Abstract
I. Introduction In Japan, water pollution became a problem during the high-growth period, but it has been rapidly improved due to legislation and raising environmental awareness, but there are areas where urbanization is progressing and water pollution is severe. Due to the problem of wastewater treatment facilities in the mountain village area, pollution is conspicuous in the upstream part rather than the downstream part in the large river basin. We have examined long-term changes in river water quality in Japan from records such as the "Water Environment Survey of Public Water Areas" and the "National Survey of Familiar Water Environments", but in this paper, the results of the "Survey" by Hosei University in 2020. We will focus on. Ⅱ Research method Long-term changes were considered from the results of "Water quality survey results of public water areas" and "National simultaneous survey of familiar water environment". Before 1971, data was organized from research results and reports, and after 2018, the observation records of the laboratory on a nationwide scale were used, and the observation results of about 2000 points conducted in the laboratory in 2020 were targeted. Ⅲ Results and consideration 1. Water quality survey results for public water areas: Approximately 1,000 points in 1971 exceeded 5,000 points in 1986, and have continued at points of just under 6,000 points since then. In terms of secular change in BOD value, 3 or more was initially half (1971), but in 1976, 2 or less was half, and recently 2 or less is about 80% (2018). The value of 4 or more has decreased, and the value of 1 or less has increased to about half of the total. 2. National simultaneous survey of familiar water environment: Approximately 2,500 points in 2004 changed to approximately 5,000 points in 2005, then around 6,000 points, and in 2018, approximately 7,000 points had a COD of 4 or less, which was about half. In 2020, the number of points decreased due to the influence of the new virus, and the number of points was 3,802, not including the results of Hosei University, but the analysis was made by adding the survey results of about 2,000 points. 3. Before 1971, systematic water quality data other than Kobayashi (1961) was difficult to obtain, highlighting the difficulty of restoring past water quality. 4. Recent water quality The characteristics of recent years have been clarified by examining the data of 2020 in addition to the data of more than 2000 locations nationwide before 2019. Ⅳ Conclusion The past water quality was restored by adding the data before 1971 to the long-term observation results on a nationwide scale. The recent water quality has been clarified by observing about 2,000 points nationwide. I would like to continue collecting data and improve accuracy in the future.
