Quantifying the production of dissolved organic nitrogen in headwater streams using 15N tracer additions
Quantifying the production of dissolved organic nitrogen in headwater streams using 15N tracer additions
复制标题
使用 15N 示踪剂添加来量化源头水流中溶解有机氮的产生
DOI：
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发表时间：
2013
期刊：
影响因子：
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通讯作者：
Suzanne M. Thomas
中科院分区：
文献类型：
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作者：
L. Johnson;J. Tank;Robert O. Hall, Jr.;P. Mulholland;S. Hamilton;H. Valett;J. Webster;Melody J. Bernot;W. McDowell;B. Peterson;Suzanne M. Thomas
湖泊和海洋生态系统中的大多数氮(N)同化通常随后通过本地溶解有机氮（DON）产生释放，但流动水体中的本地DON产生尚未量化。我们在36条水源中添加15N -硝酸盐示踪剂24小时后测量了溪流中DON的产量，这些水源是第二次Lotic站点间氮实验的一个子集。河流分布在北美的五个生态区和以原生植被、农业或城市土地利用为主的排水盆地。利用两室模型，我们可以量化15条河流的DON产量，作为生物量室中15N示踪剂得出的DO15N的函数。与未检测到DON产量的河流相比，可检测到DON产量的河流在其流域的改良土地利用（农业+城市）百分比更高。当我们使用基于1 d内氮同化的N生物量估算时（直接从添加的15N中测量），中位DON产量占总吸收量的8%。当我们使用超过42 d的氮同化时，中位DON产量为总吸收量的17%（根据之前的15N示踪剂研究推断）。DON产量变化与生态系统呼吸正相关，表明水体异养可能影响DON产量。河流中DON的产生与河流反硝化和硝化作用的大小相似，表明原生DON的产生可以代表河流N的实质性转化。我们的研究结果证实，源头河流可以迅速将无机N转化为有机形式，尽管DON的最终命运尚不清楚。
Most nitrogen (N) assimilation in lake and marine ecosystems is often subsequently released via autochthonous dissolved organic nitrogen (DON) production, but autochthonous DON production has yet to be quantified in flowing waters. We measured in‐stream DON production following 24 h 15N‐nitrate () tracer additions in 36 headwater streams, a subset of sites from the second Lotic Intersite Nitrogen eXperiment. Streams were located in five North American ecoregions and drained basins dominated by native vegetation, agriculture, or urban land use. Using a two‐compartment model, we could quantify DON production in 15 streams as a function of DO15N derived from 15N tracer in biomass compartments. The streams with detectable DON production had higher % modified land use (agriculture + urban) in their basins than did streams with undetectable DON production. Median DON production represented 8% of total uptake when we used N biomass estimates based on N assimilated over 1 d (measured directly from the 15N additions). Median DON production was 17% of total uptake when we used N assimilated over 42 d (extrapolated from previous 15N tracer studies). Variation in DON production was positively correlated with ecosystem respiration, indicating that stream heterotrophy may influence DON production. In‐stream DON production was similar in magnitude to stream denitrification and nitrification, indicating that the production of autochthonous DON can represent a substantial transformation of stream N. Our results confirm that headwater streams can quickly convert inorganic N into organic forms, although the ultimate fate of DON remains unclear.