The use of steelmaking slag as a material is being advanced as a means of improving the marine environment in coastal waters. Recently, mixing steelmaking slag with dredged material has been developed for restoring tidal flat estuaries. In this study, the control of microalgae outgrowth from dredged material by steelmaking slag was examined in a batch experiment and mesocosm experiment. The dredged material in artificial seawater showed both the release of nutrients (PO4-P, D-Inorganic N, D-Si) and the outgrowth of planktonic microalgae. Also, it was found that the predominant species of planktonic microalgae in the artificial seawater was Haptophyta, Coccolithophorids. On the other hand, when steelmaking slag was added to the dredged material, the hardness of the resulting mixture increased, and the outgrowth of microalgae from the dredged material was inhibited. The mechanism for this is follows. The application of steelmaking slag to the dredged material improved the hardness of the dredged material by forming calcium-silicate-hydrooxide (CSH), which strongly affected the microalgae outgrowth from the dredged material.
Hypoxia extending over the bottom water every year during summer involves Ohmura Bay in a serious environmental issue. Rise and fall of the hypoxic water mass was simulated with a 3D numerical eco-hydrodynamic model in order to investigate the relation with the influencing factors. The result shows that increased stratification during July-September induces and develops hypoxia in the bottom layer from June to mid-August by limiting vertical transport of oxygen. The benthic hypoxia reaches the highest stage in mid-August, then begins to decline gradually afterwards but lasts until early October. The recovery process of oxygen turned out to be closely related with change in the pathway of oceanic water intrusion into the central basin. After September, the oceanic water with rich oxygen begins to flow directly into the central basin, contributing toward alleviation of the hypoxia. Episodic wind event enhances vertical mixing and destroys the bottom hypoxic water quickly but only intermittently: hypoxia comes back and covers the seabed again immediately after the wind ceases. It is only a strong northerly wind caused by a tropical storm in the early stage of October that leads it to a termination every year.
Dissolution of silica from glass bottle sometimes influences accuracy of precision analysis of sea water, e.g. density and pH. We assessed and developed inside-coated glass vials to avoid dissolution of silica from glass at least < 1 mM for seawater sample storage. Seawater storage experiments using specially-treated vials available commercially (sulfur treatment, coating with fluoloresin or inorganic-organic hybrid material or silicone) suggests that dissolution of silica decreases by up to 60–70% related to that in uncoated glass vial at 25–40°C. As a result of storage experiments using test product of thick fluororesin coated vials, we found that dissolution of silica from glass can be avoided by repeating coating process (application and calcination) at least 10 times. We made trial products of thick fluororesin coated vials by this coating process. The results of seawater storage experiments showed that this newly developed vials can avoid dissolution of silica from glass surface at least 163 days at 25–40°C.
Battery has been one of the constraints for monitoring longer-term movement and behavior of aquatic animals using an animal-borne micro data logger. To overcome the limitation of the fixed energy in bio-logging systems, a prototype of data logger system using a vibration-powered generator was developed, and the feasibility of utilizing the oscillation energy of aquatic animals as external sources of the power was investigated. The system was composed of a vibration-powered generator and data logger part incorporating 3-axis acceleration, pressure, and temperature sensors, and these were connected via a 5 m bending resistance cable. The system can initiate sensor measurements and writing to the memory alternately when enough voltage (5 V) is charged in a capacitor in the data logger part. The generator was attached to the peduncle of the fish simultaneously with another small data logger measuring the acceleration of caudal fin movement reflected to the generator, and then the fish was released in a tank. While the fish actively swam in the experimental tank (general frequency and amplitude of the caudal fin movement in steady swimming: 1.76 Hz and 0.32 g, respectively), it was impossible to initiate the sensor measurements because there was not enough electricity charged in the capacitor. However, the voltage in the capacitor, which was manually charged to 4 V before the experiment, decreased more slowly in the data from the fish experiment than the data from the control experiment without the vibration-powered generator. This suggested that it was succeeded in producing the electricity from the fish movement while the electricity discharge rate in the capacitor was larger than the charging rate. Although this study cannot solve the technological issues around the efficiency in the vibration-powered generator, it showed the possibility of harvesting energy from the aquatic animal’s oscillation.
We developed the National Institute of Advanced Industrial Science and Technology (AIST) Risk Assessment Model for Tokyo Bay version 2.0 (AIST-RAMTB ver.2.0). This model allows users to estimate the concentrations of chemical substances in Tokyo Bay, assess the risks of those chemical substances, and display the results of the estimation and assessment on Windows-equipped personal computers. When used with the AIST-Standardized Hydrology-based Assessment Tool for Chemical Exposure Load (AIST-SHANEL), AIST-RAMTB ver.2.0 can set the riverine inputs of chemical substances. AIST-RAMTB ver. 2.0 outputs the results of visualization (a horizontal distribution map) as a KMZ file, so the results can be displayed on Google Earth. In this study, use AIST-RAMTB ver. 2.0 to estimate the environmental concentration of linear alkylbenzene sulfonate (LAS) and to assess the ecological risk of LAS in Tokyo Bay. The ecological risk was estimated by the no observed effect concentration (NOEC: 210 mg/L; Growth Reduction of diatom) and uncertainty factor 50. The results show that risk from LAS was found at river mouths, but no risk was evident in other sea areas.