Distribution and emission of N2O in the largest river-reservoir system along the Yellow River

Fang Cheng; Hong-Mei Zhang; Gui-Ling Zhang; Su-Mei Liu; Guo-Dong Song; Guan-Xiang Du

doi:10.1016/j.scitotenv.2019.02.277

Distribution and emission of N₂O in the largest river-reservoir system along the Yellow River

Sci Total Environ. 2019 May 20:666:1209-1219. doi: 10.1016/j.scitotenv.2019.02.277. Epub 2019 Feb 20.

Authors

Fang Cheng¹, Hong-Mei Zhang¹, Gui-Ling Zhang², Su-Mei Liu¹, Guo-Dong Song¹, Guan-Xiang Du¹

Affiliations

¹ Key Laboratory of Marine Chemistry Theory and Technology, Ministry of Education/Institute for Advanced Ocean Study, Ocean University of China, Qingdao 266100, China; Laboratory for Marine Ecology and Environmental Science, Qingdao National Laboratory for Marine Science and Technology, Qingdao 266237, PR China.
² Key Laboratory of Marine Chemistry Theory and Technology, Ministry of Education/Institute for Advanced Ocean Study, Ocean University of China, Qingdao 266100, China; Laboratory for Marine Ecology and Environmental Science, Qingdao National Laboratory for Marine Science and Technology, Qingdao 266237, PR China. Electronic address: guilingzhang@ouc.edu.cn.

PMID: 30970486
DOI: 10.1016/j.scitotenv.2019.02.277

Abstract

Rivers and reservoirs are affected by human activities and are sources of the greenhouse gas nitrous oxide (N₂O). Concentrations of N₂O in the middle and lower reaches of the Yellow River and Xiaolangdi Reservoir, China, were measured in June and December 2017. Fluxes were estimated by boundary layer method to explore their controlling factors, especially the impact of damming and reservoir operation. In the middle and lower reaches of the Yellow River, N₂O concentrations in surface waters were 26.65 ± 14.67 nmol L^-1 in summer and 21.16 ± 5.35 nmol L^-1 in winter. In comparison, the concentrations of N₂O in the reservoir were 32.94 ± 17.32 nmol L^-1 in summer and 23.73 ± 5.60 nmol L^-1 in winter. The longitudinal distribution of N₂O along the river exhibited different patterns with surface N₂O decreasing downstream towards the dam in summer but increasing in winter. Vertical profiles of N₂O concentrations in the reservoir showed an increase with depth in summer but were almost vertically uniform in winter. In winter, N₂O that had accumulated in the bottom water in summer was transported to the surface by vertical mixing and released into the atmosphere. Dissolved oxygen (DO), water temperature, and in situ biological production were the main factors affecting the distribution of N₂O. The mean emissions rates of N₂O from the surface waters were 13.7 ± 8.8 μmol m^-2 d^-1 in summer and 13.2 ± 7.6 μmol m^-2 d^-1 in winter. Approximately 1.31 × 10⁶ mol N₂O was released from the reservoir surface in 2017, which represents 0.12% of the annual N₂O emissions from global reservoirs. The construction of dams increased N₂O emission from the lower reaches of the river by 4.53 × 10⁵ mol and 1.22 × 10⁵ mol due to the discharge of the bottom water and the water and sediment regulation, respectively. This study demonstrates that the construction of dams and reservoir operation practices have made the Xiaolangdi Reservoir a key area for N₂O emissions.

Keywords: Damming; N(2)O emission; Water/sediment regulation scheme; Xiaolangdi Reservoir; Yellow River.