Sip the water and find out what kind of creatures are there- Environmental DNA sources

  In the water of rivers and lakes, biological cells derived from the mucous membranes and body surfaces of the organisms that live there are suspended.　Environmental DNA survey technology is a technique for extracting DNA from such cells in water and analyzing it to extract information such as the type of organisms that were there.　The work is simple: "All you have to do in the field is pump water. Therefore, it is used in the research field for surveys targeting a variety of organisms. The Public Works Research Institute is engaged in research to implement environmental DNA in environmental surveys conducted in rivers, dams, lakes, and marshes, to improve the efficiency of environmental surveys, and to enhance the sophistication of information using the biological information obtained by environmental DNA.

Environmental DNA Survey Flow

  The specific flow of an environmental DNA survey is shown in Figure 2. All that is required in the field is to draw one to several liters of water. This may seem like a very simple task, but as described below, the information obtained will vary greatly depending on where the water is drawn. The water is then filtered, and the DNA is extracted by dissolving the biogenic material contained in what is left on the filter paper (the miscellaneous material that was suspended in the water). However, the amount of DNA obtained is very small and it is difficult to immediately capture the biological information as it is. Therefore, target genes are increased by PCR, which is also used in the corona test, and the target genes are used as DNA sequence information. In the species coverage analysis, the sequence information obtained in this way is compared with the known gene sequences in the DNA database to identify the owners of miscellaneous floating cell in the sample and obtain a list of organisms.

Accuracy of environmental DNA surveys depends on "database sufficiency" and "ability to capture floating cell”

  Environmental DNA surveys cannot provide information on species that are not in the DNA database. Therefore, it is a prerequisite that many of the putative species are registered in the DNA database in order to obtain a more accurate list of organisms. There are a variety of analysis methods for various groups of organisms, such as benthic insects, frogs, birds, etc. Among them, for fish, the databases are well-developed, with not only species-level information but also DNA sequence information for local populations in various regions of Japan, making it possible to obtain good biological information using environmental DNA. The following is a brief overview of the results of the study.

  However, information on organisms for which tissue fragments were not included in the sample is not available. For example, even if the organisms are in the immediate vicinity of the sampling point, if the tissue fragments do not reach the sampling point in the stream, no information about the organisms can be obtained.

How do we capture floating cell?

  Environmental DNA surveys provide areal biological information because the sample contains floating cell of areal organisms not only from the river where the water is collected, but also from the water body leading to the point of collection. The area is said to be about 1 km from where the organisms are located (i.e., the source of the floating cell), depending on the amount of the source and the way the water flows. The results of the survey in 55 districts showed that, although there were variations from district to district, the following results were obtained. The environmental DNA was able to detect 76.2% of the fish species captured by direct sampling. Species that could not be detected by environmental DNA included small benthic fish, small fish in the vegetation zone at the water's edge, and fish in water bodies that lack continuity with the main river, such as wands and creeks. All of the rivers surveyed were large first-class rivers, which may have contributed to the fact that tissue fragments of fish from the opposite bank did not reach the opposite bank. Another factor that may have contributed to the difficulty in detecting fish in this water body was that the volume of water flowing in from wands and creeks was small compared to the volume of water in the main river.

  Based on these results, PWRI, with the cooperation of the regional development bureaus of the Ministry of Land, Infrastructure, Transport and Tourism throughout Japan, is studying ways to optimize water sampling points. We are also studying survey methods for brackish water areas, which are affected by the ebb and flow of the tide, and for dammed lakes and marshes, where the flow of water is slow, based on the characteristics of each area.

(Contact: Watershed Restoration Research Team)

Characteristics of the Complex Deterioration of Coastal Concrete Structures in Icy Waters

1. Objective of the research

  Frost damage and salt damage are among the main factors involved in the deterioration of concrete structures at ports and harbors in cold, snowy areas. In addition to these, collision with and abrasion caused by sea ice occur in icy waters when the sea ice reaches the coast (Photo 1).The deterioration of structures progresses through a combination of these factors. This is known as complex deterioration. The Port and Coast Research Team is promoting research to elucidate the characteristics of the complex deterioration of coastal concrete structures in icy waters, with the goal of establishing repair and reinforcement technology for deteriorated structures.

