关键词: 澜沧江, 氧化亚氮（N₂O）, 释放通量, 时空分布, 影响因素, 水-气界面

Abstract:

Global warming, caused by an increase in the concentration of greenhouse gases (GHGs), has gained significant international attention. Nitrous oxide (N₂O) is a trace greenhouse gas that contributes significantly to global warming. While rivers and reservoirs are considered significant sources of N₂O emissions, current research primarily focuses on monitoring individual water bodies, leaving a gap in the study of N₂O across large regions such as the Lancang River (Yunnan section). To address this gap, gas samples were collected at 24 locations along the water-air interface of the river using floating chambers in April and August 2022. Gas chromatography was used to determine nitrous oxide concentrations and examine the spatiotemporal distribution characteristics of N₂O flux in the main and tributary streams of this basin. Simultaneously, the water environmental parameters were measured to evaluate the environmental factors that affect spatiotemporal differences. The results indicate that 1) on a temporal scale, the N₂O flux during the dry season in the Lancang River (Yunnan section) is lower than that in the rainy season, with average values of 0.10 mg·m⁻²·d⁻¹ and 0.18 mg·m⁻²·d⁻¹, respectively. The dry season mean is 0.11 mg·m⁻²·d⁻¹ for the main stream and 0.05 mg·m⁻²·d⁻¹ for the tributary; the rainy season mean is 0.18 mg·m⁻²·d⁻¹ for the main stream, and 0.15 mg·m⁻²·d⁻¹ for the tributary. 2) Spatially, N₂O flux along the river showed an overall increasing trend. The main stream’s N₂O flux mean is 0.15 mg·m⁻²·d⁻¹, higher than the tributary’s 0.10 mg·m⁻²·d⁻¹. The N₂O flux above the dam of the reservoir is 0.02 mg·m⁻²·d⁻¹, while it is 0.31 mg·m⁻²·d⁻¹ below the dam, indicating that the N₂O flux below the dam is 15.5 times higher than above, suggesting that the accelerated water flow during reservoir power generation enhances the water-air interface N₂O release. 3) The relationship between N₂O flux at the Lancang River water-air interface and various factors was analyzed, revealing a positive correlation with water temperature (WT) (r=0.561, P=0.000), ammonia nitrogen (NH₄⁺) (r=0.377, P=0.015), and flow velocity (r=0.331, P=0.026) and a negative correlation with dissolved oxygen (DO) (r= −0.507, P=0.000). These findings suggest that N₂O production and release are favored under conditions of high WT, low DO, high NH₄⁺, and high flow velocity, and provide essential information on the spatiotemporal distribution characteristics and influencing factors of nitrous oxide release flux in the Lancang River (Yunnan section) river-reservoir system. This information is crucial for assessing greenhouse gas emissions in watersheds.

Key words: Lancang River, nitrous oxide (N₂O), emission flux, spatial and temporal distribution, influencing factors, water-gas interface