Denitrification as a major regional nitrogen sink in subtropical forest catchments: Evidence from multi‐site dual nitrate isotopes
Denitrification as a major regional nitrogen sink in subtropical forest catchments: Evidence from multi‐site dual nitrate isotopes
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DOI：
10.1111/gcb.14596
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发表时间：
2019-03
影响因子：
11.6
通讯作者：
Longfei Yu;J. Mulder;Jing Zhu;Xiaoshan Zhang;Zhangwei Wang;P. Dörsch
中科院分区：
文献类型：
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作者：
Longfei Yu;J. Mulder;Jing Zhu;Xiaoshan Zhang;Zhangwei Wang;P. Dörsch
中国南方亚热带森林中氮沉降的增加导致氮饱和，并伴随着大量的硝酸盐（NO3−）淋溶。强N衰减可能发生在水文上与排水良好的山坡相连的地下水排泄区，正如亚热带水源集水区“铁山坪”所示，其中双重NO3−同位素表明地下水排泄区是重要的N汇和反硝化热点。在这里，我们提出了一个区域研究报告无机氮通量在两个夏季活动中获得的双重NO3−同位素签名，在中国的7个森林流域，在气候和大气氮输入的梯度。在所有集水区，溶解无机氮通量表明，在排水良好的山坡上，NH 4+有效地转化为NO3−，随后NO3−通过含银B-层流入地下水排放区。山坡上15 N-和18 O-NO3-的消耗表明硝化作用是NO3-的主要来源。在所有集水区，除了北方的一个站点，这有低N沉积速率，NO3−的反硝化作用衰减发生在地下水排放区，如残留NO3−中的15 N和18 O同时富集所示。与南部站点相比，北方集水区缺乏连续和发育良好的地下水排放区，这解释了氮去除效率较低。使用基于15 NO3 −特征的模型，我们估计南部站点的反硝化通量为2.4至21.7 kg N ha−1年−1，占观测到的N去除量的一半以上。在整个南部集水区，估计反硝化比例与氮沉降。总之，这表明反硝化作用对氮的去除是中国南方森林氮收支的重要组成部分，NO3-的自然衰减可能会随着氮输入的增加而增加，从而部分抵消了该地区地表沃茨氮污染的进一步加剧。
Increasing nitrogen (N) deposition in subtropical forests in south China causes N saturation, associated with significant nitrate (NO3−) leaching. Strong N attenuation may occur in groundwater discharge zones hydrologically connected to well‐drained hillslopes, as has been shown for the subtropical headwater catchment “TieShanPing”, where dual NO3− isotopes indicated that groundwater discharge zones act as an important N sink and hotspot for denitrification. Here, we present a regional study reporting inorganic N fluxes over two years together with dual NO3− isotope signatures obtained in two summer campaigns from seven forested catchments in China, representing a gradient in climate and atmospheric N input. In all catchments, fluxes of dissolved inorganic N indicated efficient conversion of NH4+ to NO3− on well‐drained hillslopes, and subsequent interflow of NO3− over the argic B‐horizons to groundwater discharge zones. Depletion of 15N‐ and 18O–NO3− on hillslopes suggested nitrification as the main source of NO3−. In all catchments, except one of the northern sites, which had low N deposition rates, NO3− attenuation by denitrification occurred in groundwater discharge zones, as indicated by simultaneous 15N and 18O enrichment in residual NO3−. By contrast to the southern sites, the northern catchments lack continuous and well‐developed groundwater discharge zones, explaining less efficient N removal. Using a model based on 15NO3− signatures, we estimated denitrification fluxes from 2.4 to 21.7 kg N ha−1 year−1 for the southern sites, accounting for more than half of the observed N removal. Across the southern catchments, estimated denitrification scaled proportionally with N deposition. Together, this indicates that N removal by denitrification is an important component of the N budget of southern Chinese forests and that natural NO3− attenuation may increase with increasing N input, thus partly counteracting further aggravation of N contamination of surface waters in the region.