[Characteristics of the Dissolved Nitrous Oxide (N2O) Concentrations and Influencing Factors in a Representative Agricultural Headwater Stream in the Upper Reach of the Yangtze River]

Lin-Lin Tian; Zheng Wang; Lei Hu; Guang-Qian Ren; Bo Zhu

doi:10.13227/j.hjkx.201808251

[Characteristics of the Dissolved Nitrous Oxide (N₂O) Concentrations and Influencing Factors in a Representative Agricultural Headwater Stream in the Upper Reach of the Yangtze River]

Huan Jing Ke Xue. 2019 Apr 8;40(4):1939-1949. doi: 10.13227/j.hjkx.201808251.

[Article in Chinese]

Authors

Lin-Lin Tian^{1

2

3}, Zheng Wang^{1

2

4}, Lei Hu^{1

2

4}, Guang-Qian Ren^{2

5}, Bo Zhu^{1

2}

Affiliations

¹ Institute of Mountain Hazards and Environment, Chinese Academy of Sciences, Chengdu 610041, China.
² Key Laboratory of Mountain Surface Processes and Ecological Regulation, Chinese Academy of Sciences, Chengdu 610041, China.
³ State Key Laboratory of Subtropical Silviculture, Zhejiang A & F University, Hangzhou 311300, China.
⁴ University of Chinese Academy of Sciences, Beijing 100049, China.
⁵ School of the Environment and Safety Engineering, University of Jiangsu, Zhenjiang 212013, China.

PMID: 31087940
DOI: 10.13227/j.hjkx.201808251

Abstract

Headwater streams around agricultural farmlands can act as important sinks of active nitrogen (N) and potential sources of indirect nitrous oxide (N₂O) emissions, as well as aggravating agricultural non-point source N pollution. In this study, the dynamic characteristics of the dissolved N₂O concentration in an agricultural headwater stream in the hilly area of purple soil in the upper reach of the Yangtze River were observed during the period Dec. 2014-Oct. 2015 by measuring the headspace gaseous N₂O concentration using headspace equilibration-gas chromatography, and the dissolved N₂O concentration was calculated according to the related parameters. Simultaneously, the physical and chemical parameters of the stream water were also monitored to understand the factors that affect the dissolved N₂O concentration. The results showed that the dissolved N₂O concentration in the agricultural headwater stream ranged from 0.26 to 1.28 μg·L^-1 with an annual mean value of 0.57 μg·L^-1, with nitrate (NO₃^--N, with an annual mean concentration of 1.45 mg·L^-1) as the predominant reactive N form. The seasonal mean concentrations of the dissolved N₂O in winter, spring, summer, and autumn were 0.63, 0.45, 0.53, and 0.64 μg·L^-1, respectively, without significant seasonal variations. The annual dynamics of the dissolved N₂O concentration were primarily governed by the concentration of NO₃^--N in the stream water, with denitrification being the main process producing N₂O. The saturation levels of the dissolved N₂O in the stream water showed oversaturation, with an annual mean value of 203.9% (109.7%-546.5%), with a seasonal pattern in which the saturation levels in the summer and autumn were higher than those in the winter and spring, indicating that the agricultural headwater stream can release indirect N₂O emissions throughout the year. The temporal variations in the saturation levels of the dissolved N₂O were mainly controlled by the water temperature and the NO₃^--N concentration of the stream water. During April-October, the concentration of dissolved N₂O in the stream fluctuated obviously as a result of heavy rainfall, which resulted in an increase of the concentration of NO₃-N in the stream water in the short term after the rain, which promoted denitrification and then increased the dissolved N₂O level correspondingly.

Keywords: agricultural headwater stream; denitrification; dissolved nitrous oxide; nitrate (NO3--N); saturation; temperature.

Publication types

English Abstract