Hydro-geographical study on the long-term fluctuation of river water quality in Japan (4)

<p>ⅠIntroduction</p><p>In Japan, water pollution became a problem nationwide during the period of high economic miracle, but due to legislation and raising environmental awareness of society as a whole, water quality has improved rapidly. However, even now, not only is it concentrated in Tokyo, but urbanization is progressing in rural areas, and there are still areas where water pollution is severe, such as in the suburbs. In the large river basins, there are many polluted areas in the upstream area rather than the downstream area due to the problems of wastewater treatment facilities in the mountain village area, etc. The results of the "Water Environment Survey of Public Water Areas" that has been continued by the government since 1971, and the nationwide observation records such as the "National Simultaneous Survey of the Familiar Water Environment" that started in 2004 centered on citizen groups. We have mainly examined long-term fluctuations in river water quality in Japan, but in this paper, in addition to the 17th (2020) and 18th (2021), the 19th in 2022 was measured by Hosei University. We will also consider the results. </p><p>Ⅱ Research method </p><p>Using the National Institute for Environmental Studies database "Water Quality Survey Results for Public Water Areas", the changes in water quality since 1971 are organized, and for the "National Simultaneous Survey of Familiar Water Environments", his COD from 2004 to 2018 The results of the survey were organized and long-term changes were considered. In addition, before 1971, the data extracted from various research results were organized, and after 2018, the nationwide observation records conducted in the laboratory were used. Furthermore, for 2020, 2021, 2022, the observation results of a total of about 5,000 points carried out by the laboratory and related parties were targeted. </p><p>Ⅲ Results and consideration </p><p>1. Results of water quality survey in public water areas The number of observation points, which was about 1,000 in 1971, exceeded 5,000 in 1986, 15 years later, and observations have been continued at points of less than 6,000 since then. In terms of secular variation of BOD values, 3 or more accounted for half (1971), but in 1976, 2 or less accounted for half, and recently, 2 or less accounted for about 80% (2018). The number of points 1 to 4 has not changed, the number of points 4 or more has decreased, and the number of points 1 or less has increased to about half of the total. </p><p>2. National simultaneous survey of familiar water environment In 2004, when the survey started, there were about 2,500 points, but in 2005 it was about 5,000 points, and after that it changed to around 6,000 points, but in 2018 it was about 7,000 points. About half have a COD of 4 or less. In 2020, the number of observation points decreased due to the influence of the new virus, and the observation results of Hosei University were not included in the total, so the number was 3,802, which was the second lowest after the first time in 2004. We analyzed the survey results of Hosei University at 2,000 points. The results were observed mainly in the coastal areas and in the terminal areas of rivers of various scales nationwide, so they are suitable for examining regional differences in rivers nationwide, and can be compared with previous observation results. Further detailed analysis is expected in the future. </p><p>3. Water quality before 1971 Although there are research results by pioneering Kobayashi (1961), it is difficult to obtain systematically observed water quality data. It was not possible, and the difficulty of clarifying the past water quality was highlighted. </p><p>4. Nearest water quality From 2017 to 2021, he organized his data surveyed at more than 1,500 locations nationwide every year and clarified the current state of river water quality in recent years.</p><p>View PDF for the rest of the abstract</p>