Abstract
Fog waters and precipitations were collected at the top of Mt. Yahiko, which is located in the westerm part of the Niigata Plane. Precipitations were also collected at the foot of Mt. Kakuda, which lies about 9 km northeast of Mt. Yahiko. Major ion constituents and nitrogen isotope ratios of ammonium and nitrate ions were measured. The sea-salt constituents in both the fog waters and the precipitations increased in winter. The concentration of major ion constituents was roughly, in order from lower to higher, mountaintop's precipitation, mountain foot's precipitation and fog water. The collected-water weighed mean of nitrogen isotope ratios of ammonium ions (δ15N-NH4+) in the fog waters, the mountaintop's and the mountain foot's precipitations was -3.0, -1.8 and -4.0 %o, respectively. The δ15N-NH4+ values of the mountain foot's precipitation were lower than those of the mountaintop's precipitation, especially in May and June. This may be the result of the absorption of ammonia gas (NH3) which has lower (δ15N) values when emitted from agricultural activities and so on. On the other hand, the mean of nitrogen isotope ratios of nitrate ions (δ15N-NO3-) in the fog waters, the mountaintop's and the mountain foot's precipitation was -3.0, -4.5, -4.4 ‰, respectively. The o δ15N-NO3- values of the mountaintop's precipitation were nearly equal to those of the mountain foot's, and the values of the fog waters were somewhat higher than those of the precipitations. The monthly mean of δ15N-NO3- in these three kinds of samples showed almost the same monthly variations and were higher in winter.
