Research on the influence of sediment oxygen conditions in algae (phytoplankton) increase
In recent years, sewerage system improvements and sediment dredging have
decreased the inflow load to lakes. However, there are still some problems
caused by water-bloom (Photo 1) in some bodies of water. Water-bloom is
a rapid increase of algae. The Water Quality Research Team assumes the
rapid increase of algae is related to the oxygen conditions and the elution
of nutrients (nitrogen or phosphorus) at the bottom of the lake, and researches
to verify this assumption.
At the bottom layer of a lake, living organisms consume oxygen to decompose deposited organic matter. As the oxygen concentration at the bottom decreases, reduction reactions take place and nutrients contained in the bottom mud elute to the lake water. To analyze the relationship between the eluted nutrients and the water-bloom, we conducted a nutrient elution experiment using mud from the bottom of the lake and carried out algal growth potential tests.
To start, the bottom mud at the Nishiura and Kitaura sections of Lake Kasumigaura (Fig. 1) was sampled with a transparent acrylic pipe. Each sample was prepared in two states - aerobic (with sufficient dissolved oxygen) and anaerobic (state with no dissolved oxygen), and a nutrient elution experiment was conducted.
A few days later, the water of each pipe was sampled and relocated to a triangular flask. A small amount of alga was added to the flasks, and the growth of the alga was monitored (Photo 2). As a result (Fig. 2), we discovered that algal growth was inhibited more in aerobic conditions than in anaerobic conditions. We also confirmed that algal growth was inhibited more in Nishiura, where sewerage system improvements and sediment dredging have been undertaken, than in Kitaura, where such measures have not been implemented as often. In conclusion, we clarified that algal growth was inhibited by the improvement of sediment quality and the maintaining of aerobic bottom sediment conditions.
Further investigation is needed on trace metal and nutrient salts movement between the bottom mud and the lake water and its influence on algal growth.
(Contact: Water Quality Research Team)
To improve winter port working environment
Research on the effectiveness of the development of wind/snow protection facilities in ports
Example of fishing in winter
Stevedoring and fishing work in winter
At harbors and fishing ports in snowy, cold regions like Hokkaido, workers are exposed to very severe working conditions such as below-zero temperatures, strong winds, and snow storms. Because of this harsh environment, workers are subject to various difficult conditions such as reduced work efficiency and safety problems due to freezing of the pavement and/or diminished attention, and there are also concerns regarding the influence on the health of the elderly.
Purpose of the research
To improve such a harsh winter working environment, wind/snow protection facilities are being constructed near the piers of ports to protect people from exposure to wind and snow. It is necessary to quantitatively evaluate the wind breaking effect to realize effective development of these facilities.
CERI is engaged in research in order to propose a thermal sensation index that can appropriately express the psychological reactions of people working in cold conditions, such as sensible temperature and quantitative evaluation of the impact of low-temperature environments on working efficiency.
Experiment using subjects
In this research, the subjects, who are men and women of various age brackets ranging from their 20s to their 50s, are asked to do a few kinds of simple work in our low-temperature room under various temperature and wind velocity conditions, and parameters such as ability to detect hot and cold and working efficiency are measured. Based on the results of the subject experiments conducted to date, we propose indices that express the human ability to detect hot and cold and a model that estimates working efficiency in low-temperature environments.
Going forward, we plan to verify the proposed indices in an actual wind/snow protection facility.
(Contact: Port and Coast Research Team, CERI)
Extraction of river basins likely to cause deep-seated slope failure
Once there is heavy rainfall, the mountain slope will fail and slope failure will cause debris flow and can cause devastating damage. Landslide phenomena are divided into two types: shallow landslide, which is landsliding of the surface soil layer alone, and deep-seated slope failure, which is simultaneous landsliding of the surface soil layer and its underlying weathered bedrock (Fig. 1). Especially, a deep-seated landslide is usually very large in scale; thus, it can cause large-scale debris flow and trigger landslide dams, potentially causing devastating damage (Photo 1). In addition, as the magnitude of rainfall increases due to climate change, it can be thought that the number of deep-seated slope failures will increase in the future. To prevent or mitigate sediment disasters caused by such deep-seated slope failures, it is essential to know in advance where such failures are likely to occur and the size of such failures should they occur. However, factors related to the occurrence of deep-seated slope failure are complicated, and there is insufficient data accumulation necessary to predict places susceptible to slope failure and the scale thereof. Therefore, no practical technique to extract catchments likely to cause deep-seated slope failure has yet been established.
It has been considered that there is a relationship between the occurrence of deep-seated slope failure and the topography or geologic structure, based on the previous surveys and researches involve detailed surveys of the area around deep-seated failure sites. The results of these studies certainly clarify the topography or geologic structure often seen in areas around deep-seated failure sites but fail to identify topography or geologic structures frequently found only in areas around deep-seated failures (and found less in areas that do not contain such failures). We have redoubled our review and analysis efforts and have come to realize deep-seated slope failure is likely to occur at the following locations:
(1) Areas around past deep-seated failure sites
(2) Areas where topographical distortion or deformation, considered to be a premonitory phenomenon of deep-seated failure, is seen
(3) Steep slopes with a large upslope contributing area
Based on these results, we extracted the following catchments as those susceptible to deep-seated slope failure, as shown in the schematic diagram in Fig. 2:
(1) Catchments where deep-seated failure occurred in the past
(2) Catchments where topographical distortion or deformation highly related to the occurrence of deep-seated failure exists
(3) Catchments where there are many steep slopes with a large upslope contributing area
We then confirmed that if a catchment fits more than one condition, it has a greater possibility of generating a deep-seated slope failure, and thus proposed a method in extracting those catchments with a high risk of deep-seated failure. Topographical distortion or deformation can be identified in aerial photos by engineers with a decent level of experience.
Today, surveys using this method are conducted across the country. Fig. 3 shows an example survey result. We intend to apply these survey results in developing and implementing measures to cope with sediment disasters due to deep-seated slope failure. In addition, we will further promote survey and research to establish a method to identify pinpoint slopes that are highly likely to cause deep-seated failure from among those of catchments.
(Contact: Volcano and Debris Flow Research Team)