M.Sc Thesis

M.Sc StudentHaroush Dotan
SubjectUse of FTIR Spectroscopy for Real-Time Monitoring of
Isotopically Labeled N2O Emission from Soils
DepartmentDepartment of Civil and Environmental Engineering
Supervisors ASSOCIATE PROF. Yael Dubowski


This work focuses on applying Fourier Transformed Infra-Red (FTIR) spectroscopy for monitoring nitrous oxide (N2O) emitted by microbiological processes in soil, as a tool for studying these processes. N2O is one of the intermediate nitrogen species of denitrification process and a byproduct of nitrification. At present, isotope ratio mass spectrometry (IRMS) is the most common method for investigation and quantification of such nitrogen emission processes. However, IRMS is used off-line and requires expensive equipment as well as intensive and careful sample preparation steps. Additionally, IRMS is very expensive and less available. This work examines the potential of FTIR spectrometry as an alternative method for measuring N2O emission from a soil medium. The advantages of this method are its relatively low operating costs, availability, non-destructive nature, capability for online monitoring and for identification of different isotopologs (14N2O and 15N2O) and isotopomers (14N15NO and 15N14NO). To achieve this research goal, four specific aims were set: (1) Identification and quantification of N2O concentration by FTIR in a laboratory setup. (2) Designing a novel closed system apparatus for monitoring gas emissions from incubated soil. (3) Measure N2O emissions from different soils types during incubation under various environmental conditions (such as acetylene presence, nitrogen fertilization, Glucose addition, oxygen presence and soil thickness). (4) Measure changes in the isotopic composition of emitted N2O as a function of fertilization with isotopically labeled nitrate.

Addition of acetylene, nitrate and glucose raised the measured concentration of emitted N2O. Under aerobic conditions, which encourage nitrification process, N2O emissions were not detected when running the experiments in thin layers of soil (~2mm). However, a thickness increase (to 10 mm, still under aerobic conditions) led to a significant increase in N2O emission, suggesting existence of coupled nitrification-denitrification processes.

By using FTIR monitoring different N2O emission profiles were identified for different soil types. Addition of 15NO3- to Acre Grumosol resulted in the emission of all four N2O species (i.e., 14N2O, 15N2O, 14N15NO & 15N14NO), with changing relative proportions at different incubation times. By using inverse modeling technique it was possible to overcome the partial overlap in the absorption spectra of the four isotopic species and quantify each one of them.

In summary, it has been proven that such FTIR method is able to detect and quantify online N2O emissions from soils and to identify and quantify emissions of all four N2O species - 14N2O, 15N2O, 14N15NO & 15N14NO.