中文关键词农业源溪流溶存氧化亚氮饱和度硝态氮(NO₃^--N)反硝化温度 英文关键词agricultural headwater streamdissolved nitrous oxidesaturationnitrate (NO₃^--N)denitrificationtemperature

作者	单位	E-mail
田琳琳	中国科学院、水利部成都山地灾害与环境研究所, 成都 610041 中国科学院山地表生过程与生态调控重点实验室, 成都 610041 浙江农林大学省部共建亚热带森林培育国家重点实验室, 杭州 311300	tianll@zafu.edu.cn
王正	中国科学院、水利部成都山地灾害与环境研究所, 成都 610041 中国科学院山地表生过程与生态调控重点实验室, 成都 610041 中国科学院大学, 北京 100049
胡磊	中国科学院、水利部成都山地灾害与环境研究所, 成都 610041 中国科学院山地表生过程与生态调控重点实验室, 成都 610041 中国科学院大学, 北京 100049
任光前	中国科学院山地表生过程与生态调控重点实验室, 成都 610041 江苏大学环境与安全工程学院, 镇江 212013
朱波	中国科学院、水利部成都山地灾害与环境研究所, 成都 610041 中国科学院山地表生过程与生态调控重点实验室, 成都 610041	bzhu@imde.ac.cn

中文摘要 随着农业非点源氮（N）污染的加剧，农田周边溪流成为重要的活性N汇和潜在的氧化亚氮（N₂O）排放源.为查明长江上游农业源溪流中溶存N₂O浓度的全年动态变化特征，于2014年12月~2015年10月开展紫色土丘陵区典型农田源头溪流N₂O浓度的连续采样观测，采用水-气顶空平衡-气相色谱法测定顶空气体中N₂O浓度，根据相关参数计算出本研究水体中的溶存N₂O浓度，并同步测定溪流水体物理化学指标，分析水中溶存N₂O浓度的主要影响因素.结果表明，长江上游紫色土丘陵区的典型农业源溪流的硝态氮（NO₃^--N）是最主要的活性N赋存形态（年均1.45 mg·L^-1），溪流水体溶存N₂O质量浓度（以N计）全年平均为0.57 μg·L^-1（范围0.26~1.28 μg·L^-1），冬、春、夏和秋季的均值分别为0.63、0.45、0.53和0.64 μg·L^-1，但季节间无显著差异.溪流水体溶存N₂O浓度全年都处于过度饱和状态（饱和度年平均为203.9%，范围109.7%~546.5%），可见，农业源溪流全年均为潜在的N₂O释放源.溪流溶存N₂O浓度的变化主要由水体NO₃^--N浓度决定，N₂O的主要产生机制为反硝化作用；溪流季节平均N₂O饱和度在夏、秋季显著高于冬、春季，水中溶存N₂O饱和度的变化主要受水温和NO₃^--N浓度的共同影响.研究还发现农业源溪流中溶存N₂O浓度在4~10月（湿润季节）间波动明显，较强降雨可促使其水中NO₃^--N浓度在雨后短期内升高，进而促进水体反硝化作用，导致雨后溪流中溶存N₂O浓度的增加. 英文摘要 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.

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