New Possibilities for Biological Surveys Using Environmental DNA - Environmental DNA Archive

 　Environmental DNA refers to DNA present in the environment, such as in water, soil, or air, where organisms reside. In rivers and lakes, environmental DNA can originate from tissue fragments, such as scales or mucous membranes that had been shed by organisms. Recently, techniques for collecting and analyzing environmental DNA to identify and study organisms in aquatic environments have gained significant attention and are driving advancements in various fields of applied research.

 Environmental DNA surveys require only water samples from the target area. These surveys are expected to offer simpler processes, more detailed biological insights, shorter survey durations, and reduced labor demands for fieldwork. PWRI has been actively researching the application of environmental DNA technology to fish surveys in rivers and other aquatic environments.

 In recent years, we have explored the potential of environmental DNA archives as a new approach to biological research. Environmental DNA samples can be frozen and stored after the initial analysis, allowing for reanalysis to gather information on the distribution of additional species and taxa. This makes environmental DNA archives highly versatile for a wide range of applications.

 PWRI has collected large numbers of environmental DNA samples from rivers, lakes, and marshes across Japan. These samples are now being stored to establish an environmental DNA archive, with ongoing research into their potential applications.

 One potential use of the environmental DNA archive is the early detection of invasive alien species, which significantly impact the habitats of native species in rivers and lakes and often pose challenges for their control. Managing invasive species is typically more effective and cost-efficient during the early stages of invasion. Surveys based on highly sensitive environmental DNA analysis may be effective at low densities in the early stages of such an invasion. Additionally, environmental DNA archives could enable researchers to trace the timing of past invasions. Thus, the potential of environmental DNA archive is highlighting for early detection of invasive species.

 PWRI is currently researching the alien species Cymbella janischii (Photo 1)which recently invaded Japan and poses a threat to degrade river landscapes and ecosystems by forming cotton-like colonies. By utilizing the nationwide environmental DNA archive, we are trying to detect its invasion in various rivers at an early stage.

 The study revealed that environmental DNA of Cymbella janischii was detected in the Naka and Tama Rivers located in Kanto region of Japan, where the species’ presence has already been confirmed, as well as in the Oita River in Kyusyu region and the Sarugaishi River downstream of Tase Dam in the Kitakami River system located in Tohoku region, where its presence had not been previously confirmed. The likely spread to these rivers may be attributed to the species’ presence in nearby waterways. These findings demonstrate the effectiveness of the environmental DNA archive in identifying water systems at risk of new invasion by alien diatoms.

 Cymbella janischii is a type of microscopic algae for which effective removal methods have yet to be established. Therefore, preventing its spread within and between water systems is crucial. It is essential to apply measures such as disinfecting the boots of river users and avoiding the transport of the species outside its current range. To support these efforts, we are considering a system to alert river administrators about water systems at risk of new invasion through periodic monitoring through the environmental DNA archive.

 It is anticipate that the use of environmental DNA will increasingly be applied to practical applications in the future. PWRI remains committed to advancing research on new and innovative uses of the environmental DNA archive.

(Contact : Watershed Restoration Research Team)

Collection of Basic Data on Dew Condensation of Vehicles Traveling in Road Tunnels during the Winter

 Ventilation facilities are installed in road tunnels based on factors like tunnel length, traffic volume, and other considerations to ensure safe and comfortable travel for users. (See Figure 1. Example of ventilation facilities (jet fans).) Jet fans are typically operated to meet the requirements of the standard*1) when visibility is reduced due to soot and smoke. In recent years, the number of vehicles with low soot and smoke emissions that comply with emission standards has increased. This has led to improved visibility in tunnels and reduced jet fan operation times. However, the air in a tunnel tends to stagnate. In long road tunnels, water vapor reportedly accumulates, leading to condensation on windshields during winter conditions (Figure 2: Example of condensation occurring).。

 Against this background, the Tunnel Research Team surveyed an operational road tunnel to collect basic data to elucidate the mechanism behind condensation in tunnels. The survey took place in December under conditions of rain or snow. The ambient temperature was approximately 2°C, with a relative humidity of approximately 90%. Inside the tunnel, wind was observed blowing steadily at approximately 1 m/s in a consistent direction. The temperature of air that entered the tunnel and traveled toward the exit increased to approximately 12°C, and the relative humidity was approximately 90%.

　

 Condensation is closely associated with the dew-point temperature, which is the temperature at which water vapor in the air condenses into liquid water. The higher the dew-point temperature, the greater the likelihood of condensation. In tunnels, condensation occurs when the temperature of an object falls below the dew-point temperature. Figure 3 illustrates the relationship between dew-point temperature and the temperature of objects (in this case, windshields) in this tunnel. It also presents observations of condensation on windshields recorded at the tunnel entrances and four other observation points inside the tunnel.

 The windshield temperature of a vehicle traveling in the same direction as the wind (southbound, red text) was 3.4°C at the north entrance and increased to 9.1°C at the south entrance. No condensation was observed at the north entrance, where the windshield temperature exceeded the dew-point temperature. However, condensation was observed at observation point (4) as well as observation points (1) through (3) and the south entrance, where the windshield temperature was below the dew-point temperature. For a vehicle traveling in the opposite direction of the wind (northbound, blue text), the windshield temperature was 5.9°C at the south entrance and rose to 8.5°C at the north entrance. Condensation was observed at the south entrance and at observation points (1) and (2), where the windshield temperature was below the dew-point temperature. Conversely, no condensation was observed at observation points (3) and (4) and at the north entrance, where the windshield temperature exceeded the dew-point temperature.The above findings indicate that the dew-point temperature increases downstream as air flows through the tunnel, primarily due to the accumulation of water vapor and heat emitted by vehicles. Condensation occurs when the windshield temperature drops below the dew-point temperature. The results also demonstrate that condensation is influenced by both the wind direction and the direction in which the vehicle travels inside the tunnel.

　

 Based on the data obtained from this survey, we will explore methods to control condensation using jet fans, along with design and operational strategies to ensure road tunnel users’ safe and comfortable travel.

 *1) The Technical Standards for Road Tunnels (May 1989) specifies design concentrations for soot, smoke and carbon monoxide.

(Contact: Tunnel Research Team)