2. Assumed mechanism of complex deterioration

  Figure 1 is a conceptual diagram of the assumed mechanism of complex deterioration. Step 1: Freeze-thaw actions cause fine cracking mainly on the surface of concrete structures where the contact with moisture is the highest. Step 2: Hardened cement, fine aggregates and coarse aggregates separate from the weakened concrete surface due to the force of friction caused by the movement of sea ice while in contact with the weakened
concrete surface. It is assumed that the repetition of these
two steps accelerates the deterioration of concrete.

3. Verification of the complex deterioration mechanism by combining the freeze-thaw and abrasion tests

  To reproduce the complex action of frost damage and abrasion, the freeze-thaw test was first conducted followed by the abrasion test, using the freeze-thaw and abrasion testers shown in Photo 2. This process is called a combined test. The experience of one freezing and thawing action each is called “one cycle.” In this case, the abrasion test was conducted on a mortar sample without freezing and thawing (0 cycles) and samples subjected to the freeze-thaw test with 34, 100 and 150 cycles, respectively.

  Abrasion of concrete due to friction with ice can be divided into initial abrasion, which causes separation of hardened cement from the concrete surface, and subsequent steady abrasion, when the aggregate begins to be exposed and the abrasion rate (= average wear/friction distance) becomes steady.Figure 2 shows the results of the combined test using mortar specimens. The graph represents the relationship between the friction distance and average wear of specimens found with the abrasion test after the freeze-thaw test of the specimens subjected to different numbers of cycles. The data for a friction distance of 50 km under steady abrasion conditions are plotted here.

  Under steady abrasion conditions, the relationship between the friction distance and average wear was almost linear. The inclination of this line indicates the abrasion rate, and is greater for 150 freeze-thaw cycles (□) than 0 cycles (●).

  This result revealed that the abrasion rates due to friction with sea ice increased with progressive deterioration caused by freezing and thawing. However, there are still many unknown matters concerning complex deterioration. The team will continue research to clarify these matters.

(Contact: Port and Coast Research Team, CERI)

Efforts to Monitor the Snowfall Status in Regions with Little Snow
－Estimation based on the rain gauge, anemometer and thermometer data－

Introduction

  In recent years, intensive heavy snowfall has been occurring even in regions that usually have little snow, causing serious damage. To minimize the damage caused by heavy snow, it is important to monitor snowfall and accumulation conditions extensively and at many points.

  Snow depth gauges are usually used to monitor snowfall and accumulation conditions. However, as can be seen in Figure 1, the number of snow depth gauges in regions with little snow is smaller compared with snowy regions. Real-time mesh information of snowfall and accumulation throughout Japan is currently provided on the Meteorological Agency’s “current snow (analyzed snow depth/analyzed snowfall)” website. As this information is based on the correction process using values measured with snow depth gauges, the estimation accuracy in regions with little snow is considered to be lower than that in snowy regions.

  This study is an attempt to monitor the snowfall amounts based on data from existing rain gauges, anemometer and thermometers placed at many ground observation points (e.g., AMeDAS) in different regions, without using snow depth gauges.

Snowfall estimation method

  In this study, an attempt was made to estimate snowfall amounts using the snow/water ratio at nine observation points with snow depth gauges (Figure 2) of the Japan Meteorological Agency. The snow/water ratio is an index that shows how many centimeters of snowfall is equivalent to 1 mm of precipitation, and can be calculated backward using the observation results of fresh snow density. In this study, snowfall amounts were estimated by applying various snow/ice ratios based on previous studies to values measured with rain gauges during snowfall (after correcting for wind-induced errors), and the results were compared with the values measured with snow depth gauges

Comparison of estimated and measured values

  The following are the results of trial calculation of two heavy snowfalls on February 8-9 and 14-15, 2014 in the Kanto/Koshin district. As examples,Figure 3 (a) to (c) show the estimation results found by assuming different snow/ice ratios below and above a zero ground air temperature (below zero: 0.76, above zero: 0.38, according to Matsuda and Shimizu, 2015). The figure shows the changes in the total measured and estimated value from the time when snowfall is recorded with a snow depth gauge to the time when the maximum snow depth is reached. This result confirms that the estimated snow fall amounts almost correspond to the amounts measured using snow depth gauges. It is planned to increase the cases of heavy snowfall to be analyzed and consider the possibility of application to other regions with little snow in the future.

(Contact: Snow and Ice Research Team, CERI)