高寒森林硝酸盐氮氧同位素沿水文路径的分布

韩怡蒙; 周剑兴; 夏凡; 李秉珍; 谢丹妮

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中国环境科学 ›› 2025, Vol. 45 ›› Issue (2) : 935-942.

环境生态

高寒森林硝酸盐氮氧同位素沿水文路径的分布

韩怡蒙, 周剑兴, 夏凡, 李秉珍, 谢丹妮

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Distribution of nitrate nitrogen and oxygen isotopes along the hydrological path in alpine forests

HAN Yi-meng, ZHOU Jian-xing, XIA Fan, LI Bing-zhen, XIE Dan-ni

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摘要

为深入了解青藏高原东北部高寒森林小流域的氮循环过程,2022年4~9月,以青藏高原河湟谷地大通和湟源两处高寒森林站点的穿透水、土壤水和地表径流为研究对象,监测其可溶性无机氮(DIN)的浓度和通量,并利用稳定同位素技术分析硝酸盐(NO₃⁻)的氮氧(N、O)同位素沿水文路径(穿透水−土壤水−地表径流)的分布特征.结果表明,大通和湟源高寒森林的平均氮沉降(3.60kg/(hm²·a))高于青藏高原地区的平均氮沉降(2.94kg/(hm²·a)),并且湟源高寒森林氮沉降(4.17kg/(hm²·a))高于大通高寒森林氮沉降(3.02kg/(hm²·a)).两处高寒森林小流域土壤水中NO₃⁻的平均浓度为5.78mg/L,其δ¹⁸O−NO₃⁻平均值((−1.54±9.77)‰)低于穿透水中δ¹⁸O−NO₃⁻的平均值((74.2±0.01)‰),表明高寒森林土壤中发生了硝化作用.利用端元混合模型计算发现土壤的硝化作用贡献了土壤水中90%以上的NO₃⁻,其余约10%则来源于大气沉降.两处高寒森林地表径流中NO₃⁻的平均浓度为5.73mg/L,其δ¹⁸O−NO₃⁻和δ¹⁵N−NO₃⁻沿1:2的增长趋势富集,表明地表径流中存在反硝化过程.青藏高原高寒森林中的δ¹⁵N−NO₃⁻和δ¹⁸O−NO₃⁻沿穿透水−土壤水−地表径流均呈现先减小后增大的趋势.

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.

导出引用

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[J]. China Environmental Science. 2025, 45(2): 935-942

中图分类号： X142

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