Abstracts

Haruka Kiba¹, Fujio Hyodo², Yuichi Asano³, Morihiro Maeda¹.

¹ Okayama University, Graduate School of Environmental and Life Science, 3-1-1 Tsushima-Naka, Okayama 700-8530, Japan

E-mail: mun@cc.okayama-u.ac.jp

² Okayama University, Research Core for Interdisciplinary Science, 3-1-1 Tsushima-Naka, Okayama 700-8530, Japan

³Oyo Corporation, 2-907 Seko-Higashi, Moriyama-Ku, Nagoya 463-8541, Japan

Abstract　

Natural abundance of nitrogen-15 (δ¹⁵N) is a useful tool to estimate sources of nitrogen (N). The objective of the study was to clarify practical conditions of a sequential diffusion-based method for ¹⁵N natural abundance of inorganic N and total dissolved N (TDN) with relatively high concentration. We tested the sequential diffusion method at 40ºC for 24 hours for recovery of NH₄-N and NO₃-N (0–40 mg L^-1) and for that of TDN (0–4 mg L^-1). Results showed that the complete recovery was achieved for inorganic N with 0.3–30 mg L^-1 and for TDN 0–3 mg L^-1. Furthermore, recovery rates for TDN declined when the amount of N exceeded 120 μg N. The time required for N recovery can be shortened to 24 hours by increasing temperature to 40ºC. No discrimination of ¹⁵N occurred during the whole process under the above conditions. In conclusion, the sequential diffusion method for ¹⁵N natural abundance measurement can be applied to water samples including 0.2–20 mg L^-1 for NH₄-N or NO₃-N, and 0.25–3 mg L^-1 for TDN. The volume for TDN recovery must be adjusted so that amount of TDN in solution is less than 90 μg N.