『Abstract
　Precipitation was collected from May 15, 2001 to November 18, 2002, at the mountain top (620 m a.s.l.) and mountain foot (47 m a.s.l.) of the Yahiko-Kakuda Mountains area, which is located in the western part of the Niigata Plain in central Japan. Major ion constituents and nitrogen isotopic ratios of ammonium (δ¹⁵N-NH4⁺) and nitrate (δ¹⁵N-NO3^-) were measured in order to investigate the sources and behavior of NH4⁺ and NO3^- in precipitations. The concentrations of sea salt constituents considerably increased in the cold season from November to March, and for the majority of the ion species, the concentrations at the mountain foot were higher than those at the mountain top. The precipitation weighed monthly and seasonal means of δ¹⁵N-NH4⁺ values in the warm season were lower than those in the cold season at both the mountain top and mountain foot. The δ¹⁵N-NH4⁺ values at the mountain foot were lower than those of mountain top in both seasons. This seasonal variation of δ¹⁵N-NH4⁺ could be caused by the incorporation of ammonia gas (NH3) with lower δ¹⁵N values, emitted from agricultural activities. On the other hand, the monthly and seasonal means of δ¹⁵N-NO3^- values showed noticeable seasonal difference with higher in the cold season at both the mountain top and mountain foot; however, the elevation difference was not observed either in the warm or cold season. The obtained δ¹⁵N-NH4⁺ and δ¹⁵N-NO3^- values were regarded as intermediate in comparison with the reported values. No significant correlations were observed either between NH4⁺ concentrations and δ¹⁵N-NH4⁺ values or between NO3^-) concentrations and δ¹⁵N-NO3^- values. These results suggest that different factors may affect the nitrogen isotopic variations and concentration variations of NH4⁺ and NO3^- in precipitations collected at the two sites.

Keywords: Nitrogen isotope ratio; Ammonium; Nitrate; Precipitation; Seasonal variation』

1. Introduction
2. Methods
3. Results and discussion
　3.1. Seasonal and altitude differences in major ion concentrations and δ¹⁵N values
　3.2. Monthly variations in δ¹⁵N-NH4⁺ and δ¹⁵N-NO3^-
　3.3. Correlations between concentration variations and nitrogen isotopic ratios
4. Conclusions
References