Isotopic evidence that recent agriculture overprints climate variability in nitrogen deposition to the Tibetan Plateau

Zhengjie Li; Meredith G Hastings; Wendell W Walters; Lide Tian; Steven C Clemens; Linlin Song; Lili Shao; Yunting Fang

doi:10.1016/j.envint.2020.105614

Isotopic evidence that recent agriculture overprints climate variability in nitrogen deposition to the Tibetan Plateau

Environ Int. 2020 May:138:105614. doi: 10.1016/j.envint.2020.105614. Epub 2020 Mar 7.

Authors

Zhengjie Li¹, Meredith G Hastings², Wendell W Walters³, Lide Tian⁴, Steven C Clemens⁵, Linlin Song⁶, Lili Shao⁷, Yunting Fang⁸

Affiliations

¹ CAS Key Laboratory of Forest Ecology and Management, Institute of Applied Ecology, Chinese Academy of Sciences, Shenyang, Liaoning 110016, China; Department of Earth, Environmental and Planetary Sciences, Brown University, Providence, Rhode Island 02912, USA; College of Resources and Environment, University of Chinese Academy of Sciences, Beijing 100049, China; Key Laboratory of Stable Isotope Techniques and Applications, Shenyang, Liaoning 110016, China.
² Department of Earth, Environmental and Planetary Sciences, Brown University, Providence, Rhode Island 02912, USA; Institute at Brown for Environment and Society, Brown University, Providence, Rhode Island 02912, USA. Electronic address: meredith_hastings@brown.edu.
³ Department of Earth, Environmental and Planetary Sciences, Brown University, Providence, Rhode Island 02912, USA; Institute at Brown for Environment and Society, Brown University, Providence, Rhode Island 02912, USA.
⁴ Institute of International Rivers and Eco-Security, Yunnan University, Kunming, Yunnan 650500, China; Institute of Tibetan Plateau Research, Chinese Academy of Sciences (CAS), Beijing 100101, China.
⁵ Department of Earth, Environmental and Planetary Sciences, Brown University, Providence, Rhode Island 02912, USA.
⁶ CAS Key Laboratory of Forest Ecology and Management, Institute of Applied Ecology, Chinese Academy of Sciences, Shenyang, Liaoning 110016, China; College of Resources and Environment, University of Chinese Academy of Sciences, Beijing 100049, China; Key Laboratory of Stable Isotope Techniques and Applications, Shenyang, Liaoning 110016, China.
⁷ Institute of International Rivers and Eco-Security, Yunnan University, Kunming, Yunnan 650500, China.
⁸ CAS Key Laboratory of Forest Ecology and Management, Institute of Applied Ecology, Chinese Academy of Sciences, Shenyang, Liaoning 110016, China; Qingyuan Forest CERN, Shenyang, Liaoning 110016, China; Key Laboratory of Stable Isotope Techniques and Applications, Shenyang, Liaoning 110016, China. Electronic address: fangyt@iae.ac.cn.

PMID: 32155512
DOI: 10.1016/j.envint.2020.105614

Abstract

The stable isotopes of nitrogen in nitrate archived in polar ice have been interpreted as reflecting a shift in reactive nitrogen sources or changes in atmospheric chemical reactivity. Here, we present a novel concentration and isotopic record of nitrate (δ¹⁵N-NO₃^-) from a central Tibetan Plateau ice core over the last ~200 years. We find that nitrate concentration increased from 6.0 ± 2.3 μeq/L (mean ± 1σ) in the preindustrial period (prior to 1900s) to 7.3 ± 2.7 μeq/L in post-1950. Over the same time period, the δ¹⁵N-NO₃^- decreased from 8.7 ± 3.7‰ to 4.2 ± 3.1‰, with much larger interannual variation in δ¹⁵N-NO₃^- during the preindustrial period. We present a useful framework for quantifying the sensitivity of the isotopic composition of atmospheric nitrate to changes in both sources and chemistry (gas and aerosol phase). After 1950, nitrogen deposition is primarily driven by fertilizer use, leading to significant increases in concentration and decreases in δ¹⁵N-NO₃^-. The large interannual variability of ice core δ¹⁵N-NO₃^- in the preindustrial reflects natural processes, namely the El Niño Southern Oscillation (ENSO) and dust events. Our results highlight a new connection between the nitrogen cycle and ENSO, and the overprinting of natural climate signals by recent anthropogenic increases in reactive nitrogen release.

Keywords: Agriculture NO(x) emissions; Climate variability; Ice core; Nitrogen stable isotope.

Publication types

Research Support, Non-U.S. Gov't
Research Support, U.S. Gov't, Non-P.H.S.

MeSH terms

Agriculture
Environmental Monitoring
Nitrates / analysis
Nitrogen Isotopes / analysis
Nitrogen* / analysis
Tibet
Water Pollutants, Chemical* / analysis

Substances

Nitrates
Nitrogen Isotopes
Water Pollutants, Chemical
Nitrogen