Stream physics set the limits A combination of physical transport processes and biologically mediated reactions in streams and their sediments removes dissolved inorganic nitrogen (DIN) from the water. Although stream chemistry and biology have been considered the dominant controls on how quickly DIN is removed, Grant et al. show that physics is what sets the limits on removal rates of nitrate (a component of DIN). Residence time in the hyporheic zone (the region below the sediment surface where groundwater and surface water mix) determines the maximum rate at which nitrate can be removed from stream water. Nevertheless, at local scales, chemistry and biology modify how closely to that maximum rate removal occurs. Science, this issue p. 1266 Stream physics determines the maximum rate at which nitrate can be removed from the water. The discharge of excess nitrogen to streams and rivers poses an existential threat to both humans and ecosystems. A seminal study of headwater streams across the United States concluded that in-stream removal of nitrate is controlled primarily by stream chemistry and biology. Reanalysis of these data reveals that stream turbulence (in particular, turbulent mass transfer across the concentration boundary layer) imposes a previously unrecognized upper limit on the rate at which nitrate is removed from streams. The upper limit closely approximates measured nitrate removal rates in streams with low concentrations of this pollutant, a discovery that should inform stream restoration designs and efforts to assess the effects of nitrogen pollution on receiving water quality and the global nitrogen cycle.

中文翻译：

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在全球氮污染评估中考虑河流湍流

河流物理学设定了限制 河流及其沉积物中的物理传输过程和生物介导反应相结合，可以去除水中溶解的无机氮 (DIN)。尽管流化学和生物学被认为是 DIN 去除速度的主要控制因素，但格兰特等人。表明物理学决定了硝酸盐（DIN 的一个组成部分）的去除率。在下流带（地下水和地表水混合的沉积物表面以下区域）的停留时间决定了从河流水中去除硝酸盐的最大速率。然而，在局部尺度上，化学和生物学会修改与最大速率去除发生的接近程度。科学，这个问题 p。1266 流物理学决定了从水中去除硝酸盐的最大速率。将多余的氮排放到溪流和河流中，对人类和生态系统构成了生存威胁。一项针对美国上游源头河流的开创性研究得出结论，河流中硝酸盐的去除主要受河流化学和生物学的控制。对这些数据的重新分析表明，河流湍流（特别是穿过浓度边界层的湍流传质）对从河流中去除硝酸盐的速率施加了一个以前无法识别的上限。上限非常接近在这种污染物浓度较低的河流中测得的硝酸盐去除率，这一发现应该为河流恢复设计和评估氮污染对接收水质量和全球氮循环的影响的努力提供信息。