澜沧江(云南段)水-气界面氧化亚氮释放通量时空分布特征及其影响因素研究

Spatial-temporal Distribution and Influencing Factors of Nitrous Oxide Flux Across the Water-air Interface in Lancang River, China

温室气体浓度上升导致全球气候变暖已成为国际社会关注的焦点。氧化亚氮(N_(2)O)作为痕量温室气体,在全球气候变暖过程中扮演着重要的角色。河流和水库被认为是N_(2)O释放的活跃区域,然而目前研究多集中在对单一河流或水库的监测,对大范围河库系统的N_(2)O研究仍相对欠缺。选取澜沧江(云南段)流域作为考察对象,在2022年4月、8月采用悬浮箱采集24个点位的水-气界面的气体样品,并于实验室通过气象色谱仪检测气样氧化亚氮浓度,探究该流域干支流N_(2)O释放通量的时空分布特征;同时,测定了水体水环境参数,解析其时空差异的环境影响因素。结果表明,1)在时间尺度上,澜沧江(云南段)旱季N_(2)O通量均值低于雨季。旱季N_(2)O通量均值为0.10 mg·m^(-2)·d^(-1),雨季为0.18 mg·m^(-2)·d^(-1),其中旱季干流均值为0.11 mg·m^(-2)·d^(-1),支流为0.05 mg·m^(-2)·d^(-1);雨季干流均值为0.18 mg·m^(-2)·d^(-1),支流为0.15 mg·m^(-2)·d^(-1)。2)在空间尺度上,N_(2)O通量沿程整体呈现释放量递增的趋势。干流N_(2)O通量均值为0.15 mg·m^(-2)·d^(-1),支流为0.10 mg·m^(-2)·d^(-1),干流N_(2)O通量高于支流。水库坝上N_(2)O通量均值为0.02 mg·m^(-2)·d^(-1),坝下为0.31 mg·m^(-2)·d^(-1),水库坝下N_(2)O通量值是坝上的15.5倍,水库发电下泄高速水流加速了水-气界面N_(2)O释放。3)澜沧江水-气界面N_(2)O通量与水温(WT)(r=0.341,P=0.009)、氨氮(NH4^(+))(r=0.384,P=0.004)和流速(r=0.283,P=0.026)呈显著正相关关系,与溶解氧(DO)(r=-0.420,P=0.001)呈显著负相关关系,表明在高WT、低DO、高NH4^(+)和高流速条件下有利于N_(2)O产生与释放。研究结果揭示澜沧江(云南段)河库系统氧化亚氮释放通量时空分布特征以及影响因素,为流域温室气体排放评估提供数据支持和科学依据。

Global warming,caused by an increase in the concentration of greenhouse gases(GHGs),has gained significant international attention.Nitrous oxide(N_(2)O)is a trace greenhouse gas that contributes significantly to global warming.While rivers and reservoirs are considered significant sources of N_(2)O emissions,current research primarily focuses on monitoring individual water bodies,leaving a gap in the study of N_(2)O 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 N_(2)O 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 N_(2)O 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,N_(2)O flux along the river showed an overall increasing trend.The main stream’s N_(2)O flux mean is 0.15 mg·m^(-2)·d^(-1),higher than the tributary’s 0.10 mg·m^(-2)·d^(-1).The N_(2)O 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 N_(2)O 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 N_(2)O release.3)The relationship between N_(2)O flux at the Lancang River water-air interface and various factors was analyzed,revealing a positive correlation with water temperature(WT)(r=0.341,P=0.009),ammonia nitrogen(NH4^(+))(r=0.384,P=0.004)and flow velocity(r=0.283,P=0.026)and a negative correlation with dissolved oxygen(DO)(r=-0.420,P=0.001).These findings suggest that N_(2)O 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.