The abundance of ¹⁵N in N₂O in aquatic ecosystems with emphasis on denitrification

Abstract

Using soil-water systems under laboratory conditions several experiments were carried out to elucidate the possible factors governing the variations of δ¹⁵N in dissolved N₂O in aquatic systems. Under anoxic conditions, the δ¹⁵N value in N₂O during the initial reduction step from NO₃⁻ to N₂ was as low as –27‰ relative to that of the initial nitrate (NO₃⁻). The δ¹⁵ N value of N₂O then increased to that of NO₃ ⁻ as denitrification progressed until a stationary concentration of N₂O was established. The effects of NO₃⁻ concentrations on the reduction of N₂O to N₂ during the denitrification process were considered important to the variations in δ¹⁵N (N₂O)observed in nature. Based on data for δ¹⁵N (N₂O) in the eastern tropical North Pacific and Lake Kizaki, Japan, several possibilities for the use of δ¹⁵N as a source indicator of N₂O derived from microbial oxidation-reduction reactions are examined.