Stream Transport and Substrate Controls on Nitrous Oxide Yields From Hyporheic Zone Denitrification
Stream Transport and Substrate Controls on Nitrous Oxide Yields From Hyporheic Zone Denitrification
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河流输送和基质对高湿带反硝化一氧化二氮产生量的控制
DOI：
10.1029/2021av000517
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发表时间：
2021-10
期刊：
影响因子：
8.4
通讯作者：
M. Winnick
中科院分区：
文献类型：
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作者：
M. Winnick
河流和溪流是大气中一氧化二氮(N2O)的全球重要来源，部分是通过反硝化反应，这种反应将随着持续的人为氮负荷而增加。虽然相对于惰性氮素(N_2)，许多因素对N2O的释放有很好的描述，但从蒸气中预测N_2O产生量的能力仍然是一个根本的挑战。在这里，我回顾了第二次洛蒂克站点间氮实验(LINX II)在湍流低渗交换的背景下的结果。反硝化效率，即由水流湍流输送到河床的硝酸盐被化学还原的比例，是N2O产量的唯一最佳预测因子，并支持第一个具有统计意义的站点间N2O产量模型。这种机制上的联系得到了代表平流流动路径、流动路径混合和扩散主导的缺氧微区的低渗透带反硝化反应传输模型的支持。模拟的N2O产生量与反硝化效率呈负相关；然而，在低反硝化效率的情况下，平流模型无法捕捉到低LINX II N2O产生量。低渗带混合加剧了这种无法捕获观测到的N2O产量的情况，这是通过促进快速、有氧流动路径中的N2O释放来实现的。相反，要求缺氧微区通过持续较低的N2O产量和上游产生的N2O的消耗来解释LINX II观测结果。综上所述，这些结果为控制河流N2O产生量提供了一个框架，并表明，旨在增加地下水带修复硝酸盐负荷能力的河流廊道恢复设计，而不是增加地下水交换，也将减少N2O的比例排放。
Rivers and streams act as globally significant sources of nitrous oxide (N2O) to the atmosphere, in part through denitrification reactions that will increase in response to ongoing anthropogenic nitrogen loading. While many factors that contribute to the release of N2O relative to inert dinitrogen (N2) are well described, the ability to predict N2O yields from streams remains a fundamental challenge. Here, I revisit results from the second Lotic Intersite Nitrogen eXperiments (LINX II) in the context of turbulent hyporheic exchange. Denitrification efficiency, or the fraction of nitrate delivered to the streambed by stream turbulence that is chemically reduced, emerges as the single best predictor of N2O yields and underpins the first statistically significant models of inter‐site N2O yields. This mechanistic connection is supported by reactive transport modeling of hyporheic zone denitrification representing advective flowpaths, flowpath mixing, and diffusion‐dominated anoxic microzones. Simulated N2O yields are inversely correlated with denitrification efficiency; however, advective models are unable to capture low LINX II N2O yields at low denitrification efficiencies. Hyporheic zone mixing exacerbates this inability to capture observed N2O yields via the promotion of N2O release from fast, oxic flowpaths. Instead, anoxic microzones are required to account for LINX II observations through consistently low N2O yields and the consumption of upstream‐produced N2O. Together, these results provide a framework for controls on stream N2O yields and suggest that stream corridor restoration designs aimed at increasing the capacity of hyporheic zones to remediate nitrate loading, as opposed to increasing hyporheic exchange, will also reduce proportional N2O emissions.