The interplay between transport and reaction rates as controls on nitrate attenuation in permeable, streambed sediments
The interplay between transport and reaction rates as controls on nitrate attenuation in permeable, streambed sediments
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DOI：
10.1002/2014jg002874
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发表时间：
2015-06-01
影响因子：
3.7
通讯作者：
Zhang, H.
中科院分区：
文献类型：
--
作者：
Lansdown, K.;Heppell, C. M.;Zhang, H.
人类固氮和随后将这种氮用作肥料极大地扰乱了全球氮循环。河流是景观中公认的氮去除热点，因为地表水和沉积物之间的相互作用创造了有利于氮转化的异质氧化还原环境。我们对河床氮动态的理解主要来自于浅层沉积物或潜流交换流途径，对地下水补给的获取河段关注相对较少。我们已经使用N-15技术来量化原位速率的硝酸盐去除到1米深的地下水供水河床地下水文范围从强烈的上升流，主要是水平的水通量。我们结合联合收割机这些利率与详细的水文测量，以调查在控制氮衰减沿着上升流路径的地球化学活动和水运输之间的相互作用。硝酸盐衰减是通过反硝化作用发生的，而不是通过异化硝酸盐还原为铵或厌氧氨氧化物（范围=12至>17，000 nmol（15）NL（-1）h（-1））。总体而言，上升地下水中的硝酸盐去除受水通量而不是反应速率控制（即，Damkohler数字80%的硝酸盐去除发生在底流条件下不暴露于潜流交换流的沉积物内，说明了深层沉积物在上升流系统中作为硝酸盐汇的重要性。
Anthropogenic nitrogen fixation and subsequent use of this nitrogen as fertilizer have greatly disturbed the global nitrogen cycle. Rivers are recognized hot spots of nitrogen removal in the landscape as interaction between surface water and sediments creates heterogeneous redox environments conducive for nitrogen transformations. Our understanding of riverbed nitrogen dynamics to date comes mainly from shallow sediments or hyporheic exchange flow pathways with comparatively little attention paid to groundwater-fed, gaining reaches. We have used N-15 techniques to quantify in situ rates of nitrate removal to 1m depth within a groundwater-fed riverbed where subsurface hydrology ranged from strong upwelling to predominantly horizontal water fluxes. We combine these rates with detailed hydrologic measurements to investigate the interplay between biogeochemical activity and water transport in controlling nitrogen attenuation along upwelling flow pathways. Nitrate attenuation occurred via denitrification rather than dissimilatory nitrate reduction to ammonium or anammox (range=12 to >17,000nmol(15)NL(-1)h(-1)). Overall, nitrate removal within the upwelling groundwater was controlled by water flux rather than reaction rate (i.e., Damkohler numbers 80% of nitrate removal occurs within sediments not exposed to hyporheic exchange flows under base flow conditions, illustrating the importance of deep sediments as nitrate sinks in upwelling systems.