris flow simulator KANAKO 2D equipped with a graphical user interface (GUI); hence, a user can easily produce appropriate landform data for simulations using standard laser profiler data, and visualize the results using a GIS. Hyper KANAKO was applied to the streams around Kiyomizu-dera in Kyoto, Japan. Kiyomizu-dera is a famous temple in Japan which is visited by numerous tourists throughout the year. We simulated a disaster scenario of debris flow caused by torrential rain. We set the hydrograph using rainfall intensity data, and set the landform data using information from the Geospatial Information Authority of Japan (GSI) and a digital elevation model (DEM). We evaluated different mesh sizes and also used a digital surface model (DSM) to consider the building heights. The simulation results showed that with small mesh size, the debris flow moved through the roads, which seems realistic for a disaster situation. When buildings were considered, the flow direction changed, and a 1-m flow depth, which was deeper than in other cases, appeared in the flow path. This may pose a dangerous situation for evacuations.     

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

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.     

Bifurcation of barotropic flow and homogenization of potential vorticity in a rotating laboratory model

Laboratory experiments with a rotating tank confirm the bifurcation character of a barotropic flow driven by an inflow and an outflow described by Sakai (1986). The model, a circular basin with a topographic β-effect, simulates a mid-latitude oceanic feature. At a low Rossby number, stationary Rossby waves are observed which are symmetrical with a line connecting the inlet and the outlet. As the Rossby number increases, a bifurcation occurs and two kinds of vortex flows are observed. In the vortex, potential vorticity is almost uniform. In addition to the two vortex flows, a jet-like inertial flow can also be observed. In general, thre results of these experiments agree well with those of a low-order model and a numerical model.     

Optical,biological, and chemical properties ofAoshio,hypoxic milky blue-green water,observed at the head of Tokyo Bay

Aoshio-hypoxic water which can be distinguished from surrounding coastal water by its milky blue-green color-is often observed at the head of Tokyo Bay when coastal upwelling of sulfidic bottom water occurs during summer and early autumn. Optical properties and the biological-chemical composition of suspended matter in theaoshio water were investigated using nearby “normal” coastal water as a reference. Suspended matter in theaoshio water contributed to the large beam-attenuation coefficient and also to the strong upward radiance with maximal intensity around 550 nm as a result of the scattering process. No significant difference in bacterial density was observed between samples ofaoshio water and reference coastal water. The low chlorophylls concentration inaoshio water samples indicates that biological pigments may not play a dominant role in the color of theaoshio events. The suspended particles inaoshio water samples had much higher contents of sulfur and manganese and a lower silicon content than those in reference coastal water samples. The colloidal elemental sulfur and manganese-rich particles identified in theaoshio water appear to be oxidation products of dissolved sulfide and manganese (II) in the anoxic water. On the basis of these findings, it may be concluded that there is a high probability that elemental sulfur and manganese-rich particles are responsible for the color and turbidity inaoshio.     

Study on the oceanic environments relating to the marine living resources

This is a review of the study on the oceanic environments relating to the marine living resources carried out since 1947, during more than 35 years which are the period of the authors oceanographic research life for fisheries. Its content consists of describing the outlines of, (1) the oceanographic study of the Subarctic Region of the Northwestern Pacific as the salmon living waters, (2) the study on dilution processes of the effluent in the coastal waters in relation to marine pollution, (3) the oceanographic study on transportation and diffusion of fish eggs and larvae in relation to the recruitment of living resources and (4) the study on forecasting of the fisheries and oceanographic conditions, and a short note on direction of fisheries oceanography expected to be studied in the future.     

Study on the chemical forms of radionuclides in seawater—I

The stability constants for sulfate, chloride and hydroxide ions with cerium (III) in the solution at ionic strength of 0.67 have been determined by cation exchange method, the values of ₁ and ₂ for sulfate complexes of cerium being 40±13 and 453±140, respectively and those for chloride complexes being 1.28±0.23 and 0.56±0.076, respectively. The values of ₁, ₂ and ₃ for hydroxide complexes of cerium were (4.5±0.9)×10⁷, (3.3±0.7)×10¹⁴ and (1.8±0.7)×10²³, respectively.Using the above constants the ratios of individual chemical species of¹⁴⁴Ce were calculated in a solution at ionic strength of 0.67 containing sulfate and chloride ions approximately the same as in seawater of 35 %. The result of calculation indicates that the dominant species of¹⁴⁴Ce in this solution is Ce(OH)₃ ⁰ at pH 8.