Abstract：To deeply understand the nitrogen cycling process in alpine forest small watersheds in the northeast of the Tibetan Plateau, the throughfall, soil water and surface runoff at two alpine forest sites in Datong and Huangyuan in the Hehuang Valley in the Tibetan Plateau were studied from April to September 2022. The concentration and flux of dissolved inorganic nitrogen (DIN) were monitored, and the distribution characteristics of nitrogen and oxygen (N and O) isotopes of nitrate (NO3−) along the hydrological path (from throughfall to soil water and then to surface runoff) was analyzed via stable isotope technology. The results showed that the average nitrogen deposition in Datong and Huangyuan (3.60kg/(hm2·a)) was higher than that in the Tibetan Plateau (2.94kg/(hm2·a)), and the nitrogen deposition in Huangyuan (4.17kg/(hm2·a)) was higher than that in Datong (3.02kg/(hm2·a)). The average concentration of NO3− in soil water at the two alpine forest small watersheds was 5.78mg/L. The average δ18O-NO3− ((−1.54±9.77)‰) in soil water was lower than that in throughfall ((74.2±0.01)‰), indicating that nitrification occurred in alpine forest soil. Over 90% of the NO3− in soil water was from soil nitrification using the end member model analysis, and the remaining approximately 10% might be came from atmospheric deposition. The average concentration of NO3− in surface runoff at the two alpine forest small watersheds was 5.73mg/L. The δ18O-NO3− and δ15N-NO3− in surface runoff were enriched along the growth trend of 1:2, indicating that a denitrification process occurred in surface runoff. The δ15N-NO3− and δ18O-NO3− in the Tibetan Plateau alpine forests decreased from throughfall to soil water, and then increased from soil water to surface runoff.
韩怡蒙, 周剑兴, 夏凡, 李秉珍, 谢丹妮. 高寒森林硝酸盐氮氧同位素沿水文路径的分布[J]. 中国环境科学, 2025, 45(2): 935-942.
HAN Yi-meng, ZHOU Jian-xing, XIA Fan, LI Bing-zhen, XIE Dan-ni. Distribution of nitrate nitrogen and oxygen isotopes along the hydrological path in alpine forests. CHINA ENVIRONMENTAL SCIENCECE, 2025, 45(2): 935-942.
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