Multiyear Measurements on Δ17O of Stream Nitrate Indicate High Nitrate Production in a Temperate Forest

• Published in: Environmental science & technology Vol. 54; no. 7; pp. 4231 - 4239
• Main Authors: Huang, Shaonan, Wang, Fan, Elliott, Emily M, Zhu, Feifei, Zhu, Weixing, Koba, Keisuke, Yu, Zhongjie, Hobbie, Erik A, Michalski, Greg, Kang, Ronghua, Wang, Anzhi, Zhu, Jiaojun, Fu, Shenglei, Fang, Yunting
• Format: Journal Article
• Language: English
• Published: Easton American Chemical Society 07-04-2020
• Subjects: Atmospheric pollution deposition; Catchment scale; Catchments; Cycles; Environmental changes; Forest ecosystems; Forest watersheds; In situ leaching; Leaching; Nitrates; Nitrification; Nitrogen; Oxygen isotopes; Temperate forests
• ISSN: 0013-936X; 1520-5851
• DOI: 10.1021/acs.est.9b07839

Nitrification is a crucial step in ecosystem nitrogen (N) cycling, but scaling up from plot-based measurements of gross nitrification to catchments is difficult. Here, we employed a newly developed method in which the oxygen isotope anomaly (Δ17O) of nitrate (NO3 –) is used as a natural tracer to quantify in situ catchment-scale gross nitrification rate (GNR) for a temperate forest from 2014 to 2017 in northeastern China. The annual GNR ranged from 71 to 120 kg N ha–1 yr–1 (average 94 ± 10 kg N ha–1 yr–1) over the 4 years in this forest. This result and high stream NO3 – loss (4.2–8.9 kg N ha–1 yr–1) suggest that the forested catchment may have been N-saturated. At the catchment scale, the total N output of 10.7 kg N ha–1 yr–1, via leaching and gaseous losses, accounts for 56% of the N input from bulk precipitation (19.2 kg N ha–1 yr–1). This result indicates that the forested catchment is still retaining a large fraction of N from atmospheric deposition. Our study suggests that estimating in situ catchment-scale GNR over several years when combined with other conventional flux estimates can facilitate the understanding of N biogeochemical cycling and changes in the ecosystem N status.