『Abstract
　pH monitoring data for public water bodies in Niigata and Gifu prefectures in central Japan were tested by the nonparametric seasonal Mann-Kendall method to evaluate long-term acidification. A significant long-term declining trend in river water pH was found in several watersheds in Niigata and Gifu prefectures. In Niigata, the declining trend was observed only in areas receiving drainage from granitic rocks, and the acid neutralizing capacity of the river waters was in fact low in those areas. In Gifu, a declining trend was observed in some remote watersheds, where there was no clear relationship between the geology and the long-term trends. Since Niigata and Gifu receive the highest level of acid loading from the atmosphere in Japan, river water acidification in several watersheds may be attributable to the effects of the acid deposition. Other factors, such as hot spring drainage, changes in land use, and natural sea salt deposition, cannot adequately explain the acidification phenomena observed in this study.

Keywords: River water; Acidification; Acid deposition; Acid neutralizing capacity; Geology』

1. Introduction
2. Materials and methods
　2.1. Statistical analysis using data for public waters
　2.2. Geology of the study area
　2.3. River water sampling and chemical analysis
　2.4. Investigation of land use and hot spring drainage
3. Results
　3.1. Long-term trends
　3.2. Regional water quality characteristics
　3.3. Land use in the watersheds and hot spring drainage
4. Discussion
　4.1. Relationship between geology and river water acidification
　4.2. Effects of hot springs
　4.3. Effects of land use
　4.4. Effects of acid deposition
5. Conclusions
Acknowledgments
References