Investigating the effects of animal-specific δ15N-NH3 values volatilized from livestock waste on regional NH3 source partitioning

Abstract

The natural ¹⁵N abundance of ammonia (δ¹⁵N-NH₃) emitted from livestock waste within a specific area (δ¹⁵N-NH₃-LW) can be used to estimate its contribution to atmospheric NH₃ through an isotope mixing model. However, the limited availability of reports on δ¹⁵N-NH₃-LW hinders the accuracy of regional NH₃ source partitioning. In this study, we conducted research in the suburbs of Shenyang, China, and combined our results (n = 71) with data from published literature (n = 56) to develop a δ¹⁵N-NH₃ spectrum emitted from cattle, pig, sheep, and poultry waste. We also explored the national and global spatial distribution of δ¹⁵N-NH₃-LW based on the proportion of NH₃ emissions from these four types of livestock waste. Our results showed that the δ¹⁵N-NH₃ values ranged from −59.9‰ to −7.7‰, with a mean value of −27.3‰. This value was significantly lower than that from non-agricultural sources, such as coal combustion and motor vehicle exhaust, but overlapped with values from fertilizer N volatilization. Specifically, the δ¹⁵N-NH₃ values emitted from cattle, pig, sheep, and poultry waste were −32.1 ± 15.9‰, −20.7 ± 7‰, −24.3 ± 5.9‰, and −19.1 ± 4.9‰, respectively. Considering regional differences in livestock farming structures, δ¹⁵N-NH₃-LW exhibited a gradual decreasing trend from Southeast to Northwest across China. For example, Fujian Province, located on the southeastern coast, exhibited the highest δ¹⁵N-NH₃-LW value of −19.8‰, owing to its high proportion of poultry farming, while the Tibet Autonomous Region, in the western inland, displayed the lowest δ¹⁵N-NH₃-LW value of −30.8‰, due to its high proportion of cattle farming. Globally, the δ¹⁵N-NH₃-LW value was highest in Southeast Asia (−23.4‰) and lowest in East Africa (−30.4‰). Overall, our study revealed significant spatial variation in δ¹⁵N-NH₃-LW at both national and global scales. To more accurately assess the regional contributions of NH₃ emissions from livestock waste, it is essential to use region-specific δ¹⁵N-NH₃-LW values for future NH₃ source partitioning.