Stream Nitrogen Inputs Reflect Groundwater Across a Snowmelt-Dominated Montane to Urban Watershed.
Stream Nitrogen Inputs Reflect Groundwater Across a Snowmelt-Dominated Montane to Urban Watershed.
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DOI：
10.1021/acs.est.5b04805
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发表时间：
2016-01
影响因子：
11.4
通讯作者：
S. Hall;S. Weintraub;D. Eiriksson;P. Brooks;M. Baker;G. Bowen;D. Bowling
中科院分区：
文献类型：
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作者：
S. Hall;S. Weintraub;D. Eiriksson;P. Brooks;M. Baker;G. Bowen;D. Bowling
融雪在许多温带山地溪流的水文过程中占主导地位，但很少有人研究这些流域中从荒地到城市土地利用梯度的溪流水源和氮（N）动态如何变化。在犹他州盐湖城的一个三级流域，我们询问地下水与浅层地表水的输入何时何地控制河流流量和氮动态。溪流水同位素（δ(2)H和δ(18)O）反映了基流期间一致的融雪水源。保守离子和排放之间的近化学静态关系表明，地下水在山地和城市地区全年占据主导地位，这挑战了将雨水直接输入城市河流的概念重点。在大多数山地和城市河段的融雪和基流期间，溪流和地下水NO3(-)浓度始终保持较低水平，表明地下氮保留或反硝化作用有效，肥料或沉积氮源的影响最小。相反，NO3(-) 浓度在城市地下水输入后增加了 50 倍，这表明地下流动路径对养分负荷的影响可能大于对地表土地利用的影响。 H2O和NO3(-)的同位素组成表明，融雪产生的城市地下水拦截了泄漏下水道中的NO3(-)。下水道维护可能会减轻山/谷过渡区河流氮输入的热点，而这些热点在半干旱城市生态系统中基本上被忽视了。
Snowmelt dominates the hydrograph of many temperate montane streams, yet little work has characterized how streamwater sources and nitrogen (N) dynamics vary across wildland to urban land use gradients in these watersheds. Across a third-order catchment in Salt Lake City, Utah, we asked where and when groundwater vs shallow surface water inputs controlled stream discharge and N dynamics. Stream water isotopes (δ(2)H and δ(18)O) reflected a consistent snowmelt water source during baseflow. Near-chemostatic relationships between conservative ions and discharge implied that groundwater dominated discharge year-round across the montane and urban sites, challenging the conceptual emphasis on direct stormwater inputs to urban streams. Stream and groundwater NO3(-) concentrations remained consistently low during snowmelt and baseflow in most montane and urban stream reaches, indicating effective subsurface N retention or denitrification and minimal impact of fertilizer or deposition N sources. Rather, NO3(-) concentrations increased 50-fold following urban groundwater inputs, showing that subsurface flow paths potentially impact nutrient loading more than surficial land use. Isotopic composition of H2O and NO3(-) suggested that snowmelt-derived urban groundwater intercepted NO3(-) from leaking sewers. Sewer maintenance could potentially mitigate hotspots of stream N inputs at mountain/valley transitions, which have been largely overlooked in semiarid urban ecosystems.