Abstract
The variation in N03--N concentration and the natural abundance of 15N (δ15N value) in streamwater was measured during a rainfall event. NO3--N concentration was positively correlated with discharge rate, but δ15N value was negatively correrated. The initial increase of N03--N concentration in streamwater was accompanied by a linear decrease of δ15N value from 0.2‰ to -1.4‰. Discharge of soil solution from surface soil layer explained this variation. When the NO3--N concentration decreased, δ15N value increased exponentially from -1.2‰ to 6.0‰. This variation could not be explained by the mixing of soil solutions, but it agreed with the classical equation of Rayleigh used to calculate the change in δ15N value during denitrification. We concluded that the decrease in NO3--N concentration in streamwater was caused by denitrification in the saturated soil layer during a rainfall event.
