Yu, Zhongjie
(2019)
Examining sources and dynamics of soil nitric oxide using stable isotope techniques.
Doctoral Dissertation, University of Pittsburgh.
(Unpublished)
Abstract
Emissions of nitrogen oxides (NOx) degrade air quality and affect global tropospheric chemistry. Nitric oxide (NO) produced during microbial nitrification and denitrification in soils is an important source of atmospheric NOx. However, due to the diffuse nature, low concentrations, and high sensitivity to changing climatic and soil state variables, soil NO emissions are notoriously difficult to quantify. Consequently, it remains unclear how NO production is mediated by nitrogen (N) transformation processes in soil.
Stable isotope techniques are an emerging tool for characterizing the soil N cycle. This dissertation presents a comprehensive methodological framework for examining soil NO dynamics and its driving forces using stable N and oxygen (O) isotopes. A new analytical method was developed to measure N isotopes of soil-emitted NO (δ15N-NO) with a precision of ±1.1‰. Application of this new method in laboratory and field soil wetting experiments yielded results with important implications for understanding the mechanisms that sustain wetting-triggered NO emission pulses. To bridge NO emission with soil N transformations, a numerical model exploiting NO3- 17O anomaly (Δ17O) as a conservative tracer was developed to quantify soil nitrification and NO3- consumption rates. Field application of this model revealed co-occurring nitrification and denitrification in surface soil after a snowmelt event, leading to insights into the isotopic systematics of soil NO3- cycling. Coupling the δ15N-NO analysis with the Δ17O-based model, a series of laboratory experiments was conducted to characterize NO production during nitrification and denitrification in an agricultural soil. The results show that nitrification and denitrification have distinguishable isotopic imprints on NO production and that denitrification is a significant, yet under-characterized source of soil NO production even under conditions strongly favoring nitrification. Finally, a year-long measurement of NO3- in surface soil and lysimeter water was conducted at three field sites with contrasting N availability. The measured NO3- concentrations and dual isotopes (δ15N and δ18O) were used in an isotopic mass balance model to examine ecosystem N saturation, hydrological NO3- leaching, and denitrification. Overall, the results from this work provide process-based information about soil NO dynamics and its underlying processes that may help constrain soil NO emission at various scales.
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Details
| Item Type: |
University of Pittsburgh ETD
|
| Status: |
Unpublished |
| Creators/Authors: |
|
| ETD Committee: |
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| Date: |
31 January 2019 |
| Date Type: |
Publication |
| Defense Date: |
10 August 2018 |
| Approval Date: |
31 January 2019 |
| Submission Date: |
30 August 2018 |
| Access Restriction: |
5 year -- Restrict access to University of Pittsburgh for a period of 5 years. |
| Number of Pages: |
241 |
| Institution: |
University of Pittsburgh |
| Schools and Programs: |
Dietrich School of Arts and Sciences > Geology and Environmental Science |
| Degree: |
PhD - Doctor of Philosophy |
| Thesis Type: |
Doctoral Dissertation |
| Refereed: |
Yes |
| Uncontrolled Keywords: |
Nitric oxide, Soils, Nitrogen isotopes, Oxygen isotopes |
| Date Deposited: |
31 Jan 2019 22:41 |
| Last Modified: |
31 Jan 2024 06:15 |
| URI: |
http://d-scholarship.pitt.edu/id/eprint/35276 |
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