State Key Laboratory of Water Environment Simulation, School of Environment, Beijing Normal University, Beijing 100875, China.
State Key Laboratory of Water Environment Simulation, School of Environment, Beijing Normal University, Beijing 100875, China.
Sci Total Environ. 2018 Dec 15;645:318-328. doi: 10.1016/j.scitotenv.2018.07.090. Epub 2018 Jul 17.
Rivers are important sites of both nitrogen removal and emission of nitrous oxide (NO), a powerful greenhouse gas. Previous measurements have focused on nitrogen-rich temperate rivers, with cold, low-nitrogen river systems at high-altitude receiving less attention. Here, nitrogen removal rates were estimated by directly measuring dissolved N and NO of the Yellow River in its source region of the Tibetan Plateau, a frigid high-altitude environment. We measured the dissolved N and NO using N:Ar ratio method and headspace equilibrium technique, respectively. Dissolved N in the river water ranged from 337 to 513 μmol N L, and dissolved NO ranged from 10.4 to 15.4 nmol NO L. Excess dissolved N (△N) ranged from -8.6 to 10.5 μmol N L, while excess dissolved NO (△NO) ranged from 2.1 to 8.3 nmol NO L; they were relatively low compared with most other rivers in the world. However, N removal fraction (△N/DIN, average 21.6%) and EF values (NO - N/NO - N, range 1.6 × 10-5.0 × 10) were comparable with many other rivers despite the high altitude for the Yellow River source region. Furthermore, the EF values increased with altitude. Estimated fluxes of N and NO to the atmosphere from the river surface ranged from -67.5 to 93.5 mmol N m d and from 4.8 to 93.8 μmol N m d, respectively, and the nitrogen removal from rivers was estimated to be 1.87 × 10 kg N yr for the Yellow River source region. This is the first report of nitrogen removal for a frigid high-altitude river; the results suggest that N removal and NO emission from cold high-altitude rivers should be considered in the global nitrogen budget.
河流是氮去除和氧化亚氮（N2O）排放的重要场所，N2O 是一种强大的温室气体。以前的测量主要集中在富氮温带河流上，而高寒高海拔的低温、低氮河流系统则受到较少关注。在这里，通过直接测量青藏高原黄河源头地区的黄河水中溶解的 N 和 NO，来估算氮去除速率。我们使用 N:Ar 比法和顶空平衡技术分别测量了水中的溶解 N 和 NO。河水的溶解 N 范围为 337 至 513 μmol N L，溶解的 NO 范围为 10.4 至 15.4 nmol NO L。过量溶解 N（△N）范围为-8.6 至 10.5 μmol N L，而过量溶解的 NO（△NO）范围为 2.1 至 8.3 nmol NO L；与世界上大多数其他河流相比，这些值相对较低。然而，尽管黄河源区海拔较高，但 N 去除分数（△N/DIN，平均值为 21.6%）和 EF 值（NO-N/NO-N，范围为 1.6×10-5.0×10）与许多其他河流相当。此外，EF 值随海拔升高而增加。从河表面到大气的 N 和 NO 通量分别为-67.5 至 93.5 mmol N m d 和 4.8 至 93.8 μmol N m d，估计黄河源区河流的氮去除量为 1.87×10 kg N yr。这是首次报道高寒河流的氮去除；结果表明，应在全球氮预算中考虑到寒冷高海拔河流的氮去除和 NO 排放。
