For the purpose of clarifying the river water quality and watershed characteristics such as land use and geology, field surveys were conducted for one year in the Abukuma River basin at 21 sites on the main stream and 40 sites on the tributaries. As a result, seasonal variations in the water quality were observed, and the water quality of the entire watershed was identified, which allowed us to confirm the influence of tributary water quality on the water quality of the main stream. In addition, we clarified that some tributaries had specific water quality. The Higashine River and the Ose River had high electrical conductivity and were classified in Na+-Cl- type, suggesting the inflow of pollution load from human activities. On the other hand, the Arakawa River was categorized as Ca2+-SO42- type, indicating a strong volcanic effect. Furthermore, we found the influence of land use in the electrical conductivity and major chemical constituents.

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In rivers regions with snowfall, snowmelt has a significant impact on river water quality, so it is important to accurately understand the effects of snow accumulation and snowmelt on water quality during periods when snowmelt has little effect. However, in regions with heavy snowfall, unlike rivers with little snow cover, the effects of snowmelt water remain until early summer, and the period of no effect is short. Therefore, in order to exclude as much as possible the effects of snow cover and snowmelt in warm snow covered regions, we first tried to understand water quality characteristics during non-snowfall periods. This paper discusses the characteristics and fluctuations of water quality in the main stream of the Uono River (The Shinano River tributary) and its tributaries during the non-snow season from April to December 2009, based on the results of water quality surveys. The average value of electrical conductivity (EC) in the main stream during the observation period was highest in the middle part of the stream, and the fluctuation was larger in the upper part of the stream. The reason for the variation of EC in the upper reaches is the increase of Na+ and K+ Cl- components, which are considered to be anti-freezing agent components during the snowmelt season. The high EC values in the midstream area were suggested to be influenced by the river mixed with hot spring components such as Na+, Cl-, and SO42-.

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