分野別研究紹介

IV. Power Plants, Marine Organisms, and Their Environment

 We use field studies in the region offshore of power plants as well as laboratory studies utilizing the experimental marine organism rearing facilities at the Central and Demonstration laboratories to analyze the impact of power plant cooling water intake and discharge on the environment. Furthermore, we also investigate techniques for forecasting the impact of power plant siting on coastal ecosystems as well as technologies for preventing the fouling of cooling water intake pipes by aquatic organisms.

Combined Impacts of Thermal Effluents and Other Factors
 There is some concern that high temperature and low salinity caused by power plant thermal effluents along with low oxygen and turbidity could drive compound impacts on marine organisms particularly in the littoral zone of enclosed bays or inland seas. As a result, we have carried out experimental studies on this subject. So far, we have gained an understanding of which varieties of fish, bivalves, and large macroalgae are most vulnerable and at what developmental stages, and have determined some impact thresholds.
 Moreover, in recent years, the northward range expansion of southern herbivores has harmed seaweeds by increasing grazing pressure and has led to the reduction of seaweed beds (rocky-shore denudation). In order to examine the relationship between this phenomenon and rising seawater temperatures, we used laboratory studies to determine how the feeding rate of the principle herbivores including rabbitfishes and Longspine black urchins on large macroalgae was affected by water temperature.
 
High temperature, low oxygen concentra-tion experiments
 
Experimental investigation of rabbitfish and seaweed interspecies relationships
     
Fish Reponses to Temperature
 We used fish pens (photo at right) moored near power plant cooling system discharge sites on the Japan Sea to study the behavior of large fish in response to thermal effluents. The figure below indicates the water temperature distribution in the pens and the vertical distribution of yellowtail. Whereas in the summer, yellowtail avoided the thermal effluent water by swimming at mid and lower depths below the high temperature layer, in the winter yellowtail were actually drawn to the high temperature layer. We also carried out this research on anadromous migratory salmon including chum salmon and cherry salmon.
 
Fish pens moored in the vicinity of thermal effluent outfalls
     
The temperature distribution within fish pens moored in the vicinity of thermal effluent outfalls and the distribution of yellowtail (black dots)
     
Marine Experiments on the Impact of Thermal Effluents
 In order to reveal the magnitude and range of the impact of power plant thermal effluents on seaweed, we positioned settlement plates seeded with immature seaweed in locations experiencing various degrees of temperature change due to exposure to thermal effluents. We then observed the growth and maturation of this seaweed over time. As a result, we were able to observe differences in the growth and maturation of seaweed between regions in direct contact with thermal effluents (3–5°C increase in temperature relative to surrounding waters), in slight contact with thermal effluents (2–3°C increase in temperature relative to surrounding waters), and not in contact with thermal effluents.
 
Comparison of growth rates of seaweed attached to experimental settlement plates
     
Development of Research Methods and Forecasting Techniques for Ecosystem Impact Assessment
 We are investigating the best methods and techniques for researching and forecasting the impacts of power plants on coastal marine ecosystems as part of the power plant assessment process.
 We developed technology to input data pertaining to the organisms of interest within an ecosystem along with environmental factors into a database, model the relationship between organisms and environmental factors, and finally output the forecast results into a geographical information system (GIS). The figure on the lower right shows an analysis of the impact a hypothetical power plant would have on a species of interest, in this case a type of seaweed known as arame (red: high impact; yellow: low impact). Although much of the red area indicates arame extirpation due to land reclamation, there is also an area close to the discharge outfall that is also forecast to experience local extirpation.
 
Power plant impact range forecast for arame
     
Development of Antifouling Technologies for Cooling Water Systems
 Biofouling of power plant cooling water systems can degrade heat exchange capacity in elements such as steam condensers and can damage equipment. We are investigating ways to combat this problem by using antifouling methods that have minimum impact on marine organisms.
 We have carried out culture experiments using blue mussels to determine the effectiveness of chlorine dosing as well as to study the stable operation of antifouling methods using chlorine dosing.
 When large planktonic organisms such as moon jellies become entrained in power plant cooling water intake systems in substantial numbers they can clog the screens and cause a decline in power generation capacity due to an inability to intake sufficient seawater for cooling. Consequently, we are studying the ecology and environmental requirements of the jellyfish’s sessile polyp stage with a view to developing a method to forecast the arrival of large numbers of jellyfish. As part of this effort, we have been able to identify nursery regions for polyps in our study area.
 
Blue mussels after settling on experimental plates
 
Moon jellyfish polyps (left) and juvenile jellyfish (right)