Determination of the nitrogen isotope enrichment factor associated with ammonification and nitrification in
Lu Yu1, Tianyuan Zheng1, Yujie Hao1
1College of Environmental Science and Engineering, Ocean University of China, Qingdao, 266100, China; Key Lab of Marine Environmental Science and Ecology, Ministry of Education, Ocean University of China, Qingdao, 266100, China.
Abstract:
For nitrogen (N) migration and transformation from unsaturated soil to groundwater, the N stable isotope (δ15N) was modified due to the isotope fractionation effect. To quantitatively evaluate the N cycle in groundwater systems, the determination of isotope fractionation is decisive. In this research, for the first time, incubation experiments were conducted to quantitatively investigate the N isotope enrichment factor (ϵp/s) associated with ammonification in unsaturated soil. Under weak isotopic fractionation, the Rayleigh function cannot be directly applied during ammonification. Thus, we proposed a different method calculating the ϵp/s values during ammonification, which were -0.03‰ for 15 °C and -2.34‰ for 30 °C. Moreover, for the first time, experimental equipment is presented to explore the isotopic fractionation effects under the co-occurrence of nitrification and volatilization. The results indicated that the isotope effect of volatilization during nitrification can be ignored in this study, and the ϵp/s values during nitrification were -10.59 and -6.81‰ at 15 and 30 °C, respectively. This work provides a novel arrangement determining the crucial parameters for identifying nitrate pollution sources in groundwater systems.
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