Stable isotope natural abundance of nitrous oxide emitted from Antarctic tundra soils: effects of sea animal excrement depositions

Abstract

Nitrous oxide (N₂O), a greenhouse gas, is mainly emitted from soils during the nitrification and denitrification processes. N₂O stable isotope investigations can help to characterize the N₂O sources and N₂O production mechanisms. N₂O isotope measurements have been conducted for different types of global terrestrial ecosystems. However, no isotopic data of N₂O emitted from Antarctic tundra ecosystems have been reported although the coastal ice-free tundra around Antarctic continent is the largest sea animal colony on the global scale. Here, we report for the first time stable isotope composition of N₂O emitted from Antarctic sea animal colonies (including penguin, seal and skua colonies) and normal tundra soils using insitu field observations and laboratory incubations, and we have analyzed the effects of sea animal excrement depositions on stable isotope natural abundance of N₂O. For all the field sites, the soil-emitted N₂O was ¹⁵N- and ¹⁸O-depleted compared with N₂O in local ambient air. The mean δ values of the soil-emitted N₂O were δ¹⁵N = −13.5 ± 3.2‰ and δ¹⁸O = 26.2 ± 1.4‰ for the penguin colony, δ¹⁵N = −11.5 ± 5.1‰ and δ¹⁸O = 26.4 ± 3.5‰ for the skua colony and δ¹⁵N = −18.9 ± 0.7‰ and δ¹⁸O = 28.8 ± 1.3‰ for the seal colony. In the soil incubations, the isotopic composition of N₂O was measured under N₂ and under ambient air conditions. The soils incubated under the ambient air emitted very little N₂O (2.93 µg N₂ON kg⁻¹). Under N₂ conditions, much more N₂O was formed (9.74 µg N₂ON kg⁻¹), and the mean δ¹⁵N and δ¹⁸O values of N₂O were −19.1 ± 8.0‰ and 21.3 ± 4.3‰, respectively, from penguin colony soils, and −17.0 ± 4.2‰ and 20.6 ± 3.5‰, respectively, from seal colony soils. The data from in situ field observations and laboratory experiments point to denitrification as the predominant N₂O source from Antarctic sea animal colonies. Copyright © 2008 John Wiley & Sons, Ltd.