Abstract: To investigate the nitrogen contribution of terrestrial ecosystems along Niyaqu, a Namco lake-entering river, and to determine the role of wetlands along the river in the riverine system, the spatial pattern of nitrogen transport was monitored and analysed. During the 2019—2021 growing season, we measured flow and nitrogen component concentrations at multiple cross sections along the Niyaqu River. The results showed that locations (or cross sections) had no significant effect on total nitrogen (TN), nitrate nitrogen and ammonia nitrogen concentrations, while year and month did. The mean of TN was in the range of 0.207 ± 0.003 mg N·L^-1. The wetlands increased TN slightly by 0.022 ± 0.002 mg·L^-1(P<0.05), but not nitrate nitrogen and ammonia nitrogen. Although terrestrial ecosystems recharge water along the way into the lake, TN throughout the river is slightly lower than the wet deposition level of inorganic N, which was reported to be 0.21 ~ 0.24 mg·L^-1 in two multi-year studies at Namco Station. It could be concluded that terrestrial ecosystems along the Niyaqu River do not contribute additional nitrogen to Namco through the river.

Key words: Namco, Qinghai-Tibetan plateau, nitrogen fraction, river, spatial and temporal characteristic