11:00 AM - 11:15 AM
[HTT16-08] Comparison of river basin characteristics in different climatic zones -Focusing on the Mogami and Abukuma Rivers-
Keywords:watershed characteristics, river water quality, water environment
The differences in water quality of the Abukuma and Mogami Rivers, located in snowy regions but in different climatic zones, were compared based on various environmental factors to respond to watershed management affected by climate change in this study. The Abukuma and Mogami Rivers are typical Japanese rivers that repeatedly flow through basins and constricted areas. We compared the environmental factors such as topography, land use, and surface geology for water quality using GIS. The water quality data (EC, pH, water temperature, etc.) were obtained from field surveys and water samples taken once a month from October 2019 to September 2020 in the Abukuma River basin, and from March 2021 to July 2023 in the Mogami River basin.
As a result, this study showed differences in the strength of the effects of human and volcanic activities on river water quality in the Abukuma River basin and the Mogami River basin. The Abukuma River watershed has a basin area of approximately 1,640 km2 smaller than that of the Mogami River watershed, but the population is approximately 400,000 larger. Therefore, in the Abukuma River watershed, the percentage of land used for human activities, such as building sites, rice fields and other agricultural land, is 34.3%, which is higher than that of the Mogami River watershed (24.6%). In the Abukuma River basin, granite is widely distributed along the right bank, accounting for 31.4% of the total surface geology. In the Mogami River basin, igneous rocks accounted for 29.2%.
Water quality data indicate that the EC of the Abukuma River is 67.2 µS/cm higher than that of the Mogami River, indicating a large supply of ions to the mainstream. Ion chromatography results showed calcium bicarbonate-type water at many sites in both basins, which is typical of Japanese river water quality. Sulfate ions were predominant in the Arakawa, Matsu, Zao, and Sukawa Rivers, and nitrate ions were observed in the upper reaches of the Abukuma River, those of the Mogami River, and some tributaries. This indicates that there are both volcanic and human-caused sources of ions in the two watersheds. The load from human activities is considered to be located upstream and near Koriyama City in the Abukuma River basin and Yonezawa City in the Mogami River basin. The pH of the mainstream also changed due to the joining of tributaries containing large amounts of sulfate ions, which are thought to be of volcanic origin, and decreased by 0.2 in the Abukuma River and by 0.25 in the Mogami River. Furthermore, changes in water quality and flow were observed in the Mogami River watershed during the snowmelt season from March to June, indicating that the water environment is different from the previous one due to changes in snow cover conditions affected by climate change.
This study clarified the differences between the two river basins. In the future, we will try to further clarify the characteristics of these watersheds and systematize them by elaborating the factors that consist of water quality, so that we can proceed to clarify the response characteristics to climate change and reflect them in watershed management.
As a result, this study showed differences in the strength of the effects of human and volcanic activities on river water quality in the Abukuma River basin and the Mogami River basin. The Abukuma River watershed has a basin area of approximately 1,640 km2 smaller than that of the Mogami River watershed, but the population is approximately 400,000 larger. Therefore, in the Abukuma River watershed, the percentage of land used for human activities, such as building sites, rice fields and other agricultural land, is 34.3%, which is higher than that of the Mogami River watershed (24.6%). In the Abukuma River basin, granite is widely distributed along the right bank, accounting for 31.4% of the total surface geology. In the Mogami River basin, igneous rocks accounted for 29.2%.
Water quality data indicate that the EC of the Abukuma River is 67.2 µS/cm higher than that of the Mogami River, indicating a large supply of ions to the mainstream. Ion chromatography results showed calcium bicarbonate-type water at many sites in both basins, which is typical of Japanese river water quality. Sulfate ions were predominant in the Arakawa, Matsu, Zao, and Sukawa Rivers, and nitrate ions were observed in the upper reaches of the Abukuma River, those of the Mogami River, and some tributaries. This indicates that there are both volcanic and human-caused sources of ions in the two watersheds. The load from human activities is considered to be located upstream and near Koriyama City in the Abukuma River basin and Yonezawa City in the Mogami River basin. The pH of the mainstream also changed due to the joining of tributaries containing large amounts of sulfate ions, which are thought to be of volcanic origin, and decreased by 0.2 in the Abukuma River and by 0.25 in the Mogami River. Furthermore, changes in water quality and flow were observed in the Mogami River watershed during the snowmelt season from March to June, indicating that the water environment is different from the previous one due to changes in snow cover conditions affected by climate change.
This study clarified the differences between the two river basins. In the future, we will try to further clarify the characteristics of these watersheds and systematize them by elaborating the factors that consist of water quality, so that we can proceed to clarify the response characteristics to climate change and reflect them in watershed management.