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

作者：Shaonan Huang, Fan Wang, Emily M. Elliott, Feifei Zhu, Weixing Zhu, Keisuke Koba, Zhongjie Yu, Erik A. Hobbie, Greg M. Michalski, Ronghua Kang, Anzhi Wang, Jiaojun Zhu, Shenglei Fu, Yunting Fang · 发表于：Environmental Science & Technology · 年份：2020 · DOI：10.1021/acs.est.9b07839 · 被引用次数：62 · 研究领域：Soil and Water Nutrient Dynamics、Groundwater and Isotope Geochemistry、Hydrology and Watershed Management Studies

Abstract 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